durability criteria applied in its use as

Transcription

Editor: Editorial de la Universidad de Granada
Autor: Ana Luque Aranda
D.L.: GR 1986-2011
ISBN: 978-84-694-1165-0
DEPARTAMENTO DE MINERALOGÍA Y PETROLOGÍA
UNIVERSIDAD DE GRANADA
ANDALUSIAN MARBLES: DURABILITY CRITERIA
APPLIED IN ITS USE AS ORNAMENTAL STONE
MÁRMOLES PROCEDENTES DE ANDALUCÍA: CRITERIOS DE
DURABILIDAD APLICADOS A SU USO COMO MATERIAL
ORNAMENTAL
ANA LUQUE ARANDA
TESIS DOCTORAL
DICIEMBRE DE 2010
DEPARTAMENTO DE MINERALOGÍA Y PETROLOGÍA
UNIVERSIDAD DE GRANADA
Eduardo M. Sebastián Pardo, Profesor Catedrático de Universidad y Giuseppe
Cultrone, Profesor Titular de Universidad, adscritos al Departamento de
Mineralogía y Petrología, hacen constar:
Que la presente memoria titulada: “ANDALUSIAN MARBLES:
DURABILITY
CRITERIA APPLIED IN ITS USE AS ORNAMENTAL STONE” ha sido realizada bajo
nuestra dirección por la doctoranda Dña. Ana Luque Aranda y cumple los
requisitos necesarios para que su autora pueda optar al grado de Doctora en
Ciencias Geológicas por la Universidad de Granada.
Fdo. Ana Luque Aranda
VºBº del Director
VºBº del Director
Edurado M. Sebastián Pardo
Giuseppe Cultrone
Granada, 10 de Diciembre de 2010
A Rafa y Adi, con los que crecí
y ahora añoro
Agradecimientos
Es ahora cuando miro atrás y veo todos los años que han pasado desde que me iniciara en
este camino, primero con el estudio de cales, luego con el de morteros y finalmente con el de
mármoles. Tengo que reconocer que son muchos los que de alguna manera han contribuido a
este trabajo. No sólo al de la tesis, sino también a mi desarrollo científico y personal. Quiero, por
eso y mucho más, dejar constancia de mi mas sincero agradecimiento a todas las personas, sin
cuyo apoyo, colaboración y consejo, no hubiese sido posible terminar el trabajo de investigación
que aquí expongo.
A mis tutores, y amigos, con los que siempre estaré en deuda, el Dr. Eduardo Sebastián
Pardo y el Dr. Giuseppe Cultrone, por su confianza, paciencia y ayuda durante todo este tiempo.
Por la oportunidad que me han brindado y por hacerme científica y personalmente más
razonable.
A mis compañeros de grupo: la Dra. Encarni Ruiz Agudo, por sus revisiones y aportaciones a
esta tesis; el Dr. Carlos Rodríguez Navarro, por su siempre asequible ayuda científica; y la Dr.
Carolina Cardell, por sus acertados consejos metodológicos. A Anna Arizzi, por su amistad y
agradable predisposición a ayudar, y a Maja, Eduardo, Julia y Kerstin por su compañerismo. Y
cómo no, a mis amigas Lucía Linares y Olga Cazalla, que aunque ya no están en el grupo, me
acompañaron durante mis inicios en él.
A todos los miembros del Departamento de Mineralogía y Petrología: en especial, al Dr.
Miguel Ortega Huertas, director del departamento, por su amistosa acogida, interés y
preocupación; a Paqui, Inmaculada, Salva y Pepe Gordillo, porque siempre me han mostrado gran
aprecio y cariño, haciendo que con ello me sienta muy arropada; a Antonio García Casco, por su
ayuda en mis múltiples cuestiones pre-doctorales; a Daniel Martín, por su amable disposición y
ayuda con los análisis de Termodifracción de rayos-X. También a todo el personal técnico y
administrativo que me han facilitado la labor extra-científica: como a Rafa Loza, al que siempre le
admiré su feliz sonrisa; a Agustín Rueda, por su educada preocupación por hacer un buen trabajo;
a Juan, Jesús, Isabel, Carmen, Sonia, Inés, Noelia y Sandra, porque cuando los necesité siempre
me atendieron con confianza. Y al personal del CIC: a Isa Sánchez, Isabel Guerra, Alicia González,
Mª de Mar Abad y Miguel Ángel Salas, entre otros muchos, por su labor técnica.
De mi estancia en Oviedo, quiero agradecer la ayuda de los profesores Dr. Javier Alonso y
Dr. Jorge Ordaz, siempre tan amable y sencilla, y la amistad de Patricia Vázquez, siempre tan
alegre y generosa. Y de mi estancia en Göttingen, quiero agradecer la oportunidad brindada por
el profesor Siegfried Siegesmund, por su ayuda científica y aportaciones a esta tesis; la de Bernd
Leiss, por su ayuda con el equipo de Difracción de rayos-X de texturas y por dedicarme su tiempo
en la interpretación de los datos; a Manu Morales, por su amistosa acogida y ayuda técnica
durante mi estancia; a Birte, Stephan Mosh, Jörg Rüdrich, Christian Müller y Christian Knell, por
ayudarme en las labores de laboratorio. Y, por supuesto, al profesor Akös Törok, por regalarme su
amistad, por ayudarme personal y científicamente, y por esforzarse siempre en mejorar mi inglés.
A mis compañeros científicos, con los que he compartido muy buenos momentos y que, por
suerte, han sido muchos. Empezando con los más veteranos y ya doctores: Javi Carrillo, Raef,
Nono, Ali, Francis, Claudio, Concha, Vicente, Antonio Pedrea, Ana Ruiz, Carlos Duque y un
etcétera muy grande; y terminando con los de ahora: Silvia, Pedro, Iñaki, Marta, Vero, Carmen,
Vanesa, Aitor, Juan Cárdenas, Juan Figueroa y Mohammad Ali Muhsin. A José Alberto e Idael, por
estar siempre dispuestos a informarme y asesorarme en los trámites de doctorado. Y, cómo no, a
Pedro Álvarez, por ayudarme y adaptarse tan bién a mi desorganizada rutina.
A mis amigos y compañeros de tertulias, en especial a Paco Lobo, al que siempre le
agradeceré su sincera amistad, a Patricia Ruano por su amistad y gran disposición a ayudar, a
Annika, Julia Gutiérrez y María Lujan, mis amigas las mamis, por esos buenos ratos fuera de la uni
y a Antonio Acosta y Merche, con los que siempre se puede hablar.
A mis amigos fuera de la ciencia, los que siempre creyeron en mí, me animaron y aún
continúan, a pesar de mi abandono en estos últimos años: a José María Amar, María de la
Manzanara, Oscar Palomares, y a todo el grupo de las “niñas”.
Quiero agradecer la ayuda de las personas que han mejorado mi inglés, a Cristina Sebastián
por su gran esfuerzo e interés en entender cada cosa, a Ángela Tate, por su cariñosa ayuda, a
Encarni Ruiz Agudo, porque sé que ya tiene bastante con lo suyo, y a Nigel por su rápida
disposición.
Cómo no, a mi familia, por ayudarme a crecer, creer en mí y animarme a continuar, y a Isa y
Julio, por su cariño y porque con ellos mis hijos son felices. Por supuesto, a Julio, porque siempre
es feliz, por derrochar tanto cariño, paciencia y comprensión y también, por quererme tanto, y en
especial a Dani y a Sara, por ser los motores de mi vida y, sobre todo, por sus besos y abrazos.
Gracias a los tres por acompañarme siempre.
Esta Tesis se ha realizado con la beca asociada al proyecto FQM1635, "Nuevas metodologías
para establecer controles de durabilidad y trazadores de Indicación Geográfica Controlada en los
mármoles andaluces para su transferencia a la industria de las rocas ornamentales y para la
preservación del Patrimonio Histórico", financiado por la Junta de Andalucía.
Index
Agradecimientos
Resumen
xv
Abstract
xvii
PART I
1.
THE MEANING OF MARBLE TERM AS NATURAL STONE
25
2.
DURABILITY OF MARBLE. STATE OF THE ART
27
2.1.
THERMAL WEATHERING
30
2.2.
DECAY BY SALT SOLUTIONS
33
2.3.
DECAY BY ATMOSPHERIC POLLUTIONS
35
3.
THE USE OF MARBLE AS ORNAMENTAL STONE IN THE ARCHITECTURAL
HERITAGE OF SPAIN. HISTORY
37
3.1.
THE USE OF MARBLE DURING ROMAN HISPANIA (2nd C. B.C. TO 3rd C. A.C.)
40
3.2.
THE USE OF MARBLE FROM THE 16th THROUGH THE 18th CENTURY
42
3.3.
THE USE OF MARBLE THROUGH THE 19th AND 20th CENTURY
43
4.
OBJECTIVES OF THIS THESIS
55
PART II
5.
DESCRIPTION OF THE GEOLOGICAL AREAS OF MARBLE QUARRIES IN
ANDALUSIA
59
5.1.
GEOGRAPHY OF ANDALUSIA
61
5.2.
GEOLOGICAL SETTING
62
5.3.
MARBLES QUARRIES IN ANDALUSIA
64
5.3.1. Ossa Morena Zone: Aroche and Fuenteheridos districs
5.3.2. Internal (Betic) zones: Macael, Alhama de Granada and Mijas districts
63
65
6.
METHODOLOGY
73
6.1.
CHEMICAL AND MINERALOGICAL CHARACTERIZATION
75
6.1.1. X-ray Fluorescence (XRF)
6.1.2. X-ray diffraction (XRD)
6.1.3. Polarized optical microscopy (OM)
73
73
74
DETERMINATION OF PHYSICAL PROPERTIES
77
6.2.1. Mercury intrusion porosimetry (MIP)
6.2.2. Nitrogen adsorption
6.2.3. Colour variations
75
75
76
6.2.
xi
Ana Luque Aranda
6.2.4.
6.2.5.
6.2.6.
6.2.7.
6.2.8.
6.3.
Hydric tests
X-ray Diffraction texture
Ultrasonic waves velocity measurements
Thermal dilatation
Thermo X-ray Diffraction
76
78
78
79
80
DECAY TEST
83
6.3.1. Salt solution
6.3.2. Sulphatation test
81
82
HIGH RESOLUTION TECHNIQUE APPLIED TO SURFACE STUDY
84
6.4.1. Environmental scanning electron microscopy (ESEM)
6.4.2. Variable pressure scanning electron microscopy (VPSEM)
6.4.3. X-ray photoelectron spectroscopy (XPS)
82
83
83
6.4.
PART III
7.
ANISOTROPIC BEHAVIOUR OF WHITE MACAEL MARBLE USED IN THE
ALHAMBRA OF GRANADA (SPAIN). THE ROLE OF THERMOHYDRIC EXPANSION
IN STONE DURABILITY
89
7.1.
INTRODUCTION
93
7.2.
MATERIALS AND METHODOS
96
7.2.1. Samples
7.2.2. Analyses
94
95
7.3.
7.4.
RESULTS AND DISCUSSION
100
7.3.1. Mineralogy and texture
7.3.2. Thermal expansion
98
100
CONCLUSIONS
8.
DIRECT OBSERVATION OF MICROCRACK DEVELOPMENT IN MARBLE
CAUSED BY THERMAL WEATHERING
107
111
8.1.
INTRODUCTION
115
8.2.
MATERIALS AND METHODS
117
8.2.1. Marbles
8.2.2. Methodology
8.3.
RESULTS
8.3.1. Characterization of marbles
8.3.2. Thermal expansion tests
8.3.3. Hot-stage ESEM
9.
POTENTIAL THERMAL EXPANSION OF CALCITIC AND DOLOMITIC
MARBLES
xii
115
115
120
118
122
125
137
9.1.
INTRODUCTION
141
9.2.
MATERIALS
143
9.2.1. Marble Types
141
METHODOLOGY
145
9.3.1.
9.3.2.
9.3.3.
9.3.4.
9.3.5.
9.3.6.
143
144
145
146
146
147
9.3.
9.4.
RESULTS AND DISCUSSIONS
9.4.1.
9.4.2.
9.4.3.
9.4.4.
9.4.5.
9.4.6.
9.5.
Petrographic characterization
Anisotropy of the marbles
Thermal dilatation coefficient of marbles
Preferred crystallographic orientation of marbles
Direct observation of micro-cracks development with ESEM
Thermal coefficient of calcite and dolomite crystals
Thermal dilation coefficient of marbles
CONCLUSIONS
10.
CHANGES IN THE PORE STRUCTURE OF MARBLE AFTER SALT DECAY
TESTS
150
147
149
150
152
154
157
162
167
10.1.
INTRODUCTION
173
10.2.
MATERIALS AND METHODS
174
10.3.
175
10.3.1. Dolomitic marbles
10.3.2. Calcitic marbles
10.3.3. In situ weathering: an example from the Hospital Real (Granada)
172
174
175
CONCLUSIONS
180
10.4.
11.
ANALYSIS OF THE SURFACE OF DIFFERENT MARBLES BY X-RAY
PHOTOELECTRON SPECTROSCOPY (XPS) TO EVALUATE DECAY BY SO2 ATTACK
179
11.1.
INTRODUCTION
185
11.2.
MATERIALS
187
11.2.1. Materials
183
11.3. METHODOLOGY
188
11.3.1.
11.3.2.
11.3.3.
11.3.4.
184
184
184
185
Petrochemical features of unaltered marbles
Colour variations
XPS analyses
VPSEM observation
xiii
Ana Luque Aranda
11.4.
190
11.4.1.
11.4.2.
11.4.3.
11.4.4.
186
187
189
197
11.5.
Colour variations
XPS analyses
FESEM observations
CONCLUSIONS
202
PART IV
12.
CONCLUSIONES
13.
EXTENDED CONCLUSIONS
xiv
205
21
Resumen
Aunque antiguamente decantarse por un determinado material pétreo de construcción u
otro dependía en gran medida de la cercanía, accesibilidad y la facilidad de extracción de éste, a
medida que el tiempo pasó las preferencias se refinaron y elegir materiales que ofreciesen tanto
calidad técnica como belleza estética comenzó a ser la tendencia. En España, el uso de mármol en
construcción y obras de arte era habitual desde tiempos romanos. Por entonces, el mármol era
un símbolo de poder y nobleza; poco a poco, aunque se seguía considerando un material que
proporcionaba esplendor a los edificios, su uso se hizo más generalizado y hoy día, se puede
encontrar en una gran variedad de elementos de construcción desde encimeras de cocina a
magníficos diseños palaciegos.
En el pasado, la palabra mármol se usaba para identificar una extensa variedad de
materiales pétreos muy diferentes entre sí en cuanto a composición química y a procesos
geológicos que los formaron. Esto dio lugar a una gran confusión que se refleja en los libros de
patrimonio arquitectónico y arqueológico. Por ello, en el primer capítulo de esta tesis se hace
hincapié en las principales diferencias conceptuales entre las distintas definiciones de mármol en
términos históricos, comerciales y geológicos.
Las cualidades tan especiales y únicas del mármol hacen que éste haya cautivado a
arquitectos y artistas desde tiempos remotos. Es muy compacto, resistente, de gran belleza y se
pule fácilmente. A pesar de que tradicionalmente el mármol se ha visto como un material
resistente y de larga duración, se ha comprobado que las estatuas y las edificaciones de mármol
sufren, con el tiempo, deterioro y erosión, provocados especialmente por los agentes
ambientales y de polución atmosféricos, lo que plantea serios problemas de conservación. De
hecho, las variaciones extremas de temperatura, la presencia de sales solubles y atmósferas ricas
en SO2 causan un importante deterioro por medio de mecanismos químicos y físicos. El hecho de
que estos mecanismos afecten al mármol se debe, en gran parte, a las propiedades intrínsecas de
éste.
La calcita y la dolomita, fases minerales predominantes en el mármol, tienen un coeficiente
de dilatación térmica elevado, en particular, en una de sus direcciones cristalográficas (eje-c
cristalográfico). Por ello, repetidos cambios de temperatura pueden producir tensiones
intercristalinas en el mármol que causan microfisuras en su interior. Además de esta dilatación
térmica anisótropa de la calcita y dolomita, algunos mármoles no recuperan el tamaño y hábito
inicial de su cristales, un hecho que puede inducir a la dilatación permanente y finalmente a la
decohesión granular. La dilatación, y subsiguiente deformación de los cristales debido a
marcadas variaciones en la temperatura, pueden, por tanto, causar el deterioro físico de los
mármoles.
Pero estos cambios en la temperatura no son los únicos factores que determinan la
durabilidad del mármol, y en muchos casos, los agentes químicos son la principal causa de
deterioro. Esto se debe a que las rocas carbonatadas son muy sensibles, químicamente hablando,
a las soluciones salinas y a las atmósferas ricas en SO 2 que tienden a acidificar el ambiente en el
que el mármol está expuesto, favoreciendo así la disolución de los carbonatos (calcita y
dolomita). Esto permite que los cationes libres del carbonato puedan reaccionar con los aerosoles
atmosféricos formando nuevos productos o fases minerales en la superficie o interior del mármol.
El estudio de estos factores y mecanismos de deterioro presenta un gran interés en el sector
de la construcción civil y en la restauración de nuestro patrimonio arquitectónico, y también es
importante en las distintas disciplinas asociadas con la conservación de bienes culturales. El
segundo capítulo de esta tesis hace una amplia introducción de los mecanismos que causan el
deterioro de los mármoles afectados por estos agentes de deterioro.
En base a los diferentes aspectos relatados anteriormente, esta tesis presenta dos objetivos
principales:
1) Caracterizar los principales aspectos químicos, mineralógicos, petrológicos y petrofísicos
de los mármoles más usados en el patrimonio cultural español.
2) Identificar los principales mecanismos que afectan la durabilidad del mármol en términos
de comportamiento y evolución de sus propiedades intrínsecas cuando se encuentran bajo la
acción de los agentes ambientales de deterioro más significantes.
Los mármoles se han agrupado, según su procedencia geográfica, en cuatro áreas:
En el área de Huelva se han seleccionado dos variedades de mármoles extraídos en grandes
cantidades de la Sierra de Aracena. Se llaman “mármol de Aroche” y “mármol de Fuenteheridos”;
En el área de Málaga, se ha seleccionado un mármol que procede de la Sierra de Mijas
conocido como “mármol de Mijas”;
En Granada, se ha seleccionado un mármol de Sierra Tejeda, conocido como “mármol
Blanco Ibérico”;
Finalmente, en el área de Almería se eligieron tres tipos de mármol procedentes de la Sierra
de los Filabres: “mármol Blanco de Macael”, “Tranco Macael” y “Amarillo Triana Macael”
Los métodos y técnicas utilizados en esta investigación con el fin de identificar las
propiedades petrológicas, mineralógicas y químicas de cada mármol y los principales criterios y
parámetros que determinan la durabilidad del mármol han sido agrupados en tres categorías:
i) Técnicas que permiten determinar las composición química y mineral, y la textura y fábrica
de los mármoles: Fluorescencia de Rayos X, Difracción de Rayos X y Microscopio Óptico de luz
polarizada.
ii) Métodos y técnicas usadas en el estudio de las microsestructuras y las principales
propiedades físicas de cada mármol: Difracción de rayos X de texturas, Porosimetría por inyección
de Mercurio, adsorción de Nitrógeno, colorimetría, parámetros hídricos, ultrasonidos, Dilatación
térmica y Termodifracción de rayos X.
iii) Técnicas de alta resolución que permiten confirmar los cambios de composición y textura
que tienen lugar en la superficie de los mármoles afectados por el deterioro. Este deterioro se ha
realizado en pruebas basadas en oscilaciones térmicas y en otras de naturaleza química:
Microscopio Electrónico de Barrido Ambiental, Microscopio Electrónico de Barrido de presión
variable, y La Espectroscopia Fotoelectrónica de rayos-X.
Teniendo en cuenta los resultados obtenidos, muchos de los cuales ya han sido publicados
en revistas internacionales, se ha observado que la vulnerabilidad de los diferentes mármoles a
los agentes de deterioro viene condicionada por las propiedades petrofísicas específicas de estos.
Los resultados obtenidos también han permitido concluir que el comportamiento del
mármol cuando se encuentra bajo la acción de agentes ambientales de deterioro está controlado
por su composición mineralógica. Los mármoles calcíticos son mas sensibles que los dolomíticos
a procesos de deterioro por cambios de temperatura o de origen químico. Sin embargo, además
de la composición mineralógica, las características y parámetros de la textura y fábrica del
mármol (especialmente, la orientación preferente en sus ejes cristalográficos, el tamaño y forma
de sus cristales y la forma de sus uniones granulares) tienen también una gran influencia en su
comportamiento cuando está sujeto a procesos de deterioro y por tanto, se tendrían que tener
en cuenta cuando se evalúe la durabilidad y calidad técnica de los diferentes tipos de mármoles.
Esta investigación llevada a cabo por esta tesis, presenta una gran contribución a la
metodología científica normalmente utilizada en la evaluación de las causas de deterioro del
mármol, en base a su uso como material de construcción y ornamentación, el cuál puede
observarse tanto en edificios históricos como modernos.
Abstract
Throughout history marble has been used as a building stone in many parts of the world.
The surviving monuments and works of art of past civilizations bear witness to their great
knowledge of marble and their particular preferences when using the stone. Marble was also
widely used in the cultural heritage of Spain. For this reason the study of marble and its
properties is very important for the conservation of modern buildings and of our historical and
archaeological heritage, and these aspects form the central theme of this thesis.
Although in ancient times, the choice of a particular building stone depended to a large
extent on its proximity, its accessibility and the ease with which it could be extracted, with time
preferences became more refined and tended towards materials that offered both technical
quality and aesthetic beauty. In Spain marble has been used in both construction and artwork
since Roman times. Numerous archaeological sites and monuments, and most of the sculptures
and other decorative features dating from this period indicate that the use of marble denoted
power and nobility. As time passed, marble continued to be viewed as an attractive material that
added splendour to a building, but its use became more generalized and today it can be found in
a wide variety of construction applications from kitchen worktops to grand palatial designs.
In the past, the word marble was used to identify a wide variety of stones that were very
different in terms of both their mineralogical composition and the geological process that had
formed them. This led to enormous confusion in the bibliography on archaeological and building
heritage. The first chapter of this thesis therefore discusses the main conceptual differences
between these various definitions of marble in the historical, commercial and geological senses of
the word.
Marble’s unique qualities have captivated architects and artists since ancient times. It is very
compact, mechanically resistant and extremely beautiful and it polishes very well. Although it has
traditionally been viewed as a resistant, long-lasting material, over time marble statues and
buildings do suffer weathering and decay, particularly from atmospheric and environmental
pollution agents, which gives rise to serious conservation problems. Indeed extreme temperature
variations, the presence of soluble salts and SO2 rich atmospheres cause significant decay
through both physical and chemical decay mechanisms. The fact that these different mechanisms
are able to act on the marble is due largely to its intrinsic characteristics.
Calcite and dolomite, the predominant mineral phases in marbles have a high thermal
dilatation coefficient, in particular on one of their crystallographic directions (crystallographic c-
axis). For this reason, repeated changes in temperature can produce intercrystalline tensions in
the marble which cause microcracks to develop inside it. In addition to this anisotropic thermal
dilatation of calcite and dolomite, some marbles do not recover their initial crystal size and habits,
a fact that can lead to their permanent dilatation and ultimately to granular decohesion. The
dilatation and subsequent deformation of the crystals caused by marked variations in
temperature therefore lead to the physical deterioration of the marbles.
Temperature variations are not the only factor affecting the durability of marble, and in
many cases chemical agents are the main cause of decay. This is because carbonated rocks are
chemically very sensitive to saline solutions and SO 2 rich atmospheres, which tend to acidify the
atmosphere to which the marble is exposed, favouring the dissolution of carbonates (calcite and
dolomite). This allows free carbonate cations can react with atmospherics aerosols or soluble ions
to form other products or minerals phases on the surface or inside of marble.
The study of these decay factors and mechanisms is of great interest in the civil and
residential building sector and in the restoration of our architectural heritage, and is also
important in the various disciplines associated with the conservation of cultural assets in its
broadest sense. The second chapter of the thesis offers a broad introduction to the mechanisms
that cause the decay of marbles affected by these decay agents.
In view of the different aspects referred to above, this thesis has two main objectives:
1) Characterize the main chemical, mineralogical, petrological and petrophysical aspects of
the marbles most widely used in Spain’s cultural heritage.
2) Identify the main mechanisms affecting its durability on the basis of the behaviour and
evolution of its intrinsic properties when subject to the action of the most significant
environmental decay factors.
In terms of the geographical origin of the stone, the marbles analysed in this study have
been grouped together in four different areas:
In the Huelva area we selected two varieties of marble quarried in vast quantities from the
Sierra de Aracena. These varieties are known as “Marmol de Aroche” and “Marmol de
Fuenteheridos”;
In the Malaga area we selected a marble from the Sierra de Mijas, referred to in this thesis as
“Marmol de Mijas”;
In the Granada area we selected a marble from the Sierra Tejeda, known as “Marmol Blanco
Iberico” (White Iberian Marble);
Finally, in the Almeria area we chose three varieties of marble from the Sierra de los Filabres,
sold under the trade names of “Marmol Blanco Macael” (White Macael Marble), “Tranco Macael”
(Tranco Macael Marble) and “Amarillo Triana Macael” (Yellow Macael Marble).
The methods and techniques used in this research to identify the chemical, mineralogical
and petrological properties of each marble, and the main criteria and parameters that determine
its durability have been grouped together in three categories:
i) Techniques that enabled us to determine the chemical and mineral composition, and the
texture and fabric of the marbles: X-Ray Fluorescence, X-Ray Diffraction and Polarized Light
Optical Microscopy.
ii) Methods and techniques used in the study of the microtextures and the main physical
properties of each marble: X-ray diffraction of textures, Mercury Injection Porosimetry, Nitrogen
adsorption, Colorimetry, Hydric parameters, Ultrasounds, thermal dilatation and X-ray
thermodiffraction.
iii) High resolution techniques that enable us to confirm the textural and compositional
changes that take place on the surface of marbles affected by decay. This decay is produced in
tests based on thermal oscillations and others of a chemical nature: Scanning electron
Microscopy,
Variable-pressure
scanning
electron
microscopy,
and
X-ray
photoelectron
spectroscopy.
In accordance with the results obtained, most of which have already been published in
international journals, the vulnerability of the different marbles to the decay agents referred to
above depends on their specific petrophysical properties.
The results also indicate that the behaviour of marble when subject to the action of
atmospheric decay agents is essentially controlled by its mineralogical composition. Calcitic
marbles are more sensitive to thermal and/or chemical-related decay than dolomitic marbles.
However, in addition to the mineralogical composition, the characteristics and parameters of the
texture and the fabric of the marble (especially the preferential orientation of the crystallographic
axes, the size and shape of the crystals and the shapes of the grains boundaries) also have a
decisive influence on its behaviour when subject to decay processes, and must therefore be taken
into account when evaluating the durability and technical quality of different types of marble.
This research thesis makes a significant contribution to the scientific methodology normally
used in the evaluation of the causes of decay of marble-based construction and ornamental
materials, which can be seen and admired in both historical and modern buildings.
PART I
Part I
1. THE MEANING OF MARBLE TERM AS NATURAL
STONE
The name marble is derived from the Latin marmor and from Greek, which means “shining
stone”. Strictly the name applies to a granular, crystalline limestone, but it is also applied to a
hard limestone that can be polished (Christie et al., 2001)
The fact that throughout the history the term "marble" has been used to define any type of
polished rock, has given rise to serious problems of identification. This happens with the
provenance of some artifacts or sculptures, apparently made of marble, which after a visual and
petrographic study, have been confirmed to be made of limestone or other similar stone (Zúñiga,
1994; Soler-Huertas, 2005). Therefore, it is easy to find numerous references that use the term
"marble" to define any compact rock, without specifying its natural origin and mineralogical
composition.
Regarding its use in Architecture, the concept of marble is very broad and difficult to define
(Zuñiga, 1994). This term is used for numerous types of rocks, such as limestone, dolostone,
travertine, calcitic breccia, jasper and serpentine, which due to their grain size and hardness, are
easily polished and their aesthetical properties make them ideal for their use as ornamental and
building material (Del Pan, 1926).
The same problem occurs with the standard terminology used in some dimension stone
commercial books (ASTM C119), which use the marble definition to identify some well polished
limestones or dolostones. However, although this classification is somehow more precise in terms
of composition because it includes mainly carbonate rocks, it is also non correct and it can also
create confusion.
In this thesis, the term marble is only used to refer to a metamorphised limestone or
dolostone under pressure and temperature processes, which has been recrystallized to that
extent that much or all of its sedimentary and biologic textures has been obliterated. The result is
a crystalline compact rock, although occasionally, the bedding textures can be partially preserved
in the form of compositional layering or banding (Mead and Austin, 2006).
Marbles are mainly composed of calcite and dolomite; however, some impurities can be
present in the original carbonate sediment. Quartz and clay minerals are the main accessory
25
Ana Luque Aranda
minerals which are commonly present in these rocks. Graphite, accompanied by finely
disseminated pyrite comes from the organic material entrapped within the rock, and occasionally
talc, chlorite, amphiboles and pyroxene may be also found.
Pure calcitic marble is white, but the presence of tiny amounts of impurities can give the
marble a significant colour: golden-brown, green, pink and gray colours are due to the presence
of magnesium, iron, hematite, and graphite and pyrite respectively (Fig. 1).
Figure 1. Some coloured varieties of marbles from Macael exposed in “Tarraco, pedra a pedra” Archaeology
National Museum of Tarragona.
All these features have made marble widely used as ornamental material to make statues,
decorative pieces in monuments (pillars, colonnades, fountains, etc), slabs cladding in buildings
facades and other pieces used in interiors. Marble is resistant in a dry atmosphere and when it is
protected against the rain, but its surface crumbles readily when exposed to a moist, acid
atmosphere. The presence of certain impurities can decrease marble durability and as all
limestones, the marble is also sensitive to be altered by water, pollution and acid rain. Thus,
marble is an uneconomical material and its use is not recommended in places exposed to outer
conditions.
26
Part I
2.
DURABILITY OF MARBLE. STATE OF THE ART
Marbles exposed to atmospheric conditions, can develop adjustment mechanisms that help
them to achieve a new equilibrium between the rock and its environment. This is because
marbles, like any other metamorphic rocks, have been formed under conditions of pressure and
temperature very different from those of the Earth surface. Therefore, although along the history
marble has been considered as a durable material, over time it has been found that this type of
rock is highly susceptible to be altered, especially under outer conditions.
During the last decades it has become more evident that many sculptures and architectural
elements made of marble (Michelangelo's David in Florence, the Venus of Milo in the Louvre,
Paris, Trajan's column in Rome, the Alhambra, in Granada) suffer severe problems of conservation
(Fig. 2). This fact demonstrates that the durability of marble is relative and limited, due to intrinsic
and extrinsic factors. Intrinsic factors are related to the composition, properties and
microstructure of each marble while extrinsic ones are mainly related to the atmosphere and the
specific use of this stone (Martínez-Martínez, 2008; Al Naddaf, 2009).
Figure 2. Details of the deterioration of the sculptures on the outdoor of the Carlos V Palace
(Granada, Spain).
27
Ana Luque Aranda
As Siegesmund et al., (2002) mentioned, weathering conditions are the natural way to lead
the stone to its decay into smaller particles. Weathering is a slow and continuous process that
affects all materials exposed to the atmosphere, especially marble. The main decay processes
which affect the durability of a marble exposed to outer conditions are thermal fluctuations, salt
solutions and atmospheric pollution (Marchesini, 1969; Del Monte and Vittori, 1985; Lazzarinini
and Laurenzi Tabasso, 1986; Bell, 1993; Royer-Carfagni, 1999; Siegesmund et al., 2000a; López de
Azcona et al., 2002).
2.1. THERMAL WEATHERING
In the last decades it has been shown that the main weathering factor affecting marble
durability is thermal oscillation (Bello et al., 1992; Widhalm et al., 1996; Siegesmund et al., 2000a;
Zeisig et al., 2002; Rodríguez-Gordillo and Sáez-Pérez, 2006). Thermal oscillation produces
expansion and contraction in marble that, after successive thermal cycles, may favour the loss of
cohesion between adjacent grains. Capillary opening and development of new cracks are
favoured by this thermal mechanism, which finally leads to its mechanical failure (Winkler, 1996;
Widhalm et al., 1996; Weiss et al., 2002).
The most important intrinsic factor that controls this process is the thermal dilatation
coefficient of its constituent minerals. Calcite and dolomite are minerals that have extremely
different thermal dilatation coefficients (α) along their crystallographic directions (Klebber, 1959;
Markgraf and Reeder 1985; Reeder and Markgraf, 1986). Both minerals show expansion (α =
26×10
-6
-1
K
and 25.8×10
-6
-1
K
respectively) along their c-axis crystallographic direction, while
along their a-axis direction, dolomite show less expansion (α = 6,2×10
-6
-1
K ) and calcite shown
-1
contraction (α = -6×10-6 K ) (Fig.3).
However, other intrinsic factors of marble, such as preferred crystallographic orientation or
texture, micro-crack populations, grain size, grain aspect ratios and grain shape preferred
orientation, can determine its thermal behaviour (Royer-Carfagni, 1999; Siegesmund et al., 1999).
Therefore, all these fabric elements, in addition to the mineralogical composition of marbles, are
the main features that control the thermal weathering of marble (Siegesmund et al., 2000b;
Royer-Carfagni, 1998; Zeisig et al., 2002; Åkesson et al., 2006; Cantisani et al., 2008).
