Recent Advances in ASR Test Methods and Understanding ... · 6/7/2012 1 Recent Advances in ASR Test...
Transcript of Recent Advances in ASR Test Methods and Understanding ... · 6/7/2012 1 Recent Advances in ASR Test...
6/7/2012
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Recent Advances in ASR Test Methods and Understanding
Mitigation Mechanisms, Part 2
ACI Spring 2012 ConventionMarch 18 – 21, Dallas, TX
Karen Scrivener graduated from University of Cambridge in 1979 in Materials Science. She went on to do a PhD on “The Microstructural Development during the Hydration of Portland Cement” at Imperial College, London completed in 1984. She remained at Imperial College until 1995 as Royal Society Research Fellow and then lecturer, heading the
Cement and Concrete Group in the Department of Materials. In 1995 she joined the Central Research Laboratories of Lafarge near Lyon in France as Head of research on Calcium Aluminate cements and expert of concrete durability in general. In March 2001 she was appointed as Professor and Head of the Laboratory of Building Materials, Department of Materials at the Swiss Federal Institute of Technology at Lausanne (EPFL, Ecole Polytechnique Fédérale de Lausanne), Switzerland. She created and is co-ordinating NANOCEM – the industrial-academic research network on cement and concrete which brings together 15 industrial and 24 academic partners. She is Editor-in-Chief of the leading academic journal in the field – Cement and Concrete Research.
Théodore ChappexKaren Scrivener
Understanding the role ofSupplementary Cementitious Materials
in mitigating Alkali Silica Reaction
4 From J. Hideker
Alkali Silica Reaction
Reaction between:
Alkali
Water
Amorphous silica
Long‐term expansion reaction present in certain concretes
Alkali Silica Reaction
6 From J. Hideker
Alkali Silica Reaction
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Amorphous SiO2:
Expansive gel:
Alkali Silica Reaction Effect of blended pastes on ASR expansion
SCMs are effective in reducing deleterious ASR (empirical additions):
Silicon and Aluminium addition are involved in the reduction of expansion
Aluminium rich SCMs are more efficient against ASR
The exact mechanism by which it happens is unclear!
5%
15%SFQ
15%MK
10%SFQ
10%MK
OPCMortar bars in 0.6M NaOHAt 38°C
Presentation outline
Influence of Si and Al onalkali fixation in C‐S‐H
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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
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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 [m
mol/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 analysis28 – 90 ‐ 300 days:
‐ Lowering of pH 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!
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Due to difficulties to quantify all the phases in presence in the blends (XRD/EDS/TGA), a comparative study was done, using the TGA water loss between 30 and 150°C, corresponding to the main C-S-H water loss.
C-S-H fixation capacity estimation
(Amount of free alkalis)
=
(Batch water) – (Total bounded water(800°C))
X
(Alkali concentration from the pore solution)
(Bound alkalis)
=
(Total alkalis of the system)__
(Amount of free alkalis)
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: comparative
New approach: focus on the aggregates
90 days: 300 days:
Presentation outline
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The effect of aluminium on silica dissolution
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
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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
Silica dissolution in presence of aluminium ions
« Metal ions, particularly Al, reduce the rate of dissolution of amorphous silica» [Lewin, 1961]
“only 1.35 Al atoms/nm2 was adsorbed (less than one atom layer), and this was sufficient to minimize the solubility of silica”
[Iler, 1973]
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New approach: Focus on the aggregates
Marine chemistry and geology:
Prepared frustules (amorphous silica) in sea water with and without Al: [Koning, 2007]
Multiscale approach
Concrete / Mortar Reactive aggregates& pore solution
Amorphous silica& pore solution
Is this mechanism present in concrete systems?High alkalinity – Ca saturated
Multi scale approach:
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Concrete / Mortar
simulated pore solutionNo leaching of alkalis, good
reproducibility0.6 M NaOH
Al(OH)3 saturated
Mortar barIllsee aggregate
System at 38°CTo accelerate ASR
Mortar expansion test
MK
OPC
Q - Filler
SF
OPC
Si
Al
95, 90, 85%w
5, 10, 15%w
7.65, …%w
7.35, …%w
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Mortar expansion test
5%
15%SFQ
15%MK
10%SFQ
10%MK
OPC
The Al rich systems (MK) behave better than Al free sytems (SFQ)
The decrease in expansion goes from 10 to 30% by increasing SCM substitution
Concrete / Mortar Reactive aggregates& pore solution
The effect of Al on silica dissolution
Solutions:
‐Al ions concentrations corresponding to blended pastes(0mM / 4mM / 10mM / 30mM / saturated)
‐ 38°C / 60°C
‐ Portlandite saturated
‐0.6 M NaOH
Aggregate:
‐ Reactive Swiss Alps aggregates
Reactive aggregates test
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Reacted fraction analysis (SEM‐Image analysis):
Percentage of gel pocket surface in function of total aggregate surface
[Ben Haha & al.]
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There is a clearinfluence of
aluminium ions on aggregates gel formation!
Concrete / Mortar Reactive aggregates& pore solution
Amorphous silica& pore solution
Conc. Al(OH)4
‐ 0.6/0.2 M NaOH XPS/SEM analyses
0 mM CH sat/CH free – 20°C 14 / 28 / 60 / 90 / 120 days
1.5 mM CH sat/CH free – 20°C 14 / 28 / 60 / 90 / 120 