Aggregate characterisation Aggregate characterisation in relation to

Transcription

Aggregate characterisation
in relation to bitumenbitumen-aggregate
adhesion
M.Sc. Thesis
Diederik van Lent
March 2008
Aggregate characterisation
in relation to bitumenbitumen-aggregate
adhesion
by Diederik van Lent
Under the supervision of the Graduation Committee:
Prof. dr. ir. A.A.A. Molenaar
Ir. M.F.C. van de Ven
Ir. A.C. Pronk
Dr. J.A. Poulis
Dr. ir. A.L.A. Fraaij
Ir. L.J.M. Houben
Civil Engineering and Geosciences, Road and Railway
Engineering, TUDelft
Aerospace Engineering, Adhesion Institute, TUDelft
Civil Engineering and Geosciences, Material Science,
TUDelft
2
Acknowledgement
Acknowledgement
First of all I would like to thank the members of my graduation committee; Prof. dr. ir.
A.A.A. Molenaar, Ir. M.F.C. van de Ven, Dr. ir. A.L.A. Fraaij, Dr. J.A. Poulis, Ir. A.C. Pronk
and Ir. L.J.M. Houben for their time and for sharing their knowledge.
Sincere thanks to the Road and Railway laboratory staff members, Ing. J. Moraal, Mr. J.W.
Bientjes and Ir. R.N. Khedoe for their assistance in the sample preparations.
I would also like to thank Mr. E.R. Peekstok from the department of Materials, Mechanical
and Maritime Engineering of the Delft University of Technology for his assistance in the
roughness measurements by means of the confocal microscope.
I wish to thank Mr. A. Thijssen from the Microlab of the Delft University of Technology for
his assistance in the measurements performed by means of the electron microscope and the
mercury intrusion porosimeter.
I am grateful to Mrs. J. van Haagen from the department of Engineering Geology of the Delft
University of Technology for her assistance in the pH acidity measurements.
I would like to thank Mr. R.A. Penners from the department of Civil Engineering of the Delft
University of Technology for his assistance in crushing the stones by means of the disk mill.
Sincere thanks to Mrs. Dr. I. Cringus-Fundeanu and Mr. S.C.H. van Meer from the Adhesion
Institute of the Delft University of Technology for their assistance in the surface free energy
measurements and for the availability of the reference liquids.
I would like to thank Mrs. P.M. Meijvogel-de Koning from the department of Engineering
Geology of the Delft University of Technology for her assistance in the bitumen surface free
energy measurements by means of the Wilhelmy Plate Test.
I am very thankful to Dr. E.A. Masad from the department of Civil Engineering of the Texas
A&M University for the very useful discussion we had and for performing the quantitative
analyses of the micro roughness.
Finally I would like to thank every other person for the support during this study.
Diederik van Lent
Delft, March 2008
Aggregate characterisation in relation to bitumen-aggregate adhesion
3
Summary
Summary
Adhesion between bitumen and aggregate is one of the most important factors affecting the
service life and durability of asphalt mixtures, especially for Porous Asphalt Concrete
mixtures. The Road and Hydraulic Engineering Institute of the Dutch Ministry of Transport,
has started a research into ravelling of Porous Asphalt Concrete. As part of this research, a
quantification of the adhesion between bitumen and aggregate is made in the laboratory of
Road and Railway engineering at the Delft University of Technology. For this quantification
of the adhesion between bitumen and aggregates several experiments are conducted on
bitumen-aggregate specimens. The bitumen-aggregate specimens are assembled from two
stone columns with a small bitumen film in between. To obtain the stone columns some stone
treatments were performed. First large boulders are sawed in slices. These slices are
sandblasted to improve the reproducibility. From the slices small stone columns are drilled
using a column drill. Afterwards the stone columns are cleaned by boiling them in
de-mineralised water. Because of these treatments the surface characteristics of the stone
samples might have changed. In this study the effect on the aggregate surface characteristics
of the treatments is investigated and how these surface characteristics of the stone samples
relate to the same characteristics of 4/8 aggregates used by contractors in Porous Asphalt
mixtures.
Surface characteristics of the prepared stone samples and of untreated 4/8 aggregates that are
determined, are:
• Roughness (measured at 7 X, 20 X, 50 X and 100 X magnification)
• Specific surface area (measured at 7 X, 20 X and 50 X magnification)
• Porosity
• Chemical and mineralogical composition
• pH Acidity
• Surface free energy
The surface free energy of the SBS modified bitumen used in the Porous Asphalt Concrete
mixture is also determined. Because for the calculation of the fundamental work of adhesion
between bitumen and aggregate, both the aggregate surface energy and the bitumen surface
energy are necessary.
This study showed that sandblasting influences the roughness of the stone column samples.
The specific surface area is increased if the sawed stone samples are sandblasted. However
the specific surface area of the 4/8 aggregates is larger than the specific surface area of the
sawed and sandblasted stone columns.
No indication is found that the porosity and the chemical and mineralogical compositions of
the stone samples are affected by any of the treatments.
Sandblasting increases the surface free energy of the sawed stone samples.
From the results of this research it is concluded that the treatments used for preparations of
the stone samples for the laboratory experiments have influenced the surface characteristics of
the stone samples. However it hasn’t been possible to quantify this effect on the bitumenaggregate adhesion.
4
Content
Content
1 Introduction ........................................................................................................................... 15
1.1 General ........................................................................................................................... 15
1.2 Motivation of the research.............................................................................................. 17
1.3 Goals and objectives....................................................................................................... 17
1.4 Scope of this study ......................................................................................................... 17
2 Literature review ................................................................................................................... 19
2.1 Adhesion theories ........................................................................................................... 19
2.1.1 Chemical Reaction Theory...................................................................................... 19
2.1.2 Molecular Orientation Theory................................................................................. 19
2.1.3 Mechanical theory ................................................................................................... 20
2.1.4 Thermodynamic approach....................................................................................... 20
2.1.5 Final observation concerning adhesion theories ..................................................... 20
2.2 Parameters affecting adhesion in asphalt concrete......................................................... 20
2.2.1 Bitumen properties .................................................................................................. 21
2.2.1.1 Bitumen constitution ............................................................................ 21
2.2.1.2 Surface tension ..................................................................................... 22
2.2.1.3 Viscosity............................................................................................... 22
2.2.2 Aggregate properties ............................................................................................... 23
2.2.2.1 Mineralogical composition................................................................... 23
2.2.2.2 Chemical composition.......................................................................... 24
2.2.2.3 Surface energy...................................................................................... 25
2.2.2.4 Weathering ........................................................................................... 25
2.2.2.5 Surface texture...................................................................................... 25
2.2.2.6 Size ....................................................................................................... 26
2.2.2.7 Shape and angularity ............................................................................ 26
2.2.2.8 Porosity and pore size distribution ....................................................... 26
2.2.2.9 Aggregate surface impurities ............................................................... 26
2.2.3 Asphalt mixture properties ...................................................................................... 27
2.2.3.1 Void content and permeability ............................................................. 27
2.2.3.2 Bitumen film thickness......................................................................... 27
2.2.4 External influences .................................................................................................. 27
2.2.4.1 Presence of water ................................................................................. 27
2.2.4.2 Temperature ......................................................................................... 28
2.2.4.3 Traffic................................................................................................... 28
2.2.4.4 Workmanship ....................................................................................... 28
2.3 Literature review conclusions ........................................................................................ 28
3 Materials and Experimental design ....................................................................................... 30
3.1 Experimental basis ......................................................................................................... 30
3.2 Materials......................................................................................................................... 30
3.2.1 Stones ...................................................................................................................... 30
3.2.2 Bitumen ................................................................................................................... 32
3.3 Experiments.................................................................................................................... 32
3.3.1 Roughness of the stones .......................................................................................... 32
3.3.1.1 Macro surface roughness...................................................................... 33
3.3.1.2 Meso surface roughness ....................................................................... 34
3.3.1.3 Micro surface roughness ...................................................................... 35
5
Content
3.3.2 Specific surface area................................................................................................ 35
3.3.3 Porosity.................................................................................................................... 36
3.3.4 Chemical- and Mineralogical composition ............................................................. 37
3.3.5 Acidity..................................................................................................................... 38
3.3.6 Surface energy of the aggregate .............................................................................. 39
3.3.7 Bitumen Surface energy .......................................................................................... 40
4 Experimental results.............................................................................................................. 44
4.1 Roughness ...................................................................................................................... 44
4.1.1 Macro surface roughness......................................................................................... 44
4.1.2 Meso surface roughness .......................................................................................... 45
4.1.3 Micro surface roughness ......................................................................................... 49
4.2 Specific surface area....................................................................................................... 51
4.3 Porosity........................................................................................................................... 53
4.4 Chemical- and Mineralogical composition .................................................................... 53
4.5 Acidity............................................................................................................................ 60
4.6 Surface energy................................................................................................................ 61
4.7 Bitumen surface energy.................................................................................................. 63
5 Data analysis and discussion ................................................................................................. 67
5.1 Roughness ...................................................................................................................... 67
5.1.1 Macro surface roughness......................................................................................... 67
5.1.2 Meso surface roughness .......................................................................................... 67
5.1.3 Micro surface roughness ......................................................................................... 67
5.2 Specific surface area....................................................................................................... 69
5.3 Porosity........................................................................................................................... 69
5.4 Chemical- and Mineralogical composition .................................................................... 70
5.5 Acidity............................................................................................................................ 72
5.6 Surface energy................................................................................................................ 72
5.7 Bitumen surface energy.................................................................................................. 73
6 Conclusions and recommendations....................................................................................... 77
6.1 Conclusions .................................................................................................................... 77
6.1.1 Roughness ............................................................................................................... 77
6.1.1.1 Macro surface roughness...................................................................... 77
6.1.1.2 Meso surface roughness ....................................................................... 77
6.1.1.3 Micro surface roughness ...................................................................... 77
6.1.2 Specific surface area................................................................................................ 78
6.1.3 Porosity.................................................................................................................... 78
6.1.4 Chemical and Mineralogical composition............................................................... 78
6.1.5 Acidity..................................................................................................................... 78
6.1.6 Surface energy......................................................................................................... 78
6.1.7 Overall conclusion................................................................................................... 79
6.2 Recommendations .......................................................................................................... 81
Literature .................................................................................................................................. 83
Appendix A: Surface energy .................................................................................................... 85
A.1 Intermolecular forces..................................................................................................... 85
A.2 Relation between intermolecular forces and surface free energy.................................. 86
6
Content
A.3 Surface free energy theories .......................................................................................... 89
A.3.1 Fowkes’ theory ....................................................................................................... 89
A.3.2 Extended Fowkes’ harmonic mean ........................................................................ 90
A.3.3 Acid-Base theory.................................................................................................... 90
A.4 Modern surface energy theories in practice .................................................................. 92
A.4.1 Advancing and receding contact angles ................................................................. 92
A.4.2 Negative square roots ............................................................................................. 93
A.4.3 Condition number................................................................................................... 93
A.4.4 Acid-base components scale .................................................................................. 93
References ............................................................................................................................ 95
Appendix B: Experimental data ............................................................................................... 97
B.1 Roughness...................................................................................................................... 97
B.1.1 Macro surface roughness ........................................................................................ 97
B.1.2 Meso surface roughness.......................................................................................... 97
B.1.3 Micro surface roughness....................................................................................... 104
B.2 Specific surface area.................................................................................................... 107
B.3 Porosity........................................................................................................................ 107
B.4 Chemical- and Mineralogical composition.................................................................. 109
B.5 Acidity ......................................................................................................................... 113
B.6 Surface energy ............................................................................................................. 113
Appendix C: Procedures......................................................................................................... 114
C.1 Sessile Drop Method Protocol..................................................................................... 114
Reference............................................................................................................................ 116
C.2 Wilhelmy Plate Method Protocol ................................................................................ 116
Reference............................................................................................................................ 120
C.3 Wavelet method........................................................................................................... 120
C.3.1 Wavelet method Procedure....................................................................................... 120
References .......................................................................................................................... 122
7
List of figures
List of figures
Figure 1.1: Lab compacted Porous Asphalt Concrete sample. ................................................ 15
Figure 1.2: Stone column specimen with a 15 µm interface binder layer for use in DSR.
[Khedoe and Moraal 2007] .............................................................................................. 15
Figure 1.3: Two stone columns with a 15 µm interface binder in special clamps in the
AR1000 rheometer. [Khedoe and Moraal 2007].............................................................. 16
Figure 1.4: Two stone columns with a 15 µm interface binder in special clamps ready for a
DSR test. [Khedoe and Moraal 2007] .............................................................................. 16
Figure 1.5: Sandblasting of slice. [Khedoe and Moraal 2007]................................................. 16
Figure 1.6: Drilling the small columns from a sandblasted slice. [Khedoe and Moraal 2007] 17
Figure 1.7: Flow chart used in this study and report................................................................ 17
Figure 2.1: The fluorine atom attracts the shared electrons more than the hydrogen atom. .... 21
Figure 2.2: Examples of the important chemical functional groups present in bitumen
molecules. (1) naturally occurring and (2) formed on oxidative ageing. [Jeon and Curtis
1990]................................................................................................................................. 21
Figure 2.3: Examples of the important minerals present in aggregate and examples of the
major groups of rocks. [Mertens and Wright 1959]......................................................... 23
Figure 2.4: Classification of aggregates by surface charges. [Mertens and Wright 1959] ...... 25
Figure 2.5: Tensile strength versus film thickness. [Lytton 2004]........................................... 27
Figure 2.6: Aggregate properties affecting adhesion and their evaluation methods. ............... 29
Figure 3.1: Example of the samples: Gsawed/Gsand, Gsawedlab, Gsandlab, Gstone and
Gsurface (). ................................................................................................................... 30
Figure 3.2: Flow charts of boulder samples preparations. ....................................................... 31
Figure 3.3: Flow charts of 4/8 aggregate samples preparations. .............................................. 31
Figure 3.4: Differences in treatments (white) of the samples taken from the boulder (orange)
to determine the effects of the treatments on the adhesion characteristics. ..................... 31
Figure 3.5: Differences in treatment (white) of the 4/8 aggregate samples (orange) to
determine the effects of the treatments on the adhesion characteristics. ......................... 31
Figure 3.6: Stone surface roughness at different magnifications. [van Lent 2007] ................. 32
Figure 3.7: Laser Scanning Confocal Microscope Leica TCS NT. [TUDelft] ........................ 34
Figure 3.8: Difference between measured roughness and real surface roughness of the stones
resulting in unknown errors.............................................................................................. 34
Figure 3.9: Environmental Scanning Electron Microscope Philips XL30 ESEM. [TUDelft]. 35
Figure 3.10: A total flat area has the same values for the area of measurement (axes) and the
measured area (orange area)............................................................................................. 36
Figure 3.11: Stone surface with a SSA larger than 1 m²/m². ................................................... 36
Figure 3.12: Mercury Intrusion Porosimeter, Micromeritics PoreSizer 9320. [TUDelft] ....... 36
Figure 3.13: Contact angle of mercury on stony surface. ........................................................ 36
Figure 3.14: X-Ray Fluorescence spectrometer. [TUDelft]..................................................... 38
Figure 3.15: Acidity meter Metrohm 744 pH Meter and on the right the immersed samples. 38
Figure 3.16: Contact Angle Meter Krüss CAMS G2 tensiometer. .......................................... 39
Figure 3.17: KSV Sigma 701 tensiometer. [KSV]................................................................... 41
Figure 3.18: Principle of the Wilhelmy Plate Method. [Hefer and Little 2005] ...................... 41
Figure 4.1: Plots of the roughness of Greywacke samples at 20X magnification. Plots of other
samples in appendix B...................................................................................................... 45
Figure 4.2: Plots of the roughness of Bestone samples at 20X magnification. Plots of other
Figure 4.3: Plots of the roughness of Greywacke samples at 50X magnification. Plots of other
8
List of figures
Figure 4.4: Plots of the roughness of Bestone samples at 50X magnification. Plots of other
Figure 4.5: Picture showing the micro surface roughness of sawed Greywacke column
(Gsawedlab). .................................................................................................................... 49
Figure 4.6: Picture showing the micro surface roughness of sandblasted Greywacke column
(Gsandlab). ....................................................................................................................... 49
Figure 4.7: Picture showing the micro surface roughness of Greywacke 4/8 aggregate
(Gstone). ........................................................................................................................... 50
Figure 4.8: Picture showing the micro surface roughness of sawed Bestone column
(Bsawedlab)...................................................................................................................... 50
Figure 4.9: Picture showing the micro surface roughness of sandblasted Bestone column
(Bsandlab). ....................................................................................................................... 50
Figure 4.10: Picture showing the micro surface roughness of Bestone 4/8 aggregate (Bstone).
.......................................................................................................................................... 51
Figure 4.11: Picture of individual chemical elements at the surface of Gsawedlab3. ............. 54
Figure 4.12: Plot of chemical elements at the surface of Gsawedlab3 over an area of 1 mm².
Horizontal axis is the wavelength emitted from the elements and the vertical axis gives
the linear intensity in counts per second. ......................................................................... 54
Figure 4.13: Picture of individual chemical elements at the surface of Gsandlab1. ................ 54
Figure 4.14: Plot of chemical elements at the surface of Gsandlab1 over an area of 1 mm²... 55
Figure 4.15: Picture of individual chemical elements at the surface of Gstone1..................... 55
Figure 4.16: Plot of chemical elements at the surface of Gstone1 over an area of 1 mm²....... 55
Figure 4.17: Picture of individual chemical elements at the surface of Bsawedlab3............... 56
Figure 4.18: Plot of chemical elements at the surface of Bsawed lab3 over an area of 1 mm².
.......................................................................................................................................... 56
Figure 4.19: Picture of individual chemical elements at the surface of Bsandlab1. ................ 56
Figure 4.20: Plot of chemical elements at the surface of Bsandlab1 over an area of 1 mm². .. 57
Figure 4.21: Picture of individual chemical elements at the surface of Bstone2. .................... 57
Figure 4.22: Plot of chemical elements at the surface of Bstone2 over an area of 1 mm²....... 57
Figure 4.23: XRD plot of the mineralogical composition of the Greywacke samples. On the
horizontal axis the wavelength is given and on the vertical axis the linear intensity in
counts per second is given................................................................................................ 59
Figure 4.24: XRD plot of the mineralogical composition of the Bestone samples. On the
horizontal axis the wavelength is given and on the vertical axis the linear intensity in
counts per second is given................................................................................................ 60
Figure 4.25: Averaged acidity of the water immersed stones .................................................. 61
Figure 4.26: Example of computer recording of water droplet on the surface of sandblasted
Bestone slice..................................................................................................................... 61
Figure 4.27: Plot of bitumen sample 8 immersing in water. .................................................... 64
Figure 4.28: Plot of bitumen sample 8 immersing in diiodomethane. ..................................... 64
Figure 4.29: Plot of bitumen sample 8 immersing in glycerol................................................. 64
Figure 5.1: Indicated areas on Bstone1 which are fine or coarse textured in the quantitative
analyses. ........................................................................................................................... 68
Figure 5.2: First spreading of the droplet (left) then the droplet gets stuck in the roughness
(right)................................................................................................................................ 73
Figure 5.3: Kwok and Neuman plot of bitumen sample 1 ....................................................... 74
Figure 5.4: Kwok and Neuman plot of bitumen sample 2. ...................................................... 74
Figure 5.5: Kwok and Neuman plot of bitumen sample 3. ...................................................... 75
Figure A.1: Lewis structures of: a single oxygen atom, a single water molecule and water
molecules interacting by hydrogen bonding. [van Lent 2007]......................................... 86
9
List of figures
Figure A.2: The three-phase boundary of a liquid drop on a solid surface in vapour. [Hefer
and Little 2005] ................................................................................................................ 87
10
List of tables
List of tables
Table 2.1: Classification of rocks based on silica content. [Majidzadeh and Brovold, 1968] . 24
Table 3.1: Instrument resolutions for Leica TCS NT. [TUDelft] ............................................ 34
Table 3.2: Instrument specifications for Philips XL30 ESEM. [TUDelft] .............................. 35
Table 3.3: Instrument resolution of Metrohm 744 pH meter. [Metrohm]................................ 39
Table 3.4: Surface energy components of reference liquids in mJ/m² according to the vanOssGood-Chaudhury scale. [van Oss, Chaudhury and Good 1988] ...................................... 39
Table 3.5: Instrument specifications for KSV Sigma 701 tensiometer. [KSV] ....................... 42
Table 4.1: Measured values of parameters Pa and Pq at 7 times magnification. ..................... 44
Table 4.2: Measured values of parameters Pa and Pq at 20 times magnification. ................... 46
Table 4.3: Measured values of the parameters Pa and Pq at 50 times magnification. ............. 48
Table 4.4: Texture distribution on the pictures analysed using the wavelet method. .............. 51
Table 4.5: Specific surface area by stereomicroscope at 7 times magnification...................... 52
Table 4.6: Specific surface area by LSCM at 20 times magnification..................................... 52
Table 4.8: Porosity of the stone samples measured in the Mercury Intrusion Porosimeter. .... 53
Table 4.9: Distribution of chemical elements over the samples given in mass percentages.... 58
Table 4.10: Surface energy components of the different stone samples in [mJ/m²]. ............... 62
Table 4.11: Contact angles on the different stone samples, measured and calculated in [°]. .. 62
Table 4.12: Surface energy components of the bitumen samples using the Sessile Drop
Method in [mJ/m²]............................................................................................................ 63
Table 4.13: Contact angles on the bitumen samples, measured and calculated in [°]. ............ 63
Table 4.14: Surface energy components of the bitumen samples using the Wilhelmy Plate
Test, from advancing contact angles in [mJ/m²]. ............................................................. 65
Table 4.16: Surface energy components of the bitumen samples using the Wilhelmy Plate
Test, from receding contact angles in [mJ/m²]................................................................. 65
Table 5.1: Calculated fundamental work of adhesion between bitumen and stone samples. .. 75
Table 6.1: Relative comparisons of properties of Greywacke aggregate samples treated in
different ways to the properties of the untreated Greywacke 4/8 aggregate. ................... 79
Table 6.2: Relative comparisons of properties of Bestone aggregate samples treated in
different ways to the porperties of the untreated Bestone 4/8 aggregate. ........................ 80
Table A.1: Surface energy components of reference liquids in mJ/m² according to the vanOssGood-Chaudhury scale. [van Oss, Chaudhury and Good 1988] ...................................... 91
Table A.2: Surface energy components of reference liquids in mJ/m² according to the Taft et
al. scale. [Della Volpe and Siboni 1997].......................................................................... 94
Table A.3: Surface energy components of reference liquids in mJ/m² according to the Della
Volpe-Siboni scale. [Della Volpe and Siboni 2002] ........................................................ 94
Table A.4: Initial (theoretical) surface energy components of reference liquids in mJ/m² at
20°C according to the Lee scale. [Lee 2001] ................................................................... 94
Table A.5: Equilibrium (experimental) surface energy components of reference liquids in
mJ/m² at 20°C according to the Lee scale. [Lee 2001] .................................................... 95
Table B.1: Measured values of parameters Pa and Pq at 7 times magnification. .................... 97
Table B.2: Measured values of parameters Pa and Pq at 20 and 50 times magnification........ 97
11
List of tables
Table B.3: Texture distribution on the ESEM pictures analysed using the wavelet method. 104
Table B.4: Specific surface area at 7 times magnification. .................................................... 107
Table B.5: Specific surface area at 20 and 50 times magnification. ...................................... 107
Table B.6: Porosity of the stone samples measured in the Mercury Intrusion Porosimeter. . 107
Table B.7: Chemical element distribution of the samples given in mass percentages........... 109
Table B.8: Mass of the measured stone samples in the acidity test. ...................................... 113
Table C.1: Figure renaming for processing............................................................................ 121
12
List of definitions and abbreviations
Arrhenius acidity
Arrhenius acids consist of molecules which are able to donate protons
to water molecules if immersed in water. An example of an Arrhenius
acid is vinegar:
CH 3 COOH (aq ) + H 2 O (l ) ↔ CH 3 COO − (aq ) + H 3 O + (aq )
The Arrhenius acidity can be measured at pH scale. The pH scale is an
inverse logarithmic scale of the concentration of donated protons in
water:
− log H 3 O + ⇔ H 3 O + = 10 − pH [mol/l]
(
) [
]
Bsand
Cleaned sandblasted Bestone slice
Bsandlad
Cleaned sandblasted Bestone column
Bsawed
Cleaned sawed Bestone slice
Bsawedlab
Cleaned sawed Bestone column
Bstone
Untreated Bestone 4/8 aggregate
Bstonecl
Cleaned Bestone 4/8 aggregate
Bsurface
Cleaned surface of Bestone boulder
DMA
Dynamic Mechanical Analyser
DSR
Dynamic Shear Rheometer
ESEM
Environmental Scanning Electron Microscope
Gsand
Cleaned sandblasted Greywacke slice
Gsandlad
Cleaned sandblasted Greywacke column
Gsawed
Cleaned sawed Greywacke slice
Gsawedlab
Cleaned sawed Greywacke column
Gstone
Untreated Greywacke 4/8 aggregate
Gstonecl
Cleaned Greywacke 4/8 aggregate
Gsurface
Cleaned surface of Greywacke boulder
LSCM
Laser Scanning Confocal Microscope
Lewis acidity
Lewis acids consist of molecules which are able to receive electrons in
a non-covalent and non-ionic manner. The term mono-polar acids refers
13
to materials which solely consist of molecules which are electron
receivers. Materials consisting of molecules which are able to donate
electrons are called Lewis bases. The term mono-polar bases refers to
materials which solely consist of molecules which are electron donors.
Materials could also consist of molecules which are both electron
receivers and electron donators. The temporarily electron donating and
electron receiving causes a force acting between the two molecules.
The Lewis acidity is the measure of a part of the force acting between
the two molecules (appendix A).
LOT
Lifetime Optimisation Tool
TUDelft
Delft University of Technology
SSA
Specific surface area [m²/m³]
XRD
X-Ray powder Diffractometer
XRF
X-Ray Fluorescence Spectrometer
14
Chapter 1: Introduction
1 Introduction
1.1 General
According to the Dutch bureau for statistics (CBS) the road-network in the Netherlands has a
total length of 135470 km in 2007 and the total length is still increasing. For reasons of traffic
noise reduction much of the Dutch primary roadnetwork is surfaced with Porous Asphalt Concrete.
Additional advantage of Porous Asphalt Concrete is
the significant reduction of splash and spray in wet
weather conditions. However the service life of
porous asphalt concrete is much lower than the
service life of dense asphalt concrete. The surface
life of Porous Asphalt Concrete is limited by the
development of ravelling of the surface.
Figure 1.1: Lab compacted Porous Asphalt Concrete sample.