28
Part I
Figure 3. Relationship between crystallography and thermal dilatation coefficient of calcite and dolomite
crystals. Coefficients of thermal expansion (α) in the directions of the crystallographic c- and a-axes
(modified from Rüdrich 2003).
Bowing and granular disintegration are the main weathering stages that marble shows due
to thermal oscillations. Marble bowing is well described in numerous studies carried out on some
marble cladding of well-known modern buildings, such as the Finland Hall in Helsinki or the
Grande Arche de la Defense in Paris. In these buildings it was observed that, few years after its
construction, some marble slabs started to bow and crack due to the alternation of heating and
cooling cycles under wet conditions, and finally, they detached from the building (Logan et al.,
1993; Widhalm et al. 1996; Koch and Siegesmund, 2004; Malaga et al., 2008; Siegesmund et al.,
2008).
Kessler (1919) first observed the thermal weathering of marble exposed under outer
conditions. He noticed that gravestones made of marble bowed and expanded significantly and
argued that repeated heating and cooling cycles could lead to permanent dilatation of marbles.
Thomasen and Ewart (1984) and Bortz et al. (1988) pointed out the influence of variations in the
29
Ana Luque Aranda
moisture content during thermal weathering processes, and suggested that these variations could
also enhance the thermal decay of marble. This is due to the fact that moisture, present in the
material as continuous rows of ordered water molecules, could favour the thermal decohesion of
marble when swollen inside of micro-cracks during evaporation (Winkler, 1996). Finally, Koch and
Siegesmund (2002 and 2004), after numerous thermal tests performed on different types of
marbles, confirmed that the development of bowing is directly controlled by cyclic variations of
temperature in the presence of water (Fig. 4).
Figure 4. Detail of bowed macael marble exposed under atmospheric conditions.
The granular disintegration of marble is due to thermal cycles, which produce anisotropic
thermal dilatation of marble and consequently the progressive loss of cohesion along the grain
boundaries, which leads to the initial state of decay (Weiss et al., 2002 and 2003). Some
experimental studies on the thermal behaviour of marble have revealed that after several thermal
cycles, marble can show an increase in porosity and a decrease in the strength (Rayleigh, 1934;
Bland and Rolls, 1998). This is due to thermal dilatation of its crystals, which produces the
development of micro-cracks, structural deformations and granular decohesion, processes that
contribute to a more rapid decay and finally its mechanical failure (Rosenholtz and Smith, 1949;
Weiss et al. 1999; Siegesmund et al., 2000b).
Thermal decay leads to changes in the porosity and pore size distribution of the marble;
therefore, marbles can be also affected by the action of other decay processes. An increment in
30
Part I
porosity of the marble facilitates the penetration and action to other weathering agents, such as
the frost, salt solutions, dry depositions, and micro and macroorganisms (Franzini, 1995; RoyerCarfagni, 1999; Fassina et al., 2002). Therefore, it is necessary to have a deep knowledge of the
main factors that influence the durability of marble, because once the decay mechanisms are
understood, it is possible to predict and prevent marble deterioration.
2.2. DECAY BY SALT SOLUTIONS
It is known that crystallization of salt solutions is one of the most important decay
mechanisms to affects numerous historic buildings and statuary (Winkler and Singer, 1972;
Goudie and Viles, 1997; Rodriguez-Navarro and Doehne, 1999; Ruiz-Agudo, 2007). Salt solutions
can have a natural or anthropogenic origin, and can damage porous materials, mainly through
the production of physical stress as a result of salt crystallisation inside their porous system
(Charola, 2000; Doehne, 2002; Benavente et al., 1999, 2007a and b).
Once soluble salts are entrapped in the stone pores and fissures, salt crystallization stresses
can enhance their opening. This is due to crystallisation pressure of soluble salts in porous media
as a consequence of drying and wet cycles due to temperature and moisture variations (Fookes et
al., 1988; Rodríguez-Navarro and Doehne, 1999; Grossi and Esbert, 1994; Tsui et al., 2003; Coussy,
2006).
Sodium sulphate is one of the most damaging salts affecting porous stones. The
Na2SO4×nH2O system includes two stable phases: if the temperature is higher than 32.4ºC
thenardite (Na2SO4) crystallises, while if temperature is lower, the crystallisation of mirabilite
(Na2SO4 × 10H2O) or thenardite depends on relative humidity. Both mineral phases crystallize
such as subeflorescencias within materials with small pores size distribution. High crystallization
pressures of mirabilite which precipitates inside of capillary pores favour the develop of
microcracking inside stone. Therefore, even when small quantities of soluble salts are
concentrated in small areas, can enter inside of pores, and subsequent solubility and precipitation
processes can lead considerable damage in the stone (Arnold, 1976; Charola and Lewin, 1979;
Benavente, 2003).
Although most research on the decay effects of soluble salts have focused on porous stones,
it has been observed that less porous stones such as marble may also be affected by this decay
agent (Fig. 5) (Chabas and Jeannette, 2001). Several studies have been performed in order to
understand the influence that stone microstructures have on its durability towards salt
31
Ana Luque Aranda
weathering (Schaffer, 1932; Honeyborne and Harris, 1958; Fitzner and Snethlage, 1982; Benavente
et al., 2004). Russell (1927) introduced the idea that stones with a high proportion of micropores
are more susceptible to salt decay. Later on, Fitzner (1988) observed, after comparing the porous
network of the fresh stone from the quarry with the same altered stone from the building, that
pores with entries of size below 100 nm remained unchanged, while the proportion of pores of
higher sizes was increased due to the progressive destruction of grains.
In the same way, Benavente et al. (1999), after experimental test performed with a 4 m
Na2SO4 solution under supersaturation conditions in different porous media of stones, observed
that the porosity and pore size increased more in stones with a higher proportion of pores from
0.1 to 2500 μm. Considering that the flow is governed by capillarity in this range of pore sizes,
brines flow easily inside the stone and thus successions of imbibitions and dryings occur more
easily, favouring salt crystallization inside of pores. They also concluded that damage associated
with the smallest pores (under 0.1 μm) is difficult to observe and suggested as a solution to this
problem the use of helium pyknometry and mercury porosimetry to see how the smallest pores
are affected by salt weathering.
Figure 5. Weathering of marble by salt efflorescence in marine environment of Venice.
32
Part I
On the other hand, there are many studies on the influence of the grain size of marbles on
its susceptibility towards salt decay. Livingstone (1988) and Winkler (1988) stated that finegrained marbles can disaggregate faster than coarse-grained ones, due to their larger surface
areas. On the contrary, other authors pointed out that the degree of interlocking between finegrained marbles is stronger and they contain less porosity than coarse-grained rocks; therefore,
fine-grained marbles may deteriorate more slowly than coarse-grained ones (Bell, 1993;
Ozgenoğlu et al., 2000). Nevertheless, marbles may show different behaviours during salt
crystallization tests with thermal cycling. Therefore, further studies on marbles could provide very
useful information that may help to distinguish the effects of salt crystallization and
thermal/moisture (Yavuz and Topal, 2007).
Although there many decay agents that can attack the marble surface, the presence of salt
solutions is the main agent that produces chemical weathering of carbonate. After thermal decay
of marble, opening of micro-cracks takes place, which can favour the entry of salt solutions inside
marbles. Salt solutions can crystallize inside of pores and fissures as a consequence of
temperature or humidity fluctuations, therefore favouring marble decohesion process. However, it
is not clear if the generation of thermal stress is the first step that favours the entry of salt
solutions inside the marbles or, on the contrary, salt solutions migrating through grains
boundaries can dissolve calcite and favour the development of intercrystalline fissures (Åkesson
et al., 2006; Gómez-Heras and Fort, 2007; Al-Naddaf, 2009).
2.3. DECAY BY ATMOSPHERIC POLLUTIONS
Dry deposition is the prevailing mechanism by which atmospheric pollutants (NO, NO2, SO2,
CO, CO2, etc.) are accumulated as aerosols on the stone surface (Fig. 6); they can be activated by
subsequent wet conditions. Several studies have shown that calcium carbonate is very sensitive to
sulphur dioxide, a common atmospheric component (Grossi et al, 1994; Grossi and Murray, 1999;
Böke et al., 2002).
As Grossi et al. (1998 and 2003) indicated, calcareous stones are susceptible to deteriorate
due to chemical attack by acidic pollutants. Physical properties of the stone related to moisture
transport (such as open porosity and specific surface area) could determine the stone response in
the outer environment. The presence of open porosity, small pore size distribution and a high
surface area can contribute to the uptake of air moisture and water retention. A high moisture
content inside the pores leads to carbonate dissolution, and a high surface area favours dry
33
Ana Luque Aranda
deposition. These two processes are important because they will determine to a great extent the
growth of newly-formed products inside pores, for instance sulphates or sulphites.
Depending on the surface characteristics, the ability to “capture” pollutants from the air may
vary by more than one order of magnitude, causing significant differences in dry deposition rates
even over small areas (Kumar et al., 2005). When the stone surface is rain-washed, the moisture is
absorbed into the pores, which favours the dissolution of the pore surface (Sebastián and
Rodriguez-Navarro, 1994; Franzini, 1995). Therefore, this dissolution process, higher in calcitic
than dolomitic marble, leads to an increase in the surface area inside of pores and makes the
calcitic marble more vulnerable to deposition and the effects of other chemical weathering
agents (Bell, 1993; Roger-Carfagni, 1999; Chabas and Jeannette, 2001).
Figure 6. Black-crusts and white areas on marble surface by effect of the rain-water and air pollution in the
centre urban of Istanbul.
Combustion of fossil fuels and some natural processes (such as volcano eruptions) produce
high SO2 emissions, the most aggressive agent causing stone decay. SO2 readily reacts with
calcite (CaCO3) and dolomite (CaMg(CO3)2) in the marble, forming gypsum and epsomite. As the
34
Part I
solubilities of gypsum and epsomite are higher than the solubility of calcite or dolomite, the
former can be dissolved in rain water and penetrate into the inner pores of the material. After the
evaporation of water drops, these salts are redeposited again as aerosols which after the reaction
with carbonate at the surface can again favour the loss of material (Brown and Clifton, 1988).
Böke et al., (1999), noted that the product formed by the reaction of SO 2 with calcareous
stones under high relative humidity conditions is CaSO3×1/2H2O (calcium sulphite hemihydrate)
which is transformed into CaSO4×2H2O (gypsum) by oxidation of sulphite ions:
CaCO3 (SO2/ H2O) CaSO3×0.5H2O
CaSO3×1/2H2O (O2/H2O)  CaSO4×2H2O
However, when the sulphation process detailed above occurs on dolostones (Gauri et al.,
1992), it results in the formation of gypsum and epsomite as follows:
CaMg(CO3)2 + 2SO2 + 8H2O + O2  CaSO4×2H2O + MgSO4×6H2O + 2CO2
As it will be shown later on in this thesis, gypsum is the reaction product of calcite with SO2
and gypsum and epsomite are the two reaction products of dolomite with SO 2. According to
Gauri (1980) and Gauri et al., (1990 and 1992), both salts, as other water-soluble salts, also exert
pressure when they crystallize inside the pores during periods between the episodes of rain in
which the stone dries. Consequently, the pressure generated could produce the exfoliation of the
surface.
Finally, Malaka-Starzec et al., (2004) indicated that the differences in lateral gypsum
distributions between dolomite and calcitic marbles are controlled to a significant extent by their
different surface reactivity towards SO2. Therefore, minimum standards regarding mineralogy,
fabric, texture and thermal properties of marble should be examined in order to determine its
resistance and durability to decay.
35
36
Part I
3.
THE USE OF MARBLE AS ORNAMENTAL STONE
IN
THE
ARCHITECTURAL
HERITAGE
OF
SPAIN.
HISTORY
Throughout all the Spanish geography, we can find numerous archaeological remains of the
ancient civilizations, such as Phoenicians, Greeks, Romans and Arabs from very early ages. The use
of stone as ornamental material was clearly important and necessary for the construction of
settlements even in early times. Some examples which corroborated this use are found in the
form of megalithic and Cyclopean structures such as the Dolmen of Menga in Antequera
(Malaga), the Crag of the Gypsies in Montefrio (Granada), Dolmen of Matarrubilla (Seville) or
Dolmen of La Pastora (Huelva).
Throughout the Spanish history, there are many rocks that have been quarried and used as
construction or ornamental material. Although in the beginning the choice for one kind of stone
was basically based on the quarry accessibility and proximity to the settlement, as well as the ease
of extraction, over time, the different physical and aesthetic properties of the rocks became the
main factors taken into consideration (Barrios-Neira, et al., 2003).
The lithotypes used in the construction of the Spanish monumental heritage are numerous
and of diverse compositions, being the most common limestones, travertines, calcarenites,
serpentines, slates, granites and marbles. Marbles have been selected mainly for the construction
of sculptures and pieces of decoration in buildings of particular interest and symbolism, due to
their excellent mechanical properties, beauty and also because they are easy to polish.
Regarding the quarries and the use of marble as ornamental material throughout the
Spanish architecture, the existence of three historical periods of splendour should be mentioned:
th
the first one corresponds to the Roman Hispania, the second period (16 -18
th
centuries)
corresponds to the construction of the Monastery of El Escorial, the Palace of Carlos V (16
century), and the decoration of the new Royal Palace (18
th
th
century) and the last period is
associated with the modern construction, developed in the last century and recent decades (20
th
st
and 21 centuries).
37
Ana Luque Aranda
3.1. THE USE OF MARBLES DURING THE ROMAN HISPANIA ( 2nd C. BC TO
3rd C. AC)
It is known that the use of marble as ornamental material in the Architecture of Spain dates
back to the first and second centuries BC (Soler-Huertas, 2003). Decorative elements present in
the Roman Theatre in Carthago Nova, the Augusteum, and the sacral area from Molinete
Mountain show that the use of marble was preferred for the construction of the components of
the official and religious architecture of the city of Carthago Nova during that time. Therefore,
since then and throughout the Roman period, its presence in numerous architectural and
ornamental elements indicates that it was demanded for the construction and decoration of
imperial buildings (Cantó, 1977-78; Cisneros, 1988; Loza and Beltrán, 1990; Beltrán and Loza,
1988; Padilla; 1999; Chávez-Álvarez, 2000).
Although marble was initially used on the urban construction and official architecture
following the Roman Empire tendencies, over time, the use of this material became very popular
in the private sector. Probably due to its colour, beauty and relative softness, it was during that
time when the quarrying of marble acquired a special demand and it started eventually to be
used by rich people as a sign of wealth, becoming a symbol of prestige and social status (Fig. 7).
Figure 7. Roman artifacts made of marble, exposed in “Tarraco, pedra a pedra” Archaeology National
Museum of Tarragona.
38
Part I
There are numerous studies which mention the existence of some marble quarries during
that time, especially from Baetica (Fig. 8). Beltran and Loza (1998) indicated that during the
Roman period, many varieties of marble located in different areas of Mijas Chain (Malaga), in
Ardalejos, Alhaurin de la Torre, Alhaurin el Grande, Mijas and Monda, were quarried for its use in
the construction of imperial buildings (Cisneros, 1988; Canto, 1977-78; Chávez-Álvarez, 2000). At
the same time, white Macael marble from Alemeria was also quarried on both banks of El Marchal
stream and was used in sculptures, architectural elements and epigraphic pieces during I-II
centuries (Padilla, 1999).
Figure 8. Ancient marble front quarry of Roman Age in Almaden de la Plata (Seville).
Apart from these marbles from Baetica, there is another marble from Lusitania, quarried in Ossa-Morena
(Huelva), although it seems that it was less important during the Roman period. However, its presence in
some ornamental elements used in the construction of the Forum Censorium of Cordoba seems to ensure
its use during that time (Barrios-Neira, 2003). Also, some pieces of Roman onomastic from Aroche could
have been made with marble from the same area (Ramirez-Sabada, 2009). Due to the fact that Arucci
(Aroche) was a major Roman villa of the Roman Empire during the Flavian period (1
st
century AC), it is
possible that there were also marble quarries in this area at that time (Luzón and León, 1973; Cantó, 2004;
Bermejo-Melendez, 2010).
After the Roman Era and during centuries the quarrying of this material practically
disappeared, until the Arab period in which only some marble quarries were exploited. During
that time, according to the architectural style, marbles were used principally in the manufacture of
39
Ana Luque Aranda
decorative pieces (Lacarra Ducay, 2006). Among the various decorative elements made of
marbles, it can be cited the columns and the Lions Fountain that make up the Lions Courtyard in
Alhambra of Granada (Casares-López, 2009), the columns inside of the Haram in Mosque of
Cordoba, and some tombstones vintage Almoravide of Cordoba (Martínez-Núñez, 1996).
3.2. THE USE OF MARBLES FROM THE 16th THROUGH THE 18th CENTURY
h
One of the most important cultural changes in Spain took place during the 16t century. The
th
period after the Reconquest by the Catholic Monarchs (15 century) meant the political unity for
the first time in country and Catholicism was the only religion permitted in its geography.
This change in religion favoured a change in the architecture, especially in the buildings
designed for religious purposes. At that time, numerous palaces, cathedrals, monasteries and
churches were built and they represent the purest classical style associated with the architecture
of the Renaissance (16
th
century) and Baroque (17
th
and 18
th
centuries), the latter being
characterized by the preference in the use of marble for the construction of ornamental elements.
The facades became important and almost independent from the rest of the work. As a result of
the Italian influence, the use of Carrara’s marble in the manufacture of ornamental elements was
usual. However, many elements in the decoration of buildings facades and altarpieces of Spanish
cathedrals made of other Spanish marbles can be also found (Moreno-Mendoza, 2003; ToajasRoger, 2003).
During 15
th
century, the preference in the use of some peninsular stones to build the
ornamental elements of The Escorial could be the precedent for the use of this type of rocks in
the constructions of the 16
th
century. However, regarding the use of marble, there are only
references about the payment of some types of stone from the quarries located in Macael, which
were used in the construction of the Monastery of El Escorial (Sancho-Gaspar, 1996).
th
Nevertheless, during 16 century, the Palace of Carlos V in Granada, Palace of Velez-Blanco and
Castle of La Calahorra in Granada were built, where it is easy to find elements built with marble
from Macael (Moreno-Mendoza, 2003; Casares-López, 2009).
However, it was not till the 18
th
century when the use of marbles and other ornamental
stones returned again and achieved a significant importance, showing a high demand as building
material of important buildings. In that time, the use of marble as well as any other ornamental
stones, because of its beauty and lasting aspect, was always linked to power and contributed to
the expression of high economic, political and social status. And it was during the reign of
40
Part I
Fernando V when the first compilation of all marble quarries existing in the peninsula ( "Choice
and Marriage Project of Marbles for the Palace") was made, ordered by the monarch, after he
discovered the beauty of some marbles used in the Monastery of El Escorial. Numerous
ornamental stones were collected and listed for their use in the decoration of the Royal Palace
(Tárraga-Baldó, 2009).
Finally, Mijas, Aroche, Macael, Almaden de la Plata became the main marble quarries in
Spain during the 18th and 19th centuries, and the marbles extracted were so varied and beautiful
as any other marble in Europe (López-Burgos, 2002). The presence of some ornamental elements
of the Arzobispal Palace and the Palace of San Telmo in Seville made of marble from Mijas
confirms the use of this marble in this century (Herrera-García, 1988; Beltrán and Loza, 1998;
Terreros and Alcalde, 1996).
3.3. THE USE OF MARBLES THROUGHOUT THE 19th AND 20th CENTURIES
Direct observation of our current buildings may give an idea of the large and varied demand
that this stone has had in the last century (as cladding and pavement material in museums,
theatres, airports and commercial buildings or as countertops, fountains, tombstones, lamps,
residential buildings). A short review of different economic texts explaining the economic activity
driven by the marble quarries in the last decades and how the exploitation of marble has been a
major source of income for the Spanish regions in which this material outcrops can be found in
"The marble sector in the province of Almeria" (El sector del mármol en la provincia de Almeria,
2003), conducted by the Institute Cajamar. In this review, it is stated that 85% of the total of
peninsular quarried marble comes from Almeria (Macael), Alicante (Pinoso, Monforte del Cid and
Novelda) and Murcia (Caravaca and Cehegin). In Macael, the largest producer in the area, more
than 2.2 million tons were extracted in 2001, which represents 42% of all the marble quarried in
the Spanish geography (Fig. 9). Spain has been one of the worldwide leaders in marble
production during the last decades (IGME, 1987; Carretero, 2004).
Carretero (2004) analyzed the evolution of this sector in Spain during the last two decades
of the last century. Although his work was focused on the marble quarried in the Almeria
province as the main extractor, it is also indicated how marbles exploited in Granada, Malaga
(Sierra Blanca), Seville (Almaden de la Plata) and Huelva (Aroche and Fuenteheridos) are relatively
important (Fig. 10). Furthermore, this study indicates that, despite the growing international
competition, Spain is nowadays one of the main countries where marble is quarried.
41
Ana Luque Aranda
Figure 9. Detail of marbles quarries from Macael nowadays.
The importance that Macael marble has acquired in the last decades has been highlighted
by Gutiérrez-Pastor (2004). The large presence of this marble in some of the best national
monuments and international buildings is an indication of the importance that the quarrying of
this material has had throughout history.
Figure 10. Detail of marbles quarries from Fuenteheridos in recent times.
42
Part I
3.4. IDENTIFICATION PROBLEMS ASSOCIATE WITH THE PROVENANCE OF
MARBLE
The identification of marbles used during the Roman period is one of the topics that has
attracted a great deal of attention during the last decades (Lapuente et al., 2000; Soler-Huertas,
2005). This is reflected in the numerous studies performed on the identification and provenance
of marbles used in ornamental elements and sculptures which are part of our archaeological
heritage (Fig. 2) (Cantó, 1977-78; Cisneros, 1988; Lapuente et al., 1988; Bello et al., 1992; Espinosa
et al., 2002; Lapuente, 1995; Urbina et al., 1997). In the early sixties, due to the difficulties in
finding an exact description of white marbles as well as in identifying the different coloured rocks,
archaeologists became aware of the huge necessity of establishing interdisciplinary relationships,
especially with geologists, in order to classify the materials according to their mineralogical
characteristics (Soler-Huertas, 2005).
However, despite the fact that nowadays there is a wide knowledge regarding the different
types of marbles and the location of the quarries that were used during the Roman period, there
is still a lack of information regarding the petrography of some marble elements found in
different archaeological sites (Carrillo Díaz-Pinés, 1995; Chávez-Álvarez, 2000; Ramallo et al., 2004;
Leiva et al., 2005). This has favoured that the Archaeometry science, has been developed new
study methodologies to identify marble (Barbín et al., 1995; Lapuente, 1995; Lapuente et al., 2000;
Lapuente and Blanc, 2002).
In the same way, the urgency of characterizing the petrography of historic marbles arises
from restoration studies focused in pieces made of marble with important problems of
conservation (Bello et al., 1992; Lapuente, 1997; Galan et al., 1999). As it is impossible to work with
the original pieces, it is becoming increasingly important to identify the material and to locate the
source quarry in order to obtain the material needed for conservation essays.
From the need of identifying marbles used in the Cultural Heritage that were quarried in
Andalusia, a new work methodology in archaeology and petrology has been proposed by Galan
et al. (1999). These authors stated, “It is often necessary to locate the original quarry which
supplied the stone for a particular historical building. These stones could be used for future
restoration work and for testing in the laboratory. Generally, reviewing historical documentation
gives information about the geographical setting of quarries and location of the stones in the
monument, but this information needs to be proved by field and laboratory studies”.
43
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Tárraga-Baldó, M.L. (2009). Mármoles y rocas ornamentals en la decoración del Palacio Real
de Madrid. Archivo Español de Arte, LXXXII; 328: 367–392.
Terreros, G.G. and Alcalde, M. (1996). Investigation and treatment of the portal San Telmo
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Thomasen, S.E. and Ewart, C.S. (1984). Durability of the thin-set marble. Third International
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Toajas Roger, M.A. (2003). Capiteles del primer Renacimiento en las Descalzas Reales de
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Phenomena, Conservation Strategies and Case Studies. Geological Society, London, 65–80.
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4.
OBJECTIVES OF THIS THESIS
The use of marble, as ornamental material, has had great archaeological, social, cultural and
economic implications throughout the history of Spain. As it has already been mentioned in the
Introduction section, marble has been widely used as structural and ornamental material in many
buildings and monuments that make up our architectural heritage. In the same way, the fact that
most of the national marble quarries are located in Andalusia, and especially in the Macael
region, makes the manipulation and commercialization of this material one of its main economic
activities.
Considering the implications (mainly of historical-architectural nature) of the use of
Andalusian marbles and the sustainability criteria that these stones should present to ensure their
quality as construction materials, there are five objectives proposed in this thesis:
1) To characterize exhaustively, in mineralogical and petrographical terms, the different
types of marbles extracted from Historical Andalusian quarries. This is necessary as marbles
extracted from different areas have very different properties, even when these belong to the
same geological unit.
2) To determine the main petrophysical parameters that influence marble decay under
thermal variations and to identify the relevant aspects which favour a higher suitability for its use
outer conditions.
3) To analyze salt weathering of marbles, evaluating the role played by dissolution processes
inside the pore structure of marbles.
4) To evaluate the reactivity of marble surfaces with SO2, as a function of their mineralogical
composition (calcitic and dolomitic).
5) To make a useful guide covering the different aspects that characterize and determine the
durability of marbles from Andalusia, and how these aspects can be applied in the selection of
marbles as ornamental and construction materials, as well as those aspects related to their
identification, provenance and conservation.
55
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PART II
Part II
5.
DESCRIPTION OF THE GEOLOGICAL AREAS OF
MARBLE QUARRIES IN ANDALUSIA
5.1. GEOGRAPHY OF ANDALUSIA
Andalusia is an autonomous community of Spain, and it is the second largest in terms of
2
land area with 87.597 km . It is in the south of the Iberian peninsula, south of Extremadura and
Castile La Mancha limited; west of the autonomous community of Murcia and the Mediterranean
Seas, east of Portugal and the Atlantic Ocean and north of the Mediterranean Sea and the Strait
of Gibraltar, which separates Spain from Morocco, and the Atlantic Ocean.
The Andalusian relief is characterized by the stark altitudinal contrast of its ridges and
valleys, characterized by the presence of the highest levels of the Iberian Peninsula (e.g. Sierra
Morena in the north and Sierra Nevada in the southeast). In this region nearly 15% of the territory
is at more than 1.000m above sea level, compared to depressed areas (Valle del Guadalquivir),
which are below 100m elevation.
From a geographical point of view there are three major geomorphologic areas: Sierra
Morena, the Betic Cordillera and the Betic depression.
Sierra Morena, a monotonous system that marks a break between Andalusia and the
Plateau, has a large separation between the mountains and the countryside of Huelva, Seville,
Cordoba and Jaen. Within this mountain range Despeñaperros highlights, which forms a natural
border with Castile-La Mancha.
The Betic Cordillera (Penibetic and Subbetic) develops parallel but not aligned to the
Mediterranean and between these, the Intrabetic graven can be found. The tallest reliefs of
Andalusia are in Sierra Nevada, in the province of Granada, where the highest points of the
Iberian Peninsula are: the Mulhacen (3.478 m) and the Veleta (3.392 m).
The Betic Depression is located between these two systems. It is a territory almost entirely
flat, and it opens towards the Gulf of Cadiz in the southwest.
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5.2. GEOLOGICAL SETTING
The marbles studied in this thesis belong exclusively to the region of Andalusia. Andalusia
geology is constrained by the development of two major orogenies, the Hercinian and the Alpine
(Weijermars, 1991; Vera, 1994), resulting in the formation of two great geologic units: the
Hesperian massif and the Betic cordillera, which are separated from each other by the
Guadalquivir basin (Fig. 11).
Figure 11. Schematic representation of the main geological units that characterize the region of Andalusia,
modified from Vera (1986).
The Hesperian (or Iberian) massif forms part of the European Hercynian fold belt, which
extends along the western half of the Iberian Meseta and crops out in the northwestern region of
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Andalusia. The different nature of its rocks, Precambrian and Paleozoic materials folded during
the Hercynian orogeny, allows us to distinguish five major areas throughout the massif, arranged
in nearly parallel bands, three of which are partially represented in Andalusia, in the Central
Iberian, Ossa Morena and South Portuguese zones.
The Ossa-Morena and South Portuguese zones represent the southernmost domains of this
massif and represent the boundary between the oceanic and continental crusts. This boundary is
marked by a continous amphibolites belt, which can be followed for over 200 Km and has been
interpreted as a dismembered ophiolitic sequence (Bard, 1969). The Ossa Morena zone consists
of a wide range of volcanic, plutonic and metamorphic rocks extending from the Precambrian to
the Lower Permian, while the South Portuguese zone consists essentially of Upper Paleozoic
sediments. Within the South Portuguese zone, deformation and associated flysch deposition
migrated southwards from the ophiolitic suture between the Upper Devonian to the Upper
Carboniferous (Apalategui et al., 1990).
The Ossa Morena zone is considered to form an integral part of the so-called "Internal
zones" of the Hercynian massif, in which materials from the Precambrian to the Lower Paleozoic
ages emerge with an extensive development of plutonic rocks and high-grade metamorphism
over large areas. The South Portuguese zone is included in the "External zones" of the same units,
in which materials from the Upper Paleozoic crop out. In this zone plutonic rocks are scarce and
metamorphism is either absent or very low grade (Lotze, 1945; Julivert et al., 1972).
The Betic cordillera is a great geological unit trending S-SE through the Iberian Peninsula.
This constitutes the northern branch of the Gibraltar arc and has traditionally been divided into
two main tectonic domains: the Internal (southeast) and External zones (northwest), separated by
the flysch (or Campo de Gibraltar) units (Fallot, 1948; Egeler and Fontboté, 1976; Weijermars,
1991; Vera, 1986). The materials comprising the Betic cordilleras crop out in the provinces of
Almeria, Granada, Jaen, Cordoba, Malaga and Cadiz.
The External zone is usually divided into the Prebetic and Subbetic zones and is located on
the southern continental margin of the Iberian block. The Prebetic zone, represented by platform
deposits, is located closer to the South Iberian margin, and the Subbetic zone, which comprises
the sedimentary deposits situated at some distance from the margin, is the area that separates
the Prebetic zone in the north from the Betic zone in the south. It is mostly composed of nonmetamorphic sedimentary rocks, essentially from the Mesozoic and Tertiary eras (GarcíaHernandez et al., 1980; Sanz de Galdeano, 1992; Vera, 1994 and 98).
The materials of the Internal, or Betic, zone are formed by a thrust-stack antiform of three
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nappe complexes, which are in ascending order: the Nevado-Filabride, the Alpujarride and the
Malaguide complexes (Vera, 1994). These nappes were affected by extensional tectonics
contemporaneous with the end of the Alpine metamorphism and post-collisional deformation of
the post-Burdigalian and they are mainly composed of schists, quartzites and marbles. The
Malaguide complex, however, also contains slates, detrital rocks and a carbonate Mesozoic and
Paleogene sequence (Sanz de Galdeano et al., 1999/2000). These materials, with the exception of
the Malaguide, have undergone strong Alpine activity, showing both a high degree of
metamorphism and considerable deformation (Duran-Delga, 1966; Torres-Roldan, 1979).
According to Torres-Roldan (1979), the metamorphism in the Nevado-Filabride Complex reached
high pressure gradients at low temperature whilst that developed in the Alpujarride complex is
characterized by medium-to–low pressure and low temperature. Nevertheless, the Malaguide
complex was scarcely metamorphosed if at all (Sanz de Galdeano, 2001).
Deep-water flysch sediments from the Cretaceous to the Paleogene periods characterize the
Campo de Gibraltar domain, located in the south of Andalusia. This domain is located between
the Internal and External zones (in Cadiz and Malaga), and shows intense deformation but no
metamorphism (Paquet, 1969; Mäkel, 1985).
The marine and continental sediments filling the Guadalquivir basin are deposited on top of
the tabular cover materials and sometimes upon the material of the Iberian massif. Throughout
several million years this basin has been the subsiding sector located between the Iberian massif
(foreland) and the Betic orogen (Vera, 1994). Today it is a sunken sector compared to the rest of
the cordillera..
5.3. MARBLES QUARRIES IN ANDALUSIA
The wide variety of marbles to be found in Andalusia can be put down to its geological
history, involving the formation of a carbonate platform that was subsequently deformed and
metamorphosed during the Hercynian and Alpine orogenies. The result is that the marbles of
Almeria, Granada, Malaga, Seville and Huelva are very different in such aspects as their origin,
age, mineralogy and colour.
On the basis of the geological setting of their quarries, the marbles can be divided into two
groups: those belonging to the Ossa Morena zone and those of the Internal zones of the Betic
cordilleras.
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5.3.1.
Ossa Morena Zone: Aroche and Fuenteheridos districts
Marbles that crop out in the Ossa-Morena zone belong to the so-called Aracena
metamorphic belt, which was formed by an intense thrust associated with the convergence
between the oceanic crust (the Pulo do Lobo unit, in the South Portuguese zone) and the
continental crust (high-grade metamorphic units in the Ossa-Morena zone) (Bard, 1969). The
Aracena metamorphic belt is a high-grade metamorphic band trending NW-SE, the limits of
which are parallel to the main regional structural trends, which separate this unit from the Central
Iberian zone to the North. According to Castro et al. (1996), two different domains can be
distinguished in the Aracena metamorphic belt: a southern oceanic domain in the South
Portuguese zone, and a northern continental domain in the Ossa-Morena zone, this latter being
structurally defined by two antiforms, the Fuenteheridos antiform to the north and the Cortegana
antiform to the south (Bard, 1969).
