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Cement Chemistry for Engineers, Cape Town 31st January 2013
Lecture 5: Effect of SCMs on durability
Different forms of degradation
Generic effects of SCMs
Causes of concrete degradation
1%
4% 5%
90%
Others
Freeze / Thaw
Alkali Silica Reaction Corrosion
I am sorry I do not know the source or veracity of these figures,
but they are probably pretty close to the truth
Impact of SCMs
degradation 1st mech 2nd mech General
Impact
SCMs
Carbonation binding transport Negative
Chloride Transport Binding Positive
ASR Pore solution
pH
Alumina Positive
Freeze thaw saturation ?? Negative
Sulfate Conversion
of Afm
embedded in
CSH to
ettringite
transport Claimed
positive
CARBONATION
Reducing calcium content; reduces buffer to carbonation
Mg
S
AlFe
KNa
rest
Ca
Si
O
Reduce Ca
CaCO3
CaO Ca(OH)2
+H2O
CO2 +CO
2
C-S-H + CO2 various intermediates CaCO3 + SiO2nH2O + H2O CH + CO2 CaCO3 + H2O
Aluminate hydrates + CO2 CaCO3 + hydrated alumina
Ferrite hydrates + CO2 CaCO3 + hydrated alumina + iron oxides
All CaO content can react with CO2,
not just portlandite
Effects more pronounced with poor curing From BRE via MDA Thomas, UNB
Effect of SCMs on carbonation
Capacity to bind CO2 is most important.
Cement with less chemical CO2 inevitably has less capacity to bind CO2
Transport (through carbonated layer) is secondary.
Good curing can partially offset effects of lower binding capacity
The balance between these effects needs to be further explored
These considerations are important for reinforced concrete, but there is
no obstacle to using low CaO binders in non reinforced applications:
blocks, bricks, pavers roof tiles
CHLORIDE INGRESS
Effect of SCMs on chloride transport
• Now transport is dominant
• Binding is secondary, but important
• C-S-H (a lot which binds a little) and Freidel’s salt (a little which binds a
lot), overall play roughly equal roles in binding.
• SCMs with high alumina content will give significant increase in binding
capacity
1 10 100 1000 10000
Age (days)
Lab. Concretes
W/CM = 0.60 - 0.63
Field Concretes
W/CM = 0.57 - 0.59
OPC
Fly Ash
10-17
10-18
10-19
10-20
10-21
Per
mea
bil
ity
(m
2)
Effect of fly ash on permeability – long term effect
Source Mike Thomas
100
1000
10000
100000
1 10 100 1000
Age (days)
RC
P (
Co
ulo
mb
s)
W/CM = 0.50
Control (no slag)
25% Slag
50% Slag
Effect of slag on RCPT
Source Mike Thomas
Example of influence of fly ash on binding
CORROSION OF STEEL IN OPC & 30FA CONCRETE 35 N/mm2, 11 years FAMCET Exposure
OPC OPC/30FA
Source: CSIR Contract nr:BB078 5600 5671 Slide from
ASR, PhD Theodore Chappex, EPFL
Effect of blended pastes on ASR expansion
SCMs are effective in reducing deleterious ASR (empirical additions):
Field & Lab experience:
Silicon and Aluminium addition are involved in the reduction of expansion
Aluminium rich SCMs are more effective against ASR
The exact mechanism by which it happens is unclear!
5%
15%SFQ
15%MK
10%SFQ
10%MK
OPC
Samples in alkaline solution
Systems Studied
Experimental systems:
MK
OPC
Q - Filler
SF
OPC
Si
Al
95, 90, 85%w
5, 10, 15%w
7.65, …%w
7.35, …%w
Paste sample
Pore solution
Piston
EDS Pore solution extraction
TGA
C-S-H EDS analysis
The Si/Ca increase with increasing substitution for both systems (MK and SF-Q)
The Al/Ca is constant for SFQ at all substitutions levels and increase with MK substitution
Pastes can be compared in term of pore solution concentration
300 days:
100
150
200
250
300
350
400
450
K[mmol/l]
OPC
5SFQ
5MK
10SFQ
10MK
15SFQ
15MK
0
50
100
150
0 100 200 300 400 500
Na[m
mol/l]
me[day]
5MK
5SFQ
10MK
10SSFQ
15SFQ 15MK
Pore solution analysis
- The silanol binding capacity is confirmed - No improve of fixation is observed up to 2 years in Al rich systems
Al doesn’t increase the alkali fixation capacity of C-S-H in blended pastes! Another phenomena is involved to control ASR in presence of Al!