Ravelling may cause a reduction of driving comfort to the road users, loss of aggregate from
the top layer, a decrease of traffic safety and a strong increase of traffic noise. The DWW, the
Road and Hydraulic Engineering Institute of the Dutch Ministry of Transport, has started
research into ravelling of Porous Asphalt Concrete. As part of this research the Delft
University of Technology developed a mechanistic design tool for Porous Asphalt Concrete,
called Lifetime Optimisation Tool (LOT).
In the LOT research program [5,6,7,8] a characterisation is made of the mechanical behaviour
of the adhesive zone between the aggregate particles and the bituminous mortar, as well as a
characterisation of the bituminous mortar in Porous Asphalt Concrete mixtures. Input of data
of mechanical tests was required. Several mechanical tests were conducted on mortar and
stone-bitumen specimen. To avoid scale effects it was decided to perform the tests at a similar
scale as in practise, i.e. the scale of individual aggregates. It was considered of great
importance to get the size of the aggregate specimens as used in the test program as constant
as possible. To get similar sized samples with similar surface properties, the aggregates
received all kinds of treatments.
Stone column specimens are used in DMA and DSR fatigue tests to give insight into adhesive
zone fatigue behaviour. In principle circular column
specimens with a 6.7 mm diameter are used. Due to
limited machine capacity some specimens with a 2.75
mm diameter are used. Between two stone columns a
15 µm interface binder layer is assembled (figure
1.2).
Figure 1.2: Stone column specimen with a 15 µm interface
binder layer for use in DSR. [Khedoe and Moraal 2007]
15
Much care is taken to ensure that the two stone
columns are centred precisely and that the two
opposite surfaces are exactly parallel. A rheometer
was specially equipped with clamps to keep the two
stone column specimens in place (figure 1.3). An
AR1000 rheometer is successfully used for
assembling the two stone columns with a 15 µm
interface binder layer.
Figure 1.3: Two stone columns with a 15 µm interface binder
in special clamps in the AR1000 rheometer. [Khedoe and
Moraal 2007]
The two stone columns specimen with
a 15 µm interface binder layer are
placed in the same clamps in the
rheometer during the DSR tests
(figure 1.4).
Figure 1.4: Two stone columns with a 15 µm
interface binder in special clamps ready for a
DSR test. [Khedoe and Moraal 2007]
To obtain the stone columns some stone treatments
were performed. First slices of about 10 mm
thickness were sawed from boulders of Bestone and
Greywacke of approximately 5 kg. The sawed
surfaces of the slices are sandblasted to get a more
reproducible surface (figure 1.5).
Figure 1.5: Sandblasting of slice. [Khedoe and Moraal 2007]
16
The small columns were drilled from the
sandblasted slices using a column drill (figure
1.6). To remove grease from the sawing and
drilling process the stone columns were boiled
in de-mineralised water for 15 minutes.
Figure 1.6: Drilling the small columns from a
sandblasted slice. [Khedoe and Moraal 2007]
1.2 Motivation of the research
The effect of these treatments on the adhesive zone characteristics for the individual tests is
unknown. The question arises how the surface characteristics of the stone samples were
affected by the different treatments and how the surface characteristics of the stone samples in
the laboratory relate to the same characteristics of stones used by contractors in asphalt
concrete mixtures.
1.3 Goals and objectives
In this study the stone characteristics affecting bitumen-aggregate adhesion are investigated.
Especially the effects of the surface treatments, used in the LOT research program, on these
stone characteristics are investigated. The results of this exploring study will give an insight
in the aggregate characteristics affecting the bitumen-aggregate adhesion as well as an insight
into the effects of the different treatments on the surface characteristics.
1.4 Scope of this study
This study started by performing a literature review on adhesion of bitumen and aggregate
systems. In this literature review the properties of aggregates are describe on the basis of
adhesion theories. The results of this literature review are used to select experiments
appropriate for this research.
2 Literature Review
Literature Review Results
3 Selected Experiments
4 Experimental Results
5 Data analyses and Discussion
6 Conclusions and recommendations
Figure 1.7: Flow chart used in this study and report.
17
The results of the literature review on bitumen-aggregate adhesion are presented in chapter
two. Chapter three deals with the justification of the selected materials and experiments and
with the adopted experimental design. In chapter four the results of the experiments are
presented. Chapter five describes the analyses of the experimental results and provides a
discussion. Chapter six covers the conclusions following from this study and some
recommendations for further research. In appendix A the results are presented of a literature
review on surface energy. More detailed experimental results are given in appendix B.
Appendix C gives some procedures concerning computations and data analysis.
18
Chapter 2: Literature review
2 Literature review
In this chapter the results are given from a literature study on bitumen-aggregate adhesion. In
the first paragraphs some important adhesion theories are given. In the paragraphs thereafter
the important parameters of these theories are translated to bitumen and stone properties
affecting bitumen-aggregate adhesion.
2.1 Adhesion theories
Several theories for adhesion exist. Some theories combine elements from other theories and
others use the same elements but define it differently as a whole. In this paragraph four major
theories for bitumen-aggregate adhesion are described, first the chemical reaction theory,
followed by the molecular orientation theory, the mechanical theory and the thermodynamic
approach. This paragraph is concluded with some observations concerning the bitumenaggregate adhesion theories.
2.1.1 Chemical Reaction Theory
This theory is based on the supposition that the adhesion between bitumen and aggregate is
caused by chemical reactions. After coating the aggregate with bitumen, adsorption of the
bitumen chemical active components on the surface of the aggregate takes place. The
chemical active components from both the bitumen and the aggregate interact, resulting in
electron transfers between active components in the bitumen and the aggregate and between
active components in the bitumen itself. The electron transfers are caused by the difference in
potentials. When different active components interact, some components will have the
tendency to donate electrons and others will receive them. Bitumen consist of both type active
components, so of components, which will have the tendency to donate electrons quickly and
components, which receive electrons quickly. Also carbonate aggregates consist of both easy
donor and acceptor active components. Quartz aggregates on the other hand, predominately
consist of components, which will mainly act as electron receivers. The theory continues by
pointing out that stronger adhesive bonds develop in interface layers in which a proper
balance between donating and receiving active components from both the bitumen and the
aggregate surface exist.
2.1.2 Molecular Orientation Theory
In this theory the functional groups from both the bitumen and aggregate cause an adhesive
bond. The bitumen functional groups migrate and aim towards the aggregate surface, resulting
from the electric field caused by the dipole charges of the functional groups on the aggregate
surface. The bitumen functional groups align in accordance with the electrical field around the
aggregate. The level of adsorption and desorption of bitumen functional groups is influenced
by the distance from the particle and the magnitude of the dipole charges. At close distances
of the aggregate surface the bitumen functional group with the highest potential will form a
layer. The potential of the aggregate surface decreases over a growing distance of this surface
causing lower charged bitumen functional groups to form a less firmly attached layer around
the first layer of bitumen functional groups. The layer with the stronger bond is called the
stern layer and the secondary layer is called the Gouy-Chapman layer.
19
The adhesive bond caused by electrostatic and hydrogen bonding is lowered when water is
present on the interaction layer. Water is more polar than most of the bitumen functional
groups and molecules. Therefore a preference of the aggregate surface for water above
bitumen exists. This provides a possible explanation for stripping.
2.1.3 Mechanical theory
The main assumption for this theory is that, during coating the aggregate, bitumen enters
present pores, holes, cracks and unevenness in the aggregate surface texture. After hardening
of the bitumen, the adhesive bond is caused by the surface friction between bitumen and
aggregate surface. The theory may provide an explanation for the stronger adhesive bonds of
rougher aggregate surface textures. First of all, more irregularities provide more interlock for
the bitumen. Secondly, a rougher aggregate surface has a larger physical area of contact and
so provides a larger surface friction between bitumen and aggregate surface. Due to the
roughness of the aggregate surface the stresses in the bitumen coating are better redistributed
as well. This results in less peak stress concentrations and so a decrease in the chance of
rupture. However the theory also states that with an increasing roughness of the aggregate
surface the wetting with bitumen becomes more difficult and the wetting could become
incomplete. This may result in a less strong adhesive bond.
2.1.4 Thermodynamic approach
This approach for the adhesive bond strength between bitumen and aggregate is based on the
change of surface energy of the bitumen after coating the aggregate. This approach combines
elements from the chemical reaction and the molecular orientation theory. After wetting the
aggregate with bitumen, intermolecular forces at the aggregate surface and the bitumen
interact, resulting in a released bonding energy. The total initial and final energy state of a
system is called Gibbs energy and the release of the bonding energy results in a change of
Gibbs energy. To break the bond between the aggregate surface and the bitumen energy is
needed. This needed work to be applied equals the change in Gibbs energy before and after
coating the aggregate with bitumen. This work needed to break the bond is a measure for
adhesion of the bitumen on the aggregate surface. For further details the reader is referred to
appendix A.
2.1.5 Final observation concerning adhesion theories
Until now it is not possible to state that one of the theories is flawed or that one theory
describes the entire process of bitumen-aggregate adhesion. It is generally thought that the
phenomena of adhesion are a combination of the four described bitumen-aggregate adhesion
theories. Therefore the adhesion should be explained by (all) elements mentioned in the four
described bitumen-aggregate adhesion theories.
2.2 Parameters affecting adhesion in asphalt concrete.
Asphalt concrete consists of four major components, bitumen, coarse aggregate, sand and
filler. As mentioned before, only the bitumen-aggregate adhesion is investigated. Hereafter
the most important parameters of the bitumen affecting adhesion are given. This is followed
by a discussion on the important parameters of the aggregate. Finally some conclusions are
given.
20
2.2.1 Bitumen properties
2.2.1.1 Bitumen constitution
Bitumen used for road construction consists mainly of hydrocarbons (90-95%). Furthermore
road bitumen consists of heteroatoms (oxygen, sulphur and nitrogen (5-10%)) and
organometallic constituents (porphyrin complexes with atoms of iron, vanadium, magnesium
nickel and calcium).
The heteroatoms give the composition of molecules in bitumen functionality and electrical
polarity. This means that the bitumen has a composition, where dipole charges of molecules
are induced. A dipole charge in a molecule develops when the centres of the opposing charges
do not coincide in the centre of a molecule. This mainly occurs when atoms of different
elements are interacted with an ordinary pi-pi bonding. In a pi-pi bonding electrons are shared
between two or more atoms in an electron orbital. When a molecule consists of two atoms of
different elements, one of the atoms might dominate the other by attracting the shared
electrons (figure 2.1). This results in a small negative charge (δ-) of the atom which dominates
attracting the electrons and a small positive charge (δ+) for the other atom. The molecule of
the two atoms is called a dipole molecule. Between dipole molecules the bonding strength is
higher than the bonding strength of non-dipole
molecules. Some dipole molecules tend to have
hydrogen bonding. Opposite charges of various dipole
molecules or of the dipole parts of molecules will aim
towards each other.
Figure 2.1: The fluorine atom attracts the shared electrons more
than the hydrogen atom.
So called functional groups, are the dipole parts of molecules in bitumen or the unsaturated
molecules, e.g. double pi-pi bonding between oxygen and carbon atoms. Examples of these
functional groups in bitumen are anhydrides, carboxylic acids, ketones, phenolics,
polynuclear aromatics, pyridinics, pyrrolics, 2-quinolones, sulfides and sulfoxides (figure
2.2). Sulfoxides, anhydrides and ketons are rare in fresh bitumen. These three functional
groups are mainly formed by oxidation during the lifetime of bitumen. On the other hand
carboxylic acid for instance is found in both fresh and aged bitumen.
The functional groups influence the
adhesion between bitumen and aggregate,
because the polar parts will aim and
migrate towards the interface with the
aggregate. In this way a layer is formed.
The resulting bond strength is depending
on this phenomenon and the attraction of
functional groups to available water
molecules.
Figure 2.2: Examples of the important chemical
functional groups present in bitumen molecules. (1)
naturally occurring and (2) formed on oxidative
ageing. [Jeon and Curtis 1990]
21
2.2.1.2 Surface energy
Directly related to the chemical composition is the surface energy of the bitumen. The
intermolecular forces at the surface of the bitumen are able to interact with the molecules
from the aggregate resulting in an adhesive bond. The molecules in the bitumen have different
kinds of bonding mechanism for interaction with the molecules of the aggregate. For instance
the functional groups in the bitumen are more able to interact with polar molecules on the
surface of the aggregates. Non-polar molecules in the bitumen are more able to interact with
non-polar molecules of the aggregate. The reader is referred to appendix A for a more detailed
description of surface energy.
2.2.1.3 Viscosity
Viscosity is a measure of the resistance of liquids to flow. It is given in the unit of [Pa·s].
During mixing, the bitumen should have a low enough viscosity to ensure proper coating and
absorption of the bitumen onto the aggregates. This is established by increasing the
temperature. Higher temperatures ensure higher kinetic atom and molecule energies resulting
in weakened intermolecular bonding forces and easier diffusion of the polar functional groups
toward the adhesion layer of the bitumen and the aggregates. After mixing, the viscosity of
the bitumen should be high enough to prevent dripping off from the aggregates.
22
2.2.2 Aggregate properties
In this paragraph the aggregate properties that affect the bitumen-aggregate adhesion are
described.
2.2.2.1 Mineralogical composition
The aggregate mineralogy affects the adhesion in asphalt mixtures. The mineralogy of the
aggregate affects the relative affinity between water and bitumen at this surface. Therefore the
mineralogical
composition is one of
the major factors
affecting stripping.
Most natural
aggregates are
composed of a
combination of
different minerals.
The most important
minerals found in
aggregates are silica
minerals, feldspars,
ferromagnesian
minerals, carbonate
minerals and clay
minerals.
Figure 2.3: Examples of
the important minerals
present in aggregate and
examples of the major
groups of rocks. [Mertens
and Wright 1959]
The mineralogical composition affects the surface texture of the aggregate. Many minerals
show different kinds of texture when fractured. Quartz has a conchoidal fracture. This fracture
has the appearance of series or arcs. Native metals such as copper have a hackly fracture.
Other kinds of fractures are even and uneven fracture [14].
The mineralogical composition of aggregates depends on the origin of the rocks. On earth,
rocks can be divided in three major groups: igneous, sedimentary and metamorphic rocks.
Igneous rocks have their primary origin in molten rock within the earth’s crust, called magma.
Igneous rocks are intrusive when the magma was intruded or was forced into other rocks
underneath earth’s surface. The term extrusive is used when the molten rock is forced to the
surface resulting in lava flows or volcanic fragment blow out. Sedimentary rocks are formed
by accumulation of erosion and weathering products of crumbled and decomposed rocks. The
last group, metamorphic rock, contains igneous and sedimentary rocks, which have been
23
drastically conversed, so that the nature and original state of the rocks are lost. Heat and
pressure in the earth’s crust are contributors for creating metamorphic rocks and the formation
of entirely new minerals.
2.2.2.2 Chemical composition
The chemical composition gives a detailed view on adhesion of bitumen onto the aggregate
surface. After coating the aggregate with bitumen, the bitumen will harden and will also be
chemically bonded with the aggregate surface as a result from chemical reactions in the
interface. It is argued that the level of acidity of the aggregates has a strong influence on these
chemical reactions.
Arrhenius acidic aggregates are considered to be hydrophilic. Hydrophilic, water loving,
aggregates have a greater affinity for water than for a bitumen coating. So if such an
aggregate, coated with bitumen, is immersed in water the aggregate tends to have a stronger
attraction to the water molecules than to its bitumen layer. Through cracks water might
contact the interface layer of the bitumen and the aggregate. The bitumen might be ‘stripped’
from the surface of the aggregate and replaced by the water in time. Hydrophobic, oil loving,
and basic aggregate appear to have a better adhesion with the bitumen coating, and have a
little more resistance to stripping. In most studies this has been confirmed, but not in all.
It is found that the presence of some metal components on the aggregate surface could be
beneficial to adhesion and the presence of some metal components could be detrimental. Iron,
calcium, magnesium and to a certain extend aluminium on the aggregate surface is sometimes
beneficial. Alkali metals like potassium and sodium are considered to be detrimental. Because
no aggregate surface is totally acidic or basic, the aggregate surface is always to some extend
acidic and to some extend basic. Acidic parts of the surface could become negatively charged
in water and basic parts positively charged. Minerals at the surface containing silica could
become negatively charged, minerals containing the metals iron, calcium, magnesium and
aluminium positively charged. The theory is that with the presence of both positively and
negatively charged minerals present on the surface, a possibility exists to form salts with the
bitumen functional groups. Insoluble salts in water give a better adhesive bonding. Soluble
salts present on the aggregate surface weaken the adhesive bond, because the salts are easily
dissolved. Soluble salts are the result of a reaction of acidic functional groups in the bitumen
with potassium and sodium.
As mentioned before, aggregates are never totally acidic or basic. The aggregate surface is
always to some extend acidic and to some extend basic. Therefore a classification is made
[Majidzadeh & Brovold, 1968] based on the silica (SiO2) content of the aggregate to
determine the dominance of acidic or basic properties (table 2.1).
Table 2.1: Classification of rocks based on silica content. [Majidzadeh and Brovold, 1968]
Definition
Acidic rock
Intermediate rocks
Basic rocks
24
Percentage SiO2
> 65
52 - 65
< 52
The silica content of some aggregates is shown in figure 2.4.
Figure 2.4: Classification of aggregates by surface charges. [Mertens and Wright 1959]
2.2.2.3 Surface energy
Directly related to the chemical and mineralogical composition is the surface energy of the
aggregates. The intermolecular forces at the surface of the aggregates are able to interact with
the molecules from the bitumen resulting in an adhesive bond. Different chemicals have
different kinds of bonding mechanism for interaction with the molecules in the bitumen. For
instance the polar molecules on the surface of the aggregates are more able to interact with the
functional groups in the bitumen. Non-polar molecules at the surface are more able to interact
with non-polar molecules in the bitumen. Sandstone has a silica (SiO2) content between 60
and 100 %. In literature it is found that silica shows a mono-polar Lewis base character. This
is of influence for the selected bitumen type and their resulting work of adhesion. The reader
is referred to appendix A for a more detailed description of surface energy.
2.2.2.4 Weathering
Weathering depends on the chemical and mineralogical composition. Some research has
already been done on relating weathering to adsorption of bitumen and surface energy of the
aggregate, but no clear results were found. Generally it is thought that some aggregates tend
to weather more quickly than others and weathering has a negative effect on the adhesion
between bitumen and aggregate surface. It is thought that freshly sawed aggregate surfaces
have more polar active sites to interact with the bitumen functional groups. Weathering occurs
to different extents. When aggregates are stored outside under influence of rain, frost and
sunlight possible disintegration [16] takes years, maybe months. When aggregates are
protected from direct sunlight, frost and rainfall this weathering process will almost not occur.
Only a quick ageing of the freshly sawed surface of the aggregate under influence of the air
occurs. Some aggregate ageing effects, such as atmosphere contaminants accumulation and
oxidation of organic debris, occur within few seconds after sawing [10].
2.2.2.5 Surface texture
During mixing of the asphalt mixture, surface texture influences proper coating of the
aggregate with the bitumen binder. At first a smooth surface texture may be easier to coat
with a proper binder film, but the mechanical bond is less in comparison to a rougher surface
texture. A rougher surface has a larger surface area per unit mass (specific surface area)
25
resulting in stronger adhesive bonding. However when the aggregate is too rough it is
possible that not the whole surface of the aggregate is coated. Then the contact area between
the bitumen and aggregate is decreased resulting in a weaker adhesive bond.
2.2.2.6 Size
Aggregate particles for road construction in asphalt mixtures are normally smaller than 22
mm. For reasons of processability and aggregate shape, the maximum size of aggregates is
limited. The size of crushed stone is limited to 16 mm for surface layers and the size is limited
to 22 mm for intermediate and lower layers. The finest aggregate particles, the filler, may
approach sizes smaller than 2 µm. For larger aggregate sizes the surface texture must increase
to ensure such a surface area per unit mass that a good adhesive bond is obtained.
2.2.2.7 Shape and angularity
Like surface texture, the shape of the aggregates affects the coating process of the bitumen
binder onto the aggregates in the asphalt mixture during mixing. Rounder aggregate particles,
such as most natural gravels and sands, are coated easier with a bitumen binder than angular
shaped aggregates. During the service life angularity may offer good points of anchoring for
the bitumen binder to improve adhesion. It is known however that an increased angularity
also increases the probability of puncturing the bitumen film. In this way water can easier
penetrate the layer of adhesive bonding and possibly cause stripping.
2.2.2.8 Porosity and pore size distribution
A pore size distribution in which many pores are located at the surface of the aggregate,
results in a rougher surface texture and so a larger surface area per unit mass to ensure
stronger adhesive bonding. A high porosity at the surface also affects absorption of the
bitumen binder. Absorbed bitumen is forced into the pores and is locked in, causing an even
stronger adhesive bond. A disadvantage is that the amount of absorbed bitumen in the pores
of the aggregate is not available for proper coating the exterior of the aggregate. This amount
could be compensated with an extra amount of bitumen added during mixing,
A too high porosity of the stone can however cause a disadvantage. With a too high porosity
of the stone not all pores might be able to adsorb the bitumen.
2.2.2.9 Aggregate surface impurities
Deleterious materials on the surface of aggregate affect to some extent the adhesion between
bitumen and aggregate. These surface impurities include clay, dust (e.g. from aggregate
crushing), coal, shale, free mica, salts and vegetation. These impurities can inhibit direct
bonding between aggregate and bitumen binder. In this way no proper adhesive bond is
ensured.
Another property of the deleterious material that affects adhesion in asphalt mixtures is the
tendency to attract water. By attracting more water the probability of stripping increases.
Deleterious materials may also result in channels and trapped air on the aggregate surface
causing water to penetrate more easily.
26
2.2.3 Asphalt mixture properties
Not only the characteristics of the bitumen and aggregates influence the adhesion. Also
mixture properties play an important role. In this paragraph the most important asphalt
mixture properties affecting adhesion are described.
2.2.3.1 Void content and permeability
A higher void content and permeability provide an opportunity for water to enter the adhesive
layer in the interface between bitumen and aggregate. This increases the probability of
stripping. A higher void content and permeability of asphalt mixtures can be the result of the
aggregate grading (for instance in the case of Porous Asphalt Concrete), the result of a too
low bitumen content or the result of the workmanship of the contractor (for instance a not
correctly compacted mixture).
2.2.3.2 Bitumen film thickness
The adhesive strength between bitumen and aggregates is influenced by the thickness of the
bitumen layer around the aggregates in asphalt mixtures. A thicker bitumen film also results
in a lower cohesive strength, which increases the possibility of failure in the bitumen film
itself (cohesive failure). Experimental observations [Marek and Hennin 1968] and
micromechanical analysis [Lytton 2004] have been performed to relate tensile strength of the
bitumen and failure type to
bitumen/mastic film thickness.
Figure 2.5 shows that for thinner
bitumen films the adhesive
tensile strength is lower than the
cohesive tensile strength. For
thicker films the cohesive
strength is lower than the
adhesive strength of thinner
films.
Figure 2.5: Tensile strength versus film
thickness. [Lytton 2004]
The bitumen film thickness could therefore be dominant for the adhesion between bitumen
and aggregates compared to other material characteristics like, chemistry and surface energy.
Secondly the tensile strength of a bitumen-aggregate bond depends on the rate of loading.
2.2.4 External influences
2.2.4.1 Presence of water
As mentioned before, the adhesive bond is affected by the presence of water. In general
aggregates tend to show a hydrophilic character. This means that water in contact with a
bitumen-aggregate system tends to replace the bitumen on the surface of the aggregate. This
phenomenon is called stripping. In case of an abundance of water at the surface of the
27
aggregate a small film of water develops locally. This film of water prevents locking between
aggregate and bitumen and is in itself not able to retain the tensile forces. Therefore the
adhesive bond strength becomes lower. Some researchers mention an increased chance on
stripping if the pH increases.
2.2.4.2 Temperature
The intermolecular forces between the aggregate and the bitumen decrease with increasing
temperature resulting in a smaller work of adhesion. Therefore it is easier to break the bond
between bitumen and aggregate at higher temperatures.
2.2.4.3 Traffic
The amount of traffic travelling over a road affects the stresses and the healing of asphalt
concrete. Cracks in the bitumen caused by the stresses provide an easier access for water to
contact aggregate and bitumen interface and may cause stripping. Heavier travelled asphalt
concrete has less possibility for healing of cracks.
2.2.4.4 Workmanship
A good design and good drainage of the road prevents the presence of water in the aggregate
bitumen system, possibly resulting in striping. The same holds for good quality compaction of
the mixture.
2.3 Literature review conclusions
The literature review shows that the chemical and mineralogical composition of the
aggregates has a strong influence on adhesion. The minerals and chemical elements at the
surface do not only affect the Arrhenius acidity of the aggregate, but the surface free energy is
affected as well. Geometry has, especially according to the mechanical adhesion theory, an
important influence on the adhesive bond between bitumen and aggregate. Shape, angularity,
size and roughness all determine this geometry and have their effect on the specific surface
area of the stones, which is an important parameter on adhesion according to all four adhesion
theories. According to the mechanical adhesion theory also the geometry of the aggregates,
the porosity and the pore size distribution are affecting the interlock with the bitumen. The
chemicals interacting with the bitumen can be from the aggregate surface, but also from dust
and other surface impurities. The adhesive bond is affected by it.
The literature review shows that the bitumen composition, the bitumen viscosity and the
bitumen surface energy have an effect on the bitumen-aggregate adhesion.
Mixture properties, like bitumen film thickness and void content, have an effect on the results
of the research. This also holds for external parameters, like the presence of water, stresses
and temperature.
28
The aggregate properties affecting the bitumen-aggregate adhesion are investigated in this
study. The aggregate properties influencing the bitumen-aggregate adhesion are given in
figure 2.6.
Stereo microscope
3.2.1 Roughness
Confocal microscope
Electron microscope
Stereo microscope
3.2.2 Specific Surface Area
Confocal microscope
3.2.3 Porosity
Mercury Intrusion
Electron microscope
3.2.4 Chemical and Mineralogical
composition
XRD
XRF
3.2.5 Acidity
pH meter
3.2.6 Aggregate Surface Energy
Sessile Drop Method
Sessile Drop Method
3.2.7 Bitumen Surface Energy
Wilhelmy Plate
Figure 2.6: Aggregate properties affecting adhesion and their evaluation methods.
Figure 2.6 shows the order in which the aggregate properties are discussed in chapter 3 and
the evaluation methods of the aggregate properties. In figure 2.6 the bitumen surface energy is
also included. Because for the calculation of the fundamental work of adhesion between
bitumen and aggregate, both the aggregate surface energy and the bitumen surface energy are
necessary.
29
Chapter 3: Materials and Experimental design
3 Materials and Experimental design
This chapter describes the materials, sample preparations and experiments carried out to
determine the aggregate and bitumen characteristics affecting the adhesion.