Additionally, two groups of rock can be distinguished in the oceanic domain. In the northern
part, the Acebuches metabasites define a series of amphibolites and mafic schists, the product of
the metamorphism of a former oceanic crust with MORB affinities. To area to the south of the
Acebuches metabasites has been interpreted by Eden (1991) as being part of an old accretionary
prism. The continental domain, on the other hand, is made up mainly of pelitic gneisses and
migmatites, calc-silicates, leucocratic gneisses, amphibolites and marbles. The continental domain
has also been subdivided according to metamorphic grade criteria into a northern medium-grade
zone and a southern high-grade zone (Apalategui et al., 1983; 1984; Crespo-Blanc and Orozco,
1991; Díaz-Azpiroz, 2001; Díaz-Aspiroz et al., 2004).
Marbles from the Aracena metamorphic belt, are located inside the Cambrian-Ordovician
carbonates, which were metamorphosed during the Upper-Palaeozoic Variscan orogeny
(Apalategui et al., 1983; Crespo-Blanc and Orozco 1991; Castro et al., 1996; Díaz-Aspiroz et al.,
2004). According to their degrees of metamorphism, however, two marble sites can be identified:
marbles from Aroche and marbles from Fuenteheridos (Fig. 12).
The metamorphic gradient that characterizes the marbles from Aroche is due to the effects
of contact metamorphism developed by the intrusion of granitoids. Calc-silicate rocks with
diverse mineral assemblages were formed in the contact aureoles by metasomatic interaction
between marble and magma-derived fluids, forming extensive calcic and magnesian skarns.
Therefore, on the basis of the dominant mineralogy, two types of carbonate rocks can be
identified (calcitic and dolomitic marbles). Nevertheless, different metamorphic effects were
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Ana Luque Aranda
developed depending upon the composition of the carbonate rock (Fernández-Caliani et al.,
2001).
Figure 12. Detailed locations of the marble quarries at Aroche and Fuenteheridos in the Ossa Morena zone.
Image from Magna, nº 917-916, modified from Apalategui et al. (1983 and 1984).
The marbles have coarse-to-medium-grained granoblastic textures and correspond to the
high-grade (high temperature and low pressure) zone of the continental domain at the base of
the calc-silicate series (leucocratic gneisses, calc-silicates, amphibolites, and marbles). This series
takes the form of sporadic bands and lenticular bodies, and is associated with leucocratic
gneisses, amphibolites, quarzites and graphitic gneisses (Díaz-Azpiroz et al., 2004).
The marbles at Fuenteheridos, are located in the so-called Fuenteheridos low-grademetamorphism (medium-to-low temperature and low pressure) antiform, developed in the
Aracena dolomite series (Apalategui et al., 1984). The Aracena dolomites probably date to the
Lower Cambrian in the Aracena massif and represent the carbonate episode that occurred across
the whole Ossa Morena zone during this period (Crespo-Blanc and Orozco, 1991). These marbles
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Part II
crop out in the northern limb of the Fuenteheridos antiform and can be related to their
equivalent high-grade rocks that crop out in the southern limb in the Cortegana antiform.
Therefore, the marbles of the Jabugo-Acebuches zone represent the same lithostratigraphic
series as their equivalents in the Navahermosa-Castaño del Robledo zone because, despite their
different degrees of metamorphism, both sequences are similar (Bard, 1969).
Nevertheless, according to Crespo-Blanc and Orozco (1991), the marbles at Aroche and
Fuenteheridos correspond to the same lithostratigraphic unit, although both groups show
different metamorphic gradients. The Aroche marbles correspond to the southern, high-grade
Jabugo-Acebuches zone, whilst those at Fuenteheridos correspond to the northern low-tomedium-grade Navahermosa-Castaño del Robledo zone (Fig. 10).
5.3.2.
Internal (Betic) zones: Macael, Alhama de Granada and Mijas districts
The marbles that crop out throughout the Internal zones (in the provinces of Almería,
Granada and Málaga) belong to materials described in the Nevado-Filabres and Alpujarride
complexes, mainly carbonate-sediment sequences deposited during the Triassic. Three sites can
be distinguished: marbles from the Sierra de los Filabres (Macael district), from the Sierra Tejeda
(Alhama de Granada district) and from the Sierra Blanca (Malaga district) (Fig. 13).
The Nevado-Filabride complex crops out in the core of the antiform of the Sierra Nevada
and Sierra de los Filabres. It can be subdivided into two: a more severely deformed upper unit
comprising a mixture of marbles, quartzites, metapelites and metabasite lenses, overlying a more
uniform, apparently less-deformed unit composed of Palaeozoic graphite schists and quartzites
(Gomez-Pugnaire et al., 1976; Fontboté, 1986). These units are known as the Mulhacen (above)
and Veleta (below). The development of Alpine metamorphism in this area reaches a highpressure and medium- to high- temperature event (P = 9±20 kbar, T = 350±690 °C) (GómezPugnaire et al., 1994).
The main ornamental marble outcrops, to be found in the Nevado-Filabres complex, are
located in the Sierra de los Filabres. This mountain range is characterized by a wide variety of
carbonate materials ranging from pure, highly crystalline marble to yellowish, terrigenous
limestones. As Quereda Rodriguez-Navarro (1997) commented, apart from white marble and all
its associated ranges (veined white marble, slightly coloured, arabesques etc.), there are also
other varieties such as gray marble, cipolin (or anasol), serpentine and yellow dolomite marbles
(Macael Gold, Yellow Triana, Yellow Macael), all of which are quarried in the Sierra de Los Filabres.
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Figure 13. Details of the areas where marble quarries from Nevado-Filabride and Alpujarride Complexes are
located. From Ruano (2004) modified.
According to the stratigraphic succession described for the units of the Nevado-Filabride
(Nijhuis, 1964; García-Dueñas et al., 1988), these marbles from the Macael area correspond
specifically to the Las Casas and Huertecicas formations within the geological units of NevadoLubrín and Bedar-Macael, which is broadly equivalent to the Bedar-Macael plus Calar-Alto units
and the Veleta unit (IGME, 1975; García-Dueñas et at., 1988; Martínez-Martínez et al., 1995).
The main varieties of marble from the Sierra de los Filabres studied in this thesis are the
following: White Macael (from Macael), Tranco Macael (from Lubrin) and Yellow Triana Macael
(from Codbar), which form part of the Upper Triassic Mulhacen Group. The White Macael and
Tranco Macael varieties of marble are calcitic whilst the Yellow Triana Macael marble is dolomitic,
although in general terms the mineralogy of these carbonates is quite simple. They almost
exclusively consist of calcitic and dolomitic minerals with some occasional white mica, albite,
quartz and pyrite (Zezza and Sebastián, 1992).
The Alpujarride complex, is the most extensive unit of the three nappes of the Internal
zones. The lithostratigraphic sequence of this complex comprises, from bottom to top: the mica
schist formation, which locally includes gneisses and migmatites at its base; the grey to bluishgrey fine-grained schist or phyllite formation; and the carbonate formation, which containing
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Part II
dolomitic and calcitic marbles in the top.
The carbonate formation has been dated as Mid- to Upper Triassic age; the grey finegrained schist and phyllites, are generally attributed to Permo-Trias age, and the mica schist
formation of assumed Pre-Permian age (Alonso-Chaves et al., 2004). In general, although all these
rocks tend to betray the high-grade (HP/LT) metamorphism generated by The Alpine event, each
unit from Alpujarride complex can show its own characteristic metamorphic grade (Jabaloy et al.,
1992; Azañón et al., 1992). According to Monie (in García-Casco and Torres-Roldan, 1996),
metamorphic development within the Alpujarride domain covers a wide range of P-T conditions,
including high-P/low-T, high-P/high-T and low-P/low-T, with fairly systematic variations occurring
within particular groups of unit.
The marbles in the Alpujarride complex (carbonate formation) can be found in the Sierra
Tejeda and Sierra Almijara and the Sierra Blanca and Sierra de Mijas areas. The marble quarries in
these two areas are mainly dolomitic but levels of calcitic marble also are found intercalated
within both areas: White Iberico marble (Granada district) corresponds to the Almijara and Tejeda
units and Mijas marble (Malaga district) to the Blanca unit in the Sierra Blanca and Sierra de Mijas
(Sanz de Galdeano and Andreo, 1995; Andreo et al., 1998).
In the Almijara and Tejeda mountain range there is a substantial outcrop of carbonate
materials belonging to the Alpujarride complex and dating to the Anisian to Norian ages (Sanz de
Galdeano, 1989; Andreo and Sanz de Galdeano, 1994). These calcitic and dolomitic marbles
correspond to the Almijara unit, which is highly metamorphosed and crops out in the form of a
succession of calcitic and/or dolomitic marbles with intercalated layers of rich calco-magnesium
silicates, calc-schists, mica-schists and amphibolites (Sanz de Galdeano and López-Garrido, 2003).
These authors distinguish between three types of marble in this unit: lower marbles (dolomitic),
marbles interbedded with shales and calc-schists (dolomitic and calcitic), and upper marbles
(dolomitic).
With regard to the marble quarried in Sierra Blanca and Sierra de Mijas (Malaga), which
belong to the Ojen unit in the Blanca group, three main tectonic-metamorphic events can be
identified: an initial stage of high-pressure (at least 11-12 kbar) and high-temperature (at least
700-750 °C) metamorphic grade, followed by a decompression stage (5-7 kbar) associated with
increasing temperature (800-900°C), and a final decompression stage marked by a decrease of
the thermal gradient (from 800 to 600 °C) (Sosson et al., 1998).
Stratigraphically, the Ojen unit consists of a sequence of rich metapelitic amphibolites and
quartzites, on which is deposited an extremely thick stretch of marble. According to Tubía (1984),
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three kinds of marbles can be found in this carbonate sequence: marbles with calc-schist and
nodules of quartz, calcitic marbles and saccharoid marbles with amphibolitic levels.
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Fernández-Caliani, J.C., Miras, A., Moreno-Ventas, I., Requena, A. (2001). Las rocas
calcosilicatadas del extreme occidental de la banda metamórfica de Aracena (Huelva). Interés
mineralógico y petrogenético. XXIª Reunión annual de la Sociedad Española de Mineralogía,
Málaga; 24A: 125–126.
Fallot, P. (1948). Les Cordillères Bétiques. Estudies Geology; 4: 83–172.
Fontboté, J.M. (1986). Las Zonas Internas de la cordillera Bética. In: Geología de España,
Libro Homenaje J.M. Ríos, Ed. IGME (II): 251–343.
Galíndo-Zaldívar, J., González-Lodeiro, F., Jabaloy, A. (1989). Progressive extensional shear in
a detachment contact in the Western Sierra Nevada (Betic Cordilleras, Spain). Geodinamica Acta;
3: 78–85.
García-Dueñas, V., Martínez-Martínez, J.M., Soto, J.I. (1988). Los Nevado Filábrides una pila
de pliegue de mantos separados por zonas de cizalla. II Congreso Geológico de España: 17–26.
García-Casco,
A.
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(1996).
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Decompression in St-Bt-Grt-Ky-Sil-And Metapelites from the Betic Belt (Southern Spain). Journal
of Petrology; 5 (37): 1207–1239.
García-Hernández, M., López-Garrido, A.C., Rivas, P., Sanz de Galdeano, C., Vera, J.A. (1980).
Mesozoic paleogeographic evolution of the External Zones of the Betic Cordillera. Geol.
Mijnbouw; 59: 155–168.
Gómez-Pugnaire, M.T., Puga, E., Sassi, F.P. (1976), New data on alpine metamorphic history
of the Nevado-Filabride Complex in the Sierra de Baza area (Betic Cordilleras, Spain). MinPet Acta
(2): 29–41.
Gómez-Pugnaire, M.T., Franz, G., López Sánchez-Vizcaíno, V. (1994). Retrograde formation of
NaCl-scapolite in high-pressure metaevaporites from the Cordilleras Béticas (Spain). Contribution
Mineralogy Petrology; 116: 448–461.
IGME (1975). Mapa Geológico 1:50.000, MAGNA. Hoja nº 1013 (Macael).
Jabaloy, A., Galíndo-Zaldívar, J., González-Lodeiro, F. (1992). The Mecina extensional system:
their relation with the post-Aquitanian piggy-back basins and the paleostress evolution (Betic
Cordilleras, Spain). Geomar, Letter; 12: 96–103.
Julivert, M., Fontboté, J.M., Ribeiro, A., Conde, L. (1972). Memoria explicativa del Mapa
Tectónico de la Peninsula Ibérica y Baleares. 1:1.000.000. IGME, Madrid: 1–101.
Lotze, F. (1945). Zur Gliederung der Varisziden der Iberischen Mesetas. Geotekt. Forsch.; 6:
78–92.
Mäkel, G.H. (1985). The geology of the Malaguide complex and its bearing on the
geodynamic evolution of the Betic-Rif orogen (southern Spain and northern Morocco). Geol.
GUA. Pap; 22: 263 pp.
Martín-Algarra, A. (1987). Evolution of a Pliocene fan delta: between the Sorbas and
Carboneras Basin, SE Spain. In: Frostick, L. and Steele, R. (eds). Tectonic Controls and Signatues in
Sedimentary Successions. IAS Special Publication; 20: 177–290.
Martínez-Martínez, J.M., Soto, J.I., Balanyá, J.C. (1995). Large scale structures in the NevadoFilabride Complex and crustal seismic fabrics of the deep seismic reflexion profile ESCI-Béticas2.
Revista de la Sociedad Geológica de España; 8 (4): 1995.
Nieto, J.M., Puga, E., Monié, P., Díaz de Federico, A., Jacoutz, E. (1997). High pressure
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Nijhuis, H.J. (1964). Plurifacial alpine metamorphism in the south-eastern Sierra de los
Filabres. South of Lubrin, SE Spain. Doctoral Thesis, University of Amsterdam.
Paquet, J. (1969). Etude géologique de l`Quest de la Province de Murcia. Les Mémoires de la
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Filabres. Incidencia de su explotación en el Medio Ambiente. In: A. Navarro Flores and L. GarcíaRossell Martínez, Recursos naturales y medio ambiente en el sureste peninsular: 335–349.
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the Central Betic Cordillera. Pure and Applied Geophysics; 161: 541–563.
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Béticas. IGME, Madrid. Serie Tesis Doctorales, 5: 498 pp.
Sáez-Pérez, M.P. (2004). Estudio de elementos arquitectónicos y composición de materiales
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Zone (S Spain, N Morocco). Palaeogeography, Palaeoclimatology, Palaeoecology; 167: 157–173.
Sanz de Galdeano, C. and López-Garrido, A.C. (2003). Revisión de las Unidades Alpujárrides
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de las Sierras de Tejeda, Almijara y Guájates (Sector central de la Zona interna Bética, provincias
de Granada y Málaga). Revista de la Sociedad Geológica de España; 16 (3-4): 135–149.
Sosson, M., Morillon, A.C., Bourgois, J., Téraud, G., Poupeau, G. Saint-Marc, P. (1998). Late
exhumation stages of the alpujarride Complex (western Betic Cordilleras, Spain): new
thermochronological and structural data on Los Reales and Ojen nappes. Tectonophysics; 285:
253–273.
Torres-Roldan, R. (1979). The tectonic subdivision of the Betic Zone (Betic Cordilleras,
Southern Spain): its significance and one possible geotectonic scenario for the westernmost
Alpine belt. American Journal of Science; 279: 19–51.
Tubía, J.M. (1984). The Ronda peridotites (Los Reales nappe) an example of the relationships
between lithospheric thickening by oblique tectonics and late extensional deformation within
Betic Cordillera (Spain). Tectonophysics; 238: 381–398.
Vera, J.A. (1986). Las Zonas Externas de la Cordillera Bética. In: Geología de España, Libro
Homenaje J.M. Ríos, Ed. IGME (II): 218–251.
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310–317.
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problemas pendientes. Cuadernos de Geología Ibérica; 24: 17–42.
Weijermars, R. (1991). Geology and tectonics of the Betic Zone, SE Spain. Earth Science
Review; 31: 153–236.
Zezza, U. and Sebastián Pardo, E. (1992). El mármol de Macael (Almería) en los monumentos
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Arquitectónico y Edificación. Islas Canarias, vol. I: 153–160.
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6.
METHODOLOGY
6.1. CHEMICAL AND MINERALOGICAL CHARACTERIZATION
6.1.1.
X-ray Fluorescence (XRF)
This technique was used to analyze the spectrum of X-ray emission of the different elements
present in the samples in order to know the quantification of its chemical composition.
Major elements (SiO2; Al2O3; Fe2O3; MnO; MgO; CaO; Na2O; K2O; TiO2; P2O5 expresed in %)
were analyzed with XRF technique, using a S4 Pioneer Bruker AXS provided with 4kW excitation
source, and the fluorescence signal is received by the detector through 4 collimators and 8
diffraction crystals. The interpretation of raw data was done using Bruker-designed software
SPECTRA plus. All the elements of the periodic table from Beryllium to Uranium can be measured
quantitatively in powders marble samples (≥5 g.). Concentration of up to 100% of sample is
analyzed directly and typical limits of detection are from 0.1 to 10 ppm.
6.1.2.
X-ray diffraction (XRD)
X-ray diffraction (XRD) is used in the identification and quantification of minerals that make
up crystalline materials. In this thesis, its main role has been the identification of the predominant
carbonate phase (calcite and/or dolomite) that characterizes the studied marbles. For this analysis
all samples were ground in an agate mortar up to make sizes powder below 53 µm.
The mineralogy of marbles was determined using a Philips PW-1710 diffractometer with
automatic slit, CuKα radiation (λ = 1.5405 Å), 40kV, 40 mA. Data were collected with 0.1º
goniometer speed and 2θ from 3º to 60º. XPowder program (Martín Ramos, 2004) was used to
identify the predominant mineral phase of each marble. Semiquantitative analysis was performed
using the Reference Intensity Method (RIM) (Martín Pozas et al., 1969; Klug and Alexander, 1974),
although for doing this it has been taken into account those factors indicated by Mellinger (1979)
which affect the intensity of reflection to be analyzed. Reflective factors used in calcite and
dolomite according to reflexion at 3.03 Å and 2.88 Å were 1 and 1.03 respectively (Barahona
Fernández, 1974) and the error assumed for the quantification was ± 5%.
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6.1.3.
Polarized optical microscopy (OM)
The mineralogy and texture of marbles was performed with a polarized optical microscopy
(OM) using Olympus BX60 microscope equipped with a digital microphotography unit (Olympus
DP10). Three thin sections per marble, according to a coordinate reference system, were prepared
and observed with parallel and crossed nicols. Polarising microscopy was used for revealing
information, fabrics and textures of the minerals as well as the grains size and boundaries of the
observed materials.
Thin sections were orientated with respect to the macroscopic fabric elements (foliation and
lineation) and a coordinate reference system was established along three orthogonal directions
(X-, Y-, Z-axes). In marbles whose fabric elements could be identified, the X-axis was orientated
parallel to the lineation; the XY-plane to the foliation plane, and Z-axis indicated the coaxial
direction with the foliation plane (Fig. 14).
Figure 14. Coordinate reference system of the sample orientation according to the X-, Y- and Z-direction
determined to each marble.
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Part II
6.2. DETERMINATION OF PHYSICAL PROPERTIES
6.2.1.
Mercury intrusion porosimetry (MIP)
The volume of the pores and their size distribution are important factors to take into
account when evaluating the durability of porous materials. The most widely used technique to
characterize these properties is the mercury intrusion porosimetry (MIP).
Distribution of the pore access size as well as the pore volumes were determined using a
Micrometrics Autopore III 9410 porosimeter with a maximum injection pressure of 414 MPa. This
apparatus is able to measure pores with a diameter comprised between 0.003 and 360 μm,
approximately. The principle of the technique is based on mercury properties as its high surface
tension and its property as a non-wetting liquid for most of the surfaces. Therefore, pressure
must be applied to force mercury to enter into a porous material (Lowell and Shields, 1984). The
capillary pressure (Pc) at which mercury intrudes depends on the pore radius, r, according to the
equation:
where ζ (480×10
-3
N/m) is the surface tension between liquid/vapour interfacial energy of
mercury and θ is the contact angle. Since mercury is a non-wetting liquid, θ is greater than 90º
(usually the instrument assumes a θ ~ 130º).
6.2.2.
Nitrogen adsorption
The nitrogen adsorption isotherm helps to calculate the pore size less than 0.1 μm. Pore
3
volume (Pvol in cm /g) is calculated from the total volume of gas adsorbed at the saturated
pressure (P/P0 = 0.25), after transformation into a liquid volume:
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3
3
where, Va (cm /g) is the total volume of gas adsorbed at saturated pressure P0 (cm ) and M
(g) is the sample mass.
The adsorption isotherm was measured using a Micromeritics TRISTAR 3000 by adsorption
conditions. The analysis of gas sorption isotherm using a modified Frenkel-Halsey-Hill theory
(Tang et al., 2003) helps to determine of the surface fractal dimension (D s) from the slope (A) of
the plot of Ln(V) vs Ln[Ln(P/P0)], where V is the adsorbed volume of gas, and P and P0 are the
actual and the condensation gas pressure. When surface tension (or capillary condensation)
–3
effects are important, the relationship between A and DS is A = DS . Capillary condensation is
significant if δ = 3×(1+A)
–2
< 0. The pressure range and, hence, the thickness range of the
adsorbed layer being studied was only around monolayer (n = 1-2) coverage to ensure that the
determination of DS was reliable (Tang et al., 2003).
6.2.3.
Colour variations
Colour measurements were carried out with a MINOLTA CR-210 colorimeter. Measurements
were expressed using the CIE (Commission International de l’Eclairage) L* a* b* system (CIE,
1986). The overall colour variation (ΔE) was evaluated using the following equation:
ΔE = (ΔL*² + Δa*² + Δb*²)
1/2
where L* represents the lightness and, a* and b* are the chromatic coordinates.
6.2.4.
Hydric tests
Real and apparent density and open porosity were measured by forced water absorption
according to the UNE-EN 1936 (2007) standard.
3
The real density ρreal (g/cm ), is the ratio of the mass to the impermeable volume of the
sample:
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Part II
3
The bulk density (or apparent density) ρbulk (g/cm ), is the ratio of the mass to the bulk
volume of the sample:
Open porosity is expressed as the ratio of the volume of the pores accessible to water to the
bulk volume of the sample, P (%):
where M0 (g) is the dry mass, M1 (g) is the saturated mass and M2 (g) is the hydrostatic mass.
The parameters associated to fluid uptake and transports inside the pores were determined
by hydric tests: Water absorption (UNE-EN 13755:2001) and water vapour permeability (EN ISO
12572:2001) uptake were determined.
The water absorption Ф0 (%), is the mass of water absorbed under atmospheric pressure by
immersion:
where M0 (g) is the dry mass and M1 (g) is the saturated mass.
The water vapour permeability Kv (g / m² x 24h), is the quantity of water vapour passing per
time unit and surface units through a porous material under isothermal conditions:
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where, M0 (g) is the dry mass, M1 (g) is the saturated mass and t is the unit of time.
6.2.5.
X-ray Diffraction texture
Texture measurements were performed on an X-ray texture goniometer especially designed
for rock texture analyses (PANalytical X’pert System X-ray diffractometer). A large X-ray beam size
up to 7 mm, high X-ray intensities and automated sample measuring allow to measure relative
large sample volumes in an adequate time (≥ 12 hours), which is important for the coarse grained
marble samples. On the basis of at least five experimental pole-figures of each marble, nine
points in each section, a quantitative texture analysis was carried out.
Hypothetical textures used for the modelling of the thermal expansion coefficient (α) and
the compressional wave velocity (Vp) by calculating the orientation distribution function (ODF) by
means of the WIMV-algorithm (Matthies and Vinel, 1982) and the iterative series-expansion
method (Dahms and Bunge, 1989). The bulk rock anisotropy of the thermal dilatation coefficient
and ultrasound waves velocity were calculated by applying the VOIGT averaging method (Bunge,
1985) and are represented in equal area projections.
6.2.6.
Ultrasonic waves velocity measurements
The aim of ultrasound measurement is to determine the time of flight of ultrasonic
longitudinal waves Vp as a ratio with the distance between a transmitter and a receiver to the
corrected time (time going from the transmitter to the receiver). The velocity is related to
compositional, textural and physical characteristics such as the mineralogical composition, the
intercrystalline connections, the porosity, and the moisture content.
The measurements were performed by means of a Panametrics HV Pulser/Receiver 5058PR
coupled with a Tektronix TDS 3012B oscilloscope. The propagation velocity of compressional (Vp)
pulses was measured in accordance with the ASTM D 2845 (2005) standard on dry and wet test
samples using polarized Panametric transducers of 1 GHz. Three measurements were taken for
each spatial direction (X, Y and Z) of each marble. These data were used to give information on
the degree of compactness of marbles (a decrease in the velocity suggests the development of
fissures) as well as on the textural anisotropy of marbles (ΔM, in %), which can be calculated as
follows:
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Part II
where Vpmax is the maximum, Vpmin is the minimum and Vpmid the medium value for
ultrasonic wave velocity.
Due to their non-destructive nature, ultrasounds are useful to determine the alteration
degree of the stone, since they decrease as the number of weathering cycles increase;
enhancement of porosity is also assumed; the ultrasonic waves velocity on a weathered material
can be compared to the velocity obtained on unweathered material, and also determine
structural changes (Accardo et al., 1981; Calleja et al., 1989; Simon, 2001); changes in velocity
related to the degree of weathering led and, in particular, to the alteration classification of
marbles. Köhler (1991) related the ultrasonic velocity to the state of degradation of marble (Table
1).
Table 1. Structural damage classification on the basis of Vp for marble from Köhler (1991).
Vp (km/s)
Description
Classification
> 4.5
Fresh marble
0
3 - 4.5
Increasing porosity
1
2-3
Progressive granular disintegration
2
1-2
Danger of breakdown
3
<1
Complete structural destruction
4
categories
6.2.7.
Thermal dilatation
The 6-rod-dilatometer (Strohmeyer, 2003) consists of three main units: the heating unit, the
specimen holder in the climate chamber and the displacement register. The heating-up is done
by two copperplates directly beneath and above the specimens. The displacement sensors
permits to determine length changes of ±1 µm. Due to a sample length of 50 mm a final residual
strain of about 0.02 mm/m could be resolved. Calibration of the dilatometer was done by using
-6
-1
quartz glass standards (isotropic expansion coefficient from α = 0.5 x 10 K ). The temperature
was recorded from a sensor placed inside of a dummy cylinder made of the same material as the
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samples.
All marbles were drilling (50 mm of length × 25 mm of diameter) in three orthogonal
directions according to our coordinate system previously established. Before thermal dilatation
test, all samples were dried to constant mass at a temperature of 40 °C along 48 hours.
The thermal expansion coefficient α (10
-6
-1
K ), expresses the relative change in length (or
volume) of the stone according to changes in temperature:
α = Δl/(l×ΔT)
where, Δl (in mm) is the change in length of the simple, l (in mm) is the length of sample
and ΔT (in ºC) is the temperature interval.
Thermal expansion εrs (mm/m), represents the relationship between the change in length of
the sample after cooling down to room temperature and the original sample length and is
defined as:
εrs = Δlrt/lr
where, Δlrt (in mm) is the change in length of the sample after cooling down to room
temperature and lr (in mm) is the original length of the sample for a given temperature range.
The residual strain r (mm), generated by the thermal expansion is the irreversible damage
that takes place in a sample once it returns to its initial (environmental) temperature. This
parameter is related to anisotropic thermal expansion.
6.2.8.
Thermo X-ray Diffraction
Lattice parameters and thermal dilatation coefficient (α) were measured in calcitic and
dolomitic minerals components in all marbles by the use of Thermo X-ray Diffraction. In situ XRD
data were acquired using a Philips PW1710/00 X-ray diffractometer with PW1712 communication
card via RS232 serial port, full-duplex controlled by the XPowder PLUS software (Martín-Ramos,
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Part II
2004). The heating device is composed of an halogen lamp (Philips Capsule-line Pro 75 W, 12 V)
that heats the XRD chamber up to 230 °C, a Pt-1000 probe for T monitoring (0.5 °C precision),
and a software-controlled thermostat with digital T selection. A detailed description of the
heating system is described elsewhere (Cardell, et al., 2007).
Powder grain size samples (~100 µm) were prepared and three thermal tests were
performed to each marble. XRD patterns were scanned over 20<°2θ<60 range, with 0.1
goniometric rate and 0.4 s integration time. Backgrounds of diffraction patterns were subtracted.
The scan mode was continuous using CuKα radiation. The voltage was 40 kV, and the tube
current 40 mA. Diffraction patterns were collected at 5 °C increments from 30 to 90 °C. Thermal
dilatation coefficients were measured by changing the lens (in °2θ) with increasing temperature
(heating rate: 5 °C/min over a T range of 30-90 °C).
The use of this technique allows determined lattice parameters of calcitic and dolomitic
minerals. Reflections at (014), (006), (110), and (113) of calcite and (014), (006), (015), and (110) of
dolomite recorder in the Bragg angle region between 27 and 42 º2θ were selected to calculate
the lattice parameters (a, b and c in Å).
-6
-1
Thermal dilatation coefficients (α, in 10 K ) of calcitic and dolomitic minerals expresses the
relative change in length along their lattice parameters according to changes in temperature (ΔT,
in ºC):
α = Δl/(l×ΔT)
where, Δl (in mm) is the change in length of the lattice parameters, l (in mm) is the initial
length and ΔT (in ºC) is the temperature interval.
6.3. DECAY TESTS
6.3.1.
Salt solution
The durability of marbles was evaluated with an accelerated salt crystallization test
throughout 15 days (UNE-EN 12370:1999). One cycle of salt crystallization test consisted of the
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Ana Luque Aranda
immersion of cubic (50×50×50 mm) rock specimens in an oversaturated solution of Na 2SO4 for
16 hours and successive drying in an oven at 105º C for 4 hours and cooling at room temperature
during other 4 hours. Salt crystallization test was extended to 40 cycles; weight loss and ultrasonic
velocity were measured after experiencing every 10 cycles. At the end of test, dissolution
processes by the effect of salt inside the pore system were measured to evaluate the rugosity
along fisural space surface.
6.3.2.
Sulphatation test
Accelerated sulphatation test was performed in a Kesternich chamber at constant
atmospheric pressure (1 atm), 25º C, 90% RH and 400 ppm of SO 2 concentration during 24 hours.
A container full of water was introduced into the chamber to keep high RH concentrations.
Samples were cut into slabs of 10×10×3 mm and dried for 48 hours at 40º C before being placed
in the chamber. Visual observation and chemical analyses were used to evaluate new minerals
phases developed in marbles surface.
6.4. HIGH RESOLUTION TECHNIQUE APPLIED TO SURFACE STUDY
6.4.1.
Environmental scanning electron microscopy (ESEM)
To evaluate how grain boundaries are affected by the residual strain generated by one
thermal dry cycle, direct observation was carried out by means of an environmental scanning
electron microscope (ESEM) equipped with a heating stage. For this technique a thin section
(5000×5000×400 µm) of each marble was prepared and the thermal cycle showed the ramp: 2045-90-20 ºC. Thin slabs (2000x1000x400 µm) for each marble were prepared for experimental
procedure.
The images were obtained on a FEI Quanta 400 ESEM microscope, which operates at an
accelerating voltage of 20 kV. During heating, the detector-sample distance was set to ~12 mm
and the ESEM chamber pressure was set at ~2 Torr water vapour. This water vapour pressure is
equivalent to that of the environmental air at 20 °C and 15% RH. Each sample was heated at an
average heating rate of between 3-5 °C/min. A constant temperature was maintained during
image acquisition, after 15 min, which was the equilibration time.
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Part II
6.4.2.
Variable pressure scanning electron microscopy (VPSEM)
Visual observation in marbles surface was performed by means of a variable pressure
scanning electron microscopy (VPSEM) LEO 1430-VP, and the chemical composition of the
gypsum (and/or epsomite) crystals developed on the surface was analysed by EDX microanalysis
(SEM-EDX) Inca 350 version 17 Oxford Instrument, which enables the identification of elements
with low atomic numbers, including carbon. Images were acquired in backscattered electron (BSE)
and secondary electron (SE) modes.
6.4.3.
X-ray photoelectron spectroscopy (XPS)
In order to characterise the chemistry of the surface of the seven marbles, X-ray
photoelectron spectroscopy (XPS) analyses were performed and combined with 4 keV Ar
+
bombardment before and after sulphatation test, to enable chemical analyses to be performed at
greater depth. XPS spectra were recorded using a Physical Electronics PHI 5701 spectrometer with
a multi-channel hemispherical electroanalyzer. Non-monochromatic MgKα X-ray (300 W, 15 kV,
1253.6 eV) was used as excitation source. The spectrometer energy scale was calibrated using Cu
2p3/2, Ag 3d5/2, and Au 4f7/2 photoelectron lines at 932.7, 368.3, and 84.0 eV, respectively. The
binding energy of photoelectron peaks was referenced to C 1s core level for adventitious carbon
at 284.8 eV. High-resolution spectra were recorded at a given take-off angle of 45º by a
concentric hemispherical analyzer operating in the constant pass energy mode at 29.35 eV and
using a 720 μm diameter aperture. The residual pressure in the analysis chamber was maintained
-7
below 1.33 × 10 Pa during the spectra acquisition.
The PHI ACCESS ESCA-V8.0C software package was used for acquisition and data analysis.
Recorded spectra were fitted using Gauss-Lorentz curves in order to determine the binding
energy of the different element core levels more accurately (Brigg and Seah, 1995). After the
subtraction of a Shirley-type background, atomic concentration percentages (A.C. %) of the
characteristic marble elements were determined from high-resolution spectra and it was taking
into account the corresponding area sensitivity factor for every photoelectron line (Moulder et al.,
1992). Survey and multiregion spectra were recorded of C 1s, O 1s, Ca 2p, S 2p and Mg 2p
photoelectron peaks.