Comparatively, the fixation capacity of SFQ and MK are similar. Aluminium has no influence on the fixation capacity of alkalis
C-S-H fixation capacity estimation
New approach: focus on the aggregates
90 days: 300 days:
Pore solution composition of MK pastes
MK systems provide aluminium ions in the pore solution – A peak of aluminium appears during the first 90 days
0
0.5
1
1.5
2
2.5
3
3.5
0 100 200 300 400 500 600
Al[mmol/l]
me[day]
OPC
15MK
10MK
5MK
21
22
23
There is a clear influence of
aluminium ions on aggregates gel
formation!
• First effect is lowering of pH of pore solution
• Lower C/S C-S-H absorbs more alkalis
• SCM high in alumina also inhibit directly dissolution of amorphous
silica
Effect of SCMs on ASR
SULFATE ATTACK, PhD Cheng Yu, South East University, China and EPFL
Crystallization pressure theory Scherer, 2002 2004
IAP > Ksp
IAP = (Ca2+)6 × (Al(OH)4
-)2 × (SO4
2-)3 × (OH -)4
s c = (R ×T / vcrys. ) × ln(IAP /Ksp)
1. Supersaturated solution,
2. Confined crystal growth of solid product
s c =gCL (dA / dV) =gCL (2 / r)
6Ca2+ +2Al(OH)4
- +3SO4
2- + 4OH - +26H2O®C3A ×3CS ×H32
For pressure > 2MPa, r < 100nm Scherer, 1999
Expansion theories
This is only plausible theory
1. Large crystals of
AFm/AFt in “pocket”
3. Pore solution?
2. Fine AFm crystals
in C-S-H
OPC paste before Sufate Attack
Mapping (SO3 profiles)
BUT, mainly reflects the sulfate uptake by solid phases,
not the sulfate content in pore solution.
Amount of sulfate in solid phase (Ettr. & Gypsum) ≠ Expansion
How to measure the sulfate content in pore solution
Relationship between sulfate bound to C-S-H (S/Si) and [SO42-] in pore
solution
Barbarulo et al, 2008
Water cement ratio Sample size Sulfate concentration
M1 0.55 1×1×16 cm 3g/L
M2 0.55 2×2×16 cm 3g/L
M3 0.55 4×4×16 cm 3g/L
M4 0.55 2×2×16 cm 10g/L
M5 0.55 2×2×16 cm 30g/L
Experiment and results: OPC
V solution / V sample = 28
Renew every 2 weeks
(every week at first 4 weeks)
3 month curing
Surface removed
T = 20°C
Expansion
w/c=0.55 2×2×16cm
Effect of concentration
Very similar penetration profiles
120d
What cause the different expansion at 120d?
5mm
120d
4mm
120d
3mm
120d
2mm
120d
4mm 2mm 3mm
120d
The reaction between SO42- and solid phase buffer the [SO4
2-] in pore solution,
depth by depth.
Sample in 30g/L has more sulfate bound in C-S-H than low concentration ones,
probably can explain the difference of expansion
EDS of C-S-H
As sulfate ions penetrate in the cement paste,
they react with unconstrained aluminate phases,
mainly AFm in the pockets,
this buffers the increase of [SO42-] in pore solution.
When all freely transformable Al2O3 has reacted,
the [SO42-] in solution will increase,
constrained AFm within C-S-H can then react to ettringite
and exert expansion force.
Once cracking occurs, SO42- can entry freely and,
react even with Ca2+ to form gypsum in cracks.
Explanation of expansion
Slag blends
SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O TiO2
Slag 31.53 15.85 0.32 36.87 9.69 2.76 0.44 0.332 1.76
w/c=0.55 55S5 2×2×16cm
Expansion
3g/L
10g/L
30g/L
Surface
spalling
• Complicated
• Interaction of:
• buffering effects,
• amount of constrained AFm and
• perhaps transport effects
• Cannot say that blended cements have “chemical” resistance to
sulfate attack if they contain alumina.