3.1 Experimental basis
The purpose of this research was to determine whether or not the treatments as applied on the
aggregate specimens in the LOT project had an effect on adhesion. Therefore the same
bitumen and the same aggregate types are used. Individual aggregates are tested for their
aggregate characteristics to avoid the influence of mixture parameters, like bitumen film
thickness and void content.
3.2 Materials
In this research three different materials are tested, being two aggregate types and one type of
bitumen. In this paragraph the sample preparations of the materials before starting the
experiments are discussed.
3.2.1 Stones
In the LOT research program two different aggregate types are analysed, being Greywacke
(G) and Bestone (B). The two aggregate types are delivered as boulders, each boulder
weighing approximately 5 kg. At first the boulders were cleaned to remove dust and grit.
Then they were cast in concrete and after that sawed in slices of about 10 mm thickness.
Three slices (Gsawed and Bsawed)(figure 3.1) each from both the Greywacke and Bestone
boulder are selected. From the six slices 10 columns per slice are drilled using a column drill
with a diameter of about 6 mm. To investigate the effects of the sandblasting used in the LOT
research program, five columns per slice are directly washed in boiling de-mineralised water
for 15 min. (Gsawedlab and Bsawedlab)(figure 3.1). The other five columns per slice are first
sandblasted before boiling them in de-mineralised water for 15 min. (Gsandlab and
Bsandlab)(figure 3.1), just like in the LOT research program. To investigate the influence of
the drilling process used in the LOT research program the six slices are now boiled in demineralised water for 15 min., as well (Gsawed and Bsawed). Now some experiments are
conducted on the slices and columns.
Figure 3.1: Example of the samples: Gsawed/Gsand, Gsawedlab, Gsandlab, Gstone and Gsurface ().
After completing the experiments the sides are broken from the three Greywacke and three
Bestone slices forming six new groups (Gsurface and Bsurface)(figure 3.1), to find the
influence of the sawing process used in the LOT research program. Afterwards the slices are
sandblasted and again boiled in de-mineralised water for 15 min (Gsand and Bsand). Then on
these slices (Gsand and Bsand) and the six new formed groups the experiments are repeated.
30
Greywacke boulder of about 5 kg
Three selected slices
Selected slice 1
Gsawed 1/Gsand 1
Selected slice 2
Gsawed 2/Gsand 2
Selected slice 3
Gsawed 3/Gsand 3
10 columns
etc.
etc.
Sides broken from slice
Gsurface 1
5 columns boiled
Gsawedlab 1
5 columns first sandblasted, than boiled
Gsandlab 1
Figure 3.2: Flow charts of boulder samples preparations.
In order to allow comparisons to be made, also real aggregate particles of Greywacke and
Bestone as used in asphalt mixtures are obtained. These Greywacke and Bestone aggregate
particles have a sieve size of 4/8 mm. With these particles 6 groups are formed per stone type
(figure 3.3). Three groups per stone sort are boiled in de-mineralised water for 15 min. The
other three groups per stone sort stay untreated, to investigate the effect of the boiling process.
Greywacke 4/8aggregate
Stone group 1
Gstone 1
Stone group 2
Gstone 2
Stone group 3
Gstone 3
Stone group 1
boiled
Gstonecl 1
Stone group 2
boiled
Gstonecl 2
Stone group 3
boiled
Gstonecl 3
Figure 3.3: Flow charts of 4/8 aggregate samples preparations.
Figures 3.4 and 3.5 give a schematic overview of the surfaces tested.
Slices Gsawed
Breaking the sides
Slices Gsand
Drilling
Slices Gsurface
Boiling once more
Columns Gsawed lab
Sandblasting
Columns Gsand lab
Figure 3.4: Differences in treatments (white) of the samples taken from the boulder (orange) to determine the
effects of the treatments on the adhesion characteristics.
Aggregate 4/8 Gstone
Boiling
Aggregate 4/8 Gstonecl
Figure 3.5: Differences in treatment (white) of the 4/8 aggregate samples (orange) to determine the effects of the
treatments on the adhesion characteristics.
31
Hereafter a summary of the aggregate samples as used in the experiments is given:
Greywacke:
• Three slices first tested sawed and boiled (Gsawed 1...3) later on sandblasted and
boiled in de-mineralised water and tested again (Gsand 1...3)
• Three groups of boiled non-sawed sides of the slices (Gsurface 1...3)
• Three groups of boiled columns (Gsawedlab 1...3)
• Three groups of sandblasted and boiled columns (Gsandlab 1...3)
• Three groups of untreated 4/8 aggregates (Gstone 1...3)
• Three groups of boiled 4/8 aggregates (Gstonecl 1...3)
Bestone:
• Three slices first tested sawed and boiled (Bsawed 1...3) later on sandblasted and
boiled in de-mineralised water and tested again (Bsand 1...3)
• Three groups of boiled non-sawed sides of the slices (Bsurface 1...3)
• Three groups of boiled columns (Bsawedlab 1...3)
• Three groups of sandblasted and boiled columns (Bsandlab 1...3)
• Three groups of untreated 4/8 aggregates (Bstone 1...3)
• Three groups of boiled 4/8 aggregates (Bstonecl 1...3)
3.2.2 Bitumen
In the experiments the same binder is used as in the LOT research program, being Cariphalte
S. This is an SBS (Styrene-Butadiene-Styrene branched polymer) modified bitumen binder.
The bitumen was subjected to an ageing protocol before the experiments started. The used
protocol is adopted from [8] and according to this protocol the bitumen is first heated to a
temperature of 185°C. Then the bitumen is poured on silicone-paper and is spread to a 2 mm
thick film. This 2 mm bitumen film is left in an oven at 175°C for 1.5 hours. Afterwards the
bitumen is cooled down to room temperature and stored at a dark and cool place.
3.3 Experiments
In this paragraph the selection of the experiments and the justification of this selection are
described.
3.3.1 Roughness of the stones
To compare the roughness of the stones it is important to keep in mind that a unique
roughness number of a surface doesn’t exist, because roughness can for instance be divided in
macro-, meso- and micro levels. Therefore the roughness of the stones is viewed at different
levels of magnification. The
magnification has a strong
correlation with the
representativeness of the measured
roughness for the same type of
stones (figure 3.6).
Figure 3.6: Stone surface roughness at
different magnifications.
32
At high magnification the roughness of only small areas is determined. Because the areas are
small, it is uncertain if at the other locations of the stone or even on another stone the areas
with the same size have more or less the same roughness. At lower magnification a larger area
can be measured. This results under normal conditions in more representative measurements.
As will be explained later on (see figure 3.8) the expected error is larger at lower
magnification. Besides this, each roughness measuring system and microscope has its domain
of surface area and magnification in which the accuracy is the best. Therefore the roughness
of the stones is measured at different magnifications and with different instruments. In this
study the roughness is of the stone samples is evaluated at 7 X, 20 X, 50 X and 100 X
magnification.
3.3.1.1 Macro surface roughness
A stereomicroscope with a magnification of 7 times is used to investigate the macro surface
roughness. This instrument is more accurate than other instruments for larger surface areas, in
orders of centimetres. In this way a larger surface of the untreated aggregates (Gstone and
Bstone) and the slice samples (Gsawed, Gsand, Bsawed and Bsand) can be imaged and
compared. The stereomicroscope produces quantitative results. The quantitative results of the
roughness are given in the roughness parameters Pa and Pq. The Pa value is the sum of the
deviations of the measured points to the average peak height and the Pq value is the rootmean square value of the measured local points. In formula the Pa value is determined by:
n
where z(i)
z
nx
1 x
Pa =
∑ z (i) − z
n x i =1
= local peak height of the sample at the ith measurement
= average peak height
= number of measurements on the length x
(3.1)
And the formula for the Pq value by:
n
Pq =
where z(i)
z
nx
x
∑ z (i) − z
2
i =1
(3.2)
nx
= local peak height of the sample at the ith measurement
= average peak height
= number of measurements on the length x (see figure 3.8 for details)
The stones that are tested are Gsawed 1, Gsand 1, Gstone 1, Bsawed 1, Bsand 1 and Bstone 1.
33
3.3.1.2 Meso surface roughness
The meso surface roughness is measured by
means of a Laser Scanning Confocal Microscope,
Leica TCS NT (figure 3.7). The LSCM has a
higher resolution for smaller surface areas
because light of a smaller wavelength is used in
comparison with conventional microscopes. The
roughness at meso level of the stones is measured
with a magnification of 20 and 50 times. The
surface area of the measured area is 500 µm by
500 µm and 200 µm by 200 µm for respectively
20 times and 50 times magnification. The LSCM
produces qualitative and quantitative results. The
qualitative results are 3D projections of the
measured samples. The quantitative results are the
Pa and Pq values of the surface, mentioned
before, but now over the measured surface area.
Figure 3.7: Laser Scanning Confocal Microscope Leica TCS
NT. [TUDelft]
The resolution of the LSCM is given in table 3.1. It is possible to measure the height of the
change in roughness peaks with a resolution of 0.35 µm.
Table 3.1: Instrument resolutions for Leica TCS NT. [TUDelft]
x-/y-resolution at λ = 488 nm
z-resolution at λ = 488 nm
0.18 µm
0.35 µm
The estimated error in the roughness parameters then becomes on the basis of equation (3.1).
∆P = ∆z (i ) + ∆z = 0.35 + 0.35 = 0.70µm
This estimated error only takes into account the z-resolution. The real error in the measured
roughness and the real roughness is not known. This is because the real error is dependent on
the resolution in horizontal direction and the
roughness to be measured (figure 3.8).
The instrument combines the measured
points to the measured roughness, but when
these points don’t coincide with the
roughness of the real stones unknown errors
are included.
Figure 3.8: Difference between measured roughness
and real surface roughness of the stones resulting in
unknown errors.
34
3.3.1.3 Micro surface roughness
At this level, the surface roughness of the stones is viewed using an Environmental Scanning
Electron Microscope (Philips XL30 ESEM)(figure 3.9) at 100 times magnification. It is
possible to get a higher magnification using an ESEM, but at higher magnifications the
absolute value of the measured roughness is smaller. When the absolute value of the
roughness decreases, the influence on
the bitumen-aggregate adhesion will
decrease. Besides this, the
measurements become less
representative, because only a very
small area is viewed. The ESEM
produces images of the surface of the
stones, but the roughness is not
quantified. So the roughness of the
different stones is compared in a
qualitative way.
Figure 3.9: Environmental Scanning Electron
Microscope Philips XL30 ESEM. [TUDelft]
The stones that are tested are Gsawedlab 1...3, Gsandlab 1...3, Gstone 1...3, Bsawedlab 1...3,
Bsandlab 1...3 and Bstone 1...3. The slice stones, Gsawed 1...3, Gsand 1...3, Bsawed 1...3 and
Bsand 1...3, are not selected, because the ESEM has limitations for the dimensions of the
stones.
The instrument specifications of the ESEM are given in the table 3.2.
Table 3.2: Instrument specifications for Philips XL30 ESEM. [TUDelft]
Resolution
Magnification
Relative humidity range
Temperature range
2 nm
100 X -50000 X
0 - 100 %
-30°C to +30°C
The micro roughness of the different stone samples is compared in a qualitative way.
Therefore it is not possible to make an error estimation. However the pictures of the micro
roughness produced by the ESEM show an area of about 1000 µm by 1000 µm. The
maximum resolution of the ESEM is 2 nm. An error of 2 nm on a picture showing an area of
about 1000 µm by 1000 µm isn’t visible.
3.3.2 Specific surface area
The specific surface area is measured with the stereomicroscope and the Laser Scanning
Confocal Microscope. The specific surface area is measured with the same magnification as
the surface roughness, resulting in a magnification of 7 times with the stereomicroscope and
20 and 50 times with the LSCM. The specific surface area is given in the unit of [m²/m²].
35
A total flat area (figure 3.10) gives a specific
surface area of 1 m²/m². The area of the
measurement is the same as the measured area.
In the case of figure 3.10 both the area of
measurement and the measured area is 500 µm
by 500 µm.
Figure 3.10: A total flat area has the same values for the
area of measurement (axes) and the measured area
(orange area).
The surface of a stone isn’t totally flat (figure
3.11). The area of the measurement is the same as
in figure 3.10: 500 µm by 500 µm. However the
measured area is larger than 500 · 500 = 250000
µm², because of the roughness. The specific
surface area of the stones is calculated as the
measured surface area divided by the area of
measurement. The specific surface area of the
stones is in this way larger than 1 m²/m².
Figure 3.11: Stone surface with a SSA larger than 1 m²/m².
3.3.3 Porosity
The porosity of the stones is measured with a Mercury Intrusion Porosimeter, Micromeritics
PoreSizer 9320 (figure 3.12). To measure the samples
in the MIP the samples are freeze-dried for 14 days to
remove residual moisture present in the pore structure.
The porosity of the stones is measured by forcing
mercury in the pores of the samples. Because mercury
is a non-wetting liquid for stony surfaces with an
average contact angle of 141° (figure 3.13), mercury
has to be forced into the pores of the samples. With low
pressure only the largest pores are filled with mercury.
Figure 3.12: Mercury Intrusion
Porosimeter, Micromeritics
PoreSizer 9320. [TUDelft]
Figure 3.13: Contact angle of
mercury on stony surface.
36
By increasing the pressure, more and more pores are filled with mercury. This theory is
known as the Washburn Theory and is expressed in the Washburn equation:
R=
where R
γ
θHg
p
2 ⋅ γ ⋅ cos(θ Hg )
p
(3.3)
= pore radius
= surface tension of mercury
= contact angle of mercury
= absolute exerted pressure
The total intruded volume of mercury is measured, every time the pressure is increased. The
intruded volume of mercury is the volume of the pores. In this way the MIP automatically
produces the porosity and pore size distribution.
The manufacturer states that the Porosimeter is able to measure the volume of the intruded
mercury with an accuracy better than 0.1 µL. The porosity of the samples is measured as:
V
Po% = IM ⋅100%
(3.4)
V ss
where Po% = porosity percentage
VIM
= Volume of intruded mercury
Vss
= Volume of stone sample
This results in the estimated error in the stone porosity measurements for a sample size of 1
cm² and a porosity of 2 % of:
∆V IM ∆V ss
0.1 ⋅10 −6
0.1 ⋅10 −6
∆Po% =
+
=
+
= 5 ⋅10 −3 + 1 ⋅10 − 4 = 0.5%
−3
−3
V IM
V ss
0.02 ⋅10
1 ⋅10
3.3.4 Chemical- and Mineralogical composition
To get a good impression of the chemical elements at the surface of the stones an ESEM is
used. The non-destructive character of this method is an advantage, because in a direct way
the main elements, on the surface of the stones, normally interacting with bitumen, are
evaluated. A disadvantage is the lower accuracy by which the composition of the aggregates
can be determined. The main elements are easily recognised, but a more accurate
determination of minor elements is not possible. The elements are determined by recording
the wavelength of light emitted by the elements when an electron hits them. The ESEM gives
plots with on the horizontal axis the wavelength and on the vertical axis the linear intensity in
counts per second so the elements in focus are visible.
The stones that are tested for the chemical composition in the ESEM are Gsawedlab 1...3,
Gsandlab 1...3, Gstone 1...3, Bsawedlab 1...3, Bsandlab 1...3 and Bstone 1...3. The slice
stones, Gsawed 1...3, Gsand 1...3, Gsurface 1...3, Bsawed 1...3, Bsand 1...3 and Bsurface
1...3, are not selected, because the ESEM has limitations for the dimensions of the stones.
For a more accurate chemical- and mineralogical composition an X-Ray Fluorescence
spectrometer and an X-Ray powder Diffractometer are used. Before these tests can be
conducted, the stones have to be crushed to powder. This is done in a disk mill. The samples
37
have to be a least 8 gr. Therefore two columns or pieces per stone sample are selected from
the samples, Gsawedlab 1...3, Gsandlab 1...3, Gsurface 1...3, Gstone 1...3, Gstonecl 1...3,
Bsawedlab 1...3, Bsandlab 1...3, Bsurface 1...3, Bstone 1...3 and Bstonecl 1...3, resulting in
ten sample groups, Gsawedlab, Gsandlab, Gsurface, Gstone, Gstonecl, Bsawedlab, Bsandlab,
Bsurface, Bstone and Bstonecl. All these samples are crushed for 10 seconds in the disk mill
resulting in ten powders with particles smaller than 40 µm. After crushing, the powders are
pressed in tablets on a resin coating.
The total composition of the chemical elements in
the samples is determined by means of an X-Ray
Fluorescence spectrometer (figure 3.14). An XRF
can determine a wide range of elements in
powdered stones and shows a higher accuracy than
the ESEM.
Figure 3.14: X-Ray Fluorescence spectrometer. [TUDelft]
The XRF determines the elements by recording the wavelength of light emitted by the
elements when an electron hits them. The XRF gives the elements in mass percentage of the
total composition.
The mineralogical composition of the stones is determined with an X-Ray powder
Diffractometer. For the XRD analyses the stones have to be crushed to powder. The major
minerals in stones, like quarts, calcite and orthoclase can be determined. The minerals are
determined by recording the wavelength of light emitted by the minerals when an electron hits
them. The XRD produces a plot with on the horizontal axis the wavelength and on the vertical
axis the linear intensity in counts per second.
3.3.5 Acidity
The Arrhenius acidity of the stones is measured by immersing the stones in 7.5 cm³ distilled
water. The pH is measured over a period of two weeks at predefined moments. With an
acidity meter (Metrohm 744 pH Meter)(figure 3.15)
the acidity of the water is measured one hour, one day,
one week and two weeks after immersion. The stone
samples are measured in random order. After each
measurement the boxes (approximately 2 by 2 by 2
cm) are covered to avoid water evaporation.
Figure 3.15: Acidity meter Metrohm 744 pH Meter and on the
right the immersed samples.
The groups of stones measured in this acidity test are Gsawedlab 1...3, Gsandlab 1...3,
Gsurface 1...3, Gstone 1...3, Gstonecl 1...3, Bsawedlab 1...3, Bsandlab 1...3, Bsurface 1...3,
Bstone 1...3 and Bstonecl 1...3.
38
The specifications of the used acidity meter as provided by the manufacturer are given in table
3.3. The instrument has a thermometer for automatic compensation of the temperature in the
pH measurement. Before every measurement the instrument is calibrated.
Table 3.3: Instrument resolution of Metrohm 744 pH meter. [Metrohm]
pH resolution
Voltage resolution
Temperature resolution
0.01
1 mV
0.1°C
The acidity of the water is not really measured with a resolution of 0.01, because of the
measuring conditions. For instance the water, where the stones are immersed in, could never
be entirely homogenised. This might result in possible local pH differences. All weights of
water and samples are given in appendix B.
3.3.6 Surface energy of the aggregate
A Contact Angle Meter (Krüss CAMS G2 tensiometer)(figure 3.16) is used to measure the
contact angles of droplets of reference liquids on the surface of the stones. The droplets are
formed at 20°C using the Sessile Drop Method (appendix C). The surface energy components
are calculated using the van Oss-Good-Chaudhury theory (appendix A) and scale (table 3.4).
To calculate the surface energy components according to this theory it is necessary to use at
least three reference liquids. The reference liquids selected here are distilled water,
diiodomethane and glycerol.
Furthermore the liquids nhexane and formamide are
used to verify the computed
surface energy components
of the stones. This is done by
comparing the measured
contact angles of the liquids
n-hexane and formamide
with the back-calculated
contact angles on the surface
energy components of the
stones (appendix A).
Figure 3.16: Contact Angle Meter
Krüss CAMS G2 tensiometer.
Table 3.4: Surface energy components of reference liquids in mJ/m² according to the vanOss-Good-Chaudhury
scale. [van Oss, Chaudhury, Good 1988]
Reference liquid
Distilled water
Diiodomethane
Glycerol
n-Hexane
Formamide
γlTOT
72.8
50.8
64.0
18.4
58.0
γlLW
21.8
50.8
34.0
18.4
39.0
γl+
25.5
0.00
3.92
0.00
2.28
γl25.5
0.00
57.4
0.00
39.6
39
For the determination of the surface energy components the angles of the reference liquids are
recorded. Equation 3.5 [13] relates the recorded contact angles to the surface energy
components of the stones.
(3.5)
γ lTOT (1 + cosθ sl ) = 2 ⋅ γ sLW ⋅ γ lLW + 2 ⋅ γ s− ⋅ γ l+ + 2 ⋅ γ s+ ⋅ γ l−
TOT
LW
+
where γl ,γl ,γl ,γl = known surface energy components of the reference liquid
γsLW ,γs- ,γs+
= surface energy components of the sample (appendix A)
θsl
= measured contact angle of the reference liquid
By arranging the three equations of reference liquids (distilled water, diiodomethane and
glycerol) into a system of equations the surface energy components are calculated according
to the van Oss-Good-Chaudhury theory.
The surface energy of all the stone samples are measured in this test, so Gsawed 1...3, Gsand
1...3, Gsawedlab 1...3, Gsandlab 1...3, Gsurface 1...3, Gstone 1...3, Gstonecl 1...3, Bsawed
1...3, Bsand 1...3, Bsawedlab 1...3, Bsandlab 1...3, Bsurface 1...3, Bstone 1...3 and Bstonecl
1...3.
The accuracy of the contact angle measurements has influence on the calculated surface
energy of the aggregate surface. This influence is quantified by calculating the surface energy
with three different contact angles. For convenient reasons contact angles of diiodomethane
are used. If diiodomethane has a contact angle of 25° on the aggregate surface then the
Lifshitz-van der Waals component of the surface energy of the aggregate is:
50.8 ⋅ (1 + cos 25) = 2 ⋅ 50.8 ⋅ γ sLW ⇒ γ sLW = 46.2 mJ/m²
If diiodomethane has a contact angle of 26°(+4.0 % with regard to 25°) on the aggregate
surface then the Lifshitz-van der Waals component of the surface energy of the aggregate is:
50.8 ⋅ (1 + cos 26) = 2 ⋅ 50.8 ⋅ γ sLW ⇒ γ sLW = 45.8 mJ/m²
The change in Lifshitz-van der Waals component is – 0.87 % with regard to 46.2 mJ/m².
If diiodomethane has a contact angle of 35° (+40 % with regard to 25°) on the aggregate
surface then the Lifshitz-van der Waals component of the surface energy of the aggregate is:
50.8 ⋅ (1 + cos 35) = 2 ⋅ 50.8 ⋅ γ sLW ⇒ γ sLW = 42.0 mJ/m²
The change in Lifshitz-van der Waals component is – 9.1 % with regard to 46.2 mJ/m².
3.3.7 Bitumen Surface energy
Because the influence of the surface energy of the stones on the adhesion is dependent on the
surface energy of the bitumen (see equation A3), the surface energy of the bitumen is also
measured. The surface energy of the bitumen is measured by means of the Sessile Drop
Method and the Wilhelmy Plate method. The experiments are conducted on the bitumen with
both methods to explore a difference between the results of the surface energy measured by
both methods. The Wilhelmy Plate Method is conducted with a KSV Sigma 701 tensiometer
(figure 3.17). The surface energy components are, like the components of the stones,
40
calculated using the van Oss-Good-Chaudhury theory and scale. The three selected reference
liquids are distilled water, diiodomethane and glycerol. This set of reference liquids is
selected because of its lowest condition number (see appendix A) with bitumen, resulting in
the smallest errors [4]. Similar to the surface energy of the stones, the surface energy of the
bitumen is verified by comparing the measured
contact angles of the liquids n-hexane and formamide
with the back-calculated contact angles at the surface
of the bitumen. The advantage of using n-hexane is
that it is a pure non-polar liquid with a low surface
energy: 18,4 mJ/m². Bitumen has a non-polar surface
energy component in the range of about 8 to 35 mJ/m²
[3,4,11]. This means that if the bitumen has a nonpolar surface energy component which is high for
bitumen (>18,4 mJ/m²), n-hexane will not form a
stable droplet on the surface, but when the bitumen
has a non-polar surface energy component which is
low for bitumen (<18,4 mJ/m²), n-hexane will show a
stable droplet on the surface.
Figure 3.17: KSV Sigma 701 tensiometer. [KSV]
The experimental protocol used for both the Sessile Drop Method and Wilhelmy Plate
Method is described in appendix C [10], with only some differences with respect to, the
selected reference liquid set, the dimensions of the glass slices and the temperature at which
the experiments are conducted, 20 ±1°C instead of 25°C.
In contrast to the Sessile Drop Method
the Wilhelmy Plate test measures the
contact angle of the reference liquids
and the bitumen indirectly. A
microbalance in the tensiometer
measures the change in force when the
bitumen is immersing the reference
liquid (figure 3.18).
Figure 3.18: Principle of the Wilhelmy Plate
Method. [Hefer and Little 2005]
41
The relation between the change in force and the contact angle is:
cos θ sl =
where θsl
∆F
Vim
ρl
ρair
g
Pt
γlTOT
∆F + Vim (ρ l − ρ air ⋅ g )
(3.6)
Pt ⋅ γ lTOT
= indirectly determined contact angle of the reference liquid
= change in force measured by the micro balance
= volume of immersion of the bitumen coated plate in the reference
liquid
= density of the reference liquid
= density of the air
= local constant of gravitation acceleration
= perimeter of the bitumen coated plate
= total surface energy of the reference liquid
Knowing the contact angles, the surface energy components are calculated according the
van Oss-Good-Chaudhury theory by arranging a system of equations of the relation between
the surface energy components and the contact angles. Because of the discussion between
researchers over the application of advancing and receding angles, it is decided to calculate
the surface energy components of the bitumen from both the advancing and the receding
contact angles.
The most important specifications for the Sigma 701 tensiometer, as provided by the
manufacturer, are given in table 3.5.
Table 3.5: Instrument specifications for KSV Sigma 701 tensiometer. [KSV]
Maximum load
Weighing resolution
Force resolution
Stage positioning resolution
Contact angle range
Contact angle resolution
Calibration and locking
5g
0.01 mg
0.01 µN
0.015 µm
0-180°
0.01°
automatic
According to table 3.5 the accuracy in measured contact angles of the tensiometer is 0.01°,
but this is under ideal circumstances. The measurement of the dimensions of the plate coated
with bitumen also has inaccuracies. The measurement of the dimensions is conducted with a
digital calliper with an accuracy of 0.01 mm. On five points at one bitumen plate the thickness
is measured and then averaged. On two points the length is measured. Therefore the
measurement error is probably larger than the given 0.01 mm. For estimation of the total
measurement error a deviation in the dimensions of 5 · 0.01 = 0.05 mm is taken into account.
The estimated measurement error of the dimensions of the immersed volume of the bitumen
plate is.
∆Vim =
42
∆b ∆l ∆h 0.05 0.05 1.5 ⋅ 10 −5
+
+
=
+
+
= 0.03 = 3%
b
l
h 2.00 20.00
6.00
The estimated measurement error of the dimensions of immersed perimeter of the bitumen
plate is.