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References
Accardo G., Massa S., Rossi-Doria P., Sammuri, P., Tabasso Laurenzi M. (1981). Artificial
weathering of Carrara marble: relationships between the induced variations of some
physicalproperties. International Symposium The Conservation of Stone II, Bologna, (I): 243-273.
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85
Ana Luque Aranda
86
PART III
Part III
7.
Anisotropic behaviour of White Macael marble
used in the Alhambra of Granada (Spain). The role
of thermohydric expansion in stone durability
a
a
b
b
a
A. Luque *, G. Cultrone , S. Mosch , S. Siegesmund , E. Sebastian , B. Leiss
c
a
Departamento de Mineralogía y Petrología, Universidad de Granada, Avenida Fuentenueva s/n, 18002, Granada,
b
Geowissenschaftliches Zentrum der Universität Göttingen, Golschmidstrße 3, 37077 Göttiengen, Germany
Spain
c
Institute of Geology Dynamics of the Lithosphere (IGDL), Universität Göttingen, Golschmidstrße 3, 37077
Göttiengen, Germany
Abstract
One of the most commonly used marbles in Spain is “White Macael” marble, quarried in the
Macael area of Almeria. Throughout Spanish history, White Macael has been in great demand as
an ornamental stone and was used to build pieces of great importance and artistic beauty, such
as the Fountain of Lions in the Alhambra (Granada).
Over the centuries, such pieces have suffered from decay due to exposure to the elements,
as has happened in many other marbles all over the world.
The main purpose of this paper was to determine the durability of White Macael marble
when subjected to changes in thermal conditions. It was observed that these changes in the
presence of humidity were an important factor in marble decay. They produce a progressive loss
of cohesion along grain boundaries and an increase in porosity, which are starting points for
89
A. Luque et al. / Engineering Geology 115 (2010) 209–216
marble degradation and facilitate the development of other pathologies.
Keywords: White Macael marble; Durability; Thermal expansion; Microfabric; Residual strain.
90
Anisotropic behaviour of White Macael marbe used in the Alhambra of Granada (Spain). The role of
thermohydric expansión in Stone durability
7.1. INTRODUCTION
Marble has been used as an ornamental stone throughout history and numerous artworks of
extreme beauty have been sculpted with this material (e.g., Michelangelo’s David in Florence; the
Venus de Milo in the Louvre, Paris; Trajan’s column in Rome; the Fountain of the Lions in the
Alhambra, Granada). Marble has always been popular in sculpture because of its aesthetic
properties and because it is easy to polish. White marble is particularly sought after and some of
the most famous marbles in history were white (Carrara, Thassos, Paros, Makrana, Macael).
Marble was also popular because of its excellent physical properties (i.e. hardness, very low
porosity, etc.) which made it useful as a building material in the construction of doorways, façade
panels, etc.
In recent decades marble used in building façades has suffered serious deterioration
problems, in some cases after only relatively few years exposure. The most frequent forms of
decay include bowing, granular disintegration, flaking and cracks.
Researchers investigating the deterioration observed in certain well-known modern
buildings, such as the Finland Hall in Helsinki or the Grande Arche de la Defense in Paris, focused
on the durability of marble and showed that the alternation of heat and cold cycles under
moisture conditions was the main factor influencing its decay (Malaga et al., 2008; Siegesmund et
al., 2008; Koch and Siegesmund, 2004; Widhalm et al., 1996).
Early research into the physical and mechanical behaviour of marbles by Kessler (1919)
determined that the processes of thermal expansion in marbles were responsible for their initial
decay. More recently, Thomasen and Ewart (1984) and Bortz et al. (1988) investigated what
variations in the moisture content during decay processes could be responsible for the ultimate
decay of the marble. Bland and Rolls (1998) found that marble is very sensitive to temperature
changes, which cause granular disintegration.
Siegesmund et al. (1999) studied different types of marble and proved that one of the main
factors that influence their physical, mechanical and hydric properties are fabric and textural
anisotropy (i.e. grain size, shape and orientation). Preferred lattice orientation and grain fabric
(morphology and geometry of grain boundary) play a basic role in marble deterioration
(Siegesmund et al., 2000; Royer-Carfagni, 2000; Zeisig et al., 2002; Cantisani et al., 2008; Akesson
et al., 2005). In addition, the characterization of physical parameters such as thermal expansion,
thermal conductivity and elastic wave velocity clearly demonstrates that fabric analysis can help
91
to predict stone durability (Widhalm et al., 1997; Weiss, 2000; Sáez-Pérez and Rodríguez-Gordillo,
2009).
Weiss et al. (2002, 2003) demonstrated that anisotropic thermal expansion in marble
produced a progressive loss of cohesion along the grain boundaries, which led to an initial state
of decay. In addition, Koch and Siegesmund (2002, 2004) pointed out that the formation of
bowing is directly controlled by cyclic variations of temperature in the presence of water.
An example of the anisotropic behaviour of marbles is the residual strain presented by these
stones at the end of thermal expansion tests (Siegesmund et al., 1999, Leiss and Weiss, 2000).
These tests have also demonstrated that continuous heat-cold cycles favour marble elongation
which in many cases coincides with the “c” axis orientation of calcite crystals (Koch and
Siegesmund, 2004; Siegesmund et al., 2000; Widhalm et al., 1996; Battaglia et al., 1993).
Fabric and textural anisotropy, which are typical of certain metamorphic rocks, including
some marbles, cause samples to behave differently in physical and mechanical tests depending
on their orientation to stress forces (Zeisig et al., 2002; Siegesmund et al., 1999).
In this work we will be analysing White Macael (WM), a marble that was widely used in
Spain’s Architectural Heritage and which remains today one of Spain’s most commonly exported
building stones. Of all the artworks sculpted with WM, the Fountain of the Lions in the Alhambra
(Granada, Spain) is perhaps the most outstanding because of its exquisite decorations (Fig. 1).
This fountain is one of the best examples of 11th century Islamic art. Twelve lions stand in a
circle supporting the basin of the fountain. The water flows out through the mouth of the lions
and then along four channels that divide the courtyard into equal quadrants.
Bello et al. (1992) and Galán and Zezza, (1990) linked the state of decay of this fountain to
the environmental conditions in the courtyard. Using ultrasound, Zezza and Sebastián Pardo
(1992) discovered a marked anisotropy along WM foliation planes that were not easily
distinguishable to the naked eye.
Rodríguez-Gordillo and Saez-Pérez (2006) made an initial study of the anisotropic behavior
of WM by carrying out heat-cold cycles on freshly quarried marbles. They observed marble
deterioration (i.e. loss of small fragments) caused by thermal expansion in wet conditions, but
they did not quantify either the degree of anisotropy or the amount of deterioration.
92
Figure 1. General view and detailed images showing White Macael marble damage caused by granular
disintegration and cracks, in most of the columns of the Courtyard of the Lions in the Alhambra of Granada
(Spain).
If we summarize the most important findings made by these authors, it would seem that
microfabric, the existence of microcracks and the preferred orientation of crystallographic axes
are the factors that most affect the behaviour of marble with respect to temperature changes. The
geometric disposition of crystals in microfabric is of great importance, since the marbles with
hexagonal-shaped crystals and straight joints are the least resistant to thermal changes.
Furthermore, the existence of microcracks and their spatial disposition is the main way for other
decay agents (e.g. soluble salts) to enter the stone. Microcracks will grow or expand inside the
stone so producing an increase in fissure porosity. In calcitic marbles the main expansion factor is
the preferred crystallographic orientation, as calcite is a strongly anisotropic mineral (Kleber,
1959). This means that the crystal expands along the c-axis and contracts along the a-axis of the
93
mineral.
A detailed characterization of the anisotropic behaviour of WM during the thermohydric
expansion test is one of the main goals of the present work, because of its relevance for
conservation issues especially in fountains where cold and heat cycles can alternate frequently in
the presence of water. In general, the characterization of the anisotropic thermal expansion that
can take place in marbles is essential if we want to predict the future behaviour of this stone both
in buildings and decorative pieces.
7.2. MATERIALS AND METHODS
7.2.1.
Samples
As it is impossible to take samples from the Courtyard of Lions because of their historic
value, we used freshly quarried blocks of White Macael marble (WM) from a quarry in the Macael
area of Almeria (Spain), where the local economy largely depends on the quarrying of different
types of marble.
WM is a pearly-white stone, but sometimes, depending on the particular quarrying area or
strata, it may present a grey foliation which varies in the intensity of its colour and in the number
of lines crossing the stone. This foliation is composed of muscovite, amphibole, epidote, titanite
and deformed carbonate grains (López Sánchez-Vizcaíno et al., 1997).
From a geological point of view, WM is a Late Triassic marble that belongs to the NevadoFilabride Complex in the so-called Betic Internal Zone, which is the lowest tectonic unit of the
Alboran Domain (Balanyá and García-Dueñas, 1986).
The material selected for this research is characterized by some greyish layers which
correspond to marble foliation planes. Block cubes of 50 cm edge were cut into different
specimens. Prior to cutting, a reference-coordinate system was introduced to record the
orientation of the foliation (Fig. 2). This system was used to study the anisotropy of the fabric and,
thus, its influence on physical rock properties.
94
7.2.2.
Analyses
The texture of marbles was studied using an Olympus BX-60 polarized optical microscope
(OM) coupled with digital microphotography (Olympus DP-10). Two thin sections were prepared
in two orthogonal directions following the XY- and YZ- planes (Fig. 2a). Two more thin sections
with the same orientation were filled with fluorochrome resin and then analyzed to identify the
presence, aspect and distribution of fractures inside marbles.
Figure 2. Schematic representation of a marble cube with the disposition of reference axes according to the
foliation planes. Schimidt pole figures are shown.
To understand the spatial and geometrical configuration of all the components of a rock in
terms of fabric and microstructure, we followed the methodology proposed by Passchier and
Trouw (1996) which considers these parameters: grain size distribution, grain aspect ratio,
preferred grain orientation, grain boundary morphology, grain boundary geometry, the size and
orientation of microcracks and preferred lattice orientation.
Preferred crystallographic orientations were measured using a PANalytical X’pert System Xray diffractometer (Leiss, B. & Ullemeyer, K. 2006). A polycapillary on the primary beam side
95
provided an optically parallel beam with a diameter of at least 7 mm. To further increase the
number of grains measured, pole figures were measured at 13 different points on a sample of
70×70×10 mm. For the pole figure measurements, a 5° × 5° (tilt/rotation angle) grid was applied.
(006), <110>, {104}, {012}, {113} and {202}-pole figures were measured. The defocusing effect was
corrected by polynomial functions derived from calcite powder measurements (Ullemeyer et al.,
1998). Despite these corrections, data could only used up to a tilt angle of 75° due to the
increasing error of correction with increasing tilt angle. The 13 pole figures of each hkl were
added. On the basis of the resulting experimental pole figures, an Orientation Distribution
Function (ODF) was calculated by applying the iterative series-expansion method (Dahms &
Bunge 1989). From the ODF complete pole figures were calculated. The bulk rock anisotropy of
the thermal dilatation coefficient was calculated by applying the VOIGT averaging method (e.g.
Bunge 1985) and is represented in an equal area projection.
Real and apparent density and open porosity were measured by forced water absorption
according to the UNE-EN 1936 (2007) standard.
Of the various techniques for determining physical properties, ultrasound procedures are
particularly useful because of their non-destructive nature. The measurements were performed
with a Panametrics HV Pulser/Receiver 5058PR coupled with a Tektronix TDS 3012B oscilloscope.
The propagation velocity of compressional (VP) pulses was measured in accordance with the
ASTM D 2845 (2005) standard on dry and wet test samples using polarized Panametric
transducers of 1 GHz. These data were used to obtain information on the degree of compactness
of the marbles (a decrease in the velocity showing the development of fissures).
The modifications in the distribution of the pore access size as well the pore/fissure volume
of marbles before and after thermal stress test was determined using a Micromeritics Autopore III
9410 porosimeter with a maximum injection pressure of 414 MPa. Specimens of about 1 cm3
were dried for 48h at 50°C and then analysed. Two MIP measurements per sample were made.
6 drilled cores (15 mm diameter × 50 mm length), orientated according to the preestablished axes, were cut and analyzed: 3 cores maintain the reference-coordinate directions (X-,
Y- and Z-) while the other 3 cores show intermediate directions (XY-, XZ- and YZ-) (Fig. 3). We
measured the ultrasound wave velocity under controlled heat and humidity conditions (Tª 25 ºC
between transducers and marble samples. The transmission method was used and three
measurements were taken for each direction under consideration.
96
Figure 3. Schematic representation of the orientation of the 6 cores tested with respect to the established
coordinate system. Image of a pushrod dilatometer (Strohmeyer, 2004).
The degree of anisotropy of the WM marble was evaluated by performing a thermal
expansion test with respect to certain specific orientations (X, Y, Z, XY, XZ and YZ). The cores used
for the ultrasound and water absorption tests, once indexed according to the coordinate system,
were used again in this test.
The test carried out in this work is the test proposed by Koch and Siegesmund (2004) in
which a chamber allows the simultaneous analysis of six samples. 12 cycles were carried out: 5 in
dry conditions and 7 under wet conditions.
In order to simulate temperature changes similar to those observed in buildings, each cycle
maintains the temperature interval of 20ºC to 90ºC and back down to 20°C again over 15 hours in
dry conditions while 17 hours in wet conditions. The heating rate was 1°C per minute to ensure
the thermal equilibration of specimens.
The thermal expansion coefficient (α, in 10-6 K-1) expresses the relative change in length (or
volume) of the stone according to changes in temperature. In most calcitic marbles, α is nonlinear and depends on the temperature interval used (Siegesmund et al., 2008). It is calculated
according to the following equation:
α = ∆l/(l×∆T)
(1)
where:∆l is the change in length of the sample (mm); l is the length of sample (mm) and ∆T
97
is the temperature interval (K)
Thermal expansion (εrs in mm/m) represents the relationship between the change in length
of the sample after cooling down to room temperature and the original sample length and is
defined as:
εrs = ∆lrt/lr
(2)
where: ∆lrt: is the change in length of the sample after cooling down to room temperature
(mm) and lr: is the original length of the sample for a given temperature range (mm)
The residual strain (r in mm) generated by the thermal expansion is the irreversible damage
that takes place in a sample once it returns to its initial (environmental) temperature. This
parameter is related to anisotropic thermal expansion.
Generally, samples that undergo this test show four types of behaviour which are
characterized by: a) isotropic thermal expansion without residual strain; b) isotropic thermal
expansion with residual strain; c) anisotropic thermal expansion without residual strain and d)
anisotropic thermal expansion with residual strain (Weiss et al., 2003).
7.3. RESULTS AND DISCUSSION
7.3.1.
Mineralogy and texture
Under optical microscopy, WM shows a typical poligonal granoblastic texture with
equidimensional shapes and grains of very varied sizes (between 0.1 to 3 mm). This texture clearly
indicates a static recrystallization, in which the grain boundaries become straighter and grains
increase in size becoming hexagonal in shape. These two processes finally produce a reduction of
grain boundary area and, therefore, a reduction of the total energy of the crystalline aggregate
(Passchier and Trouw, 1996).
When we analysed the sections prepared with fluorochrome resin, we observed that the
lines that mark the grain boundaries showed different degrees of union depending on the
orientation of the marble (Fig. 4b and d). In fact, on the surface defined by ZY axes the grain
boundaries were straight, while on the XY surface, they present a degree of suturing, suggesting a
sintering mechanism among crystals. Furthermore, we must also consider the morphology of pre98
existing fissures in marble because these are different on each plane; on the ZY plane they are
intra- and interparticles and follow a rectilinear morphology, while along the XY plane they are
only interparticles, and are sinuous in shape.
Finally, small amounts of quartz, phyllosilicates (i.e., muscovite), iron oxides and opaque
minerals, probably pyrite, were also detected. These opaque minerals enable us to detect the
foliation planes even with the naked eye.
Figure 4. Optical microphotographs of WM marble. a and b images show sections taken from the plane
perpendicular to the foliation, while c and d images correspond to planes containing the foliation. Arrows
indicate the development of both interparticle and intraparticle cracks along the ZY plane (image b), but
only interparticle cracks along the XY plane (image d).
The results of the texture analyses are represented by pole diagrams in Figure 5. According
to the Leiss and Weiss classification (2000), the texture of WM marble can be defined as c-axis
fibre-type because the c-axes maxima are clearly developed and the a-axes maxima are quite
99
regularly distributed on a great circle. The c-axis maximum is only of moderate intensity and
pseudo-normal oriented to the regional foliation.
Figure 5. Pole figures of calcite recalculated from the Orientation Distribution Function on the basis of X-ray
diffraction measurements (equal area projection, lower hemisphere, maxima of multiples of random
distribution (m.r.d.) are given, lowest contour line equals 1.0 m.r.d.). The plot on the right shows the
distribution of the thermal dilatation coefficient α as calculated from the quantitative texture analysis (equal
-6
area projection, lower hemisphere, • min and ▪ max [10 1/°C] are given).
7.3.2.
Thermal expansion
The results of the thermal expansion test under dry conditions (Fig. 6a) show that the
greatest elongation occurs along the Z-axis (1.31 mm/m) and the lowest is recorded by the Y-axis
(0.43 mm/m) which is normal to the Z-axis and parallel to the foliation plane. XY, YZ and XZ
directions show intermediate values. However, only the relation between the orthogonal (X-, Yand Z-axes) values denotes the strong anisotropy of this marble (Δα = α min/αmax = 0.40% and Δε
= εmin/εmax = 0.33%).
There seems to be a correlation between residual strain values and the anisotropy of
thermal expansion. Along the direction of α-max, residual tension (0.29 mm) is three times as
high as that obtained along α-min (0.09 mm). The residual strain shows that WM deforms
irreversibly in the z-axis direction, especially after the first heating cycle.
Modal composition is known to have an influence on the thermal properties of marble.
-6
-1
According to Kleber (1959), the thermal expansion coefficient (α) of calcite is 26×10 K in the
direction parallel to the c-axis and -6×10
-6
-1
K
in the parallel to the a-axis. In the case of WM
marble, the maximum and minimum α values correspond to the Z- and Y- axes respectively,
100
which indicates that there is a direct link between the preferential orientation of the axes and the
crystalline structure of marble (Table 1).
Figure 6. Maximum expansion and residual strain of WM marble after the first and second thermal test
cycle. In a) the three orthogonal axes X, Y and Z are represented, while in b) intermediate directions are
shown.
Table 1. Representation of the maximum WM elongation and linear thermal expansion coefficients (α) along
each axis when temperature increases in the range from 25 to 90 °C
BM Axes-
Maximum elongation (ε, mm/m)
Thermal expansion coefficient
(, 10-6/K)
Residual Strain
(mm)
X
0.86
16.673
0.32
Y
0.43
9.522
0.09
Z
1.31
23.976
0.29
XY
0.53
11.892
0.20
XZ
0.87
17.609
0.22
YZ
0.77
14.982
0.17
Nevertheless, according to Siegesmund et al. (1997, 2000), the residual strain produced for
each direction is also influenced by the fabric of the rock and by the existence of microcracks
prior to the test.
The behaviour of the marble under the thermohydric expansion test was similar to that
101
observed under dry conditions. The values for residual strain obtained in the six directions
selected in WM marble showed a continued growth during the test cycles. Although the residual
strain values remained constant between the third and fifth cycle, in the following cycles and
under wet conditions, all samples were characterized by a further, progressive expansion (Fig. 7).
Figure 7. Residual strain increase of WM marble over 5 dry cycles and then 7 wet cycles in three orthogonal
axes X, Y and Z (a) and along intermediate directions (b).
The low porosity of fresh WM marble (  = 0.41 %) indicates that some, albeit few
microcracks existed prior to the test. This is a useful value for evaluating the durability of marble
when subjected to thermal changes. In fact, in all the samples we tested we observed a slight
increase in porosity (  = 0.72 %) after the thermal expansion test (Fig. 8). Although this increase
may be insignificant, it should not be ignored since an increase in fissure porosity can influence
the durability of the material. According to the Köhler classification (1991), after the thermal
expansion test, the WM marble moves from fresh to increasingly porous material.
Figure 8. WM pore volume change (η in %) before and after heat treatment.
102
The increase in porosity was clearly evidenced after MIP tests. In fact, changes in the rank of
pore size and in the total porosity were detected after thermal treatment (Table 2). The augment
in the volume of larger pores/fissures (Fig. 9) is important because they will be new ways to other
decay agents (water, salts, etc.).
Table 2. Porosimetric parameters of White Macael marble before and after thermal treatment. Average
values are presented for fresh and altered marble
Fresh samples
Altered samples
Total Pore Area (m2/g)
0.185 ± 0.55
1. 342 ± 0.76
Apparent density (g/cm3)
2.676 ± 0.05
2.548 ± 0.06
Real density (g/cm3)
2.724 ± 0.09
2.729 ± 0.06
Porosity (%)
1.780 ± 0.90
6.628 ± 1.25
Figure 9. Pore size distribution curves for White Macael marble measured in fresh and altered samples.
If we compare the data for forced water absorption with those for ultrasounds we can see
103
that both tests indicate an increase in porosity and, therefore, incipient decay. If we analyze the
ultrasound data in greater detail, the values for quarry samples are lower than that for a single
calcite crystal (Fig. 10) suggesting that microcracks may exist. In addition, if we start from the
values obtained in the three orthogonal directions (X-, Y- and Z- axes), WM marble shows a high
textural anisotropy (ΔM = 13%), which is also due to the anisotropy introduced by calcite single
crystals and the pre-existing microcracks (Siegesmund et al., 1999).
Figure 10. Ultrasound wave velocities measured in dry and saturated samples. Image a) shows fresh samples
while b) are deteriorated samples.
Finally, the strong decrease of Vp values in altered samples (Table 3) confirms the increase in
porosity.
Table 3. Schematic representation of Vp values in fresh and deteriorated (*) samples. Porosity (η) and
differential values (∆Vp and ∆η) are also shown
BM Axes-
Vp (m/s)
Vp* (m/s)
∆Vp1-Vp1*
η (%)
η (%)*
∆η (%)
X
5885
2647
3440
0.43
0.76
0.33
Y
5756
3625
2423
0.27
0.57
0.3
Z
5058
2794
2564
0.34
0.68
0.35
XY
5421
3726
1695
0.54
0.8
0.25
XZ
5549
3174
2375
0.45
0.76
0.31
YZ
5422
3009
2413
0.41
0.76
0.35
104
7.4. DISCUSSIONS AND CONCLUSIONS
After determining the texture and the crystallographic orientation of calcite grains, we
observed that calcite crystals showed c-axis orientation pseudo-parallel to the Z-axis. This
suggests that these axes are situated perpendicular to the foliation plane while the a-axis is
parallel to the foliation plane.
The petrography study revealed that most of the calcite crystals are granoblastic with
equidimensional shapes (i.e. pseudo-hexagonal) and various different sizes. We can also see that
the union between the grains varies depending on the orientation of the marble. The surface
parallel to the foliation plane (XY) shows a winding grain boundary and we can also see that some
of these boundaries have strong suture lines. In the surface perpendicular to the ZY plane, the
grain boundary is almost a straight line, with the presence of triple-points, weak boundary lines
and intra- and interparticle microcracks. As suggested by Siegesmund et al. (1999), the degree
and geometry of deformation are connected by different shapes, fabrics and textures.
On the basis of the research carried out to assess the damage that temperature changes
produce in marble, it is evident that two of the most important factors affecting behaviour are the
shape of the grains, and the grain boundaries. In White Macael marble we have observed that
both the pseudo-hexagonal shape of the grain and the straight grain boundaries mean that it is
less resistant to thermal change than crystal samples with irregular shapes and curved or complex
grain boundaries. It was also observed that weak grain boundaries facilitate dilation to a large
extent and this leads to the propagation of cracks and the appearance of gaps (Malaga et al.,
2008).
Moreover, the volume of pores calculated by water absorption and confirmed by ultrasound
data indicates the pre-existence of microcracks within the marble, which in this case were also
identified by optical microscopy for both the XY and YZ planes.
We can conclude that WM marble is not an ideal material in terms of durability criteria, as
the anisotropy of the marble (due to the anisotropy of the calcite), the texture (grain size, grain
boundaries and the preferred crystallographic orientation) and the pre-existence of microcracks
are all important negative factors in marble behaviour during heat treatment – water cycles.
Thermal expansion results show the high dilation coefficient measured in White Macael
marble in two of its three orthogonal directions (X and Z axes) and also the increase in residual
strain produced during heating cycles in the presence of water. These results must be taken into
105
account when trying to evaluate marble durability since, although Rodríguez-Gordillo and SáezPérez (2005) observed a decrease of Vp values after the first 50 cycles, this velocity remained
constant throughout the other cycles. However, the test with moisture change shows that the
increase in residual strain with the increase of cycles under wet conditions leads to a higher
granular disintegration and, therefore, a sharper reduction in velocity during the following cycles.
We can therefore conclude that the heat treatment causes significant decay in White Macael
marble, and that this decay can be measured by means of the techniques used in the present
research. Data obtained from the ultrasound test in different directions and the increase in
porosity after the thermal test clearly indicate the loss of cohesion between the grains. From this
moment on White Macael marble must be treated as a porous material.
Given that the intrinsic properties of this marble do not favour its durability in the abovementioned weathering conditions, it is probable that its initial state of deterioration will be
enhanced by other decay agents (e.g. soluble salts).
The results provided in this research can be used as a guide in the restoration of other
artworks or monuments manufactured with White Macael marble.
Acknowledgements
This research has been supported by the Research Projects FQM 1635 and HA 2007-0012
and by the Research Group of the Junta de Andalucía RNM 179. We thank Nigel Walkington for
the translation of the manuscript.
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110
Part III
8.
Direct observation of microcrack development
in marble caused by thermal weathering
(1)
(1,2)
A. Luque , E. Ruiz-Agudo
(1)
(1)
, G. Cultrone. , E. Sebastián
and S. Siegesmund
(3)
1. Department of Mineralogy and Petrology, Faculty of Sciences, University of Granada. Fuentenueva s/n; 18002 Granada,
Spain.
2. Institut für Mineralogie, University of Münster, Corrensstr. 24, 48149 Münster, Germany
3. Department of Structural Geology and Geodynamics, Geoscience Centre, University of Göttingen. Goldschmidtstr. 3; 37077
Göttingen, Germany
* e-mail: [email protected]
Abstract
One of the properties that makes marble such an excellent construction and ornamental
material is its low porosity. It is very difficult for water or decay agents to penetrate the internal
structure of materials with no or few pores, so enhancing the durability of these materials.
However, environmental temperature fluctuations bring about significant physical changes in
marbles that result in an increase in porosity, due to the appearance of new microcracks and the
expansion of existing ones. These cracks offer new paths into the marble which make it easier for
solutions containing pollutants to penetrate the material. Thermal expansion tests were
performed on three different types of marble known as White, Tranco, and Yellow Macael
(Almeria, Spain), after which an increase in porosity (from 17 to 73% depending on marble type)
was observed, mainly due to crack formation. The structural changes occurring during thermal
expansion tests were more significant in the case of White Macael samples, a fact that is not only
111
A. Luque et al. / Environ Eart Sci
related to its mineralogical composition but also to the morphology of the grains, grain
boundaries and crystal size. Our research suggests that thermally weathered White Macael
marble could be more susceptible to decay by other contaminant agents than Tranco or Yellow
Macael. The use of hot-stage environmental scanning electron microscopy is proposed as a valid
tool for observing, both in situ and at high magnification, changes in the fracture system of
building stones induced by thermal stress.
Keywords: Marble; Microcracks; Thermal expansion anisotropy; Grain boundaries.
112
Direct Observation of microcrack development in marble caused by termal weathering
8.1. INTRODUCTION
All building stones are exposed to weathering from the moment they are extracted from the
quarry and used in the construction of a building. They undergo a series of structural and
compositional changes in order to reach a new thermodynamic equilibrium (Mingarro 1996;
Aires-Barros 2000). Apart from these natural changes, building stones are also subject to different
physical, chemical and biological weathering processes (Kühnel 2000) that may affect their
durability as structural and ornamental materials (Mingarro 1996; Doehne, 2002).
Because of its low porosity, marble has historically been considered a high quality material,
and has been used in many important civil and religious buildings. Unfortunately, today there are
numerous examples of historic marble buildings and sculptures which show weathering
phenomena caused by thermal decay and the following action of soluble salts (e.g. the churches
of San Marco, Santa Maria del Giglio and Santa Maria dei Miracoli in Venice, Michelangelo’s
David in Florence and the Courtyard of the Lions in the Alhambra of Granada). Environmental
temperature fluctuations produce a series of initial physical and mechanical changes in marble
stones (i.e. the first stage of weathering) that later enhance the effect of other weathering
mechanisms (Battaglia et al., 1993; Siegesmund et al., 2000 and 2007). Granular decohesion and
bowing of marble due to temperature fluctuations have been reported in some cases, particularly
when the stone is used in façades such as in Alvar Aalto’s Finland Hall in Helsinki (Royer-Carfagni,
1999), the Grande Arche de la Defense in Paris, the Lincoln Tower in Rochester (Cohen and
Montiero, 1991) and the Amoco building in Chicago (Logan et al. 1993).
Kessler (1919) found that repeated heating may lead to permanent dilatation in marbles due
to the formation of microcracks. Other authors (Bortz et al. 1988; Thomasen and Ewart, 1984;
Winkler, 1996) have claimed that changes in moisture content may be responsible for the
deformation of marbles. More recently, Koch and Siegesmund (2004) and Siegesmund et al.
(2008) discovered that the bowing that occurs in some marbles is controlled by a combined effect
of thermal cycling and the presence of moisture. However, it seems that the response of marble
to temperature oscillations is mainly due to the thermal anisotropy of its mineralogical
components: calcite and/or dolomite (Kleber, 1959). The thermal expansion coefficient, α, for
these two minerals shows an extreme directional dependence, as a result of their different
crystallographic directions. Parallel to the c-axis, both minerals have an α value of about 26 × 10
-1
K . However, parallel to the a-axis, dolomite shows a positive α value of about 6 × 10
whereas calcite, has a negative α value (-6 × 10
-6
-6
-6
-1
K ,
-1
K ) (Grimm 1999; Weiss et al. 1999). For
113
instance, in experiments carried out on marbles with different degrees of deterioration, porosity
increased by 50% or more compared to the original material, when samples were subjected to
thermal cycles with temperatures of over 50 ºC (Koch and Siegesmund, 2004, Malaga et al., 2002).
The increase in porosity is the consequence of the effect produced by the marked anisotropy of
calcite crystals. When temperature rises, the crystal expands in one direction (i.e., along the c-axis)
and contracts perpendicularly to that direction. Such movements cause internal cleavages and the
separation of crystals from their borders (Siegesmund et al., 2000).
Even though the thermal decay process affects dolomite and calcite marbles quite
differently, the residual strain does not seem to be controlled exclusively by the composition, as
there are other intrinsic factors that also determine their behaviour when subject to thermal
expansion (Zeisig et al. 2002; Siegesmund et al., 2009). The rock fabric, which includes grain size,
grain aspect ratio, grain-shape preferred orientation, lattice preferred orientation (texture) and
microcrack populations, plays an important role in how the marble behaves when subjected to
thermal stress (Siegesmund et al., 2000; Royer-Carfagni, 1999; Akesson et al., 2006).
The main physical change produced by thermal oscillations is the change in the pore size
distribution, even when the porosity is low (around 2%), (Ruedrich et al., 2001; Siegesmund et al.,
2008). The opening of new cleavage cracks between grain boundaries in marbles due to thermal
changes increases the porosity of the stone and in most cases increases the number of large
pores, and as a consequence, facilitates the penetration of water and solutions containing soluble
salts or other pollutant agents into intergranular spaces (Zeisig, et al., 2002; Ruiz-Agudo et al.,
2008; Luque et al., 2009). This then causes different weathering phenomena such as salt
crystallization, carbonate dissolution and/or the formation of calcium sulphate, which occur not
only on the surface, but also inside the marble (Fassina et al., 2002; Simon and Snethlage, 1993).
The aim of this paper is to characterize the changes in the porous system of three different
types of marble (two calcitic marbles and one dolomitic) during thermal/humidity tests. Textural
modification will be monitored using ultrasounds, mercury intrusion porosimetry, Ar adsorption
and hot-stage environmental scanning electron microscopy. The use of this last technique is
proposed as a novel approach to study both in situ and at high magnification how grain
boundaries are affected by the residual strain generated by one thermal cycle. This tool can be
used to evaluate textural modifications caused by thermal dilatation in dry conditions.
114
8.2.1.
Marbles
Three different varieties of marble were used, two of which were calcitic, White Macael (WM)
and Tranco Macael (TM), and one dolomitic, Yellow Triana Macael (YM). These types of rocks are
widely used as building materials, mainly for cladding, flooring and paving, and sometimes show
signs of decay. All these marbles are quarried in the same geographic area, the “Comarca del
Mármol” (the Marble County) in Almeria (Spain), although they are extracted from different
quarries. The WM marble is quarried in Macael, while TM is quarried in Lubrín-Zurgena and YM in
Codbar. In geological terms, these three marbles are Late Triassic and belong to the NevadoFilabride Complex in the Sierra de los Filabres (Betic Internal Zone), which is the lowest tectonic
unit of the Alboran Domain (Balanyá and García-Dueñas, 1986): TM and YM are Nevado-Lubrín
units and WM is a Bédar-Macael unit (Weijermars, 1991).
8.2.2.