• Need for test methods more representative of reality where surface
loss is more important than macroscopic expansion
Effect of SCMs on sulfate resistance
Impact of SCMs
degradation 1st mech 2nd mech General
Impact
SCMs
Carbonation binding transport Negative
Chloride Transport Binding Positive
ASR Pore solution
pH
Alumina Positive
Freeze thaw saturation ?? Negative
Sulfate Conversion
of Afm
embedded in
CSH to
ettringite
transport Claimed
positive
• Durability is not a materials property – depends on environment
• SCMs may improve or worsen durability depending on exposure
condition
• It appears that “1.5 C/S” CSH may slow down transport of water and
chloride
• Carbonation can be a potential problem, for reinforced concrete due to
lack of buffering capacity.
• ASR undoubtedly improved by SCMs
• Sulfate attack (and probably Freeze Thaw) are complex and need to
be better understood.
Summary
Cement Chemistry for Engineers, Cape Town 31st January 2013
End Lecture 5
Further reading
Sustainability:
Sustainable development and climate change initiatives: J.S. Damtoft, J. Lukasik, D. Herfort, D.
Sorrentino, E.M. Gartner. Cement and Concrete Research 38, (2008), 115-127
Straight talk with Karen Scrivener on cements, CO2 and sustainable development: American
Ceramic society Bulletin vol 91 no. 5
http://www.nanocem.org/fileadmin/nanocem_files/documents/misc/Ceram_Bull_article_May_20
12.pdf
Hydration:
The Microstructure of Concrete, Scrivener, K.L., in Materials Science of Concrete I, Skalny, J.P.
ed (American Ceramic Society, Columbus, Ohio) 1989, 127-161
Mechanisms:
Dissolution theory applied to the induction period in alite hydration, Juilland, P. Gallucci, E.,
Flatt, R. Scrivener, K. , Cement and Concrete Research 40 (6), 831-844, 2010
Studying nucleation and growth kinetics of alite hydration using μic, Bishnoi S., Scrivener, K.L.
Cement and Concrete Research, 39, (10) 849-860, 2009
Densification of C−S−H Measured by 1H NMR Relaxometry Arnaud C. A. Muller, Karen L.
Scrivener, Agata M. Gajewicz, and Peter J. McDonald J. Phys. Chem. C 2013, 117, 403−412,
dx.doi.org/10.1021/jp3102964
Further reading
SCMs Hydration:
Supplementary cementitious materials: Review Barbara Lothenbach, Karen Scrivener, R.D.
Hooton, Cem Conc Res, 41(12) 1244-1256, 2011
Methods for determination of degree of reaction of slag in blended cement pastes, Vanessa
Kocaba, Emmanuel Gallucci, Karen L. Scrivener, Cem Conc Res 42, (3) 2012, 511–525
Cement substitution by a combination of metakaolin and limestone, M. Antoni, J. Rossen, F.
Martirena K. Scrivener, Cem Concr Res 42 (2012) 1579–1589
Durability:
Alkali fixation of C–S–H in blended cement pastes and its relation to alkali silica reaction,
Théodore Chappex, Karen Scrivener Cem Conc Res, 42(8) 2012, 1049-1054 DOI:
10.1016/j.cemconres.2012.03.010
Mechanism of expansion of mortars immersed in sodium sulfate solutions, Cheng Yu, Sun Wei,
Karen Scrivener, Cem Conc Res, 43, 2013, 105-111
All EPFL publications available though: http://infoscience.epfl.ch/
Further reading
EPFL Theses: http://library.epfl.ch/en/theses/
T. Chappex, The role of aluminium from supplementary cementitious materials in controlling
alkali-silica reaction. 2012
W. Kunther, Investigation of Sulfate Attack by Experimental and Thermodynamic Means. 2012
A. Quennoz, Hydration of C3A with Calcium Sulfate Alone and in the Presence of Calcium
Silicate. 2011
A. Chabrelie, Mechanisms of degradation of concrete by external sulfate ions under laboratory
and field conditions. 2010
P. Juilland, Early hydration of cementitious systems. 2009.
V. Kocaba, Development and evaluation of methods to follow microstructural development of
cementitious systems including slags. 2009.
R. Fernandez Lopez, Calcined clayey soils as a potential replacement for cement in
developing countries. 2009.
M. M. Costoya Fernández, Effect of particle size on the hydration kinetics and microstructural
development of tricalcium silicate. 2008.
S. Bishnoi, Vector modelling of hydrating cement microstructure and kinetics. 2008.