Conservation and monitoring of historical architecture: new

Transcription

13/04/2016
Conservation and monitoring of historical architecture:
new materials and technologies
Prof. Lucia Toniolo
Laboratory «Materials and Methods for Cultural Heritage»
Department of Chemistry, Materials and Chemical Engineering
“Giulio Natta”
[email protected]
Cultural Heritage threatening: a complex problem
The issue of conservation of the architectural heritage
is strongly related to air pollution.
Information on both the air quality and microclimate are needed to effectively
evaluate cultural heritage conservation methods !
Lucia Toniolo – Politecnico di Milano
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Heritage Conservation? What does it mean?
In Europe
60 YEARS
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Heritage Conservation? What does it mean?
In Asia
1995
2006
Angkor Wat, Cambodia
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Visual rate of stone decay
(da E.M. Winkler “Stone in Architeture” 1994)
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Degradation of outdoor exposed stone materials
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The process of degradation is the adaptation of
stone materials to the prevailing environmental
condition
The process of degradation occurs at the very
surface of the building, that is the interface
material/environment
During XXth cent. the kinetic of the process has
been dramatically increased thanks to
atmospheric pollution
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Interaction Material / Environment
Architectural
Heritage durability
material
Chemical
properties
Physical
properties
environment
Mechanical
properities
Climate
Microclimate
Air quality &
pollution
Petrographical
properties
Architectural Heritage:
Not only ceramics, not only concrete!
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Metals
Iron alloys, steel
Copper alloys, bronzes
Aluminum
Titanium
Ceramics
Natural Stones, Rocks
Lime, Gypsum, Cement
Mortars & Concrete
Bricks & Terracotta
Masonries
Organic Materials
Wood and Timber
Leather
Synthetic Polymers
Polymeric materials, Plastics
Vernishes & Paintings
Fibers
Composites
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High value Architectural Heritage
1. Milan, the Cathedral
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2000
m2
10,500
of marble
12 spires
500 sculptures
25 large low-relieves
1961
The scaffold
2003
10
2005
The scaffold has been built at the end of 2002
The conservation work has been finished at the end of 2009
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High historical-artistic value Cultural Heritage
2. Certosa di Pavia
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3. La Collegiata di Castiglione Olona (Varese)
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1425
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Fresco painting by Masolino da Panicale
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1434
Fresco painting by Masolino da Panicale
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4. Torre Velasca, Milan 1958 Architect Studio BBPR
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How to face this very difficult situations?
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4 dramatically important keywords
1. Multi-disciplinarity
2. Knowledge
3. Compatibility
4. Reversibility/Retraetability
Project guidelines
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Three Reference Books
S. Sigesmund, R. Snethlage
Stone in Architecture: Properties, Durability
Springer-Verlag
2011
E. Doehne, C.A. Price
Stone Conservation: An Overview of Current Research
(Readings in Conservation)
Getty Conservation Institute, Los Angeles 2010
S. Macdonald and G. Ostergren
Conserving Twentieth-Century Built Heritage:
A Bibliography
Getty Conservation Institute, Los Angeles 2013
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Multidisciplinarity for the Conservation project
Scientific publication on “conservation treatments” (in english) and case
studies presenting the evaluation of treatment performances are only a few !!
Book Article, Journal Article, Patent - "Conservation Treatment" as subject - in Architecture and
Archaeological conservation - in the period 2000-2014
From AATA online, Getty Conservation Institute, http://aata.getty.edu/Search
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Knowledge & Compatibility
Restoration and maintenance
for natural stone
1.Cleaning
Phases of
2.Surface Consolidation
the
conservation
3.Adhesion, Sealing
work
4.Surface Protection
... what kind of treatment?
“There is hardly a polymer which has not been suggested and
used for a conservation application”
C.V. Horie 1990
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Polymeric materials
Polymer Class
Vinyl resins
Substituted
Vinyl resins
Acrylic Resins
Polyurethanes
Epoxy Resins
Years
Types
Apllication
1950
LDPE, PE, PP
Stone, Mural Painting,
Painting, Paper
1950-60
1930
1970
1970
1950
1975
Silicon Resin
Perfluoro
polyethers
1980
Fluorurated
acrylic resins
1995
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synthetic gums
PVC, PVAC, PS,
PEG
Lucite 44/45
Paraloid, Elvacite,
Plexigum
PMMA, PBMA
DRI FILM 104,
Rhodorsil,
Silirain,TEOS,
MTMOS,
Fomblyn, Akeogard
Stone, Paper, Textile,
Painting, Wood
vernishes
Stone, Mural piantings,
Paintings, Wood
Wood, Stone
Stone, Mural paintings,
Metals
Stone, Bricks, Plaster,
Paper, Antigraffiti
Stone, Plasters,
Antigraffiti
Stone
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Ideal surface consolidation treatment
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requirements
 Good adhesion to the stone substrate
 Negligible color alteration
 Adds no gloss or sheen
 Improvement of mechanical and microstructural
properties
 Do not produce any harmful by product (salts,
VOCs, organic compounds, etc.)