∆Pt = 2
∆b
∆l
0.05
0.05
+2 =2
+2
= 0.06 = 6%
b
l
2.00
20.00
The estimated difference in total surface tension of one reference liquid is 1.0 Nm-¹. The
estimated measurement error of the difference in total surface tension is.
∆γ
TOT
l
=
∆γ lTOT
γ
TOT
l
=
1 .0
= 0.02 = 2%
50.8
The difference in liquid density and air density is estimated at 10 kg/m³. The estimated
measurement error of the external parameters is.
∆(ρ l − ρ air ⋅ g ) =
∆( ρ l − ρ air ⋅ g )
10
=
= 0.01 = 1%
3
(ρ l − ρ air ⋅ g ) 1.0 ⋅ 10 − 1.3 ⋅ 9.81
(
)
The accuracy of the microbalance of the tensiometer is given as 0.01 mg. The estimated
measurement error of the weighing resolution is.
∆F =
∆F 0.01
=
= 0.002 = 0.2%
F
5.00
The total estimated maximum error in the contact angles of the Wilhelmy Plate Method in this
application is.
∆ cos θ sl = ∆Vim + ∆Pt + ∆γ lTOT + ∆(ρ l − ρ air ⋅ g ) + ∆F ≈ 0.12 = 12%
43
Chapter 4: Experimental results
4 Experimental results
In this chapter the most important results of the experiments are given. Some additional
results are given in appendix B. All results and experimental data are stored on the CD-ROM
which is attached to this report.
4.1 Roughness
4.1.1 Macro surface roughness
By means of the stereomicroscope the macro surface roughness of the stone specimens is
measured at randomly selected locations. Table 4.1 shows the values for the roughness
parameters as measured.
Table 4.1: Measured values of parameters Pa and Pq at 7 times magnification.
Stereomicroscope (7X)
Gsawed 1
Gsand 1
Gstone 1
Bsawed 1
Bsand 1
Bstone 1
Pa [µm]
48.41
50.67
238/335
48.12
49.07
174/292
Pq [µm]
56.69
59.47
350/393
56.49
58.51
241/381
Table 4.1 shows that the measured values of the roughness parameters Pa and Pq of the
sandblasted Greywacke slice (Gsand1) are somewhat higher than those of the Greywacke
slice which surface is created by sawing (Gsawed1). The Greywacke 4/8 aggregate (Gstone1)
has 5 to 6 times higher roughness parameters than both the Greywacke slices (Gsawed1 and
Gsand1). The same is true for the Bestone samples. The Bestone 4/8 aggregate (Bstone1) has
higher roughness parameters than the Bestone sandblasted slice (Bsand1). The sandblasted
Bestone slice (Bsand1) has on its turn somewhat higher values for Pa and Pq than the sawed
Bestone slice (Bsawed1). The sandblasted slices form Greywacke (Gsand1) and Bestone
(Bsand1) have more or less the same roughness. The same is true for the sawed samples
(Gsawed1 and Bsawed1). The difference in measured roughness of the Greywacke and
Bestone 4/8 aggregates (Gstone1 and Bstone1) is somewhat larger. For instance one
measurement of Bestone 4/8 aggregate (Bstone1) results in a value of Pa = 174 µm and Pq =
241 µm. A second measurement on another diagonal of the same 4/8 aggregate results in Pa =
292 µm and Pq = 381 µm.
44
4.1.2 Meso surface roughness
The surface roughness at intermediate level is measured with the LSCM. Some of the plots of
the surface roughness at 20 times magnification are shown in figure 4.1 and 4.2.
Gsawedlab2
Gsandlab1
Gstone2
Figure 4.1: Plots of the roughness of Greywacke samples at 20X magnification. Plots of other samples in
appendix B.
Figure 4.1 shows almost no visible difference between the Greywacke sandblasted columns
(Gsandlab) and the sawed columns of the Greywacke samples (Gsawedlab). On the other
hand a clear visible distinction can be made between the columns (Gsandlab and Gsawedlab)
and the 4/8 aggregates (Gstone). The roughness figures of the 4/8 aggregates show a much
rougher surface than the Greywacke column samples (Gsandlab and Gsawedlab).
45
Bsawedlab2
Bsandlab2
Bstone1
Figure 4.2: Plots of the roughness of Bestone samples at 20X magnification. Plots of other samples in appendix
B.
The same holds for the Bestone samples. A clear visible distinction can be made between the
4/8 aggregates (Bstone) and the Bestone column samples (Bsandlab and Bsawedlab) (figure
4.2). No real visible distinction can be made between the Bestone sandblasted (Bsandlab) and
the non-sandblasted Bestone columns (Bsawedlab). Comparing the Greywacke and the
Bestone samples results in the conclusion that no visible difference between the two stone
sorts exists.
The measured parameters Pa and Pq at a magnification of 20 times are given in table 4.2.
LSCM (20X)
Gsawedlab
Gsandlab
Gstone
Bsawedlab
Bsandlab
Bstone
n
3
3
3
3
3
3
Pa [µm]
3.79
4.99
20.82
5.21
6.63
29.04
Stdev
0.59
1.01
3.33
0.75
1.50
12.45
Pq [µm]
5.14
6.85
25.16
7.26
8.57
35.32
Stdev
0.81
1.06
3.30
1.02
1.98
14.90
The averaged values of the roughness parameters measured at 20 times magnification are
shown in table 4.2. The 4/8 aggregates (Gstone and Bstone) have higher roughness
parameters, about 4 to 5 times, than the columns samples of both Greywacke and Bestone
46
(Gsawedlab, Gsandlab, Bsawedlab and Bsandlab). The sandblasted columns (Gsandlab,
Bsandlab) show a somewhat larger roughness than the sawed columns for both aggregate
types (Gsawedlab and Bsawedlab). The standard deviation in the measured roughness
parameters of the 4/8 aggregates is much larger than the standard deviation in the sandblasted
columns of both aggregate types (Gsandlab, Bsandlab). The standard deviation in the
measured parameters is smallest for the sawed columns (Gsawedlab and Bsawedlab).
Comparing the Greywacke and Bestone samples makes it clear that both the average
roughness parameters and the standard deviation in the measured data of the Bestone samples
are all larger than those of the Greywacke samples.
After the measurements of the stone samples at a magnification of 20 times, the LSCM was
used to measure the roughness of the same stone samples at a magnification of 50 times.
Gsawedlab2
Gsandlab3
Gstone3
Figure 4.3: Plots of the roughness of Greywacke samples at 50X magnification. Plots of other samples in
appendix B.
At 50 times magnification the same trends in roughness are found as at 20 times
magnification. A visible difference in roughness is only found between the 4/8 aggregates of
each aggregate type (Gstone and Bstone) and the column samples (Gsand, Gsawed, Bsand
and Bsawed) (figure 4.3 and 4.4).
47
Bsawedlab3
Bsandlab1
Bstone2
Figure 4.4: Plots of the roughness of Bestone samples at 50X magnification. Plots of other samples in appendix
B.
From the measurements at 50 times magnification the LSCM, the Pa and Pq values as shown
in table 4.3 are derived.
Table 4.3: Measured values of the parameters Pa and Pq at 50 times magnification.
LSCM (50X)
Gsawedlab
Gsandlab
Gstone
Bsawedlab
Bsandlab
Bstone
n
3
3
3
3
3
3
Pa [µm]
3.81
5.15
11.29
4.58
7.45
20.91
Stdev
0.21
0.77
5.65
0.52
2.56
6.01
Pq [µm]
5.02
7.00
13.41
6.25
9.60
26.36
Stdev
0.25
0.74
6.43
0.71
2.81
7.38
For both the Greywacke and Bestone, the average measured values of the roughness
parameters at 50 times magnification show that the roughness of the 4/8 aggregates (Gstone
and Bstone) is larger than the roughness of the columns (Gsandlab, Gsawedlab, Bsandlab and
Bsawedlab). In this case this isn’t 4 to 5 times anymore, but it is reduced to about 2 to 3 times
the average roughness parameters of the sandblasted columns (Gsandlab and Bsandlab). The
sandblasted columns (Gsandlab and Bsandlab) have again higher values for the roughness
parameters than the sawed columns (Gsawedlab and Bsawedlab).
48
4.1.3 Micro surface roughness
The Environmental Scanning Electron Microscope is used to evaluate the roughness of the
stone samples at a magnification of 100 times. All samples are viewed over an area of at least
0,5 cm² to get a better impression of the entire surface of the samples. Pictures of areas of
about 1mm2 are shown hereafter to support the findings.
The surfaces of all the three
sawed Greywacke columns
(Gsawedlab) show the same
character of the micro
roughness (figure 4.5). Over the
entire surface of the samples
areas are found with lower and
higher roughness. The areas
with a relative higher roughness
dominate.
Figure 4.5: Picture showing the micro
surface roughness of sawed
Greywacke column (Gsawedlab).
The same trend is found on all
the three sandblasted Greywacke
columns (Gsandlab) (figure 4.6).
Also in this case areas with a
relative high roughness
dominate, but also here areas
with a relative low roughness are
found.
Figure 4.6: Picture showing the micro
surface roughness of sandblasted
Greywacke column (Gsandlab).
On the surface of the three Greywacke 4/8 aggregates (figure 4.7) more areas with relative
low roughness are present compared to the Greywacke columns (Gsawedlab and Gsandlab).
49
Figure 4.7: Picture showing the
micro surface roughness of
Greywacke 4/8 aggregate (Gstone).
In the same way the Bestone samples are now evaluated. The sawed Bestone columns
(Bsawedlab) also show areas
with relative low and relative
high roughness (figure 4.8).
micro surface roughness of sawed
Bestone column (Bsawedlab).
The surfaces of the sandblasted Bestone columns (Bsandlab) also show areas with a relative
low roughness and areas with a relative high roughness (figure 4.9).
Figure 4.9: Picture showing the micro surface roughness of sandblasted Bestone column (Bsandlab).
50
The Bestone 4/8 aggregates
(Bstone) show on their surface
more areas with relative low
roughness in comparison with
the sandblasted and sawed
columns (figure 4.10).
micro surface roughness of Bestone
4/8 aggregate (Bstone).
For quantification of the measurements of the micro roughness the department of civil
engineering of the Texas A&M University performed an analysis on the pictures made by the
electron microscope using the wavelet method (appendix C). The averaged results per stone
sample are given in table 4.4.
Table 4.4: Texture distribution on the pictures analysed using the wavelet method.
Fine
Medium
Coarse
Fine
Medium
texture
texture
texture
texture
texture
[areas]
[areas]
[areas]
[%]
[%]
Gsawed
456
129
43
73
21
Gsand
460
98
36
77
17
Gstone
448
137
58
70
21
Bsawed
397
152
173
56
21
Bsand
820
219
152
68
19
Bstone
481
208
171
56
24
Coarse
texture
[%]
7
6
9
23
13
20
Table 4.4 shows that the pictures of the Greywacke sandblasted columns (Gsandlab) reveal a
higher percentage of areas with fine texture (77%) compared to the 4/8 aggregates (Gstone)
(70%) and sawed columns (Gsawedlab) (73%). The Greywacke 4/8 aggregates have less areas
of fine roughness, but more areas of coarse roughness (9%) compared to the Greywacke
sawed columns (Gsawedlab) (7%) and the sandblasted columns (Gsandlab)(7%). A larger
difference is observed between the Bestone samples. The Bestone 4/8 aggregates (Bstone)
and the Bestone sawed columns (Bsawedlab) have almost the same distribution of areas of
fine texture, medium texture and coarse texture, 56%, 21%, 22% and 56%, 24%, 20%
respectively. However the result of the sandblasted columns (Bsandlab) differs 12 percentage
points of fine texture areas and 7 to 9 percentage points of coarse texture areas compared to
the sawed columns and 4/8 aggregates of Bestone (Bsawedlab and Bstone).
4.2 Specific surface area
The specific surface area (SSA) measured by the stereomicroscope is given in table 4.5.
51
Table 4.5: Specific surface area by stereomicroscope at 7 times magnification.
Gsawed 1
Gsand 1
Gstone 1
Bsawed 1
Bsand 1
Bstone 1
SSA [mm/mm]
1.002
1.006
1.081/1.252
1.007
1.020
1.070/1.115
Table 4.5 shows that at a magnification of 7 times the measured specific surface area of the
4/8 aggregates of both Greywacke and Bestone (Gstone and Bstone) is larger than that of the
column samples (Gsandlab, Gsawedlab, Bsandlab and Bsawedlab). The sandblasted columns
(Gsandlab and Bsandlab) have a higher specific surface area than the sawed columns
(Gsawedlab and Gsawedlab).
The SSA of all the samples is measured using the LSCM at a magnification of 20 times. In
table 4.6 the average of three values and the standard deviation is reported.
Table 4.6: Specific surface area by LSCM at 20 times magnification.
LSCM (20X)
Gsawedlab
Gsandlab
Gstone
Bsawedlab
Bsandlab
Bstone
n
3
3
3
3
3
3
SSA [µm²/µm²]
1.70
1.86
2.92
2.09
2.26
2.86
Stdev
0.04
0.19
0.13
0.35
0.30
0.57
Table 4.6 shows that at 20 times magnification the specific surface area of the Greywacke and
Bestone 4/8 aggregates (Gstone and Bstone) is larger than that of the column samples
(Gsandlab, Gsawedlab, Bsandlab and Bsawedlab). Table 4.6 also shows that the sandblasted
columns (Gsandlab and Bsandlab) have a larger specific surface area than the sawed columns
(Gsawedlab and Bsawedlab). The standard deviation in the measured specific surface area of
the Greywacke sandblasted columns (Gsandlab) is higher than for the sawed columns
(Gsawedlab). For the sandblasted and sawed Bestone columns (Bsandlab and Bsawedlab) the
standard deviation is almost the same. All specific surface areas of the samples measured at
20 times magnification are larger than those measured at 7 times magnification.
Table 4.7 shows the results at 50 times magnification.
LSCM (50X)
Gsawedlab
Gsandlab
Gstone
Bsawedlab
Bsandlab
Bstone
n
3
3
3
3
3
3
SSA [µm²/µm²]
3.03
3.41
4.02
3.11
3.51
5.82
Stdev
0.08
0.24
1.21
0.06
0.29
0.94
The measured specific surface area of the 4/8 aggregates at 50 times magnification is larger
than the specific surface area of the column samples (table 4.7). The sandblasted columns
52
(Gsandlab and Bsandlab) have larger measured specific surface areas than the sawed columns
(Gsawedlab and Bsawedlab). The standard deviation in the measured specific surface area is
highest for the 4/8 aggregates (Gstone and Bstone) followed by the sandblasted columns
(Gsandlab and Bsandlab) and is smallest for the sawed columns (Gsawedlab and Bsawedlab).
The measured specific surface area at 50 times magnification is larger than at 20 times
magnification.
4.3 Porosity
The porosity of the stone samples is randomly measured with the Mercury Intrusion
Porosimeter. Per stone sample, Gsawedlab1..3, Gsandlab1..3, Gstone1..3, Gsurface1..3,
Bsawedlab1..3, Bsandlab1..3, Bstone1...3 and Bsurface1...3, two columns or pieces are
selected to be measured for their porosity. The results of the porosity tests are given in table
4.8.
Table 4.8: Porosity of the stone samples measured in the Mercury Intrusion Porosimeter.
Sample
Bstone
Bsurface
Bsandlab
Bsawedlab
Porosity of total
volume [%]
2.70 ± 0.01
2.01 ± 0.01
2.13 ± 0.01
2.15 ± 0.01
Sample
Gstone
Gsurface
Gsandlab
Gsawedlab
Porosity of total
volume [%]
2.42 ± 0.01
4.13 ± 0.01
1.65 ± 0.01
3.40 ± 0.01
The porosity of the Bestone 4/8 aggregates (Bstone) is larger than the porosity of the Bestone
columns (Bsandlab and Bsawedlab) samples (table 4.8). The Bestone column samples,
sandblasted (Bsandlab) and solely sawed (Bsawedlab), differ only slightly in porosity, 2.13 %
vs. 2.15 % respectively. The non-sawed surface of the Bestone slices, Bsurface, has a
somewhat smaller porosity of 2.01 %. The measured porosity of the Greywacke samples is
different. Here the porosity per sample, and thus per surface treatment, differs more than
observed at the Bestone samples. The untreated Greywacke 4/8 aggregate has a measured
porosity of 2.42 %. The surface of the Greywacke 5 kg boulders (Gsurface) shows a measured
porosity of 4.13 %. When the slices, sawed from this boulder, are drilled to columns
(Gsawedlab) a porosity is measured of 3.40 %. However the sandblasted columns (Gsandlab)
show a porosity of 1.65 %.
4.4 Chemical- and Mineralogical composition
To get a more representative result of the chemical elements at the surface of the stone
samples all samples are viewed over an area of at least 0.5 cm². The determination of the
chemical elements is established by the difference in wavelength emitted from all elements
when an electron hits them. Because of this, the heavier elements will have a lighter colour
than lighter elements in the pictures to follow. In this way it is easier to distinguish individual
elements at the surface. The visible elements (differently coloured compared to the
surroundings) are point identified and then the elements of the rest of the area. Afterwards an
overview of the composition of the 1 mm² area is given in plots.
All areas of 1 mm² of the sawed Greywacke columns (Gsawedlab) showed local spots of
chemical elements at the surface (figure 4.11).
53
Figure 4.11: Picture of individual chemical elements at the surface of Gsawedlab3.
These elements included Iron (Fe), sulphur (S) and calcium (Ca). The remaining area of the
surface has a high content of silicon (Si) (figure 4.12). The lighter and darker areas on the
picture have, although not dominant
and visibly indistinguishable,
magnesium (Mg), aluminium (Al),
sodium (Na), potassium (K), carbon
(C), iron (Fe) and calcium (Ca).
Figure 4.12: Plot of chemical elements at the
surface of Gsawedlab3 over an area of 1
mm². Horizontal axis is the wavelength
emitted from the elements and the vertical
axis gives the linear intensity in counts per
second.
The sandblasted Greywacke
samples (Gsandlab1...3) show a
similar result (figure 4.13). At
some areas of 1 mm² many
individual elements are found and
in some areas of 1 mm² somewhat
less. In each area of 1 mm² iron
(Fe), sulphur (S) and calcium (Ca)
are found.
Figure 4.13: Picture of individual
chemical elements at the surface of
Gsandlab1.
54
The remaining surface shows a
high content of silicon (Si) and
smaller amounts of magnesium
(Mg), aluminium (Al), sodium
(Na), potassium (K) and carbon
(C), as well as iron (Fe) and
calcium (Ca) (figure 4.14).
Figure 4.14: Plot of chemical
elements at the surface of Gsandlab1
over an area of 1 mm².
The same individual elements are also found at the surface of the Greywacke 4/8 aggregates
(Gstone 1...3) (figure 4.15)
(iron (Fe), sulphur (S) and
calcium (Ca)). The remaining
area shows a high content of
silicon (Si) and, in smaller
amounts, magnesium (Mg),
aluminium (Al), sodium (Na),
potassium (K), carbon (C), iron
(Fe) and calcium (Ca) (figure
4.16).
Gstone1.
elements at the surface of Gstone1
55
The Bestone samples are analysed in a similar way as the Greywacke samples. The visible
elements at the surface in an area of 1 mm² are point identified and after that the total
composition of the elements present at the 1mm² area is determined.
The Bestone sawed columns
(Bsawed lab 1...3) show iron
(Fe) and calcium (Ca), as
concentrated elements, at
almost every 1 mm² (figure
4.17).
Bsawedlab3.
The remaining area shows a high
content of silicon (Si) and lower
contents of magnesium (Mg),
aluminium (Al), sodium (Na),
potassium (K), carbon (C), iron
(Fe), calcium (Ca) and sometimes
titanium (Ti) (figure 4.18).
Figure 4.18: Plot of chemical elements at
the surface of Bsawed lab3 over an area of
1 mm².
Also on the surface of the
sandblasted Bestone columns
(Bsand lab1...3) iron (Fe) and
calcium (Ca) are found as
concentrated elements (figure
4.19).
Bsandlab1.
56
The remaining area shows a
high content of silicon (Si) and
lower contents of magnesium
(Mg), aluminium (Al), sodium
(Na), potassium (K), carbon
(C), iron (Fe) and calcium (Ca)
(figure 4.20). Sometimes
titanium (Ti) is found at the
surface as well.
elements at the surface of Bsandlab1
On the surface of the Bestone 4/8 aggregates (Bstone 1...3) almost no concentrated chemical
elements are found (figure 4.21). Sometimes only iron (Fe) and calcium (Ca) are found, but
even then the elements are less
dominant compared to the sawed
and sandblasted Bestone columns
(Bsawedlab and Bsandlab).
Bstone2.
The entire area shows a high
silicon (Si) content and contains
magnesium (Mg), aluminum
(Al), sodium (Na), potassium
(K), carbon (C), iron (Fe) and
calcium (Ca) (figure 4.22).
Rarely titanium (Ti) is found at
the surface as well.
Figure 4.22: Plot of chemical elements
at the surface of Bstone2 over an area of
1 mm².
57
The X-ray facilities of the department of Materials Science and Engineering of the Delft
University of Technology are used for the determination of the composition of the chemical
elements in the surface of the stone samples. Table 4.9 gives the measured mass percentages
of the most important chemical elements. In appendix B the mass percentages of all the
chemical elements are given.
Bsawed
lab
Bsurface
Bstonecl
Bstone
Gstone
Gstonecl
Gsurface
Gsawed
lab
Gsandlab
[mass %]
SiO2
CO2
CaO
Al2O3
K2O
MgO
Na2O
Fe2O3
S
P2O5
TiO2
V2O5
Cr2O3
MnO
NiO
BaO
Bsandlab
Table 4.9: Distribution of chemical elements over the samples given in mass percentages.
53.19
19.35
10.41
8.75
1.84
1.42
1.80
2.29
0.000
0.094
0.365
0.008
0.051
0.070
0.164
0.096
60.88
10.08
9.21
10.26
2.11
1.77
2.04
2.67
0.000
0.123
0.402
0.006
0.051
0.057
0.155
0.092
62.67
8.95
8.57
10.17
2.11
1.63
2.19
2.60
0.000
0.111
0.374
0.010
0.080
0.055
0.277
0.113
63.20
7.83
6.39
11.38
2.28
2.29
2.02
3.50
0.000
0.131
0.497
0.008
0.052
0.580
0.147
0.110
63.20
7.67
6.64
11.28
2.23
2.32
2.06
3.48
0.000
0.126
0.460
0.009
0.060
0.057
0.194
0.106
53.04
11.94
11.48
11.96
2.16
2.31
0.840
4.69
0.306
0.068
0.661
0.015
0.063
0.108
0.166
0.077
49.23
15.99
14.57
10.24
1.76
1.97
0.795
4.01
0.310
0.061
0.583
0.014
0.041
0.115
0.088
0.071
54.78
4.89
5.09
18.33
4.12
3.27
0.596
7.24
0.234
0.090
0.884
0.023
0.047
0.089
0.107
0.109
54.18
4.67
5.11
18.86
4.29
3.31
0.552
7.35
0.241
0.083
0.920
0.027
0.032
0.091
0.074
0.122
54.03
4.74
5.10
18.96
4.30
3.30
0.529
7.35
0.249
0.083
0.900
0.027
0.039
0.086
0.088
0.114
The results show that the Bestone samples have a higher silica content on average than the
Greywacke samples. The results of the Bestone samples show that the Bestone sandblasted
columns (Bsand) deviates in silica content from the other Bestone samples. The deviation in
silica content is much less for the Greywacke samples. However for the Greywacke samples a
higher deviation in the calcium carbonate (CaCO3) content is found. The Greywacke columns
(Gsandlab and Gsawedlab) have about 5% of calcium and 5% of carbon dioxide. The
Greywacke 4/8 aggregates (Gstone and Gstonecl) on the other hand have an 11 to 16 %
content of both calcium and carbon dioxide.
58
As mentioned before, powders were made of both aggregate types to allow a determination of
the mineralogical composition to be made by means of an X-Ray powder Diffractometer. The
wavelength is on the horizontal axis of the graph while the vertical axis gives the linear
intensity in counts per second. Figure 4.23 is an example of the XRD analyses of the
Greywacke samples.
D. v. Lent
CuKa
Sample G
backgr.subtr. & y-shift
23okt07
Lin (Cps)
40 00
0
5
10
20
30
40
50
60
70
80
2-Theta - Scale
File: Gopper_17oct7.raw
File: Gsteen_17oct7.raw
File: Gsteenschoon_17oct7.raw
File: Gzaag_17oct7.raw
File: Gzand_17oct7.raw
00-046-1045 (*) - Quartz, syn - SiO2
00-010-0393 (*) - Albite, disordered - Na(Si3Al)O8
00-047-1743 (C) - Calcite - CaCO3
00-046-1323
00-007-0042
00-031-0966
00-042-1340
(I) - Clinochlore-1MIIb - (Mg,Al,Fe)6(Si,Al)4O10(OH)8
(I) - Muscovite-3T - (K,Na)(Al,Mg,Fe)2(Si3.1Al0 .9)O10(OH)2
(*) - Orthoclase - KAlSi3O8
(*) - Pyrite - Fe S2
Figure 4.23: XRD plot of the mineralogical composition of the Greywacke samples. On the horizontal axis the
wavelength is given and on the vertical axis the linear intensity in counts per second is given.
Minerals that are found in all the Greywacke samples are:
• Quartz SiO2
• disordered Albite Na(Si3Al)O8
• Calcite CaCO3
• Clinochlore (Mg,Al,Fe)6(Si,Al)4O10(OH)8
• Muscovite (K,Na)(Al,Mg,Fe)2(Si3.1Al0.9)O10(OH)2
• Orthoclase KAlSi3O8
• Pyrite FeS2
The same mineralogical determination has been conducted for the Bestone samples. Figure
4.24 shows the results of the XRD analyses of the Bestone samples.
59
D. v. Lent
CuKa
Sample B
backgr.subtr. & y-shift
23okt07
Lin (Cps)
40 00
0
5
10
20
30
40
50
60
70
80
2-Theta - Scale
File: Bopper_15oct7.raw
File: Bsteen_15oct7.raw
File: Bsteenschoon_15oct7.raw
File: Bzaag_15oct7.raw
File: Bzand_15oct7.raw
00-046-1045 (*) - Quartz, syn - SiO2
00-010-0393 (*) - Albite, disordered - Na(Si3Al)O8
00-047-1743 (C) - Calcite - CaCO3
00-046-1323 (I) - Clinochlore-1MIIb - (Mg,Al,Fe)6(Si,Al)4O10(OH)8
00-007-0042 (I) - Muscovite-3T - (K,Na)(Al,Mg,Fe)2(Si3.1Al0.9)O10(OH)2
00-031-0966 (*) - Orthoclase - KAlSi3O8
Figure 4.24: XRD plot of the mineralogical composition of the Bestone samples. On the horizontal axis the
wavelength is given and on the vertical axis the linear intensity in counts per second is given.
Except from pyrite, the same minerals, as in the Greywacke samples, are found in the Bestone
samples. So the minerals that are found in all the Bestone samples are:
• Quartz SiO2
• disordered Albite Na(Si3Al)O8
• Calcite CaCO3
• Clinochlore (Mg,Al,Fe)6(Si,Al)4O10(OH)8
• Muscovite (K,Na)(Al,Mg,Fe)2(Si3.1Al0.9)O10(OH)2
• Orthoclase KAlSi3O8
4.5 Acidity
The pH, of the stone samples immersed in distilled water, is randomly measured over all the
stone samples on predefined moments. The averaged measured acidity per stone sample is
given in figure 4.25. All the measured acidities and the weights of the samples are given in
appendix B.
60
Acidity of the samples immersed in water
8,1
7,9
Gsawed
Gsand
Gsurface
Gstone
Gstonecl
pH
7,7
Bsawed
Bsand
Bsurface
Bstone
Bstonecl
7,5
7,3
7,1
6,9
0
2
4
6
8
10
12
14
16
Time [days]
Figure 4.25: Averaged acidity of the water immersed stones
Figure 4.25 shows that the pH of the water increases sharply during the first day. After day
one the pH remains almost constant. The non-boiled 4/8 aggregates (Gstone and Bstone)
show a slight decrease in pH after one day. Except from the non-boiled 4/8 aggregates
(Gstone and Bstone), all samples show the same pH on the predefined moments.
4.6 Surface energy
The measured contact angles of the reference liquids on the stone samples are stored on the
CR-ROM which is attached to
this report. The stone samples
are measured in random order.
First the contact angles of
distilled water are measured,
followed by n-hexane,
diiodomethane, formamide and
glycerol. It is tried to keep the
size of the droplets produced
on the surface of the stones as
constant as possible.
Figure 4.26: Example of computer
recording of water droplet on the
surface of sandblasted Bestone slice.
61
The surface energy components of the stones are given in table 4.10. Samples with at least
one not stable droplet of a reference liquid are indicated with (*MIN). A not stable droplet is
taken into account as 0°. This means that the surface energy of the surface might be larger
than calculated.
Table 4.10: Surface energy components of the different stone samples in [mJ/m²].
γsTOT Stdev γsLW Stdev
γsAB
Gsawed
Gsawedlab
Gsand*MIN
Gsandlab*MIN
Gstone*MIN
Gstonecl*MIN
Gsurface*MIN
Bsawed
Bsawedlab
Bsand*MIN
Bsandlab
Bstone*MIN
Bstonecl*MIN
Bsurface*MIN
55.53 2.72 48.82 0.75
6.71
55.52 4.11 49.11 0.62
6.41
61.34 3.54 50.32 0.27 11.02
63.71 0.42 50.53 0.09 13.18
66.98 N.A. 50.66 N.A. 16.32
67.04 N.A. 50.78 N.A. 16.26
66.83 N.A. 50.72 N.A. 16.11
55.92 6.03 46.55 1.88
9.37
56.34 7.92 46.10 2.74 10.24
61.24 3.05 48.46 1.04 12.78
60.05 3.80 48.49 0.22 11.56
66.58 N.A. 50.40 N.A. 16.18
66.93 N.A. 50.75 N.A. 16.18
66.72 N.A. 50.72 N.A. 16.00
*MIN
value is minimum value, at least one not stable droplet.
Stdev
γs+
Stdev
γs-
Stdev
1.97
3.72
3.28
0.36
N.A.
N.A.
N.A.
5.66
6.71
2.07
3.72
N.A.
N.A.
N.A.
0.27
0.23
0.62
0.95
1.53
1.52
1.48
0.43
0.53
0.87
0.68
1.49
1.50
1.46
0.13
0.27
0.44
0.06
N.A.
N.A.
N.A.
0.52
0.76
0.29
0.41
N.A.
N.A.
N.A.
41.22
45.53
49.01
45.57
43.54
43.47
43.84
50.73
49.08
46.88
48.98
43.94
43.64
43.84
5.62
2.35
3.66
0.55
N.A.
N.A.
N.A.
10.42
13.09
1.35
2.98
N.A.
N.A.
N.A.
To verify the previous calculated surface energy components, the contact angles of n-hexane
and formamide are back-calculated and compared to the measured contact angles. Samples
with at least one not stable droplet of n-hexane or formamide are indicated with (*MAX). A
not stable droplet is taken into account as 0°. This means that the real average of the contact
angles might be smaller than the calculated average of the contact angles. The results are
given in table 4.11.
Table 4.11: Contact angles on the different stone samples, measured and calculated in [°].
Gsawed
Gsawedlab
Gsand
Gsandlab
Gstone
Gstonecl
Gsurface
Bsawed
Bsawedlab
Bsand
Bsandlab
Bstone
Bstonecl
Bsurface
*MAX
62
contact
angle
n-hexane
measured
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
contact
angle
n-hexane
calculated
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
spreading
contact
angle
formamide
measured
7.50
11.50
7.32*MAX
3.87*MAX
spreading
spreading
spreading
13.12
13.62
9.96*MAX
8.19*MAX
spreading
spreading
spreading
contact
angle
formamide
calculated
17.88
15.31
spreading
spreading
spreading
spreading
spreading
10.77
9.98
spreading
spreading
spreading
spreading
spreading
value is maximum value, at least one not stable droplet. Spreading means no stable droplet at all.
4.7 Bitumen surface energy
The bitumen surface energy components are calculated using the results of contact angle
measurements done by means of the Sessile Drop Test. The measured contact angles of the
reference liquids on the bitumen samples are stored on the CR-ROM which is attached to this
report. The bitumen samples are measured in random order. First the contact angles of
distilled water are measured, followed by n-hexane, diiodomethane, formamide and finally
glycerol. It is tried to keep the size of the droplets produced on the surface of the bitumen as
constant as possible. The calculated surface energy components from the contact angles of
distilled water, diiodomethane and glycerol are given in table 4.12.
Table 4.12: Surface energy components of the bitumen samples using the Sessile Drop Method in [mJ/m²].
Sessile Drop Test
Bitumen sample 1
Bitumen sample 2
Bitumen sample 3
Bitumen*
*
γsTOT Stdev
35.77 N.A.
34.65 N.A.
35.22 N.A.
35.28 0.56
average of three bitumen samples.
γsLW Stdev γsAB Stdev γs+ Stdev γs35.59 N.A. 0.19 N.A. 0.01 N.A. 1.31
34.61 N.A. 0.04 N.A. 0.00 N.A. 0.65
35.06 N.A. 0.15 N.A. 0.01 N.A. 0.61
35.09
0.49
0.19
0.08
0.01
0.00
0.86
Stdev
N.A.
N.A.
N.A.
0.39
To verify the calculated surface energy components of the bitumen, the contact angles of nhexane and formamide are back-calculated and compared to the measured contact angles. The
results are given in table 4.13.
Table 4.13: Contact angles on the bitumen samples, measured and calculated in [°].
Bitumen sample 1
Bitumen sample 2
Bitumen sample 3
Bitumen*
*
contact
angle
n-hexane
measured
spreading
spreading
spreading
spreading
contact
contact
contact
angle
angle
angle
n-hexane formamide formamide
calculated measured calculated
spreading
74.81
68.53
spreading
77.20
71.60
spreading
77.80
70.28
spreading
76.60
69.78
average of three bitumen samples. Spreading means no stable droplet at all.
The surface energy components are also determined using the Wilhelmy Plate test. Five
bitumen samples are tested. Because it is recommended [10] to use the bitumen slides only
once and for only one reference liquid, 15 slides coated with bitumen are required. These 15
slides are selected from 20 produced slides, based on smoothness and thickness of the
bitumen film on the slides. The thicknesses of the bitumen coatings are determined by
measuring the thickness on five points using a digital calliper. The measured thicknesses are
stored on the CR-ROM which is attached to this report. First the contact angles of distilled
water are measured, followed by diiodomethane and glycerol. The computer computes the
contact angles by plotting the force against the immersion dept. For all the bitumen slides
immersed in water it is found that the plots (figure 4.27) have straight lines and the receding
forces (red line) are larger than the advancing forces (blue line).
63
Figure 4.27: Plot of bitumen sample 8
immersing in water.
For all the bitumen slides
immersed in diiodomethane
(figure 4.28) the plots are found
to have zigzag advancing lines
(blue line) and almost straight
receding lines (red line). It is
also found that the receding
forces are larger than the
advancing forces.
immersing in diiodomethane.
For all the bitumen slides
immersed in glycerol (figure
4.29) it is found that both the
advancing and the receding
lines are almost straight. It is
also found that the advancing
forces are almost the same as
the receding forces.
immersing in glycerol.
Table 4.14 gives all the surface energy components of the bitumen slides, as computed from
advancing contact angles.
64
Table 4.14: Surface energy components of the bitumen samples using the Wilhelmy Plate Test, from advancing
contact angles in [mJ/m²].
Wilhelmy Plate
Bitumen sample 4
Bitumen sample 5
Bitumen sample 6
Bitumen sample 7
Bitumen sample 8
Bitumen*
γsTOT Stdev
35.63 N.A.
31.02 N.A.
37.37 N.A.
37.03 N.A.
31.28 N.A.
γsLW Stdev
32.70 N.A.
29.38 N.A.
34.24 N.A.
34.10 N.A.
28.21 N.A.
γsAB
Stdev
N.A.
N.A.
N.A.
N.A.
N.A.
γs+
Stdev
N.A.
N.A.
N.A.
N.A.
N.A.
γs-
Stdev
N.A.
N.A.
N.A.
N.A.
N.A.
2.93
2.17
0.99
1.64
2.33
-0.29
3.13
1.90
1.29
2.93
1.97
1.09
3.07
2.48
0.95
34.38 3.10 31.73 2.77
2.65
0.62
2.17
0.24
0.81
0.63
*
average of five bitumen samples. In surface energy studies it is common to give the surface energy in two
decimals. With a, for this case, estimated error of 12% the correct notation would for instance be 34 ± 4.
To verify the calculated surface energy components of the bitumen, the contact angles of nhexane and formamide are back-calculated and compared to the average measured contact
angles measured with the Sessile Drop Method. The results are given in the table 4.15.
Bitumen sample 4
Bitumen sample 5
Bitumen sample 6
Bitumen sample 7
Bitumen sample 8
Bitumen*
contact
angle
n-hexane
measured∆
spreading
spreading
spreading
spreading
spreading
spreading
contact
contact
contact
angle
angle
angle
calculated measured∆ calculated
spreading
76.60
52.92
spreading
76.60
60.10
spreading
76.60
51.81
spreading
76.60
51.94
spreading
76.60
57.57
spreading
76.60
54.58
average of five bitumen samples. Spreading means no stable droplet at all. ∆Average contact angle by Sessile
drop Method.
*
In the same way as the surface energy components from advancing angles the surface energy
components from receding angles of the bitumen samples are computed. These results are
given in table 4.16.
Table 4.16: Surface energy components of the bitumen samples using the Wilhelmy Plate Test, from receding
contact angles in [mJ/m²].
Wilhelmy Plate
Bitumen sample 4
Bitumen sample 5
Bitumen sample 6
Bitumen sample 7
Bitumen sample 8
Bitumen*
γsTOT Stdev
44.51 N.A.
42.56 N.A.
46.30 N.A.
51.45 N.A.
41.08 N.A.
γsLW Stdev
40.63 N.A.
39.15 N.A.
40.44 N.A.
47.57 N.A.
40.29 N.A.
γsAB
Stdev
N.A.
N.A.
N.A.
N.A.
N.A.
γs+
Stdev
N.A.
N.A.
N.A.
N.A.
N.A.
γs-
Stdev
N.A.
N.A.
N.A.
N.A.
N.A.
3.88
-0.45
8.38
3.41
-0.35
8.31
5.86
-0.91
9.45
3.88
-0.47
8.00
0.79
-0.02
7.86
45.18 4.02 41.62 3.38
3.84
1.82 -0.44 0.32
8.40
0.63
*
average of five bitumen samples. In surface energy studies it is common to give the surface energy in two
decimals. With a, for this case, estimated error of 12% the correct notation would for instance be 45 ± 5.
The back-calculated contact angles of n-hexane and formamide are compared to the average
measured contact angles measured with the Sessile Drop Method. The results are given in
table 4.17.
65
Bitumen sample 4
Bitumen sample 5
Bitumen sample 6
Bitumen sample 7
Bitumen sample 8
Bitumen*
*
contact
angle
n-hexane
measured∆
spreading
spreading
spreading
spreading
spreading
spreading
contact
contact
contact
angle
angle
angle
calculated measured∆ calculated
spreading
76.60
58.44
spreading
76.60
60.16
spreading
76.60
58.03
spreading
76.60
50.76
spreading
76.60
59.15
spreading
76.60
57.30
∆
average of five bitumen samples. Spreading means no stable droplet at all. Average contact angle by Sessile
drop Method.
66
Chapter 5: Data analysis and discussion
5 Data analysis and discussion
In this chapter the results of the experiments are analysed and discussed.
5.1 Roughness
5.1.1 Macro surface roughness
It is found that the 4/8 aggregates of both the Greywacke and the Bestone (Gstone and
Bstone) have a higher measured roughness than the sawed slices (Gsawed and Bsawed). This
is an indication that the sawing results in a less rough surface on macro level. In the same way
it is found that the slices of both the Greywacke and the Bestone (Gsawed and Bsawed) have
less roughness than the same slices after sandblasting (Gsand and Bsand). So this sandblasting
results in an increase in roughness. This increased roughness is still less than the macro
surface roughness of the 4/8 aggregates (Gstone and Bstone).
It should be mentioned that not too much weight should be given to the values and the
differences between the treatments at this stage, because only one measurement per sample
has been conducted. The results show however that the macro roughness of the 4/8 aggregates
(Gstone and Bstone) is higher than the roughness of the slices (Gsawed and Bsawed). The
sandblasted slices (Gsand and Bsand) have a higher roughness than the sawed slices.
5.1.2 Meso surface roughness
The meso level roughness is determined at 20 and 50 times magnification. The measured
roughness of the 4/8 aggregates (Gstone and Bstone) is larger than the measured roughness of
the column samples. Here as well, the results indicate that sawing reduces the roughness
index in comparison to the 4/8 aggregates. Sandblasting the sawed columns increases the
roughness, but the roughness is still less than the measured roughness of the 4/8 aggregates.
At meso level this holds for Greywacke as well as for Bestone.
5.1.3 Micro surface roughness
At 100 times magnification the electron microscope pictures of the surface of the Greywacke
sandblasted columns (Gsandlab) and the sawed columns (Gsawedlab) show no clear visual
difference in roughness. Over the entire surface of the samples areas with lower and higher
roughness are found. However the number of areas with a relative higher roughness
dominates. It can be concluded that sandblasting of the Greywacke columns doesn’t result in
a visual difference in micro roughness. On the surface of the three 4/8 Greywacke aggregate
samples (Gstone), the areas with a relative low roughness are more present in comparison to
the Greywacke columns (Gsandlab and Gsawedlab).
Also for the Bestone columns (Bsandlab and Bsawedlab) it is difficult to differentiate visually
the micro roughness. All the Bestone columns show areas with a low roughness and areas
with a high roughness on their surfaces. So also here, no clear indication is found that
sandblasting of the columns results in a difference in the micro roughness. The visual
difference of the micro roughness between the Bestone 4/8 aggregates (Bstone) and the
columns (Bsandlab and Bsawedlab) is larger than the difference between Greywacke 4/8
67
aggregates (Gstone) and columns (Gsandlab and Gsawedlab). The Bestone 4/8 aggregates
(Bstone) show on their surface more areas with a relative low roughness compared to the
sandblasted (Bsandlab) and sawed columns (Bsawedlab). In some 1 mm² areas the number of
areas with a relative low roughness is dominant. An explanation for this can be that more dust
is present on the surface of the 4/8 aggregates (Bstone). Another possibility is that the 4/8
aggregates are more scraped and crushed onto each other, resulting in flat areas that are
visible at 100 times magnification.
The quantitative results of the Greywacke pictures give a more clear distinction between the
micro roughness of the differently treated samples. On the sandblasted Greywacke columns
(Gsandlab) more areas with fine texture are found than on the Greywacke sawed columns
(Gsawedlab). More coarse texture areas are found on the sawed columns than on the
sandblasted columns. This indicates that the sandblasting of the Greywacke columns results in
more areas of fine texture and thus micro roughness is added. Comparing the quantitative
results of the Greywacke columns to the Greywacke 4/8 aggregates results in the observation
that the 4/8 aggregates (Gstone) have less areas with fine texture and more areas with coarse
texture than both sawed and sandblasted column samples (Gsawedlab and Gsandlab). So in
contrast to the macro and meso roughness, the Greywacke sawed columns (Gsawedlab) have
more fine texture at micro level than the Greywacke 4/8 aggregates (Gstone). With
sandblasting additional fine texture is added to the Greywacke samples.
As mentioned above, a difference in micro roughness between the Bestone columns
(Bsawedlab and Bsandlab) and the Bestone 4/8 aggregates (Bstone) is detected by means of
the electron microscope pictures. This finding is contradicted by the quantitative analyses.
According to the quantitative analyses, the Bestone sawed columns (Bsawedlab) and the
Bestone 4/8 aggregates (Bstone) have an equal percentage of areas with fine texture. It is
found, similar to the Greywacke samples, that by sandblasting the sawed Bestone columns,
micro texture is added to the columns. The quantitative results show a shift from medium and
coarse texture at the Bestone sawed columns (Bsawedlab) to the fine texture at the Bestone
sandblasted columns (Bsandlab).
The differences found between the visual pictures and the quantitative results can however be
explained. For instance clear visible flat areas are found on the pictures (figure 5.1) of the
Bestone 4/8 aggregates (Bstone). Such areas are not found on the pictures of both the sawed
and sandblasted columns (Bsawedlab and Bsandlab). However these areas can be included in
very coarse and very fine texture in the
quantitative analyses. For instance when
these flat areas are viewed with a higher
magnification than 100 times, they might
still be flat. In this case the flat areas
should be included in the coarse areas.
However when the flat areas show
roughness at a higher magnification the
areas should be included in the fine
roughness areas.
Figure 5.1: Indicated areas on Bstone1 which are
fine or coarse textured in the quantitative analyses.
68
5.2 Specific surface area
At all magnifications the measured specific surface area of the 4/8 aggregates of both the
Greywacke and Bestone (Gstone and Bstone) is larger than that of the sandblasted and sawed
columns (Gsandlab, Gsawedlab, Bsandlab and Bsawedlab). At all magnifications the
sandblasted columns (Gsandlab and Bsandlab) have a larger specific surface area than the
sawed columns (Gsawedlab and Bsawedlab). This indicates that, for both the Greywacke and
the Bestone columns, sandblasting results in an increase of the specific surface area. This
increased specific surface area of the sandblasted columns is however found to be less than
the specific surface area of the 4/8 aggregates of both Greywacke and Bestone (Gstone and
Bstone), at 7, at 20 and at 50 times magnification.
It is important to mention that the measured specific surface area of all samples increases with
increasing magnification. An explanation for this could be that with increasing magnifications
one obtains a better representation of the real surface. The problem however is that at higher
magnifications the measurements become less representative, because a smaller area is
measured. It is not expected that the real values could be measured using whatever
microscope magnification, because of the unknown errors and the increasing values of the
measured specific surface area. Therefore other methods should be searched to measure the
specific surface area of stone samples.
5.3 Porosity
The Bestone 4/8 aggregates (Bstone) have a higher porosity than the sawed columns
(Bsawedlab). A possible explanation for this difference is the sawing and drilling process.
During sawing and drilling dust from this process might be pressed into the pores at the
surface of the stone samples. One could hypothesise that, during boiling in de-mineralised
water, not all the dust could be removed, because the dust was pressed too much and too deep
into the pores. However, the non-drilled and non-sawed samples (Bsurface) of the slices show
that this explanation is doubtful. The Bsurface samples also have a lower porosity, 2.01 %,
than the Bestone 4/8 aggregates (Bstone). Therefore it is more likely that the Bestone 4/8
aggregates have a different porosity compared to the Bestone 5 kg boulder, which is used as
the basis in the LOT research program for making the samples. This is supported by the
deviation in the measured porosity between the column samples, Bsand and Bsawed, the nondrilled and non-sawed Bestone samples, Bsurface, and the Bestone 4/8 aggregates (Bstone).
The three sample groups made from the Bestone 5 kg boulder show only a minor difference in
porosity in comparison to the Bestone 4/8 aggregates, porosities of 2.01 to 2.15 % and 2.70 %
respectively are measured.
The differences in the measured porosities of the Greywacke samples are larger. For instance
the sawed columns (Gsawedlab) have a porosity of 3.40 %. The sandblasted columns
(Gsandlab) have a porosity of 1.65 %. This means that sandblasting crushes more than half of
the pores. Significant errors in the measured porosity of the Greywacke samples are expected.
It is expected that the errors occur, because of the small sample sizes of the stones. The
Mercury Intrusion Porosimeter is mainly used for measuring the porosity of concrete, which
has in most cases a higher porosity than the measured stones. However the instrument should
be able to measure the porosity of stones if the accuracy of measurement is 0.1 µL.
69
5.4 Chemical- and Mineralogical composition
The ESEM chemical analysis of the surface of the samples doesn’t show a clear distinction
between the treated Greywacke samples and between the treated samples on one hand and the
Greywacke 4/8 aggregates on the other. However for Bestone, a difference in concentrated
individual elements on the surface was found between the 4/8 aggregates and the Bestone
columns (Bsawedlab and Bsandlab). No clear distinction was visible between the Bestone
sawed columns (Bsawedlab) and the Bestone sandblasted columns (Bsandlab). This indicates
that sandblasting has no effect on the presence of major chemical elements on the surface of
the Greywacke and the Bestone samples. However a difference in chemical elements between
the Bestone columns (Bsawedlab and Bsandlab) and the Bestone 4/8 aggregates (Bstone) is
found.
The result from this ESEM chemical analysis is just qualitative. By performing the analyses
over an area of at least 0.5 cm², a more reliable and predictable result was tried to achieve for
the stone with the same treatment and origin. It should be noticed that stones in general have a
very heterogeneous character and that the elements found on the surface are influenced by a
large number of uncontrollable external factors. In this particular case the ESEM chemical
analyses gave no evidence that sandblasting and sawing has influenced the concentrated
individual elements visible on the surface of the Greywacke samples. The difference in result
between the Bestone 4/8 aggregates (Bstone) and the Bestone treated columns (Bsawedlab
and Bsandlab) doesn’t directly have to do with the treatments. A possibility is that dust of
crushing at the quarry is present on the 4/8 aggregates. The possible presence of dust on the
4/8 aggregates however would affect the bitumen-aggregate adhesion, which is not taking into
account by using the columns.
The quantitative chemical analyses (table 4.9) of the Greywacke samples show the largest
difference between the Greywacke 4/8 aggregates samples (Gstone and Gstonecl) and the
Greywacke laboratory samples which are prepared from the 5 kg boulder (Gsawedlab and
Gsandlab). This difference is found in the CaO content. The CaO content of the 4/8
aggregates is 11.48 % (Gstone) and 14.57 % (Gstonecl), but for the Greywacke laboratory
samples, which are made from the 5 kg boulder this content, is 5.09 % (Gsurface), 5.11 %
(Gsawedlab) and 5.10 % (Gsandlab) respectively. However the silica content is almost
constant over the Greywacke samples. The explanation that due to sandblasting silica is more
abundant on the sandblasted columns is not likely. The contents of all oxides like, aluminium
oxide (Al2O3), potassium oxide (K2O), magnesium oxide (MgO), sodium oxide (Na2O) and
iron oxide (Fe3O2), show larger differences between Greywacke 4/8 aggregates (Gstone and
Gstonecl) samples and the Greywacke laboratory stones (Gsawedlab Gsandlab and Gsurface)
than between the 4/8 aggregates mutually and the laboratory stones mutually. Therefore it is
expected that not the treatments of the samples have caused a distinguishable effect on the
chemical content, but more the origin of the samples. It is known that the content per stone
type can differ, not only per quarry, but per location in a quarry as well.
The quantitative chemical analyses of the Bestone samples show the same trend as the
Greywacke samples (table 4.9). The difference in mass percentage of all oxides mentioned
before is smallest between the 4/8 aggregates (Bstone and Bstonecl) mutually and the
laboratory stones (Bsawedlab, Bsandlab and Bsurface) mutually. For instance the iron oxide
contents of the laboratory stones are found to be 2.29 % (Bsandlab), 2.67 % (Bsawedlab) and
2.60 % (Bsurface). The 4/8 aggregates showed to have an iron oxide content of 3.50 %
(Bstone) and 3.48 % (Bstonecl). Also in this case it is believed that not the treatments of the
70
samples have caused a distinguishable effect on the chemical content, but more the origin of
the samples and therefore the heterogeneity of the stone type. Important is the content of silica
of the sandblasted Bestone column (Bsandlab) and the sawed Bestone (Bsawedlab) column.
The explanation that due to sandblasting more silica is present on the sandblasted columns is
not likely, because the silica content of the sandblasted columns (53.19 %) is lower than the
silica content of the sawed columns (60.88%).
The XRD analyses showed that all Greywacke samples contain the same minerals (figure
4.23). The most important differences are found in the Greywacke plots at theta = 6, between
theta = 18 and 20 and between theta = 46 and 50. At theta = 6 one can observe that the two
4/8 aggregate samples (Gstone and Gstonecl) have a smaller peak in comparison to the other
samples. This peak indicate a difference in the presence of the mineral Clinochlore
(Mg,Al,Fe)6(Si,Al)4O10(OH)8. Between theta = 18 and 20 three small peaks are found.
However for both 4/8 aggregate samples these peaks are larger. These peaks indicate a
difference in the presence of the minerals Clinochlore and Muscovite
(K,Na)(Al,Mg,Fe)2(Si3.1Al0.9)O10(OH)2. The most significant difference in the plots is found
between theta 46 and 50. Here the 4/8 aggregates samples show two much larger peaks in
comparison to the laboratory stone samples. These peaks indicate the presence of Calcite
(CaCO3). The higher peaks for the 4/8 aggregates (Gstone and Gstonecl) point at a higher
Calcite content of the 4/8 aggregates. This is substantiated with the XRF analyses (table 4.9),
which also shows a higher content of CaO and CO2 of the 4/8 aggregate samples (Gstone and
Gstonecl) in comparison to the laboratory stone samples (Gsawedlab, Gsandlab and
Gsurface).
The minerals Quartz, disordered Albite, Calcite, Clinochlore, Muscovite and Orthoclase are
found in all investigated Bestone samples (figure 4.24). Only one major difference between
the plots of the Bestone samples is found. This difference is found in the XRD plots at theta =
6. For the Bestone 4/8 aggregate samples (Bstone and Bstonecl) a clear peak is visible.
However for the laboratory stone samples (Bsawedlab, Bsandlab and Bsurface) only one
small peak is visible, which is only a little larger than the background scatter. This peak refers
to the presence of mineral of Clinochlore (Mg,Al,Fe)6(Si,Al)4O10(OH)8 in the sample.
The results of the mineralogical analyses indicate that the difference between the 4/8
aggregates samples and the laboratory stones is larger than between the 4/8 aggregates
mutually and the laboratory stones mutually. Therefore it is expected that the treatments of
the samples have caused minor effect to the exposed mineralogical content in comparison to
the effect due to the origin of the samples and therefore the heterogeneity of the stone types.
71
5.5 Acidity
Figure 4.23 showed that the pH acidities of the differently treated samples are almost the
same. Only the non-boiled 4/8 aggregates (Gstone and Bstone) show a behaviour that differs
from the other samples. This lower acidity of the 4/8 aggregates can possibly be explained by
the presence of dust on the surface. This dust is possibly removed by boiling the 4/8
aggregates in de-mineralised water, because the boiled 4/8 aggregates (Gstonecl and
Bstonecl) show an acidity like all the other samples. It was expected that the 4/8 aggregates
would show a deviating acidity from the other samples, because of their expected larger
specific surface area. With a larger specific surface area more material is able to dissolve at a
higher rate. However the change of their acidity (from pH 7 to about pH 7.9/7.7) is lower than
of the other stone samples (from pH 7 to about pH 8.0). The rate, at which the pH changes, is
also lower for the non-boiled 4/8 aggregates (Gstone and Bstone) than the other stone samples
contradicting what was expected.
One can argue that this acidity test is not sensitive enough, because 8 of the 10 stone groups
have almost the same measured acidity. These groups all have a deviation in pH values of less
than 0.1. It is possible that, if the stones were immersed in a little less water, the measured pH
values would deviate much more and the acidity test would be more distinctive.
5.6 Surface energy
Table 4.8 shows that the sawed samples (Gsawed, Gsawedlab, Bsawed and Bsawedlab) have
the lowest surface energy. The difference in surface energy between the non-drilled samples
(Gsawed, Gsand, Bsawed and Bsand) and the drilled samples (Gsawedlab, Gsandlab,
Bsawedlab and Bsandlab) is much smaller (0.01 to 0.42 mJ/m²) than the difference between
sawed groups (Gsawed, Gsawedlab, Bsawed and Bsawedlab) and sandblasted (Gsand,
Gsandlab, Bsand and Bsandlab) (3.71 to 8.19 mJ/m²). Comparisons between the other
samples are difficult, because the other samples have non-stable droplets of the reference
liquids.
The results show that for all stone samples it was back-calculated that n-hexane would not
form a stable droplet on the surface. All measurements show that this is correct. However the
verification with formamide shows some difference between the back-calculated and the
measured contact angles. In other researches [4,10] the same deviation of formamide is found.
More details are given in the contact angle verification of bitumen in the next paragraph.
The contact angle data stored on the CD-ROM shows non-zero measurements of droplet
contact angles on the surface of the 4/8 aggregates (Gstone and Bstone). The question is
however whether or not these contact angles are a real equilibrium between interfacial tension
of the reference liquid, the vapour and the solid as described in equation A4. A possible other
explanation is the influence of the roughness (figure 5.2). The droplet of the reference liquid
spreads over the surface, because the total surface energy of the liquid is smaller than the total
surface energy of the solid.
72
Figure 5.2: First spreading of the droplet (left) then the droplet gets stuck in the roughness (right).
During spreading the droplet gets trapped between two higher areas in the roughness. It seems
that a stable droplet is formed on the basis of Young’s equation (A4), but in reality an
additional component of the gravitation is included. This causes an underestimation of the
surface energy of the stone.
5.7 Bitumen surface energy
The total average surface energy of the bitumen calculated from the contact angles measured
by means of the sessile drop method and the total average surface energy of the bitumen
calculated from the advancing contact angles measured by means of the Wilhelmy plate
method deviate (< 3%) less than the estimated maximum error in the Wilhelmy plate method
(12%). However the receding angles from the Wilhelmy plate method deviate much more.
The difference found between the advancing and receding angles can be ascribed to wetting
and dewetting (see paragraph A.4.1). The difference between the sessile drop method and the
Wilhelmy plate method can be ascribed to the fact that the sessile drop method measures
static contact angles and the Wilhelmy plate method measures dynamic contact angles.
However in this case some points of attention exists. Major point is that the dimensions of the
bitumen plate samples in this research could not be measured accurately using the calliper.
Therefore large measuring errors (12%) are estimated.
Another important point of attention is found in the figures 4.25 to 4.27. Correct
measurements should show straight lines for plots giving the force against the immersion
depth. The measurements with the reference liquids water (figure 4.25) and glycerol (figure
4.27) could therefore be seen as correct measurements. However the measurements of
diiodomethane show a clear zigzag pattern (figure 4.26). This phenomenon is known in
literature as ‘slip-stick’ behaviour. Slip-stick is caused by roughness on the measured sample,
by chemical interaction between measured sample and reference liquid or by dissolution of
the measured sample in the reference liquid. It is unlikely that the roughness of the bitumen
samples causes the slip-stick behaviour, because the plots of the measurements of water and
glycerol have straight lines. It is expected that either dissolution of the bitumen plate samples
in diiodomethane or some kind of chemical reaction between the bitumen and diiodomethane
has taken place. The slip-stick phenomenon has an effect on the measured surface energy of
the bitumen and therefore more measurement uncertainties are present in the surface energy
components of the bitumen. The computer calculates the surface energy components of the
bitumen by measuring the change in force when the bitumen is entering the reference liquid.
In the case of slip-stick behaviour the change in force is not constant over the immersion
depth. To get a constant change in force, the computer performs a regression fit.
From the experimental results it is clear that n-hexane does not form a stable droplet on the
surface as calculated in the back-calculation. The bitumen has a high non-polar surface energy
component for bitumen (>18,4 mJ/m²). However the verification with formamide shows some
difference between the back-calculated and the measured contact angles of formamide on the
bitumen slices. The difference is smaller for the contact angles measured with the sessile drop
method and larger for the contact angles measured with the Wilhelmy plate method. Because
73
γ lTOT·cos(θ )
the sessile drop method gives static contact angles and the Wilhelmy plate method gives
dynamic contact angles, it has limited use to compare the measured static angles to the backcalculated dynamic contact angles. This leaves the difference between back-calculated and the
measured contact angles of formamide by the sessile drop method. In other researches [4,10]
this same deviation of formamide is known. Kwok and Neumann (2003) developed a method
to verify the deviation of solely formamide in relation to the used other reference liquids. In
this method the total surface
energy of the reference liquid
Bitumen sample 1
is plotted against this surface
energy multiplied with the
40
diiodo
measured contact angles. The
m ethane
plot should show a straight
30
relation for the different
20
reference liquids [9]. This
form am ide
glycerol
method has been used for the
10
three bitumen samples used
in the sessile drop method.
0
w ater
The results are given in
45
55
65
75
-10
figures 5.3 to 5.5.
Total surface energy reference liquid [mJ/m²]
Figure 5.3: Kwok and Neuman plot
of bitumen sample 1.
Figures 5.3 to 5.5 show that also in this research the contact angles of the three reference
liquids water, diiodomethane and glycerol are almost on a straight line in the plots for all the
three bitumen samples.
Figure 5.4: Kwok and Neuman
plot of bitumen sample 2.
Bitumen sample 2
40
diiodo
m ethane
γ lTOT·cos(θ )
30
20
form am ide
10
glycerol
0
-10
w ater
45
55
65
75
74
Bitumen sample 3
40
30
γ lTOT·cos(θ )
However formamide shows a
clear deviation in the plots. It
is interesting that other
researchers also find this
deviation of formamide by
bitumen measurements [4].
This behaviour of formamide
is possibly caused by a
chemical interaction between
bitumen and formamide.
Another explanation is that
the bitumen dissolves in the
formamide.
Figure 5.5: Kwok and Neuman plot
of bitumen sample 3.
diiodo
m ethane
20
form am ide
10
glycerol
0
-10 45
55
65
75
w ater
-20
With the measured surface energy of the bitumen and the stone samples the fundamental work
of adhesion between them can be calculated. For this calculation it is decided to use the
average surface energy of the bitumen measured by the sessile drop method, because for the
sessile drop method the estimated measurement error in this research is the smallest. The
fundamental work of adhesion between the bitumen and the stone samples is calculated using
equation A20. The results are given in table 5.1.
Table 5.1: Calculated fundamental work of adhesion between bitumen and stone samples.
Greywacke sample
Gstonecl*MIN
Gsurface*MIN
Gstone*MIN
Gsandlab*MIN
Gsand*MIN
Gsawedlab
Gsawed
*MIN
Wa [mJ/m²]
88.0
88.0
87.9
87.4
86.9
85.3
85.0
Bestone sample
Bstonecl*MIN
Bsurface*MIN
Bstone*MIN
Bsand*MIN
Bsandlab
Bsawed
Bsawedlab
Wa [mJ/m²]
88.0
87.9
87.7
85.6
85.4
83.5
83.2
value is minimum value, at least one not stable droplet.
The contact angle measurements of the top five Greywacke samples and top three Bestone
samples are dominated by non-stable droplets. It is expected that the non-stable droplets result
in an underestimation of surface energy components of these samples. Therefore is it expected
that the fundamental work of adhesion for these samples is larger. The effect of the aggregate
treatments on the fundamental work of adhesion is uncertain.
The method of calculating the fundamental work of adhesion underestimates the fundamental
work of adhesion between bitumen and aggregate. The surface energy of the bitumen is
measured at 20°C. At 20°C the bitumen has a relative high viscosity. However in a mixing
plant of a contractor the aggregates are coated with bitumen at 150°C. At this temperature the
bitumen has a lower viscosity and therefore molecules are more able to aim and migrate
towards the surface of the aggregate. Bitumen molecules, which cause a stronger adhesive
bond, are more attracted to the aggregate surface than bitumen molecules which cause a lower
adhesive bond. This is not taken into account by this calculated fundamental work of
adhesion.
75
Van Oss, Good and Chaudhury stated correctly that their proposed ratio has no effect on the
calculated fundamental work of adhesion, in theory. Siliceous aggregates used in road
engineering are expected to be large mono-polar basic, irrespective of the ratio between the
Lewis acid and the Lewis base component of water. The estimated number of hydroxyl
groups on the surface on crystalline silica is about four to five OH groups per nm² [2,4].
Bitumen in general is expected to show a small mono-polar Lewis acidic character. The
fundamental work of adhesion is partly calculated by multiplying the Lewis base component
of the stones with the Lewis acid component of the bitumen (see equation A20) and therefore
two non-zero components are multiplied resulting in a large Lewis polar part of the
fundamental work of adhesion. However with the ratio between Lewis acid and Lewis base
component of water of 1:1, the bitumen are measured to be mono-polar basic in the sessile
drop method. Therefore the Lewis base component of the stone is multiplied by the almost
zero Lewis acid component of the bitumen and visa versa resulting in a small contribution of
the polar Lewis interaction to the fundamental work of adhesion. The problem is that the
almost zero components of the siliceous aggregates and the bitumen are possibly dominated
by errors and could therefore as well be zero. Then the calculated contribution of the Lewis
interaction to the fundamental work of adhesion between the aggregate and the bitumen is
zero. It is expected among chemists that water has a higher Lewis acid component than a
Lewis base component, under standard conditions. Therefore the measured values of the
bitumen would shift more to the acid component, resulting in a decreasing chance of errors by
the estimation of the adhesion between especially bitumen and siliceous aggregates.
76
Chapter 6: Conclusions and recommendations
6 Conclusions and recommendations
In this chapter the conclusions are given, followed by some recommendations for further
research.
6.1 Conclusions
6.1.1 Roughness
6.1.1.1 Macro surface roughness
This study showed a difference in roughness between the samples used for mechanical testing
in the LOT research program and aggregates used by contractors for road construction. At
macro level a distinct difference is found. The 4/8 aggregates (Gstone and Bstone) have a
higher roughness than the sandblasted samples (Gsand and Bsand). At macro level the results
show that sawing reduces the roughness. With sandblasting of the sawed surface the
roughness is increased, but this is still less than the macro surface roughness of the 4/8
aggregates. This is found to be true for both tested stone types, Greywacke and Bestone.
6.1.1.2 Meso surface roughness
At meso level the same is found for the roughness determined at 20 and 50 times
magnification. The measured roughness of the 4/8 aggregates (Gstone and Bstone) is higher
than the measured roughness of the column samples (Gsawedlab, Gsandlab, Bsawedlab and
Bsandlab). The results indicate that sawing reduces the roughness while sandblasting the
columns increases the roughness. This increased roughness is still less than the roughness of
the 4/8 aggregates. This holds for Greywacke as well as Bestone.
6.1.1.3 Micro surface roughness
At micro level no clear distinction was found by visual observation for the roughness between
the Greywacke stones of different origin and treatment. The quantitative results show
however a difference. Sandblasting the Greywacke columns increases the areas with fine
texture compared to the results when the columns are sawed. However more areas with fine
texture are found on the surface of the sawed columns (Gsawedlab and Bsawedlab) than on
the 4/8 aggregates (Gstone and Bstone). For the Bestone samples a clear visual difference was
found between the 4/8 aggregates (Bstone) on one side and the sawed columns and
sandblasted columns (Bsawedlab and Bsandlab) on the other side. The 4/8 aggregates show
areas with low surface roughness, possibly caused by dust on the surface, which however
would also affect the adhesion. The quantitative results show that due to sandblasting fine
texture is added. This conclusion was developed by comparing the results obtained on the
sawed columns (Bsawedlab) with the results obtained on the sandblasted columns (Bsandlab).
However this fine texture is less present on the surface of the 4/8 aggregates (Bstone),
resulting in possible different adhesion behaviour.
77
6.1.2 Specific surface area
At all magnification levels the specific surface area of the 4/8 aggregates of both Greywacke
and Bestone (Gstone and Bstone) is larger than the specific surface area of the column
samples (Gsawedlab, Gsandlab, Bsawedlab and Bsandlab). Sandblasting increases the
specific surface area of the sawed column samples (Gsawedlab and Bsawedlab).
6.1.3 Porosity
In this study a difference is found between the porosity of the Bestone 4/8 aggregates (Bstone
and Bstonecl) and the stone samples made from the 5 kg boulder (Bsawedlab, Bsandlab and
Bsurface). The Bestone 4/8 aggregates have a higher porosity. However no indication is
found that a treatment, like sawing and sandblasting has a significant effect on the porosity of
the stones.
6.1.4 Chemical and Mineralogical composition
No indication is found that boiling in de-mineralised water, sawing and sandblasting has a
significant effect on the presence of the chemical elements and the minerals of the stones.
6.1.5 Acidity
The Arrhenius acidity tests have shown that boiling could have an effect on the adhesion
characteristics of stones. The non-boiled, and therefore probably dustier, 4/8 aggregates
(Bstone) have a lower measured Arrhenius acidity than the boiled 4/8 aggregates (Bstonecl).
The lower pH value is a disadvantage when the used bitumen is more acidic. The higher
Arrhenius acidity of the laboratory stones (Gsawedlab, Gsandlab, Gsurface, Bsawedlab,
Bsandlab and Bsurface) indicates that they have more Arrhenius basic material for chemical
interaction with the bitumen resulting in a higher adhesive bond.
6.1.6 Surface energy
The surface energy measurements of the samples indicate that sandblasting increases the
surface energy of the stones. Furthermore it is found that the effect of column drilling has a
much smaller effect or even no effect on surface energy of the stones. However because of the
imperfection of the used sessile drop method on stones, an accurate surface energy
measurement could not be conducted for every sample. Therefore the effect of treatments, like
sawing and the difference between laboratory stones and 4/8 aggregates isn’t found.
Exactly the same holds for the calculated fundamental work of adhesion. The fundamental
work of adhesion between the bitumen and the stone columns increases when the columns are
sandblasted. It is found that the effect of column drilling has a much smaller effect or even no
effect on the calculated fundamental work of adhesion. Because the surface energy of the
other stone samples could not be measured, the effects of the other treatments could not be
determined.
78
6.1.7 Overall conclusion
This report shows that some surface treatments have an effect on the stone adhesion
properties. The effects are summarised in tables 6.1 and 6.2. For instance sandblasting
increases the roughness and the specific surface area of the sawed samples. The increased
roughness and specific surface area after sandblasting are however smaller than the roughness
and specific surface area of the 4/8 aggregates (table 6.1 and 6.2). At 100 times magnification
the roughness of the sandblasted samples is larger than the roughness of the Bestone 4/8
aggregates (table 6.2). It is not known if this micro roughness has any (significant) effect on
the adhesion of the stone samples.
Table 6.1: Relative comparisons of properties of Greywacke aggregate samples treated in different ways to the
properties of the untreated Greywacke 4/8 aggregate.
Sample Gsawed Gsawedlab
Property
Macro roughness
Meso roughness
Micro roughness
≈
(ESEM)
Micro texture
≈
SSA
pH
+
Porosity
+
Chemical composition
≈
(ESEM)
≠
(XRF)
Mineralogical
≈
composition (XRD)
Surface energy
-
Gsand
Gsandlab Gsurface
Gstonecl
≈
+
+
≈
?
+
+
+
≠
≠
≈
≈
≈
=
?
?
?
- means property is smaller than property of the 4/8 aggregates (Gstone). = means property is the same as the
property of the 4/8 aggregates (Gstone). + means property is larger than the property of the 4/8 aggregates
(Gstone). ≈ means property is more or less the same as the property of the 4/8 aggregates (Gstone). ≠ means
property is different than the property of the 4/8 aggregates (Gstone). ? means property is unknown.
79
Table 6.2: Relative comparisons of properties of Bestone aggregate samples treated in different ways to the
properties of the untreated Bestone 4/8 aggregate.
Sample Bsawed
Property
Macro roughness
Meso roughness
Micro roughness
(ESEM)
Micro texture
SSA
pH
Porosity
(ESEM)
(XRF)
Mineralogical
composition (XRD)
Surface energy
-
Bsawedlab
Bsand
Bsandlab
Bsurface
Bstonecl
+
-
+
+
+
≈
+
≠
+
+
≠
≠
≈/ ≠
≈/ ≠
=
≈
≈
≈
=
-
?
?
-
-/?
- means property is smaller than property of the 4/8 aggregates (Bstone). = means property is the same as the
property of the 4/8 aggregates (Bstone). + means property is larger than the property of the 4/8 aggregates
(Bstone). ≈ means property is more or less the same as the property of the 4/8 aggregates (Bstone). ≠ means
property is different than the property of the 4/8 aggregates (Bstone). ? means property is unknown.
The chemical compositions of the Greywacke 4/8 aggregates (Gstone and Gstonecl) are
almost the same (table 6.1). The chemical compositions of the samples prepared from the 5 kg
boulder (Gsawedlab, Gsandlab and Gsurface) are almost the same as well (table 6.1).
However the chemical compositions of the Greywacke 4/8 aggregates (Gstone and Gstonecl)
are different from the chemical compositions of the samples prepared from the 5 kg boulder
(Gsawedlab, Gsandlab and Gsurface). The same holds for the Bestone samples (table 6.2).
In general aggregates are known to be heterogeneous. The adhesion characteristics of single
aggregates can be determined. However the adhesion characteristics of aggregates made from
one stone type might show a lot of variation. This variation in adhesion characteristics of
aggregates made from one stone type might be more important than the change in aggregate
characteristics found in this study.
In a similar way external parameters might be dominating the adhesion behaviour. In
mechanical tests as used in the LOT project, the effect on the adhesion behaviour of for
instance the selected bitumen film thickness might be more important than the effect of the
aggregate characteristics, for instance the micro roughness.
Because it isn’t possible to quantify the effects of any of the surface treatments, it is
concluded that more research is necessary to determine the effects on the adhesion
characterisation of the treatments used in the LOT research program.
80
6.2 Recommendations
To find the effects of the other treatments on the surface energy of the stones it is
recommended to use other types of surface energy instruments, e.g. tensiometer, microcalori
meter, universal sorption device.
In the LOT research program it was decided to use sandblasted columns in the mechanical
tests, because it was assumed that sandblasting improved the reproducibility. However the
tables 6.3 to 6.6 show that the standard deviation in the results of the sawed columns
(Gsawedlab and Bsawedlab) is smaller than in the results of the sandblasted columns
(Gsandlab and Bsandlab). This could however be a coincidence. It is recommended to
conduct more measurements to determine if the surface of the sawed columns is more
reproducible than the surface of the sandblasted columns.
LSCM (20X)
Gsawedlab
Gsandlab
Bsawedlab
Bsandlab
n
3
3
3
3
Pa [µm]
3.79
4.99
5.21
6.63
Stdev
0.59
1.01
0.75
1.50
Stdev/ Pa
0.156
0.202
0.144
0.226
Pq [µm]
5.14
6.85
7.26
8.57
Stdev
0.81
1.06
1.02
1.98
Stdev/ Pq
0.158
0.155
0.140
0.231
Stdev
0.25
0.74
0.71
2.81
Stdev/ Pq
0.050
0.106
0.114
0.293
LSCM (50X)
Gsawedlab
Gsandlab
Bsawedlab
Bsandlab
n
3
3
3
3
Pa [µm]
3.81
5.15
4.58
7.45
Stdev
0.21
0.77
0.52
2.56
Stdev/ Pa
0.055
0.150
0.114
0.344
Pq [µm]
5.02
7.00
6.25
9.60
LSCM (20X)
Gsawedlab
Gsandlab
Bsawedlab
Bsandlab
SSA [µm²/µm²]
1.70
1.86
2.09
2.26
Stdev
0.04
0.19
0.35
0.30
Stdev/ SSA
0.024
0.102
0.167
0.133
LSCM (50X)
Gsawedlab
Gsandlab
Bsawedlab
Bsandlab
SSA [µm²/µm²]
3.03
3.41
3.11
3.51
Stdev
0.08
0.24
0.06
0.29
Stdev/ SSA
0.026
0.070
0.019
0.083
It is recommended to determine which type of roughness (macro, meso or micro level) has the
biggest effect on adhesion. The same is recommended for the specific surface area. It would
furthermore be interesting if a relation could be found between the chemical and
mineralogical composition of the stones and the adhesive bond strength.
In general it is also recommended to do more research in the field of surface energy, the
surface energy theories and their application in road engineering. Finally it is recommended to
81
perform more research into the reliability of the assessment of the Lewis acid and Lewis base
components as well as the ratio between those parameters.
82
Literature
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[2]
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[4]
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[5]
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[7]
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[8]
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[9]
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[10]
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[11]
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84
Appendix A: Surface energy
In this chapter the results are given of a literature review on surface free energy.
A.1 Intermolecular forces
In 1873 Johannes Diderik van der Waals proposed the existence of electrodynamic forces
interacting between molecules. Continuing on this work Keesom described a type of these
forces acting between permanent dipole molecules. A molecule is dipole charged when atoms
with different electronegativity are bonded. The atom with the higher electronegativity tends
to attract the shared electrons more, causing a delta negative charge for this atom and a delta
positive charge for the other less electronegative atom. A second requirement is that the
spatial structure of the molecule doesn’t neutralise the effects of the dipole charge, i.e. the
centre of the negative charge doesn’t coincide with the centre of the positive charge. Between
molecules opposite charged ends attract. These Keesom dipole-dipole interactions are called
orientation forces.
Debye proposed an electrodynamic force between a dipole molecule and a non-dipole
molecule. The end of a charged dipole molecule causes an opposite interaction between the
nuclei and the electron clouds in a non-polar molecule, resulting in a polarisation. The nonpolar molecule is induced to behave as a dipole. These Debye dipole-induced dipole
interactions are called induction forces.
Electrodynamic forces between non-polar molecules were described by London. London
stated that, because electrons are able to move freely through the electron clouds of atoms in a
molecule, a temporarily dipole resulting in electrodynamic forces might occur when electrons
are coincidentally more on one side of the molecule. These instantaneous dipole molecules
interact with other molecules. These London forces are called dispersion forces.
Another intermolecular bond occurs when a nucleiphilic atom in a molecule, called the donor,
has at least one unshared pair of electrons. The atom “feels” an abundance of electrons. The
atom in the molecule interacts with an electrophilic atom in another molecule, called the
acceptor, by sharing an unshared pair of electrons. This type of interaction resembles
characteristics of covalent and ionic bonding, but isn’t interacting between atoms/ions but
between molecules. A special example of this interaction is called hydrogen bonding. For
instance in a water molecule, the oxygen atom has a much higher electronegativity than one
of the two hydrogen atoms. Together with the asymmetry, because the angle between the HO-H atoms is about 104.5°, water molecules are polar. The oxygen atom attracts the shared
electrons more than one of the two hydrogen atoms and becomes in this way delta negatively
charged, the hydrogen atoms become delta positive. An oxygen atom has six electrons in its
outer electron orbitals. A noble gas has a noble gas configuration of eight electrons in its outer
orbitals. Non noble gas atoms, like oxygen, try to copy this noble gas configuration, known as
the octet rule, by producing shared electrons with other atoms forming molecules. That is why
an oxygen atom has two covalent bonds, one covalent bond per hydrogen atom. But a water
molecule is as stated before a very strong dipole, therefore the shared electrons are more
‘possessed’ by the oxygen atom. In this way the oxygen atom in a water molecule becomes
nucleiphilic (Lewis base). Because it has too many electrons, it wants to interact with a
nucleon. The hydrogen atoms in the same molecule on their turn behave electrophilic (Lewis
acid), and want to search for electrons. Because this phenomenon occurs in all water
85
molecules, the oxygen atoms interact by electrostaticly sharing electrons with hydrogen atoms
from other molecules. It should be said again that this electron sharing between two
molecules is not covalent and is much weaker compared to covalent atomic bonding.
Figure A.1: Lewis structures of: a single oxygen atom, a single water molecule and water molecules interacting
by hydrogen bonding. [van Lent 2007]
Lewis proposed this intermolecular bonding by electron donor and acceptor molecules. He
extended his work by including hydrogen bonding. Lewis’ overall work was supported by
introducing so called Lewis structures for visualising the possible donors and acceptors of
electrons. In figure A.1 an example of Lewis structures is given.
A.2 Relation between intermolecular forces and surface free energy
In the bulk of a material the molecules are surrounded with other molecules. This results in
intermolecular forces described in the previous paragraph. The molecules direct at the surface
on the other hand, are at least on one side not surrounded with other molecules. Therefore the
molecules direct at the surface have free intermolecular forces to interact with passing
molecules. For liquids it is generally accepted that the intermolecular forces in the bulk and
the free intermolecular forces at the surface are equal, only for solids this is not the case.
When a bulk is split into two pieces, two new surfaces are created. This results in a change of
the Gibbs free energy of the system. Because two new surfaces are created the total change of
the Gibbs free energy is given as:
where ∆G11
γ
∆G11 = 2 ⋅ γ 1
= change of Gibbs free energy per unit area
= surface free energy
(A1)
Although surface free energy is the correct term in thermodynamics for the energy acting
between the two surfaces, surface energy is sometimes referred to this as well. In this
report surface free energy and surface energy will be used interchangeable and both terms
will refer to the same thermodynamic characteristic. Surface free energy is given in the unit
of [J/m²] or [N/m¹].
86
Under ideal circumstances, like for instance no energy dissipation in the material, the total
work of cohesion, so the total work that is needed to make two new surfaces from the bulk, is
equal in absolute value to the change in Gibbs free energy:
c
where W
∆G11
W c = − ∆G11c
= work of cohesion
(A2)
This relation was the basis for the relation for the work of adhesion of two different materials.
Dupré postulated this relation for the work of adhesion under ideal circumstances, like for
instance no energy dissipation in the material, so the total work that is needed to split the two
materials from each other as:
a
where W
∆G12
γ1
γ2
γ12
W a = − ∆G12a = γ 1 + γ 2 − γ 12
= work of adhesion
= surface free energy of material 1
= surface free energy of material 2
= interfacial energy between materials 1 and 2
(A3)
Young proposed a relationship between contact
angles of a liquid on an ideal flat solid and the
surface free energies of both the liquid and the
solid (figure A.2).
Figure A.2: The three-phase boundary of a liquid drop on a
solid surface in vapour. [Hefer and Little 2005]
This relation, know as Young’s equation, is given as:
γ sv = γ sl + γ lv ⋅ cos θ sl
where γsv
γsl
γlv
θsl
(A4)
= interfacial energy between solid and vapour
= interfacial energy between solid and liquid
= interfacial energy between liquid and vapour
= contact angle between solid and liquid
The relationship between the surface free energy of a solid in vacuum and the surface free
energy in vapour can be written as:
γ sv = γ s − π esv
where γsv
γs
πesv
(A5)
= interfacial energy between solid and vapour
= surface free energy of solid
= equilibrium spreading pressure of solid in the saturated vapour of the
solid
The same can be done for the surface free energy of a liquid in vacuum:
87
γ lv = γ l − π elv
where γlv
γl
πelv
(A6)
= surface free energy of liquid
= equilibrium spreading pressure of liquid in the saturated vapour of the
liquid
Rewriting equation (A4) and substituting (A5) and (A6) gives:
( γ l − π elv ) + ( γ l − π elv ) ⋅ ( cos θ sl ) = γ s − π esv + γ l − π elv − γ sl
where γl
πelv
θsl
γs
πesv
γsl
(A7)
= equilibrium spreading pressure of liquid in the saturated vapour of
liquid
= equilibrium spreading pressure of solid in the saturated vapour of
liquid
In surface free energy measurements by means of contact angle measurements, for example
the sessile drop method, it is common to neglect the contributions of the spreading pressure,
because these contributions are thought to be magnitudes of orders smaller than the surface
free energies. This results in the next equation:
γ l ⋅ (1 + cos θ sl ) = γ s + γ l − γ sl
where γl
θsl
γs
γsl
(A8)
The relation (A3) can be rewritten for a liquid-solid system as:
a
where W
γs
γl
γsl
W a = γ s + γ l − γ sl
= work of adhesion
(A9)
So from equations (A7), (A8) and (A9) it is clear that the work of adhesion between liquid
and solid equals the surface free energy of the liquid multiplied by the contact angles between
liquid and solid. This is known as the Young-Dupré equation:
a
where W
∆G12
γlv
γl
θsl
88
W a = −∆G12a = γ lv ⋅ (1 + cos θ sl ) ≈ γ l ⋅ (1 + cos θ sl )
= work of adhesion
(A10)
A.3 Surface free energy theories
Many different theories concerning the composition of the surface energy components and the
derivation of the work of adhesion have been proposed. In this paragraph some important
theories are described.
A.3.1 Fowkes’ theory
Fowkes proposed that the surface free energy is a superposition, e.g. the total surface free
energy of a material is the sum of all the intermolecular forces:
γ = γ d + γ o + γ i + γ ab + γ h
where γ
γd
γo
γi
γab
γh
(A11)
= total surface free energy
= energy of London dispersion forces
= energy of Keesom orientation forces
= energy of Debye induction forces
= energy of Lewis acid-base bond forces
= energy of hydrogen bond forces
Fowkes stated that the energy from dispersion and induction forces could be combined to one
non-polar component. Furthermore one polar component was introduced to combine the
energies of the other intermolecular forces.
γ = γ n +γ
where γ
γn
γp
p
(A12)
= total surface free energy
= energy of non-polar forces
= energy of polar forces
Fowkes showed that the work of adhesion between two materials of the non-polar forces is
equal to the square root of the product of the non-polar energies of both materials:
where Wa
γln
γsn
n
Wan = 2 γ ln ⋅ γ sn
= Work of adhesion of non-polar energy components
= energy of non-polar forces of liquid
= energy of non-polar forces of solid
(A13)
Fowkes stated that the non-polar surface energy component of a solid can be measured by
making a droplet with one known non-polar liquid on the solid’s surface and using the
following equation:
γ l (1 + cos θ sl ) = 2 γ ln ⋅ γ sn
where γl
θsl
γln
γsn
(A14)
89
A.3.2 Extended Fowkes’ harmonic mean
Continuing on this work the polar surface energy components were added by Owens and
Wendt in equation (A14) to become:
γ l (1 + cos θ sl ) = 2
where γl
θsl
γln
γsn
γlp
γsp
(
γ ln ⋅ γ sn + γ lp ⋅ γ sp
)
(A15)
= total surface free energy of liquid
= energy of polar forces of liquid
= energy of polar forces of solid
Both the non-polar and polar components of the surface free energy of a solid can be
measured by using two reference liquids, preferably one non-polar and one polar, for making
droplets on the surface of the solid.
A.3.3 Acid-Base theory
Also known as the van Oss-Good-Chaudhury theory, the acid-base theory uses the harmonic
mean. Van Oss, Good and Chaudhury stated that the true polar surface energy components are
attractive if charged opposite. Chaudhury proposed that the Keesom orientation forces are
additives of the Debye and London forces. So the Keesom orientation forces were combined
with the Debye induction and the London dispersion forces to form the non-polar Lifshitz-van
der Waals component.
γ LW = γ d + γ o + γ i
where γ
γd
γo
γi
(A16)
= surface free energy of non-polar Lifshitz-van der Waals interactions
= energy of London dispersion forces
= energy of Keesom orientation forces
= energy of Debye induction forces
The true polar component was subscribed to the Lewis electron donor and acceptor
interactions, hydrogen bonds included. To include the electron donating and electron
accepting attraction the polar component was decomposed in an acid and a base component.
Van Oss, Good and Chaudhury used the harmonic mean to combine the acid and base
component to result in the total polar acid-base component.
γ
where γ
γγ+
90
= 2 γ − ⋅γ +
= surface free energy of polar acid-base interactions
= contribution of Lewis base, electron donating
= contribution of Lewis acid, electron accepting
AB
(A17)
With the superposition of the Lifshitz-van der Waals and the acid-base component of the
liquid and the solid the following relation between contact angle and surface energy
components is found.
γ l (1 + cos θ sl ) = 2
where γl
θsl
γlLW
γsLW
γlγs+
γl+
γs-
(
γ lLW ⋅ γ sLW + γ l− ⋅ γ s+ + γ l+ ⋅ γ s−
)
(A18)
= total surface free energy of liquid
= free energy of Lifshitz-van der Waals forces of liquid
= free energy of Lifshitz-van der Waals forces of solid
= contribution of Lewis base of liquid
= contribution of Lewis acid of solid
= contribution of Lewis acid of liquid
= contribution of Lewis base of solid
In contrast to the two components extended Fowkes’ theory, not all the surface energy
components of the acid-base theory are known. For polar liquids like water and formamide
the contributions of the acid and base components to the total surface free energy are
unknown. Until now it is still not possible to determine the separate values of the acid and
base components. Van Oss, Good and Chaudhury therefore proposed, an arbitrary but
convenient, ratio of 1:1 for the acid and base component of water at 20°C. This results in
γwater+ = γwater- = 25,5 mJ/m². With all the known components of the alkanes, because the
alkanes are non-polar and thus they all only have a Lifshitz-van der Waals component, the
surface energy components of other liquids were measured. These surface energy components
are given in table A.1.
Table A.1: Surface energy components of reference liquids in mJ/m² according to the vanOss-Good-Chaudhury
scale. [van Oss, Chaudhury and Good 1988]
Reference liquid
Distilled water
Diiodomethane
Glycerol
n-Hexane
Formamide
γlTOT
72.8
50.8
64.0
18.4
58.0
γlLW
21.8
50.8
34.0
18.4
39.0
γlAB
51.0
0.00
30.0
0.00
19.0
γl+
25.5
0.00
3.92
0.00
2.28
γl25.5
0.00
57.4
0.00
39.6
Although diiodomethane is a polar liquid, both the acid and the base component are set to
0.00 mJ/m² at the van Oss-Good-Chaudhury scale. It is argued that the electron acceptor
component is experimentally found to be γl+ = 0.7 mJ/m², but that diiodomethane doesn’t
show any affinity for electron donating surfaces. And so diiodomethane shows a virtual nonpolar behaviour for practically all contact angle measurements [11].
The surface energy components of a solid can be determined by arranging equation (A18)
three times, one for each reference liquid, into a system of equations. In equation (A19) a
system of equations is given for a liquid set consisting of water, diiodomethane and glycerol.
91
(
(
(
)
)
)
72.8 ⋅ (1 + cos θ ) = 2 21.8 ⋅ γ LW + 25.5 ⋅ γ + + 25.5 ⋅ γ −
sw
s
s
s


LW
+
−
(A19)
50.8 ⋅ (1 + cos θ sm ) = 2 50.8 ⋅ γ s + 0.00 ⋅ γ s + 0.00 ⋅ γ s

64.0 ⋅ (1 + cos θ ) = 2 34.0 ⋅ γ LW + 57.4 ⋅ γ + + 3.92 ⋅ γ −
sg
s
s
s

where θs...
= contact angles between solid and liquids
LW
γs
= unknown free energy of Lifshitz-van der Waals forces of solid
γs+
= unknown contribution of Lewis acid of solid
γs= unknown contribution of Lewis base of solid
With three equations and the three unknown surface energy components, a solution can be
found for the surface free energy components. Equation (A19) shows that the second equation
in the system, the equation of diiodomethane, is independent on the other two equations. This
is because diiodomethane is non-polar and therefore has two zero components in its equation.
The diiodomethane has therefore one unknown, the Lifshitz-van der Waals component of the
solid. This non-polar component can therefore also be determined as a start, and then
substituting the value in the two remaining polar equations of the system for calculating the
polar surface energy components of the solid. Both ways of calculating the surface energy
components of the solid give the same results.
If the surface energy components of the solid, e.g. a stone, and the liquid, e.g. bitumen, are
measured and known, the fundamental work of adhesion can be calculated. This fundamental
work of adhesion is the energy that is needed to split the bitumen from the stone in two new
surfaces. The fundamental work of adhesion between bitumen and stone is given as:
(
where Wa
γlLW
γsLW
γlγs+
γl+
γs-
)
Wa = 2 γ lLW ⋅ γ sLW + γ l− ⋅ γ s+ + γ l+ ⋅ γ s−
= work of adhesion
= free energy of Lifshitz-van der Waals forces of bitumen
= free energy of Lifshitz-van der Waals forces of stone
= contribution of Lewis base of bitumen
= contribution of Lewis acid of stone
= contribution of Lewis acid of bitumen
= contribution of Lewis base of stone
(A20)
A.4 Modern surface energy theories in practice
The acid-base theory has been used by different researchers for civil engineering applications.
Therefore in this paragraph some important issues about application of this theory are
described, but first attention is given for the use of receding and advancing contact angles,
which is important for all used surface energy theories.
A.4.1 Advancing and receding contact angles
The difference between advancing and receding angles is that advancing angles interact with
new, untouched surface of the solid, in contrast to receding angles, which interact with the
wetted surface of the solid. The difference between advancing and receding angles is called
hysteresis. In literature it is stated that hysteresis is possibly caused by surface roughness and
chemical heterogeneity. The application of advancing or receding contact angles for
92
calculating the work of adhesion between liquid and solid is disputed. Most researchers argue
that the real surface energy of a solid can only be determined when the solid is dry and hasn’t
been wetted yet with the reference liquid. Else the measured surface energy of the solid is
partially from the surface energy of the reference liquid. Some other researchers claim that
because surface energy of solids is used for adhesion proposes, the receding, and thus
withdrawing, angles are a better parameter to quantify the surface energy of solids.
A.4.2 Negative square roots
Especially in the acid-base theory negative surface energy components are sometimes found,
referring to negative values for the acid and/or base components. Some researchers state that
this is reality, because negative surface energies are known to exist from Atomic Force
Microscopy [12]. Another explanation is that the standard deviation of the negative
component is larger than the component value itself, caused by possible measurement
inaccuracies and/or possible ill-conditioning of the liquid set. Using an over-determined
system of equations may reduce the chance of negative square roots. This means that at least
four reference liquids are used resulting in four times equation (A18). The arranged system
now has at least four equations and only three unknowns, the surface energy components of
the solid. Solving this over-determined system of equations requires special programs, which
should be available. A numerical procedure developed, called singular value decomposition,
for solving these systems of equations determines the unknown surface energy components
and the condition number. The meaning of condition number is described in the following
paragraph.
A.4.3 Condition number
In literature it is found that the use of different reference liquids influences the result of the
value of the determined surface energy components, probably due ill-conditioning of the
system of equations. Therefore van Oss, Good and Chaudhury proposed to use a set of
reference liquids in which the ratios of the acid and base components differ as much as
possible between the reference liquids. They suggested using a polar, a mono-polar and a nonpolar liquid. For instance water, with a ratio between acid and base components of 1:1,
glycerol, with γl+/ γl- ≈ 0.07 and non-polar diiodomethane can be used. Later on it was found
that, although a polar, a mono-polar and a non-polar liquid were used, the values of the
determined surface energy components were still influenced by the chosen liquid set.
Therefore a mathematical feature, the condition number, was developed to monitor the illconditioning of the system of equations. Ill-conditioning of a mathematical system of
equation means that a small change in the parameters of one equation, e.g. the measured
contact angles, results in a large change of the outcome of the unknowns, thus the surface
energy components to be determined. The condition number of each set depends on the
reference liquids in the set and the material, which is investigated. A larger chance on larger
errors and inaccuracies in the surface energy components occurs when the condition number
of the set of liquids is large, for instance larger than 10, and the chance on errors is reduced by
using a liquid set with a lower condition number. The condition number can be calculated
with a special program, if available.
A.4.4 Acid-base components scale
As stated before van Oss, Good and Chaudhury proposed a ratio of 1:1 between the acid and
the base component of water at 20°C. The conviction that water is a stronger Lewis acid than
93
Lewis base is becoming more generally accepted. Van Oss, Good and Chaudhury stated
correctly that the value of the calculated work of adhesion between two materials is not
influenced by the chosen ratio of acid and base components, when the ratios are consistently
used. However a classification of for instance bitumen on the basis of Lewis acidic and basic
components is not possible, because it is not possible to compare between acid and base
components. Acid components are only allowed to be compared to acid components and base
components to base components. To solve this problem many relative scales for acid and base
components are proposed. Some of these scales are now described.
Della Volpe and Siboni [1] cite an article by Taft, Kamlet, Abboud and Abraham in which it
is considered that water has a 6.5 times stronger acid than base component. Della Volpe and
Siboni have extended hypothetically the ratio of γl+/ γl- = 6.5 for water to other liquids. Some
of these results are given in table A.2.
Table A.2: Surface energy components of reference liquids in mJ/m² according to the Taft et al. scale. [Della
Volpe and Siboni 1997]
Reference liquid
Distilled water
Diiodomethane
Glycerol
Formamide
γlTOT
72.8
50.8
64.0
58.0
γlLW
21.8
50.8
37.8
31.1
γlAB
51.0
0.00
26.1
26.8
γl+
65.0
0.00
4.00
1.30
γl10.0
0.00
42.7
14.3
Della Volpe and Siboni have also proposed a scale themselves. They proposed a ratio
between the acid and base component of water and have adjusted some Lifshitz-van der
Waals components as well. Their results are given in table A.3.
Table A.3: Surface energy components of reference liquids in mJ/m² according to the Della Volpe-Siboni scale.
[Della Volpe and Siboni 2002]
Reference liquid
Distilled water
Diiodomethane
Glycerol
n-Hexane
Formamide
γlTOT
72.8
50.8
64.0
18.4
58.0
γlLW
26.25
50.8
35.05
18.4
35.5
γlAB
46.53
0.00
28.55
0.00
22.6
γl+
48.5
0.00
27.8
0.00
11.3
γl11.16
0.00
7.33
0.00
11.3
Lee [7] used another method and found another scale. Lee distinguishes initial (theoretical)
work of adhesion from long-term equilibrium (experimental) work of adhesion, because in the
beginning contact angles first have to meet equilibrium. Initial work of adhesion should
therefore be larger when the equilibrium spreading pressure is substantial. Lee comes to the
following initial (table A.4) and equilibrium (table A.5) surface free energy components of
some reference liquids.
Table A.4: Initial (theoretical) surface energy components of reference liquids in mJ/m² at 20°C according to the
Lee scale. [Lee 2001]
Reference liquid
Distilled water
Diiodomethane
Glycerol
Formamide
94
γlTOT
72.8
50.8
64.0
58.0
γlLW
21.8
50.8
34.0
28.0
γlAB
51.0
≈0
19.0
30
γl+
34.2
≈0
17.4
22.4
γl19
≈0
12.9
10.1
Table A.5: Equilibrium (experimental) surface energy components of reference liquids in mJ/m² at 20°C
according to the Lee scale. [Lee 2001]
Reference liquid
Distilled water
Diiodomethane
Glycerol
Formamide
γlTOT
72.8
50.8
64.0
58.0
γlLW
21.8
50.8
34.0
39.0
γlAB
51.0
≈0
30.0
19
γl+
34.2
≈0
5.3
3.1
γl19
≈0
42.5
29.1
References
[1]
Della Volpe, C. and Siboni, S. (1997); Some reflections on acid–base solid surface
free energy theories; Journal of Colloid and Interface Science, 1997, 195, pp. 121–136
[2]
Fowkes, F.M. (1964); Attractive forces at interfaces; Journal of industrial and
engineering chemistry, vol. 56, no 12, December 1964, pp. 40-52.
[3]
Groenendijk, J. (1998); Accelerated testing and surface cracking of asphaltic concrete
pavements; Ph.D. dissertation, Civil engineering; November 1998; Delft University of
Technology, Delft, NL.
[4]
Hansen, F.K. (2000); The measurement of surface energy of polymer by means of
contact angles of liquids on solid surfaces; A short overview of frequently used
methods; Department of Chemistry; University of Oslo, Oslo, Norway.
[5]
Hefer, A. and Little, D. (2005); Adhesion in bitumen-aggregate systems and
quantification of the effects of water on the adhesive bond; report ICAR/505-1; Texas
Transportation Institute; Texas A&M University System, College Station, Texas,
USA.
[6]
Jacobasch, H. J., Grundke, K., Schneider, S. and Simon, F. (1995); Surface
characterization of polymers by physico-chemical measurements; Journal of Adhesion,
48:1, pp. 57 - 73
[7]
Lee, L.-H. (2001); The unified Lewis acid – base approach to adhesion and solvation
at the liquid-polymer interface; The Journal of Adhesion, 76:2, pp. 163–183.
[8]
[9]
Lytton, R.L., Masad, E.A., Zollinger, C. and Bulut, R. (2005); Measurements of
surface energy and its relationship to moisture damage; report FHWA/TX-05/0-45242; Texas Transportation Institute; Texas A&M University System, College Station,
Texas, USA.
[10]
Oss, C.J. van, Chaudhury, M.K. and Good, R.J. (1988); Interfacial Lifshitz-van der
Waals and polar interactions in macroscopic systems; Chemical Reviews, 1988, 88,
pp. 927-941.
95
[11]
Oss, C.J. van, Giese, R.F. and Good, R.J. (2002); The zero time dynamic interfacial
tension; Journal of Dispersion Science and Technology, 2002, 23:4, pp. 455-464.
[12]
Woodward, R.P. (2000); Prediction of adhesion and wetting from Lewis acid base
measurements; Presentation at TPOs in Automotive 2000; First Ten Ångstroms Inc,
Portsmouth, UK.
96
Appendix B: Experimental data
In this chapter more detailed results of the experiments are given. The values and numbers are
given in the decimals as obtained from the instruments. All the other data and results are
stored on the CD-ROM which is attached to this report.
B.1 Roughness
B.1.1 Macro surface roughness
Table B.1: Measured values of parameters Pa and Pq at 7 times magnification.
Gsawed 1
Gsand 1
Gstone 1
Bsawed 1
Bsand 1
Bstone 1
Pa [µm]
Pq [µm]
48.41
56.69
50.67
59.47
0.238·10³/0.335·10³ 0.350·10³/0.393·10³
48.12
56.49
49.07
58.51
0.174·10³/0.292·10³ 0.241·10³/0.381·10³
B.1.2 Meso surface roughness
Table B.2: Measured values of parameters Pa and Pq at 20 and 50 times magnification.
LSCM (20X)
Gsawed 1
Gsawed 2
Gsawed 3
Gsand 1
Gsand 2
Gsand 3
Gstone 1
Gstone 2
Gstone 3
Bsawed 1
Bsawed 2
Bsawed 3
Bsand 1
Bsand 2
Bsand 3
Bstone 1
Bstone 2
Bstone 3
Pa [µm]
4.47
3.45
3.45
6.13
4.23
4.61
19.42
18.42
24.62
5.19
5.97
4.47
5.62
5.92
8.36
17.80
42.42
26.90
Pq [µm]
6.07
4.65
4.70
7.91
5.79
6.84
24.55
22.20
28.72
7.61
8.05
6.11
7.07
7.83
10.81
22.41
51.62
31.93
LSCM (50X)
Gsawed 1
Gsawed 2
Gsawed 3
Gsand 1
Gsand 2
Gsand 3
Gstone 1
Gstone 2
Gstone 3
Bsawed 1
Bsawed 2
Bsawed 3
Bsand 1
Bsand 2
Bsand 3
Bstone 1
Bstone 2
Bstone 3
Pa [µm]
3.77
4.04
3.63
4.64
6.03
4.78
6.98
17.68
9.20
5.06
4.65
4.02
5.49
6.51
10.34
25.61
14.14
22.97
Pq [µm]
5.10
5.23
4.74
6.74
7.83
6.43
8.67
20.73
10.82
6.92
6.33
5.50
7.40
8.64
12.77
29.99
17.87
31.22
97
Bestone 4/8 aggregate 1 (Bstone1)
20 X
20 X
Bestone 4/8 aggregate 3 (Bstone 3)
20 X
Bestone sawed column 1 (Bsawedlab1)
20 X
20 X
Bestone sawed column 3 (Bsawedlab 3)
20 X
Bestone sandblasted column 1 (Bsandlab1)
20 X
20 X
20 X
98
Greywacke 4/8 aggregate 1 (Gstone1)
20 X
20 X
Greywacke 4/8 aggregate (Gstone3)
20 X
Greywacke sawed column 1 (Gsawedlab1)
20 X
20 X
20 X
Greywacke sandblasted column 1 (Gsandlab1)
20 X
20 X
20 X
99
50 X
50 X
100
50 X
50 X
50 X
50 X
50 X
50 X
50 X
101
50 X
50 X
50 X
50 X
50 X
50 X
102
50 X
50 X
50 X
103
B.1.3 Micro surface roughness
Table B.3: Texture distribution on the ESEM pictures analysed using the wavelet method.
Sample
BSTONE01.TIF
BSTONE02.TIF
BSTONE03.TIF
BSAWED02.TIF
BSAWED04.TIF
BSAND01.TIF
BSAND02.TIF
BSAND03.TIF
GSTONE01.TIF
GSTONE02.TIF
GSTONE03.TIF
GSAWED02.TIF
GSAWED03.TIF
GSAWED04.TIF
GSAND01.TIF
GSAND02.TIF
104
image00.tif
image01.tif
image02.tif
image04.tif
image06.tif
image07.tif
image08.tif
image09.tif
image10.tif
image11.tif
image12.tif
image14.tif
image15.tif
image16.tif
image17.tif
image18.tif
Fine
texture
[areas]
428
383
631
307
486
656
670
1133
560
363
421
458
450
459
479
445
Medium
texture
[areas]
202
163
260
110
193
186
200
272
162
99
149
125
130
133
107
95
Coarse
texture
[areas]
199
140
173
88
258
148
129
180
66
46
63
52
40
37
31
39
Fine
texture
[%]
52
56
59
61
52
66
67
71
71
71
67
72
73
73
78
77
Medium
texture
[%]
24
24
24
22
21
19
20
17
21
19
24
20
21
21
17
16
Coarse
texture
[%]
24
20
16
17
28
15
13
11
8
9
10
8
6
6
5
7
100 X
100 X Bestone 4/8 aggregate 3 (Bstone 3)
100 X
100 X
100 X
100 X
100 X
100 X
105
100 X
100 X
Greywacke 4/8 aggregate 3 (Gstone 3)
100 X
100 X
100 X
Greywacke sawed column 3 (Gsawedlab 3)
100 X
100 X
100 X
100 X
106
B.2 Specific surface area
Table B.4: Specific surface area at 7 times magnification.
Gsawed 1
Gsand 1
Gstone 1
Bsawed 1
Bsand 1
Bstone 1
SSA [mm/mm]
1.00242
1.00612
1.08086/1.25195
1.00711
1.01978
1.06988/1.11494
Table B.5: Specific surface area at 20 and 50 times magnification.
LSCM (20X)
Gsawed 1
Gsawed 2
Gsawed 3
Gsand 1
Gsand 2
Gsand 3
Gstone 1
Gstone 2
Gstone 3
Bsawed 1
Bsawed 2
Bsawed 3
Bsand 1
Bsand 2
Bsand 3
Bstone 1
Bstone 2
Bstone 3
SSA [mm²/mm²]
1.73
1.65
1.72
1.89
1.66
2.04
2.92
2.79
3.04
1.93
2.52
2.32
1.89
1.89
2.50
2.66
3.50
2.41
LSCM (50X)
Gsawed 1
Gsawed 2
Gsawed 3
Gsand 1
Gsand 2
Gsand 3
Gstone 1
Gstone 2
Gstone 3
Bsawed 1
Bsawed 2
Bsawed 3
Bsand 1
Bsand 2
Bsand 3
Bstone 1
Bstone 2
Bstone 3
SSA [mm²/mm²]
3.10
3.04
2.95
3.38
3.66
3.19
2.93
5.32
3.80
3.17
3.06
3.11
3.31
3.38
3.84
6.01
4.79
2.19
B.3 Porosity
Table B.6: Porosity of the stone samples measured in the Mercury Intrusion Porosimeter.
Sample
Bstone
Bsurface
Bsand
Bsawed
Porosity of total
volume [%]
2.7036
2.0096
2.1274
2.1477
Sample
Gstone
Gsurface
Gsand
Gsawed
Porosity of total
volume [%]
2.4223
4.1310
1.6500
3.3972
107
Bestone 4/8 aggregates (Bstone)
Bestone non-sawed surfaces of slices (Bsurface)
Bestone sandblasted columns (Bsandlab)
Cumulative Pore Size Distribution
of Bestone samples
Cumulative Pore Size Distribution
of Greywacke samples
Bestone sawed columns (Bsawedlab)
Greywacke non-sawed surfaces of slices (Gsurface)
108
Greywacke 4/8 aggregates (Gstone)
Greywacke sandblasted columns (Gsandlab)
Greywacke sawed columns (Gsawedlab)
B.4 Chemical- and Mineralogical composition
Bsawed
lab
Bsurface
Bstonecl
Bstone
Gstone
Gstonecl
Gsurface
Gsawed
lab
Gsandlab
[mass %]
SiO2
CO2
CaO
Al2O3
K2O
MgO
Na2O
Fe2O3
S
P2O5
TiO2
V2O5
Cr2O3
MnO
NiO
BaO
Rb2O
SrO
ZrO2
Co3O4
ZnO
SO3
F
P
Cl
Ar
Sc2O3
CuO
Ga2O3
GeO2
As2O3
SeO2
Br
Y2O3
Nb2O5
MoO3
RuO2
Rh2O3
PdO
Ag2O
CdO
In2O3
SnO2
Sb2O3
TeO2
I
Cs2O
La2O3
Bsandlab
Table B.7: Chemical element distribution of the samples given in mass percentages.
53.19
19.35
10.41
8.75
1.84
1.42
1.80
2.29
0.000
0.094
0.365
0.008
0.051
0.070
0.164
0.096
0.010
0.041
0.033
0.000
0.000
0.009
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
60.88
10.08
9.21
10.26
2.11
1.77
2.04
2.67
0.000
0.123
0.402
0.006
0.051
0.057
0.155
0.092
0.011
0.043
0.038
0.000
0.000
0.006
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
62.67
8.95
8.57
10.17
2.11
1.63
2.19
2.60
0.000
0.111
0.374
0.010
0.080
0.055
0.277
0.113
0.011
0.045
0.037
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
63.20
7.83
6.39
11.38
2.28
2.29
2.02
3.50
0.000
0.131
0.497
0.008
0.052
0.580
0.147
0.110
0.011
0.043
0.043
0.006
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
63.20
7.67
6.64
11.28
2.23
2.32
2.06
3.48
0.000
0.126
0.460
0.009
0.060
0.057
0.194
0.106
0.011
0.043
0.037
0.000
0.000
0.009
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
53.04
11.94
11.48
11.96
2.16
2.31
0.840
4.69
0.306
0.068
0.661
0.015
0.063
0.108
0.166
0.077
0.012
0.065
0.036
0.000
0.005
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
49.23
15.99
14.57
10.24
1.76
1.97
0.795
4.01
0.310
0.061
0.583
0.014
0.041
0.115
0.088
0.071
0.010
0.083
0.040
0.006
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
54.78
4.89
5.09
18.33
4.12
3.27
0.596
7.24
0.234
0.090
0.884
0.023
0.047
0.089
0.107
0.109
0.021
0.040
0.030
0.000
0.006
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
54.18
4.67
5.11
18.86
4.29
3.31
0.552
7.35
0.241
0.083
0.920
0.027
0.032
0.091
0.074
0.122
0.023
0.039
0.029
0.006
0.005
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
54.03
4.74
5.10
18.96
4.30
3.30
0.529
7.35
0.249
0.083
0.900
0.027
0.039
0.086
0.088
0.114
0.023
0.040
0.029
0.008
0.005
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
109
CeO2
Pr6O1
Nd2O3
Sm2O3
Eu2O3
Gd2O3
Tb4O7
Dy2O3
Ho2O3
Er2O3
Tm2O3
Yb2O3
Lu2O3
HfO2
Ta2O5
WO3
Re2O7
OsO4
IrO2
PtO2
Au
HgO
Tl2O3
PbO
Bi2O3
ThO2
U3O8
PuO2
Am2O3
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
110
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
Appendix B: Experimental results
Bestone 4/8 aggregate 3 (Bstone 3)
Greywacke 4/8 aggregate 3 (Gstone 3)
Greywacke sawed column 3 (Gsawedlab 3)
112
B.5 Acidity
Table B.8: Mass of the measured stone samples in the acidity test.
after 2
at 0 hours
weeks
Sample
Box weight Water weight Total weight Water weight
weight [gr]
[gr]
[gr]
[gr]
[gr]
Gsawed 1
7.04
1.98
7.51
15.27
6.25
Gsawed 2
7.29
2.03
7.51
15.02
5.70
Gsawed 3
7.22
2.00
7.50
15.71
6.49
Bsawed 1
6.92
1.99
7.52
15.29
6.38
Bsawed 2
7.16
1.98
7.52
13.29
4.15
Bsawed 3
7.01
2.01
7.50
15.01
5.99
Gsand 1
6.27
1.99
7.52
14.54
6.28
Gsand 2
6.75
2.03
7.51
15.01
6.23
Gsand 3
6.97
2.00
7.51
15.44
6.47
Bsand 1
6.81
2.01
7.50
15.19
6.37
Bsand 2
6.96
1.98
7.51
15.38
6.44
Bsand 3
6.49
2.02
7.51
14.83
6.32
Gstone 1
7.06
2.00
7.53
15.63
6.57
Gstone 2
6.87
1.98
7.53
15.29
6.44
Gstone 3
7.07
1.99
7.51
15.52
6.46
Bstone 1
7.05
1.99
7.51
15.54
6.50
Bstone 2
7.05
2.04
7.50
15.53
6.44
Bstone 3
6.92
1.99
7.52
15.41
6.50
Bsurface 1
8.18
2.01
7.52
16.55
6.36
Bsurface 2
6.46
1.98
7.52
14.95
6.51
Bsurface 3
7.33
2.03
7.50
15.56
6.20
Gsurface 1
6.26
1.99
7.50
14.53
6.28
Gsurface 2
6.57
2.06
7.51
15.00
6.37
Gsurface 3
6.22
1.99
7.50
14.71
6.50
Gstonecl 1
6.94
2.01
7.52
15.31
6.36
Gstonecl 2
6.90
2.05
7.50
15.30
6.35
Gstonecl 3
6.88
1.98
7.52
15.14
6.28
Bstonecl 1
6.96
2.03
7.53
15.43
6.44
Bstonecl 2
6.99
1.98
7.50
15.42
6.45
Bstonecl 3
6.82
2.00
7.50
15.31
6.49
Water loss
[gr]
1.26
1.81
1.01
1.14
1.37
1.51
1.24
1.28
1.04
1.13
1.07
1.19
0.96
1.09
1.05
1.01
1.06
1.02
1.16
1.01
1.30
1.22
1.14
1.00
1.16
1.15
1.24
1.09
1.05
1.01
The measured pH values per stone sample are stored on the CD-ROM which is attached to
this report.
B.6 Surface energy
The contact angles of the reference liquids measured on the aggregate surfaces are stored on
the CD-ROM which is attached to this report.
113
Appendix C: Procedures
C.1 Sessile Drop Method Protocol
PROPOSED TEST METHOD TO USE A SESSILE DROP DEVICE TO DETERMINE
SURFACE ENERGY COMPONENTS OF ASPHALT BINDERS. [1]
1. Scope
1.1 This test method covers the procedures for preparing samples and measuring contact
angles using the sessile drop method to determine the three surface energy components of
asphalt binders.
1.2 This standard is applicable to asphalt binders that do not contain particulate additives such
as crumb rubber.
1.3 This method must be used in conjunction with the manual for mathematical analysis to
determine surface energy components from contact angle measurements or the computerised
spreadsheets that were developed to carry out this analysis.
1.4 This standard may involve hazardous material, operations, and equipment. This standard
is not intended to address all safety problems associated with its use. It is the responsibility of
the user of this procedure to establish appropriate safety and health practices and to
determine the applicability of regulatory limitations prior to its use.
2. Referenced Documents
2.1 AASHTO Standards T40 Sampling of Bituminous Materials
3. Definitions
3.1 Surface energy, γ, or surface free energy, of a material is the amount of work required to
create unit area of the material in vacuum. The total surface energy of a material is divided
into three components: the Lifshitz–van der Waals component, the acid component, and the
base component.
3.2 Contact angle, θ, refers to the equilibrium contact angle of a liquid on a solid surface
measured at the point of contact of the liquid-vapour interface with the solid.
3.3 Probe liquid, within the context of this test, refers to any of the pure, homogeneous liquids
that do not react chemically or dissolve with asphalt binders and are used to measure the
contact angles with the binder. The three surface energy components of the probe liquid must
be known at the test temperature from the literature.
3.4 Mixing temperature, within the context of this test, refers to the temperature at which the
viscosity of the asphalt binder is approximately 0.170 Pa·s, or any other temperature that is
prescribed or determined by the user for use as the mixing temperature with aggregates to
prepare hot mix asphalt.
4. Summary of Method
4.1 A probe liquid is dispensed over a smooth horizontal surface coated with asphalt binder.
The image of the drop of liquid formed over the surface of the binder is captured using a
camera. Contact angles are obtained by analysing the image manually or using software.
4.2 Contact angles measured with different probe liquids are used with equations of work of
adhesion to determine the three surface energy components of the asphalt binder.
114
5. Significance and Use
5.1 Surface energy components of asphalt binders are important material properties that are
related to the performance of hot mix asphalt. Surface energy components of asphalt binders
can be used to determine the total surface energy and cohesive bond strength of this material.
The cohesive bond strength of asphalt binders is related to the work required for microcracks
to propagate within the asphalt binder in an asphalt mix, which is related to the fatigue
cracking characteristics of the mix.
5.2 Surface energy components of asphalt binders also can be combined with the surface
energy components of aggregates to compute the work of adhesion between these two
materials and the propensity for water to displace the asphalt binder from the asphalt binderaggregate interface. These two quantities are related to the moisture sensitivity of the asphalt
mix.
6. Apparatus
6.1 A sessile drop system comprises a microsyringe and a CCD (charge-coupled device)
camera to create and capture images of sessile drops, respectively.
6.2 Image analysis software is required to determine contact angles from captured images.
Alternatively, contact angles can also be determined from manual measurements on the drop
images.
6.3 An oven capable of heating up to 150°C is required to heat asphalt binders for sample
preparation. Glass slides or thin aluminium sheets are required to serve as substrates for the
asphalt binder.
6.4 An environmental control system using a thermoelectric module is optional to conduct
tests at temperatures other than room temperature.
7. Sampling
7.1 Obtain a representative sample of the asphalt binder according to procedure T40. Heat the
asphalt binder to the mixing temperature, stir it thoroughly, and transfer it to smaller
containers approximately 50 mL in capacity. Fifteen containers of the asphalt binder are
required to test three replicates with five probe liquids. These containers will be heated only
once more to prepare samples for testing.
8. Preparation of Test Samples
8.1 Clean the surface of the glass slide or aluminium sheet that is used as a substrate for the
asphalt binder.
8.2 Heat the container with asphalt binder in an oven to the mixing temperature. Stir the liquid
asphalt binder in the container and pour a small quantity on the substrate. The quantity of
asphalt poured must be adequate to form an area of approximately 5 cm by 5 cm in size.
8.3 This binder sample is stored in a desiccator and allowed to cool to room temperature.
9. Procedure
9.1 Place the substrate with the asphalt binder between the light source and the camera. If a
thermo-electric temperature control module is used, then place the sample over the module,
which is fixed at the proper location between the light source and the camera. A transparent
glass cover also may be used to reduce thermal flow to the atmosphere. Set the temperature of
the module to the test temperature and allow the sample to remain at this temperature for at
least an hour before starting the test.
9.2 Rinse the microsyringe with the probe liquid. Position the tip of the microsyringe needle
approximately 5 mm away from the top of the sample. Dispense a small drop of the probe
liquid from the syringe. As more volume of the probe liquid is added, the drop on the asphalt
115
binder surface expands to a point when its interfacial boundary with the binder surface just
begins to expand. Stop addition of probe liquid at this point and capture an image of the drop
using the CCD camera.
9.3 At least five probe liquids are recommended for use with this test. These are water,
ethylene glycol, methylene iodide (diiodomethane), glycerol, and formamide. All reagents
must be high-purity grade (>99%). Contact angles must be measured for at least three
replicates with each probe liquid for each asphalt binder.
9.4 When methylene iodide is used as a probe liquid, cover the light source with a red film
because methylene iodide is a light-sensitive material and must not be exposed or stored in
light for prolonged duration.
9.5 Store all probe liquids in airtight containers and do not use probe liquids after they have
been exposed to air for prolonged duration.
10. Calculations
10.1 Analyse each sessile drop image to obtain two contact angles. Report the average of
these two contact angles as the contact angle for that specific replicate and probe liquid
combination.
10.2 The typical standard deviation for the contact angle measured for each pair of probe
liquid and asphalt binder based on tests with three replicates is less than 5°.
10.3 The contact angle of each replicate and probe liquid is used with the surface energy
analysis workbook that conducts the required analysis to determine the three surface energy
components of the asphalt binder and the standard deviations in these components. This
workbook also verifies the accuracy and consistency of the measured contact angles and
integrates data from other test methods such as the surface energy components of aggregates
to determine various parameters of interest that are related to the performance of asphalt
mixes.
Reference
[1]
C.2 Wilhelmy Plate Method Protocol
PROPOSED TEST METHOD TO USE A WILHELMY PLATE DEVICE TO
DETERMINE SURFACE ENERGY COMPONENTS OF ASPHALT BINDERS. [1]
1. Scope
1.1 This test method covers the procedures for preparing samples and measuring contact
angles using the Wilhelmy plate device to determine the three surface energy components of
asphalt binders.
1.2 This standard is applicable to asphalt binders that do not contain particulate additives such
as crumb rubber.
1.3 This method must be used in conjunction with the manual for mathematical analysis to
determine surface energy components from contact angle measurements or the computerised
spreadsheets that were developed to carry out this analysis.
1.4 This standard may involve hazardous material, operations, and equipment. This standard
is not intended to address all safety problems associated with its use. It is the responsibility of
116
the user of this procedure to establish appropriate safety and health practices and to
determine the applicability of regulatory limitations prior to its use.
2. Referenced Documents
2.1 AASHTO Standards T40 Sampling of Bituminous Materials
3. Definitions
3.1 Surface energy, γ, or surface free energy, of a material is the amount of work required to
create unit area of the material in vacuum. The total surface energy of a material is divided
into three components: the Lifshitz–van der Waals component, the acid component, and the
base component.
3.2 Contact angle, θ, refers to the equilibrium contact angle of a liquid on a solid surface
measured at the point of contact of the liquid-vapour interface with the solid.
3.3 Advancing contact angle, within the context of this test, refers to the contact angle of a
liquid with the solid surface as the solid surface is being immersed into the liquid.
3.4 Receding contact angle, within the context of this test, refers to the contact angle of a
liquid with the solid surface as the solid surface is being withdrawn from the liquid.
3.5 Probe liquid, within the context of this test, refers to any of the pure, homogeneous liquids
that do not react chemically or dissolve with asphalt binders and are used to measure the
contact angles with the binder. The three surface energy components of the probe liquid must
be known at the test temperature from the literature.
3.6 Mixing temperature, within the context of this test, refers to the temperature at which the
viscosity of the asphalt binder is approximately 0.170 Pa·s, or any other temperature that is
prescribed or determined by the user for use as the mixing temperature with aggregates to
prepare hot mix asphalt.
4. Summary of Method
4.1 A glass slide coated with the asphalt binder and suspended from a microbalance is
immersed in a probe liquid. From simple force equilibrium conditions, the contact angle of
the probe liquid with the surface of the asphalt binder can be determined. The analysis to
obtain the contact angle is performed using software accompanying the Wilhelmy plate
device.
4.2 Contact angles measured with different probe liquids are used with equations of work of
adhesion to determine the three surface energy components of the asphalt binder.
5. Significance and Use
5.1 Surface energy components of asphalt binders are important material properties that are
related to the performance of hot mix asphalt. Surface energy components of asphalt binders
can be used to determine the total surface energy and cohesive bond strength of this material.
The cohesive bond strength of asphalt binders is related to the work required for microcracks
to propagate within the asphalt binder in an asphalt mix, which is related to the fatigue
cracking characteristics of the mix.
5.2 Surface energy components of asphalt binders also can be combined with the surface
energy components of aggregates to compute the work of adhesion between these two
materials and the propensity for water to displace the asphalt binder from the asphalt binderaggregate interface. These two quantities are related to the moisture sensitivity of the asphalt
mix.
117
6. Apparatus
6.1 The Wilhelmy plate device comprises a microbalance with a motor-controlled stage that
can be raised or lowered at desired speed to immerse a slide with asphalt binder in the probe
liquid in advancing mode and to withdraw the slide from the probe liquid in receding mode.
6.2 Data acquisition and analysis software is required to collect the data and determine the
contact angles.
6.3 An oven capable of heating up to 150°C is required to heat asphalt binders for sample
preparation. Microscope glass slides (24 mm by 60 mm No. 1.5) are required to serve as
substrates for the asphalt binder, and a vernier caliper is required to measure the dimensions
of the slide. A heating plate with temperature control is required for maintaining the
temperature of the asphalt binder during the sample preparation process.
6.4 The tests are conducted at 25±1°C. If the room temperature is significantly different from
the test temperature, then an appropriate environmental chamber may be required to house the
apparatus.
6.5 A slotted slide holder is required to hold the finished asphalt binder slides.
7. Sampling
7.1 Obtain a representative sample of the asphalt binder according to procedure T40.
Approximately 50 g of asphalt binder stored in a small metallic container is required for this
test.
8. Preparation of Test Samples
8.1 Heat the container with asphalt binder in an oven to the mixing temperature for about 1 h
and place it over a heating plate. Set the temperature of the heating plate so that the asphalt
binder remains at the mixing temperature. Stir the liquid asphalt binder from time to time
throughout the sample preparation process.
8.2 Pass the end of the glass slide intended for coating through the blue flame of a propane
torch six times on each side to remove any moisture. Dip the slide into the molten asphalt
binder to a depth of approximately 15 mm. Allow excess binder to drain from the slide until a
very thin (0.18 to 0.35 mm) and uniform layer remains on the slide. The thickness of asphalt
binder must be uniform on both sides of the slide throughout its width and for at least 10 mm
from the edge that will be immersed in the probe liquid. A thin coating is required to reduce
variability of the results. Turn the slide with the uncoated end downward and carefully place it
in the slotted slide holder. If necessary, the heat-resistant slide holder with all the coated
slides is placed in the oven for 15 to 30 s to obtain the desired smoothness. Place the bindercoated slides in a desiccator overnight.
9. Procedure
9.1 The user must ensure that the microbalance is calibrated in accordance with the
manufacturer specifications before the start of the test.
9.2 Remove one asphalt binder–coated slide from the desiccator at a time. Measure the width
and thickness of the asphalt binder slide to an accuracy of 0.01 mm to calculate its perimeter.
The measurements must be made just beyond 8 mm from the edge of the slide to avoid
contamination of the portion of coating that will be immersed in the probe liquid.
9.3 Suspend the glass slide coated with asphalt binder from the microbalance using a
crocodile clip. Ensure that the slide is horizontal with respect to the base of the balance. Fill a
clean glass beaker with the probe liquid to a depth of at least 10 mm and place it on the
balance stage. Raise the stage manually to bring the top of the probe liquid in proximity to the
bottom edge of the slide
118
9.4 During the test, the stage is raised or lowered at the desired rate via a stepper motor
controlled by the accompanying software. A rate of 40 micrometers/s is recommended to
achieve the quasi-static equilibrium conditions for contact angle measurement. Set the depth
to immerse the sample in the probe liquid to 8 mm. Larger depths up to 15 mm may be used if
the thickness of asphalt coating on the slide is uniform. The weight of the slide measured by
the microbalance is recorded continuously by the software accompanying the device during
the advancing (stage is raised to dip the slide) and receding (stage is lowered to retract the
slide from the liquid) process.
9.5 At least five probe liquids should be used with this test. These are water, ethylene glycol,
methylene iodide (diiodomethane), glycerol, and formamide. All reagents must be high-purity
grade (>99%). Contact angles must be measured for at least three replicates with each probe
liquid for each asphalt binder.
9.6 Because methylene iodide is a light-sensitive material, the beaker containing methylene
iodide must be covered with black tape to reduce the effect of light.
9.7 Dispose of the probe liquid in the beaker after testing three asphalt binder slides, and use a
fresh sample of the probe liquid for each different type of binder. Store all probe liquids in
airtight containers and do not use probe liquids after they have been exposed to air in openmouthed beakers for prolonged periods.
9.8 Tests must be completed within 24 to 36 h from the time of preparation of the slides.
10. Calculations
10.1 From simple force equilibrium considerations, the difference between weight of a slide
measured in air and partially submerged in a probe liquid is expressed in terms of buoyancy
of the liquid, liquid surface energy, contact angle, and geometry of the slide. The contact
angle between the liquid and surface of the slide is calculated from equilibrium. The
accompanying software requires the density of the liquid, total surface tension of the liquid,
dimensions of the sample, and local acceleration due to gravity as inputs to compute the
contact angle using the force measurements from the microbalance.
10.2 Buoyancy correction based on slide dimensions and liquid density can introduce
unwanted variability into the resulting contact angles. To eliminate these effects, the
accompanying software performs a regression analysis of the buoyancy line and extrapolates
the force to zero depth. The user must select a representative area of the line for regression
analysis. The software reports the advancing and receding contact angles based on the area
selected using the aforementioned equation.
10.3 If the force measurements are not smooth (i.e., if sawtooth-like force measurements are
observed because of slip-stick behaviour between the probe liquid and the asphalt binder),
then report this along with the advancing and receding contact angles.
10.4 The typical standard deviation of the measured contact angle for each pair of liquid and
asphalt binder based on measurements with three replicate slides is less than 2°.
10.5 The contact angle of each replicate and probe liquid is used with the surface energy
analysis workbook that conducts the required analysis to determine the three surface energy
components of the asphalt binder and the standard deviations of these components. This
workbook also verifies the accuracy and consistency of the measured contact angles and
integrates data from other test methods such as the surface energy components of aggregates
to determine various parameters of interest that are related to the performance of asphalt
mixes.
119
Reference
[1]
C.3 Wavelet method
The wavelet method has the advantage of decomposing an image into different levels. Each
level corresponds to a certain texture scale. Wavelets have the advantage of capturing the
sharp changes in texture in an image since its basis functions have variable durations that can
fit these sharp changes. However, the harmonic functions that constitute the basis for the
Fourier analysis do not have limited duration, and they are not efficient in modelling these
abrupt changes in texture on an image.
As discussed by Chandan et al. (2004), the wavelet analysis gives the texture details in the
horizontal, vertical, and diagonal directions in three separate images. The texture index is
taken at a given decomposition level as the arithmetic mean of the squared values of the
wavelet coefficients for all three directions. The texture index is expressed mathematically as
follows:
2
1 3 N
TextureIndex
Indexn =
(C1)
Texture
D
x
,
y
∑∑ ( i, j ( ) )
3 N i =1 j =1
where D
= wallet coefficient
N
= total number of coefficients
j
= wavelet coefficient index
i
takes a value 1,2 or 3, for the three directions of texture, and.
The analysis was conducted to measure three texture levels (fine, medium and coarse)
following the method described by Masad (2003). It should be emphasised that a change in
image magnification causes a change in the actual size of texture analysed by the wavelet
method. For example, coarse texture for an image captured at high magnification could
correspond to fine texture of the same material if an image is captured at a lower
magnification (see figure 3.2). Therefore, the texture levels analysed by the wavelet method
can only be compared for images that are captured at the same magnification.
The results can be used to compare the influence of different treatments of aggregate surfaces
on the different texture levels. Some treatments could reduce the coarse texture but increase
the fine texture or vice versa.
C.3.1 Wavelet method Procedure
Need a 640 by 480 Image
1.
2.
3.
4.
120
Originally 712 by 484
crop 60 from bottom (to remove the writing) (Produce 712 by 424)
480/424 is 1.132, so, need to change 712 to 565, since 640/565 is 1.132
crop 73 and 74 (left & right) (to achieve point 3)
5. resize to 640 by 480
6. Change from RGB to Gray Scale
7. rename as in the table C.1
BSTONE01.TIF
BSTONE02.TIF
BSTONE03.TIF
BSAWED01.TIF
BSAWED02.TIF
BSAWED03.TIF
BSAWED04.TIF
BSAND01.TIF
BSAND02.TIF
BSAND03.TIF
GSTONE01.TIF
GSTONE02.TIF
GSTONE03.TIF
GSAWED01.TIF
GSAWED02.TIF
GSAWED03.TIF
GSAWED04.TIF
GSAND01.TIF
GSAND02.TIF
GSAND03.TIF
image00.tif
image01.tif
image02.tif
image03.tif
image04.tif
image05.tif
image06.tif
image07.tif
image08.tif
image09.tif
image10.tif
image11.tif
image12.tif
image13.tif
image14.tif
image15.tif
image16.tif
image17.tif
image18.tif
image19.tif
Table C.1: Figure renaming for processing
Example:
Original Image:
121
Processed Image:
.
References
[1]
Masad, E. (2003); The development of a computer controlled image analysis system
for measuring aggregate shape properties; NCHRP-IDEA Project 77 Final Report;
Transportation Research Board, Washington, D.C., 2003
[2]
Chandan, C., Sivakumar, K., Fletcher, T., and Masad, E. (2004); Geometry analysis of
aggregate particles using imaging techniques; Journal of Computing in Civil
Engineering, ASCE, Vol. 18, No. 1, 2004, pp. 75-82.
122

Aggregate characterisation Aggregate characterisation in relation to

Transcription

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