Methodology
Textural analysis of selected marbles was performed using an Olympus BX-60 polarized
optical microscope (OM) coupled with digital microphotography (Olympus DP-10). The spatial
and geometrical configuration of all the components of the three marbles in terms of fabric and
microstructure was determined using the methodology proposed by Passchier and Trouw (1996),
where normally the Z-axis is perpendicular to the foliation (Fig. 1). In order to obtain more
information about the type of grain boundaries in each marble, we treated the negatives of
optical micrographs using Photoshop® Elements® 2.0 to provide the same brightness, contrast
and gamma values for all the samples.
Due to their non-destructive nature, ultrasounds (US) are particularly useful for determining
the physical properties of building stone. Measurements were performed using the transmission
method and three measurements were taken for each spatial direction (X, Y and Z). These data
were used to infer information on the degree of compactness of marbles (a decrease in the
velocity suggests the development of fissures) as well as on the textural anisotropy of marbles
(∆M, in %), the value of which can be calculated as follows:
115
1  (2  Vp min )
 100
Vp max  Vp mid
∆M =
ultrasonic wave velocity (Guyader and Denis, 1986; Weiss et al., 2002b; Sáez-Pérez and RodríguezGordillo, 2009).
Figure 1. Schematic representation of the marble samples with the reference axes positioned according to
the foliation planes.
The flow of water into the stone pore system was determined by carrying out a water
absorption test (WA). Real and apparent density and open porosity were measured by forced WA
according to the UNE-EN 1936 (2007) standard. The modifications in the distribution of the pore
access size and the pore/fissure volume of the marbles before and after the thermal stress test
were determined using a Micromeritics Autopore III 9410 mercury intrusion porosimeter (MIP),
which is able to exert a maximum injection pressure of 414 MPa. Ar-sorption isotherms (GS) of
sample fragments before and after the thermal salt tests were obtained at 77 K using a
Micromeritics Tristar 3000 under continuous adsorption conditions. In samples with less than 5
2
m ×g
-1
surface area, Ar-sorption measurements are more realistic than N2 measurements that
usually yield excessively high values and BET analysis was used to determine the total specific
116
surface area (Brunauer et al., 1938). The BJH method (Barrett et al., 1951) was used to obtain pore
size distribution curves, the pore volume and the mean pore size of the samples. The surface
fractal dimension, DS, was used to characterize surface roughness. The analysis of the gas
sorption isotherm using a modified Frenkel-Halsey-Hill theory (Tang et al., 2003) allows the
determination of surface fractal dimension from the slope (A) of the plot of Ln(V) vs Ln[Ln(P/P 0)],
where V is the adsorbed volume of gas, and P and P 0 are the actual and the condensation gas
pressure. When surface tension (or capillary condensation) effects are important, the relationship
between A and DS is A = DS–3. Capillary condensation is significant if δ = 3×(1+A)–2 < 0. The
pressure range and hence the thickness range of the adsorbed layer being studied was only
around monolayer (n = 1-2) coverage to ensure that the determination of DS was reliable (Tang et
al., 2003).
The degree of thermal anisotropy of the marbles was evaluated by performing a thermal
expansion test with respect to specific orientations (X, Y, and Z), according to pre-established
axes. The test was carried out following the methodology proposed by Koch and Siegesmund
(2004) in a chamber which allows the simultaneous analysis of six samples. 10 cycles were
performed: 3 in dry conditions and 7 under wet conditions. In order to simulate temperature
changes similar to those observed in buildings, each cycle follows the same temperature
sequence of 20ºC to 90 ºC and back down to 20 °C again over 15 hours in dry conditions, and 17
hours in wet conditions. The heating rate was 1 °C per minute to ensure the thermal equilibration
of the specimens.
This technique allows us to calculate the thermal expansion coefficient (α):
=
l
l  T
which expresses the relative change in length (l) or volume of the sample due to
temperature changes (∆T), as well as the thermal expansion (εrs =
l rt
), which is the ratio of the
lr
change in length of the sample after cooling down to room temperature (∆lrt) to the original
sample length (lr). The residual strain (r) generated by the thermal expansion can be also obtained
using this test. This parameter is a measurement of the irreversible damage that takes place in the
sample once it returns to its initial (environmental) temperature (Kessler, 1919).
An environmental scanning electron microscope (ESEM) equipped with a heating stage was
used to observe the formation of new cracks and the widening or closure of pre-existing ones
117
during the following thermal cycle: 20-45-90-20 ºC. The images were obtained on a FEI Quanta
400 ESEM, which operates at an accelerating voltage of 20 kV. During heating, the detectorsample distance was set to ~12 mm and the ESEM chamber pressure was set at ~2 Torr water
vapour. This water vapour pressure is equivalent to that of environmental air at 20 °C and 15%
RH. Each sample was heated at an average heating rate of between 3-5 °C/min. A constant
temperature was maintained during image acquisition, after 15 min as equilibration time.
The stone pore system (pore volume, pore size distribution, surface area and fractal
dimension) was characterized using WA, MIP and GS (Xie et al., 1996; Pérez Bernal and Bello,
2000, 2001). Surface area and fractal dimension are important as they frequently indicate the
presence of surface rugosity due to chemical weathering (Ruiz-Agudo et al., 2008).
8.3. RESULTS
8.3.1.
Characterization of marbles
Although samples are quarried in the same area, OM analysis showed important differences
in the petrography of the three varieties of marble we tested (Table 1). White Macael, a calcitic
marble, has a granoblastic micro-fabric with polygonal shapes, a grain size of between 0.1 and 3
mm and straight to slightly curved grain boundaries (Fig. 1a). Micro-cracks and open cleavage
planes are straight and intra-particular. The micro-fabric in XY-plane indicates a static
recrystallization, in which grain boundaries become straighter and grains increase in size
becoming hexagonal in shape (Luque et al., 2009). Tranco Macael, a white calcitic marble with a
notable presence of irregular grey bands shows a granoblastic micro-fabric with irregular shapes
and grain sizes of between 0.2 and 1 mm (up to 1.5 mm). Grain boundaries are mainly
“interlobate”, although occasionally pseudo-linear unions were observed (Fig. 1b). Yellow Macael
is a yellowish dolomitic marble which includes disperse calcite grains of residual origin and with
preferred orientation and secondary calcite filling cracks and fractures. It shows a granoblastic
micro-fabric with sizes of 0.05 to 0.8 mm for dolomite and 0.5 to 1 mm for calcite grains and it
has interlobate grain boundaries. Fe-oxides, quartz, pyrite, muscovite and feldspars are also found
as accessory minerals (Fig. 1c).
118
Table 1. Mineralogical and petrographic features of the three marbles we tested
White Macael
Tranco Macael
Yellow Macael
Mineralogical compositions (%)
Cc
99 ± 1
98 ± 2
4±1
Dol
-
-
95 ± 3
Others
1 ± 0.01
1 ± 0.01
1 ± 0.1
Cc
0.1-3
0.2-1.5
0.5-1
Dol
-
-
0.05-0.8
Others
≤ 0.01
≤ 0.01
≤ 0.01
Grain size (mm)
Texture
Granoblastic
Granoblastic
Granoblastic-seriate
Cc calcite, Dol dolomite
The main petrophysical properties of the quarried marbles are shown in Table 2. According
to Weiss et al. (2002b), the propagation velocity of ultrasonic waves (Vp) within the stone matrix
can determine the intrinsic and extrinsic properties of marbles, and therefore, the structural
anisotropy of these crystalline materials, as well as the existence of microcracks when the Vp
values are measured in dry and saturated conditions (Siegesmund et al., 1999, 2009). Taking into
account the Vp values measured by Dandekar (1968) in a single calcite crystal (Vp max = 7730 m/s
and Vpmin = 5710 m/s) and a single dolomite crystal (Vpmax = 8450 m/s and Vpmin = 6280 m/s), we
can see that all three marbles types always have lower values, but the same tendency of single
calcite and dolomite crystals (Table 2 shows the dry and water-saturated values, and the
anisotropy in the three cases).
119
Figure 2. Optical microscopy image of a White Macael, b Tranco Macael and c Yellow Macael marble microfabric.
120
This suggests that the three types of marble show some degree of textural preferential
orientation, when the c-axis (minimum values in the three marbles) is parallel to the z-axis
established in our coordinate system. Moreover, microcracks, whose existence was confirmed by
comparing dry and water-saturated values, have certain directionality, perpendicular to the c-axis
(maximum difference between Vpdry and Vpsat).
The existence of pores (or fissures), of which there are generally very few, is confirmed by
the porosity values obtained by water absorption, mercury intrusion porosimetry and gas
adsorption tests in fresh marbles (Table 2).
Table 2. Petrophysical characterization of White Macael, Tranco Macael and Yellow Macael (fresh samples)
White Macael
Tranco Macael
Yellow Macael
Ultrasound tests Vp [m/s]
x
y
z
dM (%)
x
y
z
dM (%)
x
y
z
dM (%)
Dry samples
5885
5756
5058
13.10
6210
5678
5387
9.37
6597
6573
5165
21.56
Water-saturated samples
6405
6386
6246
2.34
6589
6253
6073
5.42
7452
7304
6816
7.62
(a)
Ф [Vol.-%]
0.41
0.35
0.94
Ρ real [g/cm³]
2.70
2.73
2.92
P [%]
1.76
0.75
2.42
Ρ real [g/cm³]
2.72
2.75
2.92
SA [m2/g]
0.185
0.258
0.754
Df
2.77
2.87
2.79
P vol. [cm3/g]
0.00006
0.00021
0.00022
SA BET [m2/g]
0.198
0.316
0.347
Ds
2.88
2.82
2.68
(b)
(c)
Df and Ds parameters are consistent with the fissure morphology and the degree of fissure
surface roughness observed under OM. Therefore, we can affirm that WM has a fissure system
with rectilinear trend morphology (Df = 2.77) and high surface roughness (Ds = 2.88), YM has
more irregular morphology fissures (Df = 2.79) and low surface roughness (Ds = 2.68) and TM has
interlobate fissures (Df = 2.87) and high surface roughness (Ds = 2.82).
These values give us some idea of the pore structure at different scales; in particular, Ds can
be considered as an index of the pore structure at the nanoscale, i.e. the rugosity of the pore
surface.
121
8.3.2.
Thermal expansion tests
Table 3 shows the thermal expansion coefficient (α, in 10
-6
-1
K ), thermal expansion (εrs, in
mm/m) and residual strain (r, in mm/m) values obtained along the X, Y and Z perpendicular
directions for each marble during the first thermal dry-cycle (20-90-20 ºC), as well as the degree
of anisotropy of the marbles. WM and YM samples show the highest α and εrs values. However, in
the three marbles the highest value for these two parameters is observed along the Z-axis, which
may indicate a preferred orientation of carbonates along this direction. Moreover, if we take into
account the anisotropy values of each parameter (∆α y ∆ε) in the three marbles, we can see that
the anisotropy in WM (∆α = 53.15%; ∆ε = 60.37%) and TM (∆α = 62.13%; ∆ε = 71.43%) marbles is
much higher than in YM marble (∆α = 13.67%; ∆ε = 13.73%), which indicates that calcite causes a
stronger anisotropy than dolomite.
Table 3. Thermal parameters of White Macael, Tranco Macael and Yellow Macael marbles
White Macael
Tranco Macael
Yellow Macael
X
Y
Z
∆ (%)
X
Y
Z
∆ (%)
X
Y
Z
∆ (%)
α (10-6 K-1)
16.67
9.52
23.97
53.15
4.66
10.69
13.92
62.13
12.91
13.34
16.57
13.67
εrs (mm/m)
0.86
0.43
1.31
60.37
0.18
0.54
0.72
71.43
0.66
0.68
0.85
13.73
r (mm/m)
0.31
0.09
0.29
69.80
0.08
0.06
0.13
42.57
0.01
0.01
0.07
74.97
r* (mm/m)
0.6423
0.2789
0.7723
60.57
0.3229
0.4843
0.5101
35.05
0.1695
0.1222
0.4677
61.63
α thermal dilatation coefficient, ers thermal expansion, r residual strain after first thermal dry cycle, r*
residual strain after ten thermal cycles (3 in dry conditions and 7 in wet conditions) (mm/m), D anisotropy
determined in each marble for each parameter.
These values only reflect the behaviour of the marbles during the first dry-cycle and they
tend to remain constant during the following 2 dry-cycles (Fig. 3). However, when these cycles are
performed in wet conditions, α and ε values show a significant increase (see Figure 3). This is
mainly due to the effect of water and the pressure it exerts at high temperature (90 ºC), when it is
retained in the grain boundaries of the marble samples (Winkler, 1994). Finally, after 10 thermal
cycles (3 dry-cycles and 7 wet-cycles) have been carried out, the residual strain (r) is the main
parameter that evaluates the damage induced in the three types of marble. Although r values are
very different in the three marbles, all of them increase as the number of cycles increases. The
increase follows this order: YM (X = 0.01 mm/m; Y = 0.01 mm/m; Z = 0.07 mm/m) < TM (X = 0.08
mm/m; Y = 0.06 mm/m; Z = 0.13 mm/m) < WM (X = 0.31 mm/m; Y = 0.09 mm/m; Z = 0.29
122
mm/m) after the 3 first dry-cycles; YM (X = 0.17 – Y = 0.12 – Z = 0.47 mm/m) < TM (X = 0.32 – Y
= 0.48 – Z = 0.51 mm/m) < WM (X = 0.64 – Y = 0.28 – Z = 0.77 mm/m) after the following 7 wetcycles (Fig. 4).
Figure3. Maximum elongation of marbles heated up to 90ºC during the first three consecutive dry cycles
along the three perpendicular directions (X, Y and Z). WM White Macael, TM Tranco Macael, YM Yellow
Macael
Figure 4. Residual strain versus number of cycles for White Macael (WM), Tranco Macael (TM) and Yellow
Macael (YM) marbles during thermal expansion tests (3 dry cycles and 7 wet cycles). The dotted line divides
dry (left) from wet (right) cycles.
To quantify the damage induced by the thermal expansion test in each marble, the main
petrophysical properties (compactness and porosity) were measured again in marble core
samples. The new values are shown in Table 4. The decrease in Vp values was higher in WM
marble (between 37 and 55%) compared to YM (between 29 and 45%) and TM (between 19 and
25%), and this may be related to the damage induced by thermal changes, leading to an
123
important loss of compactness (Köhler, 1991; Siegesmund et al., 2000; Weiss et al, 2002a). By the
end of the tests porosity had increased in all three types of marble. The pore size distribution had
also changed, as was confirmed by the values for fractal dimension, D f and Ds.
Table 4. Petrophysical characterization of White Macael, Tranco Macael and Yellow Macael after the thermal
expansion tests.
White Maacel
Tranco Macael
Yellow Macael
Ultrasound test Vp [m/s]
x
y
z
dM (%)
x
y
z
dM (%)
x
y
z
dM (%)
Dry samples
2647
3625
2794
17.53
5010
4550
4057
15.13
4714
4567
2866
38.24
Water-saturated samples
5985
6214
5964
2.22
6148
6023
5577
8.36
6824
6965
6367
7.65
Difference (%)
55
37
45
26
19
20
25
13
29
31
45
24
Ф [Vol.-%]
0.67
0.48
0.92
Ρ real [g/cm³]
2.71
2.74
2.93
P [%]
6.63
1.21
2.91
Ρ real [g/cm³]
2.72
2.70
2.92
SA [m2/g]
1.342
0.573
0.449
Df
2.69
2.92
2.94
P vol. [cm3/g]
0.00005
0.000111
0.00020
SA BET [m2/g]
0.116
0.143
0.205
Ds
2.84
2.67
2.56
(a)
(b)
(c)
Although an increase in porosity was observed in all 3 marble types, they each underwent
different changes in pore size distribution. Figure 5 shows the pore size distribution of the
samples before and after thermal expansion tests. The number of pores of less than 1 μm
increased in TM and YM marbles, however, WM marble experienced a substantial increase in the
number of pores of around 1 μm and above 30 μm, with no significant change in the pore
volume below 1 μm. This coincides with the observed magnitude of D s for the three marbles. The
main changes in the WM pore system occur in pores of > 1 μm, which cannot be quantified by
GS; and this is why the Ds value remains relatively unchanged compared to that for the fresh
sample (ΔDs = 1.4%). On the contrary, TM and YM samples show significant modifications in the
pore system below 1 μm, which is reflected by a higher relative decrease of the fractal dimension
determined using GS (ΔDs is 5.3% and 4.5% for TM and YM, respectively).
124
Figure 5. Pore size distribution plots for the three marbles tested, in fresh and altered samples, after the
thermal expansion tests.
8.3.3.
Hot-stage ESEM
The use of hot-stage environmental scanning electron microscopy (ESEM) allowed a direct
observation of the evolution of the marble microcracks system during thermal cycles.
ESEM images were obtained using the same temperature range used in the thermal
expansion test (from 20 ºC to 45, 90 and again to 20 °C). At 20 ºC no modifications were
observed, but when the temperature rose to 45 °C the samples started to suffer textural
modifications, which were further enhanced when the temperature reached 90 ºC. Nevertheless,
although grain boundaries in the three marbles were observed to seal when the temperature was
reduced back to 20 °C, none of them returned to their initial state. In the case of the WM marble,
slight textural changes were detected at 45 °C (Fig. 5b); at this temperature, the space between
the calcite grains began to widen. This change was better observed when the temperature was
increased to 90 °C (Fig. 5c), and microcracks that were just a few microns wide (~1 μm) but over
50 μm in length appeared. When the marble returned to its starting temperature (20 °C), the
separation between the crystals decreased (~0.5 μm) but the length remained the same, allowing
connectivity between microcracks. The behaviour of TM marble during the thermal cycle in the
ESEM chamber was considerably different. Slight changes were detected in the marble crack and
fissure system when the temperature rose to 90 °C; at the end of the first thermal cycle, when the
marble went back to 20 °C, cracks and fissures had sealed and were almost invisible (Figure 6)
and connection along the grain boundaries was lost. Finally, in spite of the different mineralogical
125
composition of YM marble, significant alterations also occurred in its fissure system when
samples were subjected to temperature fluctuations. This marble behaved in the opposite manner
to the TM marble, as crack opening reached a maximum when the sample temperature fell back
to 20 °C after reaching 90 °C. At this temperature (20 ºC), the development of microcracks was
evident (Figure 7). These cracks were large (~2 μm × 10 μm), but there was less connection
between the grains than with WM.
Figure 6. ESEM images of White Macael marble surfaces during thermal cycles in the microscope chamber.
Cracks are observed to widen as temperature is increased (a 20ºC, b 45ºC, c 90ºC, d 20ºC), and are still
visible once the sample returns to 20ºC (d). Black arrows indicate the position of microcracks.
126
Figure 7. ESEM images of Tranco Macael marble surfaces during thermal cycles in the microscope chamber.
Slight changes in the crack system are observed during the temperature rise (a 20ºC, b 45ºC, c 90ºC, d
20ºC); however, when the sample returns to 20ºC, the fractures seal up (d). Black arrows indicate the position
of microcracks.
127
Figure 8. ESEM images of Yellow Macael marble surfaces during thermal cycles in the microscope chamber.
Widening of cracks is observed as the temperature (a 20ºC, b 45ºC, c 90ºC, d 20ºC) is increased, and is still
visible once the sample returns to 20ºC (d). Black arrows indicate the position of microcracks.
8.4. DISCUSSION AND CONCLUSIONS
The results of our research have shown that numerous factors contribute to marble
weathering due to thermal changes. All of these results indicate that marble mineralogical
composition, fabric, grain size and shape, and the type of union between crystals are the main
128
factors influencing marble behaviour towards thermal changes.
Four aspects of the Hot-stage ESEM test should be considered. The first two are based on
the technique we have used; the other two depend on the finite elements models applied to the
expansion and development of microcracks in marbles with the increase of temperature (Weiss et
al., 2002a, 2003).
1) This test confirms that the main decay agent in marble is thermal change, due to the
anisotropic expansion of calcite and dolomite crystals.
Thermal expansion harms calcite marbles more than dolomite marbles and this effect is even
more dangerous if the marbles have straight grain boundaries.
2) The ESEM technique allows us to view directly the formation and propagation of
microcracks generated by thermal stress in marbles, and, thus gain a better knowledge of the
kinematics displayed by the crystals and the grain boundaries during heating.
3) From the images obtained during the thermal test in all marbles, the greatest expansion
and the largest separation between grain boundaries occur at the highest temperature selected in
this work (90º C). The microcracks are intergranular and/or transgranular.
4) It is important to bear in mind that, once microcracks have developed, the elastic energy
is mitigated and the largest concentration of residual elastic energy moves toward the boundaries
between the grains. When the marble returns to its initial temperature at the end of a heating
cycle (20º C), most of the edges of the carbonate grains along the xz-plane are brighter (see Fig.
5-7), which may indicate a higher concentration of electrical charge produced in this area by
increased residual energy.
5) The development of microcracks obtained with this experiment is consistent with the
porosity observed using MIP. In the case of WM the microcracks are bigger than in TM and YM.
This justifies our MIP results for this marble, which showed an excessive pore volume (over 6%)
and a range of pores of over 10 μm. We can therefore also conclude that a large grain size with
straight grain boundaries helps the formation of microcracks of great length and connectivity.
These four aspects show that the Hot-stage ESEM test is an effective technique for directly
observing the different mechanisms of expansion-contraction and the distribution of microcracks
generated during the thermal change in different types of marble.
From the results of the thermal expansion tests and the in situ observations during hotstage ESEM simulation, it is clear that the three selected marbles, regardless of their mineralogy,
129
fabric or texture, undergo significant changes in their crack and fissure systems.
If we compare the petrographic properties of fresh and weathered samples, it can be
inferred that well-developed crystal shapes, larger grain size and linear grain boundaries are the
main properties responsible for the dramatic effects of environmental thermal oscillations on the
pore system of the marbles and, as a consequence, in their potential susceptibility to weathering.
In the case of the WM marble, its strong textural anisotropy and high degree of thermal
expansion are the main parameters that determine its response to thermal changes. Its bigger
crystal size (compared to TM and YM samples) and its simple, almost linear grain boundaries may
result in a high degree of thermal expansion and the development of microcracks. As thermal
expansion is a linear property and the induced elongation is going to be proportional to the
initial length of the axes under consideration, it seems reasonable to assume that the highest
elongation is going to take place in the marble with the biggest grain size (WM) and, vice versa,
the lowest elongation will occur in marbles with smaller grain sizes (TM and YM). This may result
in higher impact energies when bigger crystals interact than when smaller grains do. On the other
hand, as has already been mentioned, the type of grain boundaries is an important factor which
determines the behaviour of marbles during thermal tests. Simple grain boundaries indicate lower
binding energy between them and interlobate-type unions reflect higher binding energy between
grains; thus, crystal separation will occur more easily in WM marble than in TM and YM marbles,
which show tortuous boundaries and a higher binding energy. This is important when considering
the results of the study of the porous system by MIP and GS, as these tests help to predict the
behaviour of marbles that are thermally altered when they come into contact with soluble salts or
other contaminant agents. The most pronounced modification of the stone porous system after
the thermal expansion tests (in terms of porosity and pore size distribution, as well as other
parameters such as compactness –inferred from the value of the propagation velocity of
ultrasound waves-, surface area or fractal dimension) was observed for WM marble. These
changes can be explained by the formation of new linear fractures (~ 1 μm in size) or the
widening of pre-existing ones (~ 10 to 100 μm). As explained earlier, even though these openings
are large, they are consistent with those produced (during a single cycle) in the hot-stage
attached to the ESEM. The opening of new linear fractures exposes new, flat surfaces that result in
lower fractal dimension compared to fresh samples. In general, these modifications may enhance
the weathering action of dissolved contaminants such as soluble salts or sulphuric acid, mainly
due to both increased accessibility of such pollutants to the stone matrix and the increase in the
volume of material affected by decay agents.
Another interesting aspect is that the marbles we studied exhibit different mechanisms of
130
grain rearrangement when they return to 20 °C after a thermal cycle. ESEM image sequences
confirm such differences. Whereas in the case of TM marble calcite grains reorganize themselves
resulting in the closure of cracks, in WM and YM marbles the cracks that open or widen during
thermal cycles remain visible after the test has finished. Differences in crystal shape and size and,
overall, grain size distribution may explain the mechanisms observed in each marble.
Equidimensional and homogeneously-sized crystals (such as those observed in WM and YM
samples) cannot easily rearrange, which means that cracks remain open. Non-equidimensional
crystals with a polydisperse size distribution can be reorganized in a more compact way, thus
resulting in the closure of cracks and fissures. This may also help to interpret the residual strain
values, which are higher in the case of TM marble and the changes in the rate of ultrasound wave
propagation and porosity after thermal tests, both of which indicate that TM samples show the
smallest degree of alteration when subjected to thermal oscillations. We can therefore deduce
that in TM marble a temperature rise results in length changes, but once the temperature falls
back to its original level, grain reorganization leads to crack closing, which is in turn reflected in
the small change in porosity and pore size distribution.
We are aware that the duration of the test is limited (10 cycles in total) and that the test
does not exactly reproduce the real weathering process that occurs when a material is exposed to
temperature changes for decades or centuries. However, it is likely that the structural
modifications will be more pronounced as the number of cycles is increased. This work offers an
accurate representation of the physical processes taking place during exposure to environmental
temperature oscillations and, also allows us to compare different materials in terms of their
response to thermal stress. The results of this work may contribute to a better understanding of
the processes that cause the weathering of marbles used as building or ornamental materials. In
particular, the environmental temperature oscillations that generally affect marbles result in
changes in the structure of the pore system (i.e. a first stage of decay) of the stones that enhances
or facilitates the potential action of other contaminant agents.
Acknowledgements
This research was financed by Research Project FQM 1635, the Integrated Action HA 20070012, the European Commission VI
th
Framework Program (Contract no. SSP1-CT-2003-501571)
and Research Group RNM-179 (Junta de Andalucía, Spain). We thank I. Sanchez-Almazo (CEAMA,
Junta de Andalucía-Universidad de Granada) for her assistance with ESEM analysis.
131
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136
Part III
Submitted to: Construction and Building Materials
9.
Potential thermal expansion of calcitic and
dolomitic marbles
1*
1
2
1
1
2
1
A. Luque , P. Álvarez-Lloret , B. Leiss , G. Cultrone , C. Cardell , S. Siegesmund and E. Sebastián
1
2
Dept. Mineralogy and Petrology, University of Granada, Faculty of Sciences, Granada, 18071, Spain
Geowissenschaftliches Zentrum der Universität Göttingen, Göttingen, D- 370077, Germany
* Dep. Mineralogy and Petrology, Faculty of Science, University of Granada. Avenida Fuentenueva s/n, 18002,
Granada, Spain
e-mail: [email protected]
Abstract
Marbles have been historically used worldwide as ornamental stone due to their aesthetic
properties, easy polishing and excellent physical properties. One of the main factor that influence
marbles durability and decay is related to their thermal behavior. In spite of the extensive use of
marbles as construction and decorative stone in Spain, thermal studies remain scarce. In this work
the textural and microstructural properties of seven calcitic and dolomitic marbles from Andalusia
(South Spain) were characterized to unravel how they affect their thermal behavior. Thus, rock
fabric features (grain morphology, boundaries and micro-cracks populations) were studied by
polarized microscopy; lattice preferred orientation was investigated by an X-ray texture
goniometer; thermal features were determined by ultrasounds (anisotropic thermal expansion), 6rod-dilatomer (thermal dilatation) and Environmental Scanning Electron Microscopy. Moreover,
thermal coefficients of calcite and dolomite crystals for each marble were determined by ThermoX-ray diffraction (novel application).
Results show that marble thermal dilatation coefficients are related to preferred
crystallographic orientations, which helps to identify decay directions on marbles. Moreover, for
the first time it is shown that the anisotropic thermal expansion of marble main components, i.e.
137
A. Luque et al. / Submittedto: Construction and Building Materials
calcite and dolomite, are singular for each studied marble, playing a key role in their different
thermal changes. Also thermal properties depend on mineral composition, existence of microcracks, and hydric properties.
Keywords: marbles petrography, thermal dilation coefficient, thermo-X-ray Diffraction,
ultrasounds test; texture analyses.
138
Potential termal expansión of calcitic and dolomitic marbles
9.1. INTRODUCTION
Marbles are widely used as ornamental stones at monuments and statues. However, when
they are exposed to natural environments they can show destructive and complex weathering
phenomena.
Since Kessler (1919), who found that repeated heating and cooling cycles lead to irreversible
expansions of marbles, many researchers focused on this aspect of decay (Rosenholtz and Smith,
1949; Zezza et al., 1985; Royer Carfagni, 1999). Thomasen and Eward (1984) and Bortz et al. (1988)
studied the role of moisture in this mechanical deterioration of marbles. Monk (1985), in
particular, considered that water permeability of marble panels was crucial to their lack of
durability and Winkler (1996) explained that water molecules (i.e. those present in the moisture)
may favour stone dilatation, which results in the development of cracks and flakes which
continous granular disintegration. The same author also describes that thermo-hydric fluctuations
initiate the activity of other decay agents attack (e.g. salt solution, freezing water, etc.) which can
affect internal structures of marbles.
It has been observed that not all marbles had the same behaviour after thermal changes
which was related to their different petrophysical properties (Rayleigh, 1934; Widhalm et al., 1996;
Leiss & Weiss, 2000, Koch and Siegesmund, 2004). Siegesmund et al. (1999) proposed that
crystals preferred lattice orientations (textures) and grain microstructures (morphology and
geometry of grain boundary) play a basic role for the thermal behaviour of marble. They
concluded that the early stage of marble decay is due to thermal weathering which causes a
progressive granular decohesion, starting with microcracks development along fabric
discontinuities, like grain boundaries, cleavage planes and pre-existing cracks, which then favours
an increase of porosity and the loss of strength of marble.
The mechanical behaviour of marble due to thermal changes depends on the anisotropic
thermal expansion of calcite and dolomite crystals, the main mineral phases of this type of stone.
It is well know that the temperature increase leads to an dilatation along the crystallographic caxis direction in calcite and dolomite single crystals, while there is a contraction along the a-axis
direction of calcite crystals and an expansion in the a-axis of dolomite minerals (Kleber, 1959).
Zeisig et al. (2002) distinguished the following three types of thermal behaviour on marbles
proceeding from different countries (Italy, Greece, Portugal, Poland and Austria) when submitted
139
to thermal test: i) isotropic thermal dilatation coefficient and large residual strain; ii) anisotropic
thermal dilatation coefficient and not or small isotropic residual strain and iii) anisotropic thermal
dilatation coefficient and anisotropic residual strain. These authors concluded that marble thermal
behaviour was partially controlled by the single-crystal properties (calcite and/or dolomite).
Siegesmund et al. (2000) stated that the texture, as well other microstructural parameters
determines the magnitude and directional dependence of thermal dilatation coefficient.
Microstructure-based finite element simulations have been performed by Weiss et al. (2002,
2003) to determine the thermo-mechanical behaviour of calcitic and dolomitic marbles stating
that differences in marble textures (induced by their composition) significantly affect the
distribution of thermal stresses and suggested that marble textures are the key in determining
their durability. Marbles are the only wide rock type where preferred crystallographic orientation
can cause certain directional dependences to thermal expansion coefficient and residual strain
(Weiss et al., 2004).
From the last decade Spain has been one of the main countries in quarrying and trading
marble. This material, has been quarried since ancient times in different areas from Andalusia
(Padilla, 1999; Beltran, 1998). In fact it is common to found numerous archaeological and
monumental pieces made with marbles from Mijas (Malaga), Macael (Almeria), Aroche and
Fuenteheridos (Huelva) and in many cases, when these marbles are emplaced in contact to the
environment for a long time, they can appear highly weathered (Bello et al., 1992; Sáncho-Gómez,
2006; Álvarez de Buergo, 2008) (Fig. 1). Also some researches focused on the physical properties
of Andalusian marbles (Zezza and Sebastián-Pardo, 1992; Sáez-Pérez, 2003; Sáez-Pérez and
Rodriguez-Gordillo, 2009; Benavente et al., 2007; Martínez-Martínez, 2008), the thermal behaviour
has not been considered as a prominent factor in Andalusian marbles deterioration, except for
some partial investigation carried out on White Macael (Sáez-Pérez and Rodríguez-Gordillo, 2009;
Rodriguez-Gordillo and Sáez-Pérez, 2010; Luque et al., 2010).
The objective of this research is twofold: i) to acquire a comprehensive knowledge of the
fabric of the most common Andalusian marbles, and ii) to understood how thermal oscillations
may influence marble decay when they are used for constructions. Therefore, the anisotropic
thermal expansion, rock fabrics (grain size, grain boundary morphology, grain shape and the
micro-cracks populations) and lattice preferred orientations of marbles will be quantitatively
analyzed.
140
Figure 1. Detail of a marble column that make up the Lions Courtyard in the Alhambra of Granada (Spain)
showing flakes and granular desintegration.
9.2. MATERIALS
9.2.1.
Marble Types
Seven marbles from Andalusia were analyzed: three from Sierra de los Filabres quarries
(Almeria): White (WM), Tranco (TM) and Yellow (YM) Macael; two from Sierra de Aracena quarries
(Huelva): Aroche (AR) and Fuenteheridos (FH); one from Sierra Tejeda quarry (Granada): white
Iberico (IB) and another one from Sierra Blanca quarry (Malaga): White Mijas (MI) (Figure 2).
Marbles from Andalusia show different geological settings which be grouped in three
different districts: marbles from Nevado-Filabride Complex (WM, TR and YM); marbles from
Alpujarride Complex (IB and MI) and marbles from Ossa Morena Zone (AR and FH). Different
metamorphic degrees are described for each districts: low temperature and high pressure for
WM, TR and YM; low temperature and medium-high pressure for IB; high temperature and high
pressure for MI; high temperature and low pressure (HT/LP) for AR and medium-low temperature
and low pressure for FH (Gómez-Pugnaire et al., 1994; Torres-Roldan, 1979; Sosson, 1998; Díaz-
141
Azpiroz, 2004; Crespo-Blanc and Orozco, 1991).
WM
TM
YM
AR
IB
FH
MI
Figure 2. Photographs of polished specimens of the seven Andalusian marbles studied in this work (7×7 cm,
YZ-plane, WM: White Macael; TM: Tranco Macael; AR: Aroche; FH: Fuenteheridos; YM: Yellow Macael; IB:
Iberico; MI:, Mijas).
White Macael (WM) is a white calcitic marble with some gray bands composed of opaque
minerals (biotite, epidote, tremolite, zoisite and bluish-green amphiboles) forming parallel levels.
This marble also contains quartz, muscovite and albite (Sáez-Pérez, 2003). The visual inspection
shows that the fabric is homogeneous and compact, the texture vareis from granoblastic to
xenoblastic with medium-big grain sizes (0.1-3 mm) and it is scarce fissured.
Tranco Macael (TR) is a calcitic marble with numerous gray-dark bands composed of
dolomite, pyrite, chalcopyrite, micas and apatite forming parallel levels (Martínez-Martínez, 2008).
Macroscale observation reveals an homegeneous fabric with compact homeoblastic fabric
(texture) composed of small to medium grain sizes (0.2-1.5 mm) and it is scarce fissures.
Yellow Triana Macael (YM) is a yellow dolomitic marble with an heterogeneous and fissured
fabric with homeoblastic texture. Scarce grains of calcite are also present mainly cementing
cracks. Some Fe and Mn oxides and hydroxides can also be detected (Martínez-Martínez, 2008).
Grain size (0.02-0.8 mm) is small compared to the previous marbles and only calcitic veins shows
high grain sizes (0.5-1 mm).
White Aroche (AR) is a calcitic marble extremely heterogeneous characterised by a very
coarse-to-medium-grained (0.4-4 mm) granoblastic fabric. It is white coloured with some
142
green/grey veins. A compositional banding parallel to the foliation is defined by modal variations
of diopside and phlogopite. Dolomite is irregularly distribution, plus quartz and wollastonite as
accessory phases (Díaz-Aspiroz et al., 2004).
Fuenteheridos (FH) it is white calcitic marble with small grain size (0.1-0.8 mm) and some
marked heterogeneous greenish banding. This marble shows granoblastic fabric and is
characterized by the presence of quartz and dolomite as accessory or trace phases (Espinosa et
al., 2002).
White Iberico (WI) is a pure dolomitic white marble with numerous gray-dark minerals bands
forming parallel levels (Sanz de Galdeano and López-Garrido, 2003). Macroscopically, the fabric is
homogeneous and compact, and the fabric is granoblastic with small to medium grains sizes (0.21.5 mm); fissures are scarce.
White Mijas (MI) is a white dolomitic marble that occasionally shows blue or gray shades.
Variable but low amounts of plagioclase and organic matter can be found (Lapuente et al., 2002).
Macroscopically the fabric is homogeneous with a compact heteroblastic microstructure with a
bimodal grain size distribution (fine-grained and coarse-grained) (0.1-3.5 mm). Fissures are
scarce.
According to their mineralogical compositions the seven marbles can be divided in two main
groups: calcitic (WM, TM, AR and FH) and dolomitic (YM, IB and MI) marbles.
9.3. METHODOLOGY
9.3.1.
To understand the spatial and geometric configuration of marble components in terms of
fabric and microstructure, the methodology proposed by Passchier and Trouw (1996) has been
adapted to this work. The parameters considered have been: grain size distribution, grain aspect
ratio, grain boundary geometry and preferred lattice orientation. The petrographic features of the
marbles were observed by means of a polarized optical microscope (Olympus BX-60) coupled
with a microphotographic unit (Olympus DP10). This technique was used to identify the minerals
and to characterize their microstructure (grain sizes and boundaries). Three thin sections normal
to each other were prepared for every sample and analyzed with parallel and crossed nicols. A
143
coordinate reference system (X-, Y- and Z-axes) was applied where the Z-axis normally represents
the normal of the foliation and the X-axis, where possible, parallel to the lineation (Fig. 3).
Figure 3. XYZ-reference system of the samples oriented according to the macroscopic fabric elements
foliation and lineation.
9.3.2.
Anisotropy of marbles
Due to their non-destructive nature, ultrasounds are particularly useful for determining the
physical properties of construction and ornamental materials. Measurements were performed
with a Panametrics HV Pulser/Receiver 5058PR apparatus coupled with a Tektronix TDS 3012B
oscilloscope. Ultrasounds waves velocity measurements were carried out using transmission
method and three measurements were made for each spatial direction (X, Y and Z).
The propagation velocity of compressional (Vp) pulses was measured in accordance to the
ASTM D 2845 (2005) standard test on dry (during 48 h at 25 ºC) and wet saturated (under high
vacuum pressures) samples (3 drilled cores of 15 mm diameter × 50 mm length per each marble
spatial direction) using polarized Panametric transducers of 1 GHz.
These data were used to infer information on the degree of compactness of marbles (a
decrease in the velocity between saturated and dry samples suggests the development of
144
microcracks) as well as on the fabric anisotropy of marbles (∆M, in %), the value of which can be
calculated as follows:
M =
1  (2  Vpmin )
 100
Vpmax  Vpmid
(1)
ultrasonic wave velocity (in m/s) (Guyader and Denis, 1986).
Vp values can be used to determine the intrinsic and extrinsic properties of marbles and
thus, the structural anisotropy of these crystalline rocks, as well the existence of micro-cracks
when the Vp values are measured in dry (low pressure) and saturated (high pressure) conditions
(Weiss et al., 2002).
9.3.3.
Thermal dilatation coefficient of marbles
The thermal dilatation coefficient (α, in 10
-6
-1
K ) of marbles has been measured using a 6-
rod-dilatometer (Strohmeyer, 2003) and represents the relationship between the change in length
of the sample after cooling down to room temperature and the original sample length; in this
work the temperature oscilation of one cycles moves from 20 ºC to 90 ºC until it cooles down
again to 20 ºC. Three drilled cores orientated according to the previously established axes (X, Y
and Z), were cut and analyzed.
Thermal dilation coefficient (α) was calculated according to the following equation:
α = ∆l/(l×∆T)
(2)
where: ∆l (in mm) is the change in length of the sample, l (in mm) is the length of sample
and ∆T (in K) is the temperature interval.
Thermal expansion (εrs, in mm/m) represents the difference length of the sample after
cooling down to room temperature and the original sample length. It is defined as:
εrs = ∆lrt/lr
(3)
where: ∆lrt (in mm) is the change in length of the sample after cooling down to room
temperature and lr (in mm)is the original length of the sample for a given temperature range.
145
9.3.4.
To geometrically relate the lattice preferred orientation of the samples with the
experimentally determined tensors of the anisotropic physical properties (anisotropic thermal
expansion and ultrasound waves velocity), texture measurements were carried out on a X-ray
texture goniometer especially designed for rock texture analyses (PANalytical X’pert System X-ray
diffractometer). A large X-ray beam size up to 7 mm in diameter, high X-ray intensities due to
fibre optics and automated sample measuring allowed to measure relative large sample volumes
within a reasonable time (25 minutes per pole figure). On the basis of at least five experimental
pole-figures of each sample, a quantitative texture analysis was carried out by calculating the
orientation distribution function (ODF) by means of the WIMV-algorithm (Matthies and Vinel,
1982) and the iterative series-expansion method (Dahms and Bunge, 1989). The bulk rock
anisotropy of the thermal dilatation coefficient and ultrasound waves velocity were calculated by
applying the VOIGT averaging method (Bunge, 1985) and were represented in equal area
projections. To increase the number of grains measured, pole figures were measured at 13
different spots on each sample of a size of 70×70×10 mm for the three sample direction X, Y and
Z, For the pole figure measurements, a 5° × 5° (tilt/rotation angle) grid was applied. According to
Leiss and Ullemeyer (2006), (006), <110> and {104}-pole figures were determined
9.3.5.
An environmental scanning electron microscope (ESEM) equipped with a heating stage was
used to observe the formation of new cracks in marbles and the widening or closure of preexisting cracks during the following thermal cycle: 20 to 90 to20 ºC. The images were obtained on
a FEI Quanta 400 ESEM, which operates at an accelerating voltage of 20 kV. During heating, the
detector-sample distance was set to ~12 mm and the ESEM chamber pressure was set at ~2 Torr
water vapour. This water vapour pressure is equivalent to that of environmental air at 20 °C and
15% RH. Each sample was heated at an average rate of between 4 ± 1 °C/min. The thermal
behaviour of the seven marbles were studied on one thin slab (400 µm) according to ZY-plane of
our coordinate system.
146
9.3.6.
Thermal dilatation coefficients (α) of calcite and dolomite crystals, which compose studied
marbles were measured by Thermo-X-ray diffraction (TXRD). In situ XRD data were acquired using
a Philips PW1710/00 X-ray diffractometer with PW1712 communication card via RS232 serial port,
full-duplex controlled by the XPowder PLUS software (Martín-Ramos, 2004). The heating device is
composed of an halogen lamp (Philips Capsule-line Pro 75 W, 12 V) that heats the XRD chamber
up to 230 °C, a Pt-1000 probe for T monitoring (0.5 °C precision), and a software-controlled
thermostat with digital T selection. A detailed description of the heating system is described
elsewhere (Cardell, et al., 2007).
Powder grain size samples (~100 µm) were prepared and three thermal tests were
performed of each marble. XRD patterns were scanned over 20<°2θ<60 range, with 0.1
goniometric rate and 0.4 s integration time. Backgrounds of diffraction patterns were subtracted.
The scan mode was continuous using CuKα radiation. The voltage was 40 kV, and the tube
current 40 mA. Diffraction patterns were collected and thermal dilatation coefficients were
measured by changing the lens (in °2θ) with increasing temperature (heating rate: 5 °C/min over
a T range of 30-90 °C).
9.4.1.
Although all marbles are highly compact, some fabric differences are visible, even when
marbles quarries are localized in the same lithostratigraphic unit. This is because of differences in
physical and mechanical properties depending to local or regional variations in the
tectonometamorphic history (Siegesmund, 1999).
Fig. 4 shows the difference in grain size distributions between the samples Samples WM and
MI shows the largest grain sizes, samples AR, TR and IB medium and samples FH and YM the
smallest grain sizes. Differences of grain boundary geometriesy can be also observed in all
marbles (e.g. WM shows straight grain boundaries; TR and IB are embayed; AR and MI are
serrated and FH and YM are lobate).
147
WM
TM
YM
AR
FH
IB
MI
Figure 4. Microstructure of the marbles represented by thin sections of the XY-, XZ- and YZ-planes. Legend:
WM, White Macael; TM, Tranco Macael; AR, Aroche; FH, Fuenteheridos; YM, Yellow Macael; IB, Iberico; MI,
Mijas.
Table 1, shows the petrographical properties of the studied Andalusian marbles. Marked
differences with respect to grain shape, grain size, grain boundaries and twinning are evident and
indicate
different
metamorphic
degrees,
deformation
processes
and
post-deformative
recrystallization.
Table 1. Main petrographic parameters for the seven studied marbles. Legend: WM, White Macael; TM,
Dolomitic
Calcitic
Tranco Macael; AR, Aroche; FH, Fuenteheridos; YM, Yellow Macael; IB, Iberico; MI, Mijas.
Fabric
Grain size (mm)
Grain shape
Grain boundaries
Twin types
WM
Grbl
0.1-3
Eq. Polyg
Straight
I - II
TM
Hombl
0.2-1.5
Inq. Sub-ang
Embayed
II - III
AR
Porfido-Grbl
0.4-4
Inq. Decus
Serrated
III - IV
FH
Grbl
0.1-0.8
Eq. Round
Lobate
II
YM
Hombl
0.02-1
Eq. Sub-round
Lobate
I
IB
Grbl
0.2-1.5
Eq. Sub-ang
Embayed
II - III
MI
Heterobl
0.1-3.5
Eq. Decus
Serrated
I - II
Fabric terms means: Grbl: granoblastic; Hombl: homeoblastic; and Heterobl: heteroblastic. Grain shape terms
means: Eq: equidimensional; Inq: inequidimensional; Polyg: polygonal; -ang: angular; Decus: decussate and
Round: rounded.
148
According to Burkhard (1993) twins can be used to correlate the temperature of
deformation occurred during metamorphism processes and four different types of twin can be
distinguished: type I (T< 200 ºC); type II (T compresed between 150-300 ºC); type III (T > 200 ºC)
and type IV (T > 250 ºC). Following this classification, our marbles fit adequately with their
geological setting (described above), being YM and FH those with the lowest metamorphic
degree and AR and MI those with the highest metamorphic degree.
9.4.2.
Table 2 summarizes the ultrasounds waves velocity (Vp) for dry and water-saturated
samples, and the anisotropy values of the seven marbles.
If we consider the Vp values measured by Dandekar (1968) in singles calcite (Vpmax = 7730
-1
-1
-1
-
m×s and Vpmin = 5710 m×s ) and dolomite crystals (Vpmax = 8450 m×s and Vpmin = 6280 m×s
1
), the values obtained by our work for dry samples are generally lower, while the values obtained
for the saturated samples always are closer to these values (Table 2). The maximum velocities
belong to dolomitic marbles (YM, IB and MI).
Vp values measured in dry samples denote a higher degree of anisotropy compared to
saturated samples. The dry sample with highest anisotropy is FH (27%), followed by YM (22 %),
while the less anisotropic sample is AR (6 %). However, the same tendency is not maintained by
saturated samples.
According to Strohmenyer and Siegesmund (2002), the calculated ΔVp (Vpsaturated-Vpdry)
gives an idea of crack-induced anisotropy. This is due to the effect of open cracks is reduced but
not completely closed, because Vp compressibility of air (Vpdry) is higher than that of water
(Vpsaturated). When Vp in marbles are measured in dry conditions (low pressures) the micro-cracks
and pore spaces are open, thus the velocity anisotropy is a result of oriented micro-cracks and
preferred orientations of anisotropic rock-forming minerals. In saturated conditions (high
pressures) the micro-cracks are closed and therefore, the residual anisotropy is only controlled by
their single-crystals (calcite or dolomite) elastic anisotropy and their preferred orientation
(texture) in marble (Siegesmund et al., 1999).
149
-1
Table 2. Velocity of compressional pulses (Vp in m×s ) in dry and saturated samples in the three (X, Y and
Z) perpendicular directions. ∆M (%) indicates the anisotropy of each marble. Legend: WM, White Macael;
TM, Tranco Macael; AR, Aroche; FH, Fuenteheridos; YM, Yellow Macael; IB, Iberico; MI, Mijas.
-1
Calcitic
WM
TM
AR
FH
Vp (m×s )
Dry
Saturated
X
5885
6405
Y
5756
6386
Z
5058
6246
∆M (%)
13.10
X
-1
Dolomitic
Vp (m×s )
Dry
Saturated
X
6597
7452
Y
6573
7304
Z
5165
6816
2.34
∆M (%)
21.56
7.62
6210
6589
X
5146
7044
Y
5678
6253
Y
4348
6772
Z
5387
6073
Z
4298
6766
∆M (%)
9.37
5.42
∆M (%)
9.46
2.06
X
5061
6185
X
5299
7436
Y
4705
5952
Y
4841
7325
Z
4971
6024
Z
5966
7514
∆M (%)
6.20
2.50
∆M (%)
14.05
2.01
X
4055
6588
Y
4513
6640
Z
3129
6456
∆M (%)
26.96
3.12
YM
IB
MI
ΔVp values observed in studied marbles can suggest that FH and YM marbles are more
influenced by the previous existence of micro-cracks while IB and AR can be rule out the previous
existence of cracks.
9.4.3.
Thermal dilation coefficient of marbles
Table 3 shows the results of the thermal expansion coefficient (α, in 10
-6
-1
K ) and residual
strain (r, in mm/m) measured along the X, Y and Z orthogonal directions of the seven marbles
during one thermal cycle (20-90-20 ºC) in dry conditions. WM, YM and AR samples show the
150
-6
-1
highest α values in Z direction (α = 24, 17 and 16×10 K , respectively) while the others marbles
-6
-1
(TM, FH, IB and MI) show lowest values, particularly, MI (α = 8.8×10 K ). However the residual
strain does not show this trend; in fact only the WM (0.29 mm/m) and the TM (0.13 mm/m)
marbles show the highest values while in the other marbles (AR, FH, YM, IB and MI) the residual
strain are almost zero (below 0.07 mm/m).
Moreover, is can be observed that αmax value was measured in WM, TR, FH, YM and IB
marbles in the same direction that the Vpmin value measured in dry samples, which suggest the
preferred crystallographic orientation of calcite or dolomite c-axis along Z-direction in the
marbles. Only AR and MI marbles show different behaviour for Vp min along their Y-directions
regarding their αmax value along Z- and X-direction respectively.
Table 3. Thermal dilation coefficient (α) and residual strain of the seven marbles. Legend: WM, White
Macael; TM, Tranco Macael; AR, Aroche; FH, Fuenteheridos; YM, Yellow Macael; IB, Iberico; MI, Mijas.
-6
Calcitic
WM
TM
AR
FH
-1
α (10 K )
r (mm/m)
X
16.67
0.31
Y
9.52
0.09
Z
23.97
X
Dolomitic
-6
-1
α (10 K )
r (mm/m)
X
12.91
0.01
Y
13.34
0.01
0.29
Z
16.57
0.07
4.66
0.08
X
5.65
0.01
Y
10.69
0.06
Y
8.01
-0.02
Z
13.92
0.13
Z
11.60
-0.02
X
4.22
0.03
X
13.36
-0.02
Y
6.72
0.05
Y
10.46
0.01
Z
16.42
0.01
Z
8.80
-0.01
X
7.45
0.05
Y
8.00
0.03
Z
12.26
0.06
YM
IB
MI
151
9.4.4.
Fig. 5 represents the results of texture analyses by means of pole figures recalculated from
an ODF. According to the classification proposed by Leiss and Ullemeyer (1999), the texture of
WM, AR, FH, YM and MI marbles can be defined as c-axis fibre-type because the c-axis maxima
form single maxima, while the a-axis are quite regularly distributed on a great circle. The c-axis
maxima of these marbles are of moderate intensity and are sub-normal oriented to the regional
foliation. In contrast, TM and IB marbles can be defined as a-axis fibre types because one of the
a-axes forms the rotation axis for the great circle distribution of the c-axis.
To get an idea about the quantity of the texture-induced contribution physical anisotropy of
marbles, these two hypothetical textures, which idealize the natural texture types, were created to
model the dependence of the thermal expansion coefficient and the compressional wave velocity
of calcitic and dolomitic rocks (Fig. 5).
Thermal expansion coefficients (α) and ultrasound wave velocites (Vp) were calculated and
are represented in pole figure plots for all samples (Fig. 5). Although α was calculated by the
VOIGT averaging method, it is quite low regarding to direct measurement of marbles. The Vp,
however, correlates better with the direct measurement of saturated marbles (Fig. 5).
Calculated measures of α and Vp show the same trend in all marbles; highest values of α are
clearly connected with the lowest values of Vp and viceversa. However, the coincidence between
their crystallographic axes and our coordinate system shows scattering differences in all marbles.
WM is the only marble that shows a clear relation between the direction of its calculated α and
Vp measures along its two orthogonal axes with its experimental α and Vp measures obtained
with our coordinate system (X- and Z-direction), therefore the preferred crystallographic
orientation in this marble is reflected quite well. In the rest of marbles, preferred crystallographic
orientation shows some rotation and therefore, the calculated values of maximum and minimum
α and Vp are not well linked with experimental values obtained in our previous coordinate
system. TM, YM and FH marbles show their maximum and minimum values in two orthogonal
directions which are slightly rotated regarding experimental values determined with our
coordinate system. However, AR, IB and MI show maximum and minimum values at intermediate
directions.
152
731
11.0
783
1.5
14.2 746
771 10.6
13.7 750
= minima
= maxima
11.8
α
2.4
Vp
1.2
α
(001)
1.8
Vp
<110>
Sample
IB
Sample
YM
(001)
<110>
15.5
1.6
α
(001)
2.7
Vp
<110>
Sample
MI
713 1.9
15.0 624
-1.5
698
8.0 661
0.9
694
8.5 658
1.6
782
696
655
9.6
Vp
2.7
α
Vp 2.9
α 9.4
1.5
Vp
2.0
α
Vp
2.6
α
Sample
WM
(001)
<110>
1.7
(001)
Sample
TM
<110>
(001)
Sample
AR
<110>
(001)
Sample
FH
<110>
1.4
Figure 5. Upper row: Pole figures of the preferred orientations along the c(001)-axes and a<110>-axes (YZsection as projection plane, equal area projection, lower hemisphere, maxima of multiples of random
distribution (m.r.d.) are given. Lower row: texture based calculations of the thermal expansion coefficients (α)
and velocities of compressional pulses (Vp). Legend: WM, White Macael; TM, Tranco Macael; AR, Aroche; FH,
Fuenteheridos; YM, Yellow Macael; IB, Iberico; MI, Mijas.
153
9.4.5.
The use of hot-stage environmental scanning electron microscopy (ESEM) allowed a direct
observation of the evolution of marble micro-cracks system during thermal cycles. ESEM images
were obtained using the same temperature range used in the thermal expansion test (from 20 to
90 and again to 20 °C). At 20 ºC no modifications were observed, but when the temperature gets
to 90 ºC some marbles opened grain boundaries and micro-cracks were observed. Nevertheless,
although grain boundaries have been opened or fractured in most of marbles when the
temperature was reduced back to 20 °C, in the most of them the micro-cracks have been closed
again.
As can be seen in fig. 6, only WM and FH marbles exhibit the highest opening of microcracks at 90 ºC (Fig. 6 -a2 and -d2). New micro-cracks developed are more opened in the case of
FH, which are ~3 μm-wide, although those opened does not exceed 40 μm. Nevertheless, when
the sample returned to room temperature (20 °C), the separation between the crystals closed
again (Fig. 6-d3). In WM, new micro-cracks are opened only few micrometers (~0.5 μm) but the
length is higher than 75 μm, and when the temperature returns to 20 ºC, fissures remained
opened (Fig. 6-a3).
The rest of marbles, with the exception of IB, showed slight changes during the thermal
cycle. When the temperature rose to 90 °C some fractures (light tension lines) of were detected
but at the end of the thermal cycle, when marbles returned to 20 °C, cracks and fissures closed
again (Fig. 6 series b and c, and Fig. 7 series a and b). Minimal changes were observed in IB
marble, only smooth brightness observed among grain junctions when temperature reached 90
ºC (Fig. 7 -b1, -b2 and -b3). When the initial temperature was reached all lines and fissures
disappeared.
We suggest that even in marbles with a strong anisotropy, i.e. large thermal dilatation, grain
size and grain boundary configuration can influence the development of preferred oriented
microcracks of marbles and, as a consequence, their thermally controlled decay (Zeisig et al.,
2002; Weiss et al., 2002)
154
Figure 6. ESEM images of calcitic marbles surfaces during thermal cycles in the microscope chamber. Slight
changes in the crack system are observed during the temperature rise (1: 20ºC, 2: 90ºC, 3: 20ºC) in the four
marbles. Legend: a: WM (White Macael); b: TM (Tranco Macael); c: AR (Aroche) and d: FH (Fuenteheridos).
155
Figure 7. ESEM images of dolomitic marbles surfaces during thermal cycles in the microscope chamber.
Slight changes in the crack system are observed during the temperature rise (1: 20ºC, 2: 90ºC, 3: 20ºC) in the
three marbles. Legend: a: YM (Yellow Macael); b: IB (Iberico) and c: MI (Mijas).
156
9.4.6.
Temperature increase leads to anisotrophic thermal expansion of marble as a consequence
of the anisotrophic thermal expansion of calcite and dolomite (Kleber, 1959). Both single crystals
(calcite and dolomite) show an dilatation along its crystallographic c-axis direction (α = 26×10
-1
K
and 25.8×10
-6
-6
-1
K ), while dilatation of a-axes directions differs widely in both minerals,
-6
-1
dolomite shows lower expansion degree (α = 6.2×10 K ) and calcite show an contraction (α = -6
-1
6×10 K ) (Markgraf and Reeder, 1985; Reeder and Markgraf, 1986).
However, calcite and dolomite crystals that make up the marbles cannot have the same
crystal structural parameters (unit cell) of pure single crystals (a = 4.988; b = 4.988 and c = 17.061
Å for calcite and a = 4.815, b = 4.815 and c = 16.119 Å for dolomite) (Markgraf and Reeder, 1985;
Steinfink and Sans, 1959). Variable incorporation of Mg and / or Ca ions, in addition to other trace
elements (Mn, Sr, Fe, etc.), the existence of dislocations and metamorphic process, may affect the
crystal lattice structure of calcite and dolomite (Althoff, 1977; Hartley and Mucci, 1996; Sternbeck,
1997; Wogelius et al., 1997; Titiloye et al., 1998). Therefore, structural differences of unit cell may
influence in their anisotropic thermal properties.
Thermal behaviour of a marble is closely related to the thermal behaviour of the single
crystals which compouse these (Fredrich and Wong, 1986; Weiss et al., 2004). However,
metamorphic processes could induce few changes in lattice parameters of these minerals.
Therefore, to evaluate the crystallographic parameters of calcite and dolomite minerals and to
determine how they vary with the increase of temperature, thermal X-ray diffraction test were
carried out.
Reflections at (014), (006), (110), and (113) of calcite and (014), (006), (015), and (110) of
dolomite recordered in the Bragg angle region beyween 27 and 42 º2θ were selected to calculate
the lattice parameters at 30 ºC and 90 ºC. In general, calcitic and dolomitic marbles (at 30 ºC)
show good similarity between their lattice parameters (a and c, in Å) and related measures for the
single crystals of calcite and dolomite, although some length differences can be observed (Table
4).
Table 4 summarize the lattice parameters (Å) obtained in the seven marbles at 30 ºC and 90
ºC. Linear thermal expansion coefficient (αa and αc) measured according to the length changes
produced along a- and c-axes when the temperature increases (from 30 to 90 ºC) were calculated
in calcite and/or dolomite minerals presents in each marble. The main change is the value of α c
157
parameter which represents the maximum thermal expansion coefficient produced in all marbles
-6
-1
along their c-axe. WM shows the highest value (25.7×10 K ), followed by TR, AR, FH, IB and MI,
-6
-
while only YM show the lowest thermal dilation value (9.8×10 K 1).
Table 4. Lattice parameters of calcitic and dolomitic marbles at 30 and 90 ºC. Thermal dilatation coefficient
α
is calculated for each parameter. Legend: WM, White Macael; TM, Tranco Macael; AR, Aroche; FH,
Fuenteheridos; YM, Yellow Macael; IB, Iberico; MI, Mijas.
WM
Calcitic
a/b (Å)
c (Å)
Dolomitic
a/b (Å)
c (Å)
30 ºC
4.9826
16.9722
30 ºC
4.8078
16.0427
90 ºC
4.9841
16.9984
90 ºC
4.8104
16.0521
α (10 K )
5.02
25.70
α (10 K )
9.01
9.77
30 ºC
4.9700
16.9200
30 ºC
4.7886
15.8854
90 ºC
4.9160
16.9460
90 ºC
4.7930
15.9045
α (10 K )
5.37
25.60
α (10 K )
15.30
20.00
30 ºC
4.9667
16.8752
30 ºC
4.8048
15.9802
90 ºC
4.9681
16.9011
90 ºC
4.8074
16.0037
α (10 K )
4.70
25.60
α (10 K )
9.02
24.50
30 ºC
4.9795
16.9344
90 ºC
4.9832
16.9548
12.40
20.10
-6
TR
-6
AR
-6
FH
-6
-1
-1
-1
-1
α (10 K )
YM
-6
IB
-6
MI
-6
-1
-1
-1
Thermal expansion coefficient obtained in our marbles show some difference with respect to
pure single crystals of calcite and dolomite (Krishna Rao et al., 1967; Markgraf and Reeder, 1985;
Reeder and Markgraf, 1986). However it can be seen how the higher expansion values are always
obtained along c-axis of each sample (Kleber, 1959) and in calcitic marbles. In contrast to the
-6
-1
determined value along a-axes for a calcite single crystal (α = -6×10 K ), all calcitic marbles also
show an expansion along this parameter (α a). Nevertheless, this is not strange if we consider that
positive values along two perpendicular directions of Yule marble after thermal test carried out by
Rosenholtz and Smith (1949) were also measured.
Differences measurement regarding lattice parameters obtained in a single crystal of calcite
158
and dolomite with our measurements can be due to the different context of geological formation
among them. The measurement obtained for a single crystal shows an ideal formation conditions,
without the action of pressure, temperature and flow mobility, while marbles minerals have been
formed under different metamorphism processes, therefore the presence of impurities and
development of dislocations in these minerals could be taken into account.
9.5. CONCLUSIONS
From the results we drew the following conclusions which represent a basic information for
marble thermal behaviour:
i) The use of complementary analytical techniques to evaluate the thermal behaviour of
different Andalusian marbles, have helped to obtain novel data about the factors which influences
their thermal behaviour when exposed to temperature changes.
ii) Thermal dilatation coefficient values (α) obtained by dilatometer in each marble samples
are partially linked to the crystallographic preferred orientations of these marbles. Therefore,
using this technique, the direction of the marble along which it can suffer more damage due to
temperature changes can be predicted with great accuracy. However, no relationship has been
observed which explain the residual strain observed in some samples. Further analyses are in due
course to determine the factors controlling this parameter.
iii) Ultrasound and X-ray diffraction texture analyses have demoustrated that the
anisotropies of physical parameters in all marbles are mainly due to the anisotropy of the
constituent minerals.
iv) Visual inspection of formation and propagation of micro-cracks generated by thermal
stress in marbles were observed by ESEM. This technique is crucial to determine how grain
boundaries influence in marble behaviour. With this regard, all marbles show either changes or
fractures in their grain boundaries when temperature increases; however, only WM and FH exhibit
micro-cracks opening when temperature reaches 90 ºC. WM was the only marble that maintained
opened the fissures at the end of the thermal test.
v) The main relevant data were obtained by the use of the novel application of Thermo-X ray
Diffraction in marbles. Not all marbles show the same thermal dilatation coefficient. In Macael
marble (WM) the maximum thermal expansion of calcite fits quite well with its maximum thermal
expansion along Z-direction. Therefore, the thermal expansion of WM marble is directly
159
controlled by the thermal expansion of its crystals and marble texture. The other marbles, TR, AR,
MI, FH and IB, also show high thermal expansion of their constituent minerals. However, some
differences in their textures could explain why there is no clear corresondence with the thermal
expansion of marbles, which are lower. Only YM show less connection among its data, however
the presence of calcite in this marble could influence its behaviour. Future research should form
on the thermal expansion of the calcite in this marble.
vi) Measures obtained in powder samples provide the potential thermal expansion of calcite
and dolomite crystals when they are in free stage, that is, without confining pressures (Luque et
al., 2010). Therefore, in addition to the idea that fabric (grain sizes, grain boundaries and other
texture parameters) is the main factor that influences thermal decay, we propose another factor
to be taken into account: the potential thermal expansion based on TXRD data. The results
obtained with this technique corroborate that thermal expansion coefficient in marbles is directly
connected with the thermal expansion coefficient of its constituent minerals.
We also suggest that the existence of impurities and the presence of dislocations in single
calcite or dolomite crystal in each marble can determine its thermal behaviour
vii) Finally, from the seven Andalusian marbles studied in this work, it was confirmed that
White Macael (WM) is the marble that show more dilatation and opening of micro-cracks with
the increment of temperature. Thermal expansion coefficient, fabric and crystallographic
preferred orientation are the main factors that controlling the thermal behaviour of White Macael
marble (WM), which could lead to its granular decohesion after successive thermal cycles.
Therefore, we suggest that the exposure of this marble under environmental conditions must be
controlled.
Acknowledgements
This research was financed by the Research Project FQM 1635, the Integrated Action HA
2007-0012, the European Commission VI
th
Framework Program (Contract no. SSP1-CT-2003-
501571) and Research Group RNM-179 (Junta de Andalucía, Spain). We thank Daniel MartínRamos for her assistance with Thermo X-ray diffraction analysis.
160
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Part III
10. Changes in the pore structure of marble after
salt decay tests
E. Ruiz-Agudo(1), A. Luque(2), E.M. Sebastián (3), C. Rodríguez-Navarro(4)
Dpto. de Mineralogía y Petrología. Facultad de Ciencias. Universidad de Granada. Fuentenueva s/n 18002
Granada, España
[email protected](1) [email protected](2) [email protected](3) [email protected](4)
Abstract
The pore structure of a stone is an indicative (along with other physical-mechanical
properties) of the material resistance towards weathering processes, in particular salt decay. It
changes during weathering and thus can give information regarding the decay process itself and
its evolution, as well as about the degradation state of the material. Here, we present a
comprehensive study using gas adsorption of the pore structure (porosity, pore size distribution,
micropore volume, surface area and fractal dimension) of a series of Spanish calcitic and
dolomitic fresh and weathered (after salt decay tests) marble stones profusely used for sculptural
and building purposes. These data can be used as descriptors of the conservation state of the
stone. SEM observations of the marble surface complemented the pore system study. Finally, the
results of the analysis of artificially weathered samples (subjected to salt crystallization tests) were
compared with those of a naturally weathered Macael marble sample from the columns of the
Hospital Real (Granada, Spain), in order to asses its degree of damage and to validate the
analytical methodology used here.
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E. Ruíz-Agudo et al. /
168
Changes in the pore structure of marble after salt decay tests
10.1. INTRODUCTION
The resistance of a stone towards weathering processes (e.g., dissolution, freeze-thaw cycles,
and salt crystallization) largely depends on the characteristics of the stone pore system. In
particular, pores in stone control moisture and salt transport as well as mechanical properties.
Micropores and microcracks develop during salt weathering of rocks, due either to physical (i.e.
crystallization pressure) and/or chemical processes (i.e. dissolution of rock forming minerals).
Therefore, the study of the pore system of a stone may help predicting the behaviour of the
stone towards weathering phenomena or the application of conservation treatments as well as to
assess the alteration degree of the stone [1, 2].
There is a variety of parameters (e.g. surface area, pore volume or mean pore diameter) that
characterize the pore system of a stone, but a single magnitude is not enough to predict the
expected behaviour of the material towards salt weathering or to characterize its degree of
alteration. In the last two decades, several works have used fractal geometry to describe stone
pore systems. In general, the pore surface of rocks can be considered as a fractal structure [3].
The fractal dimension has been used to predict the porosity of sandstone [4], to analyse the
fracture surface of rocks [5], to measure marble damage due to load application [3], to describe
the weathering degree of sedimentary stones [1, 2] or to asses the effect of atmospheric pollution
on marble surfaces [6]. These works have used mainly scanning electron (SEM) and optical
microscopy digital image analysis (DIA) and mercury intrusion porosimetry (MIP). However, these
studies have ignored the smaller pores (that frequently cannot be detected either by MIP or DIA)
and that are to a large extent responsible for the susceptibility of stone towards weathering,
particularly salt decay.
In this work we have used gas adsorption (GA) to determine the surface area, fractal
dimension, pore size distribution, pore volume and average pore diameter of a series of selected
calcitic and dolomitic marbles from Andalucia (Spain) and to study the effects of salt decay on
their pore system in the size range between 10 and 1000 Å.
169
Three calcitic (Blanco Macael and Tranco, Almería; Aroche, Huelva) and three dolomitic
(Amarillo Triana, Almería; Mijas, Málaga; Ibérico, Granada) marbles were selected to performed
salt decay tests. Marble samples with size 5×5×5 cm were submitted to salt crystallization tests
according to the standard UNE-EN 12370 (1999). These tests consist of 15 immersion-drying
cycles. Each cycle starts with the immersion the samples in a 14 wt% Na 2SO4•10 H2O solution for
4 hours. Afterwards the samples are subjected to drying in an oven at 105 ºC for 16 hours and
drying at room temperature for 4 hours. Pieces of samples before and after the tests were used
2
-1
for analysis of the pore system using gas adsorption. In samples with less than 5 m •g surface
area, Ar-sorption measurements are more realistic than N 2 ones, that usually yield excessively
high values. The Ar-sorption isotherms were obtained at 77 K on a Micromeritics Tristar 3000
under continuous adsorption conditions. Prior to measurement, samples were heated at 250 °C
for 8 h and outgassed to 10
-3
Torr using a Micromeritics Flowprep. BET analysis was used to
determine the total specific surface area [7]. The BJH method [8] was used to obtain pore size
distribution curves, the pore volume and the mean pore size of the samples. The surface fractal
dimension, DS, has been used to characterize surface roughness. The analysis of the gas sorption
isotherm using a modified Frenkel-Halsey-Hill (FHH) theory [9] allows the determination of
surface fractal dimension from the slope (A) of the plot of Ln(V) vs Ln[Ln(P/PO)], where V is the
adsorbed volume of gas, and P and P0 are the actual and condensation gas pressure. When
surface tension (or capillary condensation) effects are important, the relationship between A and
DS is A = DS – 3. Capillary condensation is significant if δ = 3•(1 + A) – 2 < 0. The pressure range,
and hence range of thickness of the adsorbed layer coverage considered, was only around
monolayer (n=1-2) coverage to ensure that the determination of DS is reliable [9]. Additionally,
changes in sample texture after salt tests were observed using SEM (LEO 1430-VP).
Samples of Blanco Macael marble from the columns of the Hospital Real (Granada, Spain)
were studied using the techniques described above in order to assess the damage condition of
the material by comparison with artificially weathered samples of the same marble type.
170
The results of BET surface area, fractal dimension, pore volume and mean pore size for the
different marbles studied are presented in Figure 1. The BET surface area showed slightly higher
values for calcitic marbles (except for the sample Blanco Macael, which displays the lowest surface
area of all the marbles tested). The pore size distribution (Figure 2) is quite similar in all the
marbles, with a maximum around 2.5 nm, although the pore volume is considerably higher in
calcitic ones. Together with the mineralogical composition, this variation in the pore volume may
determine the differential behaviour with respect to salt tests. The mean pore size of Mijas,
Ibérico, Tranco and Aroche is around 5 nm (in fresh samples). Interestingly, in Amarillo Triana and
Blanco Macael the average pore diameter goes down to 3 nm (before the decay tests). As it will
be shown later, this has implications in their relative resistance towards salt decay tests.
Figure 1. Characterization of the pore system of studied dolomitic and calcitic (shadowed background)
marbles: (a) surface area, (b) pore volume, (c)fractal dimension and (d)average pore diameter. Filled bars
correspond to fresh samples, while empty bars correspond to samples after salt decay tests.
171
3
-1
-1
dV/dD (cm •A •g )
10
100
1000
Pore Diameter (Å)
Figure 2. Typical pore size distribution curve for the studied marbles (this example corresponds to Tranco
marble).
10.3.1.
Dolomitic marbles
These marbles were found to be more resistant towards salt decay tests than calcitic ones. In
general, the surface area of the studied dolomitic marbles remains unaltered or shows a slight
reduction after salt decay tests. The mean pore size of Mijas and Ibérico marbles was constant
before and after salt crystallization experiments, but the pore volume of Mijas samples increased
after the tests. In the case of Amarillo Triana a significant increase in both pore volume and mean
pore diameter was observed. Amarillo Triana samples suffered the highest weight loss (83%)
during the salt tests. Their alteration degree (which was visually detected) was the highest of all
tested dolomitic marbles. On the other hand, Mijas and Ibérico suffered minimal damage during
the tests (incipient sanding and scaling, respectively; weight loss: Mijas, 6 %; Ibérico 0%). In these
marbles, it seems that physical processes (i.e. crystallization within stone pores and disintegration
due to crystallization pressure exerted by crystals growing within them) are dominant in the
overall process of salt weathering. It is expected that crystallization will take place within cracks,
pores and grain boundaries resulting in a widening of these spaces which is in agreement with
the observed increase in the pore volume. However, and due to the low pore volume of these
samples, the amount of saline solution that can access the stone pore network is very limited in
comparison with the calcitic marbles studied. Therefore, less damage to the stone induced by
physical salt crystallization processes will occur.
172
The mean pore size in the case of Amarillo Triana is considerably lower than that of Mijas
and Ibérico; therefore, it is expected (according to Everett’s equation, which relates the
-l
crystallization pressure, P, the crystal-solution interfacial energy γc and the pore radius r as
-l/r
follows: P=-2 γc ; [10]) that the crystallization pressure exerted by salt crystals growing within
such pores will be higher than in the other two dolomitic marbles. This may explain the higher
damage and weight loss observed in this marble after the crystallization tests. It should be
considered, however, that the rise in temperature above 100 ºC indicated by the normative may
also contribute to the widening of cracks due to thermal expansion of the material [11].
During salt weathering, two processes control the change in fractal dimension. The
formation of new pores on mineral surfaces increases the rugosity of the surfaces and therefore
the value of DS. Additionally, both thermal expansion and crystallization within cracks opens fresh,
flat surfaces. This second process (i.e. crack opening and widening) decreases the fractal
dimension and increases the pore volume. In this case, little contribution (although nonnegligible, particularly after long-term exposure to saline solutions) of chemical weathering
(dissolution) is expected, due to the lower solubility of dolomite in the sodium sulfate solution if
compared with calcite; this is in agreement with the observed reduction in the fractal dimension.
Figure 3. SEM image of calcitic marble after salt decay tests showing precipitation of a Mg-bearing phase,
determined by EDX (inset).
173
10.3.2.
Calcitic marbles
Fractal dimension increases in both Tranco and Aroche marbles. This indicates an increase in
the complexity of pore surfaces [1], which is in agreement with the formation of pits and new
pores due to dissolution of calcite. The occurrence of dissolution processes (chemical
weathering), which are less important in the case of dolomitic marbles, may explain the highest
weight loss of calcitic marbles subjected to salt weathering (Blanco Macael, 100%; Tranco 89%;
Aroche 72%). However, the pore volume and the average pore diameter decrease in both
samples after the decay tests. The formation of a Mg-bearing phase was detected by SEM-EDX
(Figure 3); this newly-formed phase may have contributed to the filling of the pores of these
stones, thus reducing their pore volume. It must be considered that immersion of both calcitic
and dolomitic marbles on the saline solution was carried out at the same time in the same
container. Therefore, limited dolomite dissolution may have been the source of magnesium which
precipitates most probably as magnesian calcite on the calcitic marbles. It appears that this phase
has also contributed to the observed increase in rugosity. Note that the dissimilarity between
dolomite and Mg-calcite structures and the strong similarity between calcite and Mg-calcite [12]
may help explain why the newly-formed phase only precipitates heterogeneously on the calcitic
marbles, but not on the dolomitic ones where such a pore filling and development of rough
surfaces were not detected.
Blanco Macael was the marble with the highest degree of alteration after the decay tests as
shown by weight loss measurements and visual observations. Again, precipitation of a Mgbearing phase may be the responsible of the observed decrease in pore volume. The decrease in
the fractal dimension in combination with the rise in the average pore size suggest that physical
phenomena are predominant during weathering tests, which can be explained considering the
lower pore size and surface area of the fresh sample.
174
Figure 4. Sample of Blanco Macael marble of the Hospital Real columns: (a) location of the sample; (b) SEM
image of a sample from the columns base showing dissolution pits and the presence of magnesium sulfate,
determined by EDX (inset).
10.3.3.
In situ weathering: an example from the Hospital Real (Granada)
The sample was located in a column base where white Macael marble sugary chips and
flakes were detected. Although in general the state of conservation of the marble in the columns
is good, our results show that the stone is in fact heavily weathered. The presence of magnesium
sulphate (which was also found affecting different materials in other areas of the building) was
detected by SEM-EDX, particularly at grain contacts (Figure 4). Surface area and fractal dimension
is higher than that of fresh and even laboratory-weathered material (Table 1). This indicates,
together with the occurrence of dissolutional features (pits with regular morphologies) that
chemical phenomena are important in the weathering of the stone. The pore volume shows again
a decrease which may be the result of precipitation of Mg-bearing phases within pores; on the
contrary, the mean pore diameter increase in weathered sample (Table 1). In this case GA
analyses were complemented by mercury intrusion porosimetry (MIP). These measurements
showed and increase in the overall porosity of the sample from 0.12 % in fresh samples to 5.76 %.
All in all, these results suggest a high weathering degree of the marble most probably due to the
detected presence of salts, which are the responsible of mineral dissolution and precipitation
processes (as shown by the increase in Ds and surface area and the decrease in pore volume as
well as SEM images) and physical disintegration (increase in mean pore size).
175
Table 1. Pore system of Blanco Macael marble in Hospital Real.
2
-1
Surface area (m ·g )
0.0484
Ds
2.27
3
-1
Pore volume (cm ·g )
0.000039
Average Pore Diameter (Ǻ)
49.863
10.4. CONCLUSIONS
Our study shows that both calcitic and dolomitic marbles are susceptible to salt decay, in
spite of their low porosity. Calcitic marbles (Macael, Tranco and Aroche) showed a higher weight
loss during salt decay tests, which may be the result of their higher pore volume (which enables
the access of a higher volume of saline solution to the stone pore network) and/or the higher
solubility of calcite (if compared with dolomite), which increases the influence of mineral
dissolution in the overall weathering process. During the weathering process, the pore system of
both types of marbles changes considerably, although this change is more pronounced in the
case of calcitic marbles, which were less resistant to decay tests. Marbles with the lower pore size
(Amarillo Triana and Blanco Macael) are the samples which showed the highest variation in their
pore system, as a consequence of their lowest resistance towards salt decay tests. However, it
should be considered that intergranular decohesion in marbles due to thermal expansion at high
temperatures may also contribute to pore widening, introducing some uncertainty in the results
of salt decay tests. The analysis of the fractal dimension may help overcome (at least, partially)
such problem. A rise in this parameter suggests an increase in pore surface rugosity which is
consequence of the formation of new pores as a result of mineral dissolution enhanced by the
presence of salts. A decrease in fractal dimension is the result of crack widening which may be
consequence of both intergranular decohesion due to thermal expansion or salt crystallization
within cracks. Additional tests at lower temperatures should be performed to determine the
influence of thermal expansion in the change of the pore system of the studied marbles and, as a
consequence, their relative resistance towards salt decay.
In general, it can be said that not a single parameter (surface area, pore volume, mean pore
diameter or fractal dimension) may be used to unambiguously characterize the alteration degree
or the susceptibility of a marble towards salt weathering. However, an in-depth study of the stone
176
pore system (particularly sub-micrometric pores) may give detailed information of the state of
conservation of the material. Additionally, it allows us to predict the relative resistance of a set of
stones towards salt decay tests. Finally, the mineralogical composition of the material (and
specially the solubility of the rock-forming minerals) will determine the relative influence of
chemical phenomena (i.e. dissolution enhanced by saline solutions) in the overall salt weathering
process.
Acknowledgements
This work has been financially supported by the Spanish government under contract
MAT2004-06804 and the Junta de Andalucía under contract FQM-1635 and Research Group
RNM-179. SEM analyses were performed at the Centro de Instrumentación Científica of the
Universidad de Granada.
References
[1] J.L. Pérez Bernal, M.A. Bello López, “The fractal dimension of stone pore surface as
weathering descriptor” Applied Surface Science, 2000, 161, pp. 47-53.
[2] J.L. Pérez Bernal, M.A. Bello López, “Fractal geometry and mercury porosimetry.
Comparison and application of proposed models on buildings stones” Applied Surface Science,
2001, 185, pp. 99-107.
[3] H. Xie, J. Wang, P. Qan, “Fractal characters of micropore evolution in marbles” Physics
Letters A, 1996, 218, pp. 275-280.
[4] A.J. Katz, A.H. Thompson, “Fractal Sandstone Pores: Implications for Conductivity and
Pore Formation” Physical Review Letters,1985, 54(12), pp. 1325-1328.
[5] X. Heping, C. Zhida, “Fractal geometry and fracture of rock” Acta Mechanica Sinica, 1988,
4(3), pp. 255-264.
[6] A. Moropoulou, E.T. Delegou, E. Karaviti, V. Vlahakis, “ Assesment of atmospheric
pollution impact on the microstructure of marble surfaces”, Measuring, Monitoring and Modeling
Concrete Properties, 2006, pp. 695-701.
177
[7] S. Brunauer, P.H. Emmett, E.J. Teller, “Adsorption of gases in multimolecular layers”,
Journal of the American Chemical Society, 1938, 60, pp. 309-319.
[8] E. P. Barrett, L.S. Joyner, P.P.J. Halenda, “The Determination of Pore Volume and Area
Distributions in Porous Substances. I. Computations from Nitrogen Isotherms” Journal of the
American Chemical Society, 1951, 73, pp. 373-380.
[9] P. Tang, N. Y. K. Chew, H.-K. Chan, J. A. Raper, “Limitation of Determination of Surface
Fractal Dimension Using N2 Adsorption Isotherms and Modified Frenkel-Halsey-Hill Theory”
Langmuir, 2003, 19, pp. 2632-2638.
[10] D.H. Everett, “The thermodynamics of frost damage to porous solids” Journal of the
Chemical Society, Faraday Transactions, 1961, 57, pp. 1541-1551.
[11] K. Malaga-Starzec, U. Akesson, J.E. Lindqvist, B. Schouenborg, “Microscopic and
macroscopic characterization of the porosity of marble as a function of temperature and
impregnation”, Construction and Building Materials, 2006, 20, pp. 939-947.
[12] F. Lippmann, Sedimentary Carbonate Minerals. Springer-Verlag, Berlin, 1973.
178
Part III
11. Analysis of the surface of different marbles by
X-ray Photoelectron Spectroscopy (XPS) to evaluate
decay by SO 2 attack
Luque, A.(1)*; Martínez de Yuso, M.V.(2); Cultrone, G.(1); Sebastián, E.(1)
1. Department of Mineralogy and Petrology, Faculty of Sciences, University of Granada.
Fuentenueva s/n; 18002 Granada, Spain
2. Central Research Services, University of Malaga. Bulevar Louis Pasteur, 33; Teatinos
Campus 29071, Malaga, Spain
* Dep. Mineralogy and Petrology, Faculty of Science, University of Granada
Avenida Fuentenueva s/n, 18002, Granada, Spain
e-mail: [email protected]
Abstract
Atmospheric pollution is one of the main agents of decay in monuments and other works of
art located in industrialized urban centres. SO2 is a permanent and abundant component of air
pollution and, although it does not have an immediate visual effect, after continuous exposure, it
can cause irreversible damage to building materials.
Marble is one of the most commonly-used ornamental stones in historical monuments and
its mineralogical composition makes it very susceptible to damage caused by exposure to SO 2.
To measure the damage caused to marble by atmospheres rich in SO 2, selected calcitic and
dolomitic samples were exposed to sulphur dioxide for 24 h in a climate chamber under
controlled temperature and humidity conditions (20 ºC and > 90% HR).
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Ana Luque Aranda
The damage to the surfaces of the marbles caused by SO2 was studied using two nondestructive techniques: chromatic change by means of colorimetry, and chemical analysis using
X-ray photoelectron spectroscopy (XPS). The development of new mineral phases was also
observed by scanning electron microscopy.
Colorimetric analysis revealed a decrease in lightness and chromatic parameters suggesting
that these changes were due to the development of new mineral phases.
The XPS technique, which is generally used in the analysis of metals, is relatively new in the
field of stone deterioration. It enabled us to recognize the development of sulphites and
sulphates on marble surfaces with high precision, after just 24 hours of exposure to SO2 and to
distinguish different decay paths for calcitic and dolomitic marbles.
Keywords: Marble decay; XPS; Calcium Sulphite and Sulphate; Magnesium Sulphite and
Sulphate.
180
Analisis of the surface of different marble by X-Ray Photoelectron Spectroscopy (XPS) to evaluate decay by SO 2
attack
11.1. INTRODUCTION
During the last century, the industrial process and the burning of coal in cities released
increasing amounts of sulphur dioxide into the atmosphere, causing a severe pollution problem
which became a subject of great concern in a variety of different scientific fields. Sulphur and
nitrogen emissions are responsible for the formation of “acid rain” (or acid deposition), which
influences climate change by modifying atmospheric and freshwater environments and damaging
ecosystems and forests [1-3]. Buildings in general, and historical monuments in particular, are
also seriously affected by airborne pollution. [4].
Many researchers have focussed on gas emissions and have demonstrated that air pollution
is a key factor in the decay of the materials used in the construction of our architectural heritage,
which in many cases causes chromatic, chemical, biological and physical changes [5-9].
A large part of our architectural heritage is located in the centre of historic cities, areas in
which there is a high concentration of motor vehicles and, in some cases, industries. Vehicles are
the main source of aerosols enriched in C, S and N in the form of acids and, when they come into
contact with construction materials (stone, brick, mortar, bronze, glass, etc.), they start to react on
the surface [10-13]. The principal effect of this reaction is the formation and development of
chemical weathering on the surface of the material, which enhances its decay and can cause
irreparable damage. [14].
The most frequently used construction and ornamental stones in historical monuments are
carbonate-based, because they were easily quarried and in abundant supply. They are however
very sensitive to atmospheric pollution, especially sulphur dioxide. A great deal of research has
been done on the effects of atmospheric pollution on old and new buildings made of limestones
and/or calcarenites [15-17], dolostones [18,19] and marbles [20-22]. It has been demonstrated
that the final effect of airborne SO2 on calcareous materials is the development of sulphated
black crusts on the stone surface [9].
Other researchers have investigated the mechanisms involved in the reaction and oxidation
of SO2 in calcitic carbonates [23-25] and, in many cases observed that calcium sulphite is the first
stage in the process of calcium sulphate formation on the calcitic substrate. However, there are
relatively few works that describe the chemical sulphation process on dolostones, and a full,
detailed description of the reaction between SO 2 and dolomitic carbonates has so far not been
provided [26-28].
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Ana Luque Aranda
According to Böke [29], the product formed by the reaction of SO 2 with calcareous stones
under high relative humidity conditions is CaSO3•1/2H2O (calcium sulphite hemydrate) which, by
oxidation of bisulphite ions is transformed into CaSO 4•2H2O (gypsum) as follows:
CaCO3 (SO2/ H2O) → CaSO3•0.5H2O
(1)
CaSO3•1/2H2O (O2/H2O) → CaSO4•2H2O
when the sulphation process detailed above occurs on dolostones, it results in the formation
of gypsum and epsomite as follows (Equation 2) [30]:
CaMg(CO3)2 + 2SO2 + 9H2O + O2 → CaSO4•2H2O + MgSO4•7H2O + 2CO2
(2)
However, in this reaction there is no mention of an intermediate stage characterized by the
formation of magnesium sulphite.
Hydrates of magnesium sulphite are well-known salts in wet flue gas desulphurization
technology, and are used as reagents to absorb the SO 2 generated by coal-fired industrial
processes or metal works (e.g. in wood, pulp and paper production) [31].
The reaction of SO2 from flue gases with an aqueous suspension of MgO results in the
formation of MgSO3•6H2O or MgSO3•3H2O phases depending on the prevailing conditions [32]:
below 40-42.5°C magnesium sulphite hexahydrate (MgSO3•6H2O) is the stable equilibrium solid
phase, while above this temperature the stable phase is the trihydrate (MgSO3•3H2O) [33,34].
Because of the metastability of both phases, sulphur can react and form magnesium bisulphite,
Mg(HSO3)2. This last phase can make the desulphurization process more difficult. Data on the
solubility of magnesium sulphites are therefore of great importance, as this is directly related to
the increase in magnesium sulphate (MgSO4) [34].
In addition, when magnesium sulphite comes into contact with O 2, it undergoes the same
oxidation process as occurs when calcium sulphite (CaSO 3) changes into calcium sulphate
(CaSO4). Magnesium sulphite (MgSO3) can therefore be converted into magnesium sulphate
(MgSO4) as follows:
CaSO3• ½ H2O + ½ O2 + 3/2 H2O → CaSO4•2H2O
(3)
MgSO3 + ½ O2 + 7H2O → MgSO4•7H2O
(4)
In this paper we want to identify the sulphated compounds that form on the surface of
different types of marble by using X-ray photoelectron spectroscopy. We also want to
demonstrate that the mineralogical composition of marbles (calcitic and dolomitic) influences
182
attack
sulphite and sulphate development. To this end, Malaga-Starzec et al. [35] observed that the
stability of CaSO3 on the surface of calcite was twice as high as on the surface of dolomite, which
is why the sulphation process has a more serious effect on calcitic marbles than on dolomitics.
Finally, we also want to find out if marble grain size and grain boundaries are other variables that
play a role in sulphate development.
X-ray photoelectron spectroscopy (XPS) is a technique for surface analysis that provides
information about the elemental and chemical composition of the uppermost atomic layers. In
combination with low energy ion bombardment, which is used for depth profiling, this technique
can be used for compositional and chemical analysis at different depths [36]. In this case,
secondary effects such as ion bombardment can induce chemical and compositional changes. As
a consequence, only indirect information is obtained regarding the chemical and compositional
state of the material being studied. From a technological point of view, ion bombardment can
also be used for the modification of chemical and physical properties of surfaces, thus producing
changes in the solid surface that can be exploited for certain applications of the stone [37] or
metal [38] and even in research into nanoparticles [39,40].
11.2. MATERIALS
11.2.1.
Materials
We began by selecting seven marbles commonly used in Spain as construction and
ornamental stones. Three of them (White Macael, Tranco Macael and Yellow Macael) came from
quarries in the Sierra de los Filabres (Almeria), two (Aroche and Fuenteheridos) from the Sierra de
Aracena (Huelva), one (White Iberico) from Sierra Tejeda (Granada), and the last (White Mijas)
from Sierra Blanca (Malaga).
From a mineralogical point of view, all these marbles belong to the calcitic (White Macael,
Tranco Macael, Aroche and Fuenteheridos) or the dolomitic (Yellow Macael, Iberico and Mijas)
marble groups. However, within these groups, each marble has its own distinctive textural
variations [41].
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Ana Luque Aranda
11.3. METHODOLOGY
11.3.1.
The petrographic features of the marbles were determined by means of polarized optical
microscopy (OM, Olympus BM-2).
Major element contents were measured by X-ray Fluorescence (XRF) using a Bruker AXS S4
Pioneer apparatus. Interpretation of data was carried out using Bruker-designed software
SPECTRA plus.
The sulphation test was performed in a Kesternich chamber (details on the experimental set
up are reported in Luque et al. [42]), at constant atmospheric pressure (1 atm), 25º C, 90% RH and
400 ppm SO2 concentration for 24 hours. A container full of water was introduced into the
chamber to maintain high RH concentration. Samples were cut into slabs of 10×10×0.3 cm and
dried for 48 hours at 60º C before being placed in the chamber.
11.3.2.
Colour variations
Before and after the sulphation test, colour measurements were carried out with a MINOLTA
CR-210 colorimeter. Measurements were expressed using the CIE (Commission International de
l’Eclairage) L* a* b* system [43], where L* represents the lightness and, a* and b* are the
chromatic coordinates. The overall colour variation (ΔE) was evaluated using the following
equation:
ΔE = (ΔL*² + Δa*² + Δb*²)
11.3.3.
1/2
XPS analyses
In order to characterise the chemistry of the surface of the seven marbles, X-ray
photoelectron spectroscopy (XPS) analyses were performed and combined with 4 keV Ar+
bombardment to enable chemical analyses to be performed at greater depth. XPS spectra were
184
attack
recorded using a Physical Electronics PHI 5701 spectrometer with a multi-channel hemispherical
electroanalyzer. Non-monochromatic MgKα X-ray (300 W, 15 kV, 1253.6 eV) was used as the
excitation source. The spectrometer energy scale was calibrated using Cu 2p3/2, Ag 3d5/2, and
Au 4f7/2 photoelectron lines at 932.7, 368.3, and 84.0 eV, respectively. The binding energy of
photoelectron peaks was referenced to C 1s core level for adventitious carbon at 284.8 eV. Highresolution spectra were recorded at a given take-off angle of 45º by a concentric hemispherical
analyzer operating in the constant pass energy mode at 29.35 eV and using a 720 μm diameter
aperture. The residual pressure in the analysis chamber was maintained below 1.33 × 10-7 Pa
during the spectra acquisition. Marbles were mounted on a sample holder without adhesive tape
and kept overnight under high vacuum in the preparation chamber before being transferred to
the analysis chamber of the spectrometer for testing. Each spectral region was scanned with
several sweeps until a good signal-to-noise ratio was observed. The PHI ACCESS ESCA-V8.0C
software package was used for acquisition and data analysis. Recorded spectra were fitted using
Gauss-Lorentz curves in order to determine the binding energy of the different element core
levels more accurately [44]. Atomic concentration percentages (A.C. %) of the characteristic
marble elements were determined from high-resolution spectra after the subtraction of a Shirleytype background, and taking into account the corresponding area sensitivity factor for every
photoelectron line [45]. Survey and multiregion spectra were recorded of C 1s, O 1s, Ca 2p, S 2p
and Mg 2p photoelectron peaks.
A depth profiling study was carried out by 4 keV Ar+ bombardment. The at-depth scale of
2.4 nm/min is assumed to be equivalent to the sputter rate of Ta 2O5 under the same sputter
conditions. Differences in sputtering yield between the sample being studied and Ta2O5 were not
considered. Two depths were considered, after 2 minutes Ar+ bombardment (which corresponds
to ~ 4.8 nm depth), and after 19 minutes Ar+ bombardment (~ 45.6 nm depth).
11.3.4.
VPSEM observation
Visual observation of the marbles after the sulphation test was performed by means of a
variable pressure scanning electron microscopy (VPSEM) LEO 1430-VP and the chemical
composition of the crystals that developed on the surface was analysed by EDX microanalysis Inca
350 version 17 Oxford Instrument, which enables the identification of elements with low atomic
numbers, including carbon.
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11.4. RESULTS AND DISCUSSIONS
11.4.1.
Table 1 summarizes the main petrochemical characteristics of the seven marbles.
Starting with the calcitic marbles, White Macael (WM) is characterized by a white pearl
colour and a saccaroid texture. However, depending on the quarrying level, it may show a marked
gray band with varying numbers of veins. Tranco Macael (TM) is a white marble with a
heterogeneous gray banding and a smaller crystal size than WM. Aroche (AR) is a heterogeneous
marble with extreme variability of grain size. It is saccaroid white in colour with some green/grey
veins. Fuenteheridos (FH) differs from AR mainly in its smaller grain size and marked
heterogeneous greenish banding.
As for the dolomitic marbles, Yellow Macael (YM), as its name suggests, is yellow and is
characterized by its small grain size, White Iberico (WI), is a white marble with a marked grey
band and small grain size, and White Mijas (MI) is a translucent white marble with the largest
grain size of the dolomitic marbles.
Table 1. Chemical analysis of selected major elements of unweathered marbles (wt. %). Some petrological
features are listed. Legend: WM, White Macael; TM, Tranco Macael; AR, Aroche; FH, Fuenteheridos; YM,
Yellow Macael; WB, White Iberico; MI, White Mijas.
CaO
MgO
Fe2O3
Al2O3
SiO2
Fabric
Grain
Grain size
Dolomitic
Calcitic
boundary
186
WM
54.91
0.64
0.06
0.09
0.18
Xenoblastic
Straight
0.1-3
TM
54.59
0.62
0.37
0.06
0.10
Granoblastic
Emabyed
0.2 – 1.5
AR
53.86
0.46
0.10
0.20
0.98
Porf-Granobl
Serrated
0.4 - 1
FH
52.99
2.05
0.38
0.07
0.26
Granoblastic
Lobate
0.1 - 0.4
YM
38.25
17.25
0.17
0.07
0.11
Homeoblastic
Lobate
0.02 - 1
WI
34.67
21.08
0.03
0.04
0.06
Granoblastic
Embayed
0.1 - 0.4
MI
34.98
20.72
0.08
0.04
0.08
Granoblstic
Serrated
0.1 - 4
attack
The results of XRF analyses of the marbles are listed in Table 1. Depending on their
mineralogical composition, the main differences between the two groups (calcitic and dolomitic)
were in their CaO% and MgO% concentrations. Some small differences can also be observed
within each group: in calcitic marbles, AR and FH have a lower CaO content and higher Fe 2O3 and
SiO contents compared to WM and TM, while of the dolomitic marbles, YM has the lowest MgO
content and the highest FeO and SiO2 values. WI and MI have MgO2 concentrations of over 20
wt.%.
11.4.2.
Colour variations
Colour parameters were determined before and after exposure of the marbles to SO2 and L*
a* b* values were plotted on two diagrams: the main chromatic changes were observed in a 2D
diagram, while the lightness variations were better checked on a 3D diagram (Figures 1).
Figure 1. Chromatic parameters (a* and b*) for unweathered and weathered marbles (the arrow indicates
the change from fresh to altered samples). Legend: WM, White Macael; TM, Tranco Macael; AR, Aroche; FH,
Fuenteheridos; YM, Yellow Macael; WI, White Iberico; MI, White Mijas.
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Ana Luque Aranda
The YM sample appears separately from the other marbles (b* is aprox.18) because of its
distinctive yellow colour. The other samples fall near the origin of the axes (between -2 and 1 a*
values and 0 and 10 b* value). The lightness (L*) of all the marbles was very high, ranging
between 92.72 and 104.18.
After a weathering test (24 hours exposure to SO2) significant variations could be observed
in all samples. Chromatic values for all the marbles had shifted approximately one unit towards –
a*, while b* remained almost unchanged. As for L* values, all marbles showed a noticeable
decrease (the average ΔL* decrease is ~17.3) (Fig. 2). The marble that suffered the highest
chromatic changes was YM (3.76) and the highest lightness change was AR (19.07), while the
smallest chromatic changes were for FH (1.65) and the smallest lightness change was in WM
(13.91).
Figure 2. CIE L* a* b* parameters for unweathered (square) and weathered (circle) marbles: chromaticity (a*
and b*) versus lightness (L*). Legend: WM, White Macael; TM, Tranco Macael;
Fuenteheridos; YM, Yellow Macael; WI, White Iberico and MI, White Mijas.
188
AR, Aroche; FH,
attack
The colour change undergone by all the samples (∆E ≥ 14) denotes a significant alteration
on the surface of all the marbles (Table 2), even if these changes are very small and are not visible
to the naked eye.
Table 2. Overall colour change (∆E) in marbles after sulphatation test. Legend: WM, White Macael; TM,
Tranco Macael; AR, Aroche; FH, Fuenteheridos; YM, Yellow Macael; WI, White Iberico; MI, White Mijas.
Calcitic
∆E
11.4.3.
Dolomitic
WM
TM
AR
FH
YM
WI
MI
14.08
18.46
19.13
17.51
17.03
17.57
17.63
XPS analyses
The chemical processes that induced these colour changes on the surface of the marbles
after 24 hours’ exposure to SO2 were also identified by XPS measurements.
Two aspects must be considered with this technique:
i) First survey spectra recorded for the seven marbles reveal the chemical composition in
terms of the atomic concentration percentage (A.C. %) of C, O, Ca, Mg, and S on the surface of
the marbles and the oxidation stages of each element can be determined by the binding energy
measured at each peak.
ii) The interpretation of the high-resolution spectra of the photoelectron peak S 2p signal
recorder in both marble groups can determine the different contribution that identifies the
different sulphur compounds present on calcitic and dolomitic marble surfaces.
As regards the first survey spectra, the A.C. percentages of C, O, Ca, S and Mg values
measured on the surface and at depth (~ 45.6 nm) are summarized in Table 3. The binding
energy (eV) values measured in these spectra are used to identify the oxidation states of these
atoms and, therefore, to identify the development of different mineral phases in the two marble
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Ana Luque Aranda
groups (Table 3).
Table 3. Binding energy (in eV) of Oxygen-O; Carbon-C; Calcium-Ca; Magnesium-Mg and Sulphur-S peaks
for different oxidation states of chemical compounds. Legend: WM, White Macael; TM, Tranco Macael; AR,
Aroche; FH, Fuenteheridos; YM, Yellow Macael; WI, White Iberico; MI, White Mijas.
Carbonates
Ca-Sulphite
Ca-Sulphate
O1s
531.2
531.9
532.0
C1s
289.2
Ca 2p
346.6
346.5
348
Mg 2p
48.6
S 2p
Mg-Sulphite
Mg-Sulphate
51.4
167.4
169.4
166.6
168.6
Calcitic marbles. Surface analysis showed that the S content (~ 16%) measured in all marbles
was approximately three times higher than the C (as carbonate) content (~ 5.75%), while Ca plus
Mg values (~ 16%) versus S content were constant. When we carried out the analysis at a greater
depth (~ 45.6 nm), the S content (~ 9.5%) decreased significantly with respect to C content (~
4%) and the sum of Ca and Mg content (~ 25%) was now approximately twice the S content
(Table 4).
Dolomitic marbles. Surface analysis showed that the S content (~ 6%) was approximately
half the C content (~ 14%) and the sum of the Ca and Mg values (~ 19%) was clearly twice that of
the S content. At a greater depth (~ 45.6 nm), the S content fell by half (~ 3%), C slightly
decreased (~ 10%) and the Ca plus Mg content (%) increased noticeably to up to 20 times higher
than the S content (Table 4).
This shows that the sulphur content (S%) measured in both marble groups is higher in
calcitic marbles than in dolomitics, regardless of their grain size and grain boundaries.
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attack
Table 4. Atomic concentration of O, Ca, Mg and S elements relative to C concentration (in %) calculated for
all marbles on the surface and after 19 minutes sputtering. Legend: WM, White Macael; TM, Tranco Macael;
Calcitic
Dolomitic
After 19 minutes
Dolomitic
Surface
Calcitic
AR, Aroche; FH, Fuenteheridos; YM, Yellow Macael; WI, White Iberico; MI, White Mijas.
C (%)
O (%)
Ca (%)
Mg (%)
S (%)
WM
8.4
61.7
11.4
2.4
14.9
TR
5.0
61.5
13.6
0.9
17.5
AR
4.5
66.0
13.4
5.1
15.2
FH
5.1
61.5
12.3
3.6
16.0
YM
13.0
61.2
6.7
12.7
6.4
WI
15.3
61.9
9.8
9.8
3.2
MI
14.1
59.4
6.0
10.8
9.7
WM
8.6
56.0
24.0
0.8
10.6
TR
2.6
62.4
26.2
0.4
8.4
AR
2.8
65.0
23.2
0.5
8.5
FH
3.2
60.2
23.1
2.9
10.6
YM
9.7
59.0
15.6
12.9
2.8
WI
8.2
58.0
13.7
13.6
6.5
MI
12.0
61.0
13.6
12.1
1.3
As regards the interpretation of high resolution spectra, the S 2p core level spectra (binding
energy) obtained on the surface and after 19 minutes (~ 45.6 nm depth) of Ar+ bombardment in
calcitic marbles can be deconvoluted into two contributions (Figures 3 and 4); CaSO3 (167.4 eV)
and CaSO4 (169.4 eV). In dolomitic marbles the same spectra can be deconvoluted into four
contributions (Figures 5 and 6): CaSO3 (167.4 eV), MgSO3 (166.6eV), CaSO4 (169.4eV) and MgSO4
(169.4eV). S 2p core level spectra after Ar+ bombardment shows another photoemission at a
binding energy of 161.5 eV associated with reduced sulphur compounds induced by ionbombardment [44].
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Figure 3. S 2p core level Spectra region (dashed lines) deconvoluted into each contribution (CaSO3 and
CaSO4) on surface of calcitic marbles. Binding energy (eV) versus Intensity (a.u.). Legend: WM, White Macael;
TM, Tranco Macael; AR, Aroche¸FH, Fuenteheridos.
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attack
Figure 4. S 2p core level Spectra region (dashed lines) deconvoluted into each contributions (CaSO 3 and
CaSO4) in-depth (~ 45.6 nm) of calcitic marbles. Binding energy (eV) versus Intensity (a.u.). The component
corresponding to reduced sulphur (dotted lines) is clearly evident after the ion bombardment. Legend: WM,
White Macael; TM, Tranco Macael; AR, Aroche; FH, Fuenteheridos.
Calcitic marbles. On the surface, the high-resolution spectra of the photoelectron peak S 2p
shows two different photoemissions in each marble with the same trend (Fig. 3); CaSO3 contents
(~ 83%) are four times higher than the CaSO4 values (~ 17%) (Table 5). At a greater depth (~ 45.6
nm), two contributions of S 2p core level obtained in these marbles show (Fig. 4) a strong
decrease in calcium sulphite content (~ 53%) and a slight increase in calcium sulphate content (~
34%).
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Table 5. Calcium sulphite and calcium sulphate content in calcitic marbles on the surface and after 19
minutes sputtering (45.6 nm) Ar+ bombardment. Legend: WM, White Macael; TM, Tranco Macael; AR,
After 19
minutes
Surface
Aroche; FH, Fuenteheridos.
Sulphite Ca (%)
Sulphate Ca (%)
WM
79.6
20.4
TR
86.1
13.9
AR
85.3
14.7
FH
79.7
20.3
WM
50.8
30.8
18.4
TR
54.2
33.9
11.9
AR
51.6
36.0
12.4
FH
53.8
35.7
10.5
Dolomitic marbles. On the surface, four contributions of S 2p core level spectra in each
marble show (Fig. 5) slightly lower concentrations of sulphite (~ 46%) than of sulphate (~ 54%)
(Table 6). The same contributions of the photoelectron peak S 2p obtained at depth (~ 45.6 nm)
show (Fig. 6) that the sulphite concentration remained stable (~ 46%) and sulphate concentration
fell slightly (~ 41%).
Table 6. Magnesium and calcium sulphite and magnesium and calcium sulphate content in dolomitic
marbles on the surface and after 19 minutes sputtering (45.6 nm) Ar+ bombardment. Legend: YM, Yellow
After 19
minutes
Surface
Macael; WI, White Iberico; MI, White Mijas.
194
Sulphate Ca
(%)
Sulphate Mg
(%)
Sulphite Ca
(%)
Sulphite Mg
(%)
YM
23.7
30.0
20.2
26.1
WI
20.1
26.5
21.6
31.8
MI
20.3
26.2
22.4
31.1
YM
23.4
17.7
27.6
21.0
10.2
WI
22.6
11.3
39.3
6.6
20.1
MI
25.1
17.8
30.7
16.9
9.5
attack
If we study the same spectrum morphology and the same intensity, it is interesting to
observe that the calcitic and dolomitic marbles follow different trends. This means that sulphation
processes can vary a great deal depending on mineralogical compositions.
Figure 5. S 2p core level Spectra region (dashed lines) deconvoluted into each contribution (CaSO 3; CaSO4;
MgSO3 and MgSO4) on the surface of dolomitic marbles. Binding energy (eV) versus Intensity (a.u.). Legend:
YM, Yellow Macael; WM, White Mijas; MI, White Iberico.
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Ana Luque Aranda
Figure 6. S 2p core level Spectra region (dashed lines) deconvoluted into each contribution (CaSO 3; CaSO4;
MgSO3 and MgSO4) at depth (~ 45.6 nm) for dolomitic marbles. Binding energy (eV) versus Intensity (a.u.).
The component corresponding to reduced sulphur (dotted lines) is clearly apparent after the ion
bombardment. Legend: YM, Yellow Macael; WM, White Mijas; MI, White Iberico.
Moreover, although the sulphation processes affecting calcitic materials have been
described well in the literature, this is not the case for dolomitic materials, in which magnesium
sulphite development has so far never been identified. Even if the magnesium sulphite binding
energy is not reported in the bibliography, the excess in Mg atomic concentration respect to Ca
atomic concentration (Table 4), is not equivalent to the rates of magnesium and calcium sulphate
formation, which leads us to think that some of this magnesium is present as magnesium
sulphite.
196
attack
11.4.4.
FESEM observations
VPSEM images corroborate the sulphation process in marble surfaces after a very short
period (24 h) of exposure to SO2. The morphology and the size of the new sulphate phases can
also be identified. Calcitic marbles show the biggest crystal size of the sulphated products
scattered on the surface of the sample (see White Macael and Tranco Macael, Fig. 6.a and b),
whereas dolomitic marbles have few crystallized areas but have a high concentration of small
crystals of sulphated products (see White Iberico and White Mijas, Fig. 7).
Figure 7. Microphotographs showing the development of different crystal shapes on the surfaces of four
marbles (a. White Macael; b. Aroche; c. White Iberico and d. Mijas) at the end of the sulphation test.
Finally, the main difference between the calcitic (WM and TM) and the dolomitic marbles (WI
and MI) is in the morphology of the new crystals that develop. In calcitic marbles the crystals are
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Ana Luque Aranda
like tabular aggregates, whereas in dolomitic marbles two different morphologies can be
observed: rosette and tabular crystals in WI and a radiating cluster of needle-like crystals in MI.
11.5. CONCLUSIONS
In this work we have demonstrated that the surfaces of calcitic and dolomitic marbles suffer
chemical attack after just 24 hours’ exposure to SO2, The techniques used in this research have
identified and confirmed early stages of sulphation on the surface of the marbles.
Air pollution is a decay factor that produces several colour changes in the stone surface,
even with minimal exposure to air pollution. The chromatic parameters and, above all, the
lightness measured before and after exposure to SO2 suggest that some chemical processes have
occurred on the surface of the marbles.
XPS analyses showed great accuracy in the identification and quantification of sulphite and
sulphate phases formed on the marbles. These phases were then observed under scanning
electron microscopy (VPSEM) showing the different morphologies, sizes and the population
density of the new minerals that developed.
We have noticed that calcitic marbles show higher rates of sulphation than dolomitic
marbles. According to Malaga-Starzec et al. [35] this is due to the stability of sulphite on calcite
which is twice as high as on dolomite. Nevertheless, in all marbles (calcitic and dolomitic), sulphite
concentrations are always higher than sulphate concentrations.
The sulphation process in calcitic marbles begins with the development of calcium sulphite
which is then transformed by oxidation into calcium sulphate. As we have seen at the depths of
both layers (4.8 and 45.6 nm), this reaction occurs early and fast. In dolomitic marbles, the
sulphation process begins with the initial, albeit slower, development of calcium and magnesium
sulphite, which are then transformed by oxidation into calcium and magnesium sulphate.
As regards our architectural heritage, the absence of magnesium sulphite in marbles
damaged by exposure to SO2, may be caused by both the higher solubility of MgSO 3 in the
presence of MgSO4 [34] and the early oxidation of MgSO3 in MgSO4, thus preventing the
formation of magnesium sulphite. The absence of sulphite may even explain why less magnesium
sulphates (epsomite) develop on dolomite substrates than calcium sulphates (gypsum).
It is evident that the mineralogical composition of marbles is the main factor influencing the
formation of sulphites and sulphates on surface, while the grain size and grain boundaries do not
198
attack
have much influence on these reactions. We have observed that the sulphation trend is the same
for all calcitic and dolomitic marbles, regardless of their particular fabric.
Our research confirms that XPS is a great tool to help us understand the different chemical
processes that occur in stone surfaces after a very short period of exposure to air pollution,
because it is able to detect the development of decay crusts measuring only a few micrometers.
Acknowledgements
This research was financed by Research Projects MAT 2008-06799-CO3-03 and FQM 1635
and the Research Group RNM-179 (Junta de Andalucía, Spain). We thank E. Ruiz-Agudo and C.
Rodriguez-Navarro for their assistance in the interpretation of chemical analyses and Nigel
Walkington for the translation of the manuscript.
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[45] J. F. Moulder, W. F. Stickle, P. E. Sobol, K. D. Bomben, Handbook of X-Ray Photoelectron
Spectroscopy, Chastain J, ed. Minneapolis: Perkin-Elmer Corporation (1992).
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PART IV
PART IV: Conclusiones generales
12. CONCLUSIONES GENERALES
En este capítulo se presenta un resumen de las principales conclusiones del conjunto de
estudios realizados en esta tesis.
Las principales diferencias mineralógicas y petrológicas de los siete mármoles objeto de
estudio se deben a los procesos geológicos que han tenido lugar en las áreas donde estos
mármoles se ubican. Estos procesos determinan tanto las condiciones de formación, como son la
composición original de los carbonatos y las características del metamorfismo que los creó, de tal
forma que cada mármol tiene sus propias cualidades e incluso se pueden observar diferencias
entre mármoles que pertenecen a la misma unidad geológica.
Los mármoles estudiados en esta tesis han sido divididos en tres grupos en base al grado de
metamorfismo desarrollado en cada contexto geológico en el cual los mármoles han sido
extraídos: a) mármoles de la Sierra de Aroche y de la Sierra de Mijas se formaron bajo
condiciones de metamorfismo de alta presión y temperatura, b) el mármol de Sierra Tejeda
(Mármol Blanco Ibérico) se formó en condiciones de altas temperaturas y presión media-baja; c)
los mármoles de Macael (Blanco, Tranco y Amarillo) y el mármol del área de Fuenteheridos se
formaron en condiciones de media-baja temperatura y alta presión.
Diversos factores causados por cambios de temperatura contribuyen al deterioro del
mármol. Los resultados indican que la composición mineralógica (calcítica o dolomítica), la
fábrica, el tamaño y forma de los granos, y el tipo de uniones de grano son los principales
factores que determinan el comportamiento del mármol cuando está expuesto a cambios de
temperatura. El uso de técnicas analíticas complementarias ofrece nueva información sobre los
factores que afectan el comportamiento del mármol bajo estas circunstancias.
1) La Termodifracción de rayos-X confirmó que el principal agente de deterioro en el
mármol es el cambio térmico, debido al coeficiente de dilatación térmico anisotrópo de los
cristales de calcita y dolomita. La expansión térmica produce mayor daño a los mármoles
calcíticos que a los dolomíticos, y además, este daño es mayor si los mármoles presentan uniones
de grano rectas.
2) El Miscroscopio Electrónico de Barrido Ambiental, con pletina de calentamiento adosada,
permitió observar la formación y propagación de microfisuras causadas por el estrés térmico en
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los mármoles, y gracias a esto, se pudo llegar a un mayor conocimiento de la cinemática que los
cristales y las uniones granulares presentan cuando los mármoles se calientan.
3) La mayor expansión y la mayor separación entre las uniones de grano pasó cuando se
alcanzó la temperatura más elevada (90 ºC), las microfisuras son intergranulares y/o
transgranulares. Una vez que se forman las microfisuras, la energía elástica se reduce y la mayor
concentración de energía elástica residual se mueve hacia las uniones de grano. Cuando el
mármol recupera su temperatura inicial al final del ciclo de calentamiento (20 ºC), la mayor parte
de los bordes de grano de los mármoles son más brillantes, lo que puede indicar una mayor
concentración de carga eléctrica debida al aumento de la energía residual. Es interesante saber,
que cuando los mármoles recuperan los 20 ºC, después de un ciclo térmico, el reajuste de los
granos es diferente. Esto puede deberse a las diferencias en la forma y el tamaño de los cristales
y, principalmente, a la distribución del tamaño de los granos. Cristales con dimensiones similares
u homogéneas no se recolocan fácilmente, lo que indica que la fisura sigue abierta. Los cristales
que no tienen formas equidimensionales y la distribución irregular se pueden reorganizar de una
manera más compacta, lo que permite el cierre de fisuras y grietas.
4) Si se comparan las propiedades petrográficas de los mármoles frescos y alterados,
podemos concluir que las formas cristalinas bien desarrolladas, los tamaños de grano grandes y
uniones de grano rectas, como es el caso del mármol Blanco Macael, son las principales
propiedades responsables del efecto dramático que producen los cambios de temperatura en el
sistema poroso del mármol. Por ello, se puede decir que estas propiedades son las causantes del
potencial de susceptibilidad del mármol al deterioro. La apertura de nuevas fracturas lineales da
lugar a superficies nuevas y lisas, lo que representan una dimensión fractal más baja, comparada
con las muestras frescas. En general, estas modificaciones pueden favorecer la acción del
deterioro por contaminantes disueltos como las sales solubles y el ácido sulfúrico, principalmente
por favorecer la accesibilidad de contaminantes a la matriz de la piedra y el incremento del
material afectado por agentes de deterioro.
5) Los valores del coeficiente de dilatación térmica (α) están parcialmente vinculados a la
orientacion cristalográfica preferente de los mármoles. Esto significa que se puede predecir con
gran precisión la dirección cristalográfica a largo de la cual el mármol puede sufrir más daños
debido a los cambios de temperatura. Los siete mármoles muestran diferentes valores de α. En
mármol blanco Macael la expansión térmica máxima de la calcita se ajusta bastante bien a la
expansión térmica máxima del propio mármol. Por tanto, la expansión térmica de este mármol,
está controlada directamente por la expansión térmica de los cristales de calcita y la textura del
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mármol. También hay una clara relación entre la expansión térmica de los otros mármoles y la de
los minerales que los constituyen. En este caso los minerales constituyentes se expanden más que
los mismos mármoles, lo que se puede deber a la influencia de la fábrica y la textura de los
mármoles. Las medidas obtenidas en muestras de polvo mostráron que el potencial de expansión
térmica de los cristales de calcita y dolomita en un estado libre (es decir, sin presiones de
confinamiento) es siempre mayor. Esto demuestra que a además de la fábrica (tamaños de grano,
límites de grano y otros parámetros de textura) parece ser que el principal factor que influye en el
deterioro térmico relatado, es el coeficiente de expansión térmica de los minerales que
constituyenten el mármol es otro, lo que también es importante.
6) Todos los mármoles muestran una marcada orientación cristalográfica preferente de sus
cristales. Sin embargo, en base a las figuras de polos calculadas para cada mármol mediante
difracción de rayos X de texturas es posible distinguir entre dos tipos de textura: uno definido por
la orientación cristalografía preferente del c-eje de la calcita y/o dolomita (Blanco Macael, Aroche,
Fuenteheridos, Amarillo Macael y Mijas), conocido como textura tipo fibra del eje-c, y el otro
definido por la orientación preferente de los cristales de acuerdo al eje-a de la calcita y/o
dolomita (Tranco de Macael y Ibérico) denominados como textura tipo fibra del eje-a. Estas
texturas están a su vez, estrechamente relacionadas con el sistema de coordenadas previamente
establecido (basado en la orientación del corte de los bloques de cantera o del patrón del
bandeado y/o de la alineación de los mármoles en el frente visible de la cantera) en todos los
mármoles. Además, de acuerdo a la relación que tienen estas texturas con el grado de dilatación
térmica de los mármoles, podemos concluir que los mármoles con textura tipo fibra del eje-c
tienen coeficientes de dilatación térmica más altos (α) que los mármoles con textura tipo fibra del
eje-c tipo. El mármol Blanco Macael, que tiene una textura tipo fibra del eje-c, presentó el mayor
coeficiente de dilatación térmica, mientras que el mármol Tranco Macael y el mármol Ibérico, con
texturas de tipo fibra del eje-a, presentaron valores del coeficiente de dilatación térmico
considerablemente más bajos.
7) Ambos mármoles calcíticos y dolomíticos son susceptibles al deterioro por sales, a pesar
de su baja porosidad. Los mármoles calcíticos muestran las mayores pérdidas de peso durante el
ensayo de deterioro por sales, lo que se puede ser como resultado de un incremento en el
volumen de poros (lo que permite el acceso de un mayor volumen de solución salina a los poros
de la piedra) y/o la mayor solubilidad de la calcita (si se compara con la dolomita), lo que
incrementa la influencia de la disolución de minerales en el proceso de envejecimiento en
general. Durante el proceso de deterioro, el sistema de poros de ambos tipos de mármoles
cambió considerablemente, aunque este cambio fue más pronunciado en el caso de los
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mármoles calcíticos, indicando que eran menos resistentes a los ensayos de deterioro.
8) Durante el ensayo de sales, la decohesión intergranular de los mármoles debido a la
expansión térmica a altas temperaturas también pudo contribuir al incremento de la porosidad,
esto incroduce un cierto grado de incertidumbre en los resultados del ensayo de deterioro por
sales. El análisis de la dimensión fractal puede ayudar a solventar este problema (al menos
parcialmente). Un aumento de este parámetro indica un aumento de la rugosidad de la superficie
del poro, como consecuencia de la formación de nuevos poros producidos por la disolución de
minerales reforzada por la presencia de sales. Una disminución de la dimensión fractal es el
resultado de la ampliación de fisuras, que a su vez puede ser una consecuencia tanto de la
descohesión intergranular debido a la expansión térmica como a la cristalización de sales en las
grietas.
9) Las superficies de los mármoles calcíticos y dolomíticos sufren el ataque químico después
de tan sólo 24 horas de exposición a SO2. Las técnicas utilizadas en esta tesis han identificado y
confirmado las primeras etapas de sulfatación en la superficie de los mármoles. Los parámetros
cromáticos y, sobre todo, la luminosidad medida antes y después de la exposición al SO 2 sugieren
que algunos procesos químicos se han producido en la superficie de los mármoles.
10) Los análisis mediante Espectroscopía de Fotoelectrones de rayos X han mostrado una
gran precisión en la identificación y cuantificación de fases de sulfito y sulfato formadas en las
superficies de los mármoles. Estas fases se observaron a continuación, utilizando el Microscópio
Electrónico de Barrido de presión variable y los mármoles calcíticos mostraron mayores índices de
sulfatación que los mármoles dolomíticos. Esto se debe a la estabilidad del sulfito en la calcita,
que es dos veces mayor que en la dolomita. Sin embargo, en mármoles calcíticos las
concentraciones de sulfito son siempre superiores a las concentraciones de sulfato, mientras que
en mármoles dolomíticos, las diferencias entre las concentraciones de sulfato y sulfito son menos
pronunciadas.
11) El proceso de sulfacion en mármoles calcíticos empieza cuando el sulfito de calcio se
transforma en sulfato de calcio por oxidación. Esta reacción es rápida y sencilla. En los mármoles
dolomíticos, este proceso comienza con el desarrollo inicial y lento de sulfito de calcio y
magnesio. La falta de sulfito de magnesio en mármoles en nuestro Patrimonio Arquitectónico
dañado por la exposición al SO2, puede ser debido tanto a la elevada solubilidad del MgSO3 en
presencia de MgSO4 como a la temprana oxidación de MgSO 3 en MgSO4. La ausencia de sulfito
puede incluso explicar por qué son menos los sulfatos de magnesio (epsomita) los que se
desarrollan en substratos dolomitas que los sulfatos de calcio (yeso).
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12) Es evidente que la composición mineralógica de los mármoles es el factor principal que
favorece la formación de sulfitos y sulfatos en la superficie, mientras que el tamaño del grano y
las uniones granulares tienen muy poca influencia. La tendencia en el proceso de sulphation es la
misma en mármoles calcíticos y dolomíticos , a pesar de sus particulares fábricas.
Los resultados que se exponen en esta tesis pueden utilizarse como guía en el uso del
mármol en nuevos edificios y en la restauración de obras de arte o monumentos hechos de
mármol. Esta investigación favorece un mejor entendimiento de los procesos que causan el
deterioro de mármoles usados como elementos de construcción y ornamentación.
La información que se trata aquí ofrece una representación precisa de los procesos químicos
y físicos que tienen lugar cuando los mármoles se exponen al mediambiente y nos permite
comparar la respuesta de los diferentes mármoles al estrés térmico, los procesos de sales y una
atmósfera rica en SO2 son los factores extrínsecos mas importantes en el deterioro de las piedras
usadas en muchos edificios históricos y monumentos.
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210
PART IV: Extended conclusions
13. EXTENDED CONCLUSIONS
This chapter presents a summary of the main conclusions of the set of studies conducted in
this thesis.
The main mineralogical and petrological differences between the seven marbles we studied
are due to the geological processes that have taken place in the areas in which the marbles
appear. These processes determine both the formation conditions and the original composition
of the carbonates, and the characteristics of the metamorphisms that created them, in such a way
that each marble has its own particular qualities and there are differences even between marbles
from the same geological unit.
The marbles studied in this research project have been divided into three groups on the
basis of the degree of metamorphism in each of the geological contexts in which they were
quarried, as follows: a) the marbles from the Sierra de Aroche and the Sierra de Mijas were
formed in metamorphic conditions of high pressure and high temperature; b) the marble from
Sierra Tejeda (White Iberian Marble) is a metamorphic rock formed under high temperature and
medium-low pressure conditions; c) the marbles from Macael (White, Tranco and Yellow) and the
marble from the Fuenteheridos area were formed in conditions of medium-low temperature and
high pressure.
Numerous factors contribute to the weathering of marble due to changes in temperature.
The results of this study indicate that marble mineralogical composition (calcitic or dolomitic),
fabric, grain size and shape, and the type of boundary between the crystals are the main factors
influencing marble behaviour when exposed to variations in temperature. The use of
complementary analytical techniques has enabled us to obtain new data about the factors that
influence the behaviour of marble under these circumstances.
1) The Thermo-X-ray-diffraction technique has confirmed that the main decay agent in
marble is thermal change, due to the anisotropic thermal dilatation coefficient (α) of calcite and
dolomite crystals. Thermal expansion harms calcite marbles more than dolomite marbles and this
effect is even more dangerous if the marbles have straight grain boundaries.
2) The Hot-stage Environmental Scanning Electron Microscopy test enabled us to view
directly the formation and propagation of microcracks created by thermal stress in marbles, and,
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thus gain a better knowledge of the kinematics displayed by the crystals and the grain
boundaries during marble heating.
3) The greatest expansion and the largest separation between grain boundaries occur at the
highest temperature used in this research (90º C). The microcracks are intergranular and/or
transgranular. Once microcracks have developed, the elastic energy is reduced and the largest
concentration of residual elastic energy moves toward the boundaries between the grains. When
the marble returns to its initial temperature at the end of a heating cycle (20º C), most of the
edges of the carbonate grains are brighter, which may indicate a higher concentration of
electrical charge produced in this area by increased residual energy. It is interesting to observe
that when marbles return to 20 °C after a thermal cycle, the grain rearrangement is different. This
may be due to differences in crystal shape and size and above all grain size distribution.
Equidimensional and homogeneously-sized crystals cannot rearrange easily, which means that
cracks remain open. Non-equidimensional crystals with a polydisperse size distribution can be
reorganized in a more compact way, thus resulting in the closure of cracks and fissures.
4) If we compare the petrographic properties of fresh and weathered marbles, we can
conclude that well-developed crystal shapes, larger grain size and linear grain boundaries, such as
those observed in White Macael marble, are the main properties responsible for the dramatic
effects of changes in ambient temperature on the pore system of the marbles. These properties
therefore have the strongest influence on their potential susceptibility to weathering. The
opening of new linear fractures exposes new, flat surfaces that result in lower fractal dimension
compared to fresh samples. In general, these modifications may enhance the weathering action
of dissolved contaminants such as soluble salts or sulphuric acid, mainly due to both increased
accessibility of such pollutants to the stone matrix and the increase in the volume of material
affected by decay agents.
5) Thermal dilatation coefficient values (α) are partially linked to the crystallographic
preferred orientations of marbles. This means that we can accurately predict the crystallographic
direction along which the marble may suffer most damage due to temperature changes. The 7
marbles show different α values. In White Macael marble the maximum thermal expansion of
calcite fits quite well with the maximum thermal expansion of the marble itself. The thermal
expansion of this marble is therefore directly controlled by the thermal expansion of its calcite
crystals and the texture of the marble. There is also a clear relation between the thermal
expansion of the other marbles and that of their constituent minerals. In this case the constituent
minerals expand more than the marbles themselves, which can be due as a result of the influence
212
of the fabric and the texture of the marbles. Measurements obtained in powder samples showed
the potential thermal expansion of calcite and dolomite crystals in a free state (i.e., without
confining pressures) always are higher. This shows that although fabric (grain sizes, grain
boundaries and other texture parameters) seems to be the main factor influencing thermalrelated decay, the thermal expansion coefficient of the marble’s constituent minerals is also
important.
6) All the marbles show a marked preferential crystallographic orientation of their crystals.
Nonetheless, on the basis of the pole figures calculated for each marble using X-ray diffraction of
textures it is possible to distinguish between two types of texture: one defined by the preferential
orientation of the crystallographic c-axes of the calcite and/or dolomite (White Macael, Aroche,
Fuenteheridos, Yellow Macael and Mijas) known as c-axis fibre, and the other defined by the
preferential orientation according to the a-axes of the calcite and or dolomite (Tranco Macael and
Ibérico) crystals referred to as a-axis fibre. These textures are in turn closely related to the
previously established system of coordinates (based on the orientation of the cut of the blocks in
the quarry or the striped pattern and/or alignment of the marbles at the quarry face visible with
the naked eye) in all marbles. In addition, in accordance with the relation these textures have with
the degree of thermal dilatation of the marbles, we can conclude that the marbles with c-axis
fibre type textures have higher thermal dilatation coefficients (α) than the marbles with a-axis
fibre type textures. White Macael marble, which has a c-axis fibre type texture, was found to have
the highest thermal dilatation coefficient, whereas the Tranco Macael and Iberian marbles, with aaxis fibre type textures, had considerably lower dilatation coefficient values.
7) Both calcitic and dolomitic marbles are susceptible to salt decay, in spite of their low
porosity. Calcitic marbles show a higher weight loss during salt decay tests, which may be the
result of their higher pore volume (which enables the access of a higher volume of saline solution
to the stone pore network) and/or the higher solubility of calcite (if compared with dolomite),
which increases the influence of mineral dissolution in the overall weathering process. During the
weathering process, the pore system of both types of marble changes considerably, although this
change is more pronounced in the case of calcitic marbles, which were less resistant to decay
tests.
8) During salt decay test, intergranular decohesion in marbles due to thermal expansion at
high temperatures may also contribute to pore widening, introducing some uncertainty in the
results of the salt decay tests. The analysis of the fractal dimension may help overcome this
problem (at least, partially). A rise in this parameter suggests an increase in pore surface rugosity
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as a consequence of the formation of new pores produced by mineral dissolution enhanced by
the presence of salts. A decrease in fractal dimension is the result of crack widening, which in turn
may be a consequence of both intergranular decohesion due to thermal expansion or salt
crystallization within cracks.
9) The surfaces of calcitic and dolomitic marbles suffer chemical attack after just 24 hours’
exposure to SO2. The techniques used in this thesis have identified and confirmed early stages of
sulphation on the surface of the marbles. The chromatic parameters and, above all, the lightness
measured before and after exposure to SO2 suggest that some chemical processes have occurred
on the surface of the marbles.
10) X-ray Photoelectron Spectroscopy analyses showed great accuracy in the identification
and quantification of sulphite and sulphate phases formed on the marbles surfaces. These phases
were then observed using variable pressure scanning electron microscopy and calcitic marbles
showed higher rates of sulphation than dolomitic marbles. This is due to the stability of sulphite
on calcite which is twice as high as on dolomite. Nevertheless, in calcitic marbles sulphite
concentrations are always higher than sulphate concentrations, whereas in dolomitic marbles, the
differences between sulphate and sulphite concentrations are less pronounced.
11) The sulphation process in calcitic marbles begins with the development of calcium
sulphite which is then transformed by oxidation into calcium sulphate. This reaction occurs early
and fast. In dolomitic marbles, the sulphation process begins with the initial, albeit slower,
development of calcium and magnesium sulphite, which are then transformed by oxidation into
calcium and magnesium sulphate. The absence of magnesium sulphite in marbles from our
Architectural Heritage damaged by exposure to SO 2, may be due both to the higher solubility of
MgSO3 in the presence of MgSO4 and the early oxidation of MgSO3 into MgSO4, thus preventing
the formation of magnesium sulphite. The absence of sulphite may even explain why fewer
magnesium sulphates (epsomite) develop on dolomite substrates than calcium sulphates
(gypsum).
12) It is evident that the mineralogical composition of marbles is the main factor influencing
the formation of sulphites and sulphates on the surface, while the grain size and grain boundaries
have little influence on these reactions. The sulphation trend is the same for all calcitic and
dolomitic marbles, regardless of their particular fabric.
The results provided in this thesis can be used as a guide in the use of marble in new
buildings and in the restoration of artworks or monuments manufactured with this stone. This
214
research has contributed to a better understanding of the processes that cause the weathering of
marbles used as building or ornamental materials. The data it contains offer an accurate
representation of the chemical and physical processes taking place during exposure to the
environment and also allow us to compare the response of different materials to thermal stress,
salt weathering processes and an SO2-rich atmosphere, the most important extrinsic factors in the
decay of the stones used in so many historic buildings and monuments.
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durability criteria applied in its use as

Transcription

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