MATERIALS FOR SURFACE CONSOLIDATION
Inorganic compounds - Low molecular weight
•Lime (Ca (OH)2) and nanolime
•Barium hydroxide (Ba(OH)2)
•Ammonium oxalate
Organic esters of silicic acid
•Tetraethyl orthosilicate (TEOS)
•Tetramethyl orthosilicate (MTMOS)
Organic synthetic polymers
•Siloxanes
•Acrylic polymers
•Fluorinated polymers
•Epoxy resins
TEOS
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Ideal protection/water-repellent treatment
Requirements:
Negligible color alteration
Adds no gloss or sheen
Applies as a waterborne system
Water repellent
Water vapor permeable
Stable under a variety of environmental
conditions, including temperature cycling and UV
exposure
 Reversible or retreatable






MATERIALS FOR SURFACE PROTECTION
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Polymeric materials
•Acrylic resins, partially fluorunated acrylic resins
•Silicon resins, polysiloxanes
•Perfluoropolyethers
•Fluorinated elastomers
They play the role of water-repellent coating for stones
The effectiveness depends on:
•Chemical nature
•Molecular weight
•Glass transition temperature
•Filming properties
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Conservation project and intervention
3D Survey-Mapping
and sampling
preliminary in field inspection
Material
characterization
In field diagnostic
investigations
Environment
characterization
In Lab diagnostic
analyses
Guidelines for
conservation
Conservation
project
In field testing of
materials and
methods
executive
Conservation and maintenance project
Some experiences in surface consolidation & protection
Pavia – S. Michele - 1962
S. Maria delle inorganico
Grazie – 1985
consolidamento
a basso p.m.
consolidamento
e protezione
con fluosilicati
Milano
– Duomo
facciata
– 1972
con materiali
organici
polimerici
Consolidamento e integrazione con materiali organici
Milano – Cortile richiniano della Ca’ Granda 1993
polimerici
Consolidamento con materiale organico polimerico
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The faҫade of the Milan Cathedral –
Conservation work 2002-2009
Comparison between two well known marbles
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Certosa di Pavia
Carrara marble
Candoglia marble
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Cathedral façade, Milan
Situation of the marble sculptures in 2003
San Giacomo Minore,
Elia Vincenzo Buzzi 1812
Restored in 1972
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Surface consolidation carried out in 1972
Cathedral of Milan
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Polished cross-section observed by optical
microscopy
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White vernish layer
Titanium dioxide
Surface consolidation
layer, epoxy resin
Marble substrate
Polished cross section of a marble fragment
Microphoto
Sample observed by Scanning Electron Microscopy
White film,
Titanium rich
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Epoxy resin
Area interested by
microorganisms
colonization
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Surface protection carried out in 1972
Presence of yellowish surface film
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in sezione trasversale
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in superficie
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Nanotechnology in building materials
Innovative strategy for surface consolidation and protection
Cement and concrete:
 Nano-SiO2 to increase mechanical
properties and durability
 nano-TiO2 to reduce carbon monoxide
and NOx emissions
 Carbon nanotubes to enhance the
strength, to effectively hinder crack
propagation
Glass:
 nano-TiO2 to avoid pollutant deposition
 nano-TiO2 super-hydrophilic
Coatings:
 Addition of nanoparticles
(Ag, ZnO,TiO2 ) antimicrobial
and self-cleaning surfaces
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TiO2-based materials for the conservation of
Architectural Heritage
Self-cleaning
property
De-polluting
property
Biocidal
property
• Degradation of gaseous pollutants that can be washed away by rain
• Preventive strategy towards stone degradation and biocolonization
• Reduction of time and costs for maintenance
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TiO2 nanoparticles used in the research
 Non hydrolytic sol-gel synthesis from TiCl4 and benzyl alcohol at T= 40 °C [1,2]
 Pure phase anatase
 Nanoparticles size: 30±10 nm ( in water)
 Benzyl groups anchored on the titania surface : photo-active not only under UV-light
but also under solar light irradiation
 Highly stable dispersions of NA_TiO2 in aqueous systems, as they do not
aggregate and precipitate
Commercial P25
nanoparticles
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[1] Niederberger, M. et al. Chemistry of Materials. 2002, 14 , 4364-4370
[2] Colombo, A., et al. RSC Adv., 2012,2, 6628-6636
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Set-up of formulations of protective treatments for stone
and paint materials of Cultural Heritage,
modified by appropriate photocatalytic TiO2 nanoparticles
1. Assessment of the efficacy and durability of the
nanocomposite based on poly(2-ethyl-2-oxazoline) as
consolidant and protective film for matte painting
surface
2. Characterization of nano-TiO2 dispersions and study of
their application on natural stones
3. Set-up and study of different hydrophilic SiO2-nano TiO2
treatments for the application on natural stones
4. Set-up and study of different water repellent
nanocomposites for the application on natural stones
5. Assessment of the best formulations for the protection of
the façade of Monza cathedral
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Set-up of SiO2–NA_TiO2 treatments for stone conservation
TiO2
TiO2
SiO2
NA_TiO2
Hydrophilic
SiO2-NA_TiO2 treatment
Application of the consolidant
Tetraethyl orthosilicate-TEOS as grafting agent
Two commercial TEOS have been selected:
- TEOS (A): Estel 1000, 75 wt% in white spirit D40 solvent
- TEOS (B): Silres BS OH, about 100 wt%, without solvent
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Materials:
Application of NA_TiO2 water dispersions (3%) by brush on Noto stone
and thermally aged Carrara marble:
Wet stone surface
(“wet on wet” technique)
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After the complete hydrolysis
and gelation of the consolidant
(four weeks) (“wet on dry”
technique)
Evaluation of the aesthetic compatibility: Colorimetry
• Every treatment shows high aesthetic compatibility with both
lithotypes
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Chemical interactions between TEOS and nano-TiO2:
diamond cell micro-FTIR spectroscopy
TEOS after 4 weeks of curing
SiO2 – nano TiO2 treatment on wet surface (AWet)
SiO2 – nano TiO2 treatment on dried surface (ADry)
νa Si-O-Si
Absorbance
ν Si-OH
νs Si-O-Si
950
δ O-H
940
δa C-H
1800
1600
1400
νa Si-O-Ti
910
1200
‐1
1000
800
Wavenumber (cm )
• Formation of the silica gel
• Incorporation of TiO2 into the silica network
• Modification of silica network in SiO2 – NA_TiO2 treatment on dried
surface (ADry)
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Evaluation of the morphology of SiO2–NA_TiO2 treatments
applied on Carrara marble section treated with Awet: SEM-EDX
Ca
Si
Ti
Si and Ti
signals in
the same
regions
• Combined SiO2–NA_TiO2 layer where nanoparticles are inserted in
the silica network in the “wet on wet” treatments
44
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Evaluation of the photocatalytic activity
Noto stone
+85%
• Higher values for
specimens treated with
“wet on wet” SiO2-NA_TiO2
treatments for both
lithotypes, compared to
those treated only with
NA_TiO2 dispersions
Carrara marble
+200%
+165%
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Set-up of water repellent TiO2-based nanocomposites for stone
conservation
Materials
Development of water-repellent nanocomposites based on
commercial coatings for stone protection:
1. Water dispersion of
functionalized
perfluoropolyethers (10%),
Fluoline PE, CTS srl
2. Water dispersion of
organosiloxanes(10%),
Silo 112, CTS srl
3. A solution of SiO2 functionalized
by silicon alcoxides in isopropyl
alcohol (20 % by weight),
SIOX-5 S, Siltea srl
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Materials
Preparation of the nanocomposites:
1. Blend:
Fluoropolymer: 16wt% (F16mix)
Polysiloxane: 16, 28 and 44 wt% (S16mix, S28mix, S44mix)
Functionalised SiO2 : 16wt% (SO16mix)
2. Layered nanocomposites:
a) Application of NA_TiO2 water dispersions (3%) on wet surface
a) Application of NA_TiO2 water dispersions (3%) on dry surface
TiO2
Polymer
47
Evaluation of the aesthetic compatibility : Colorimetry
Fluoropolyethers
Polysiloxanes
Functionalised
SiO2
 ΔΕ* <4 after the application of the treatments
 Lower ΔΕ* of nanocomposites compared to pristine polymers
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Evaluation of the morphology of the treatments: SEM-EDX
Polysiloxanes+ NA_TiO2 blend
Polysiloxanes
S Ref
S44mix
Si
Ca
Si
Homogeneous distribution of
treatments on the surface of both the
pristine polymer (S ref) and the blends
(S16mix, S28mix and S44mix)
49
Ti
Ca
Evaluation of the morphology of the treatments: AFM
Untreated
Polysiloxanes
Pristine polymer S REF
Blend nano TiO2 / polymer (16 wt% pol.) S16mix
Blend nano TiO2 / polymer (28 wt% pol.) S28mix Blend nano TiO2 / polymer (44 wt% pol) S44mix
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Evaluation of the morphology of the treatments: AFM
Polysiloxanes
Fluoropolyethers
Functionalised SiO2
 Increase of the roughness in nanocomposites (F16mix, S16mix,
S28mix and S44mix) compared to pristine polymers (F REF and S REF)
 Comparable roughness for SO16mix and SO REF
51
Evaluation of the wettability properties: Static contact angle
+28%
+50%
 Higher contact
angles by
increasing the
NPs concentration
Functionalised
SiO2
 For samples
treated with
functionalised
SiO2, the
introduction of
NPs dcreases the
contact angles
-43%
Polysiloxanes
Fluoropolyethers
NT
S REF
52
F REF
S44
mix
F16mix
SO REF
SO16mix
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Evaluation of the photocatalytic activity
Polysiloxanes
Fluoropolyethers
Functionalised SiO2
53
•
Polysiloxane-based blends
show the highest
photoactivity
•
Increase of the
photocathalytic activity with
the increase of the NPs
concentration
Working areas
Selected pilot areas:
Exposition
•
Architectural elements
•
period of time
North
South
•
High relief
Nascita di
Eva
High relief
Davide e
G
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Monitoring of the Cathedral of Milan
Site 5: Upper balcony. H = 32.00 m - colour
changes, characterization of the deposit
Site 4: Rear Façade (lateral nave roof).
H = 30.00 m.
Evaluation of protective treatment
Site 3: Main balcony. H = 19.70 m - colour
Site 2: Southern Portal. H = 9.00 m - colour
Site 1: Road level - colour changes,
characterization of the deposit
Site 4: exposition conditions
REFERENCE
SPECIMENS
PROTECTED
SPECIMENS
South exposition
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Specimen sheltered by rain: particulate matter accumulation
85
SITE 3:
Variation of
Luminosity L*
82
79
L*
76
9
73
Before exposition
8
6
5
4
3
64
T‐ zero
BEFORE EXPOSITION
67
7
b*
70
Variation of b*
T‐ zero
T1 ‐ 6m expo T2 ‐ 1m expo
T1 ‐ 6m expo T2 ‐ 1m expo
Exposed specimen: effects of rain washing out
µm
1,2
pre expo
set I ‐ 6 mesi
1,0
0,8
Ra
0,6
0,4
0,2
mm
0,0
85
86
UNTREATED
94
95
WITH SILOXANE COATING
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Treatment effectiveness: water repellency
pre expo
contact angle θ
130
post 6m expo
110
90
70
25 misure/campione
50
94
95
96
BEFORE-EXPOSITION
AFTER-EXPOSITION
BEFORE EXPOSITION
untreated
SEM observations 500x
untreated
AFTER EXPOSITION
treated
treated
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BEFORE EXPOSITION
untreated
SEM observations 1500x
untreated
AFTER EXPOSITION
treated
treated
What about reversibility?
62
….some final remarks
Most of the treatments and chemicals used in the
conservation yards aren’t reversible, that is they cannot be
removed from surfaces after years.
Polymeric materials are not very durable, as it is well known
for industrial products and coatings. Studies to assess
durability of treatments are rare and often carried out on in
laboratory not in real cases.
Conservation scientists don’t have the magic wand but are
aware of limits and advantages of using different materials
during intervention
Conservation projects of Heritage buildings should benefit
from interdisciplinary work.
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13/04/2016
MIDAR Materials and Imaging
in Arts & Architecture
http://midar.chem.polimi.it/
PLEASE VISIT OUR
WEBSITE!!
63
Thank you for your kind attention!
32

Conservation and monitoring of historical architecture: new

Transcription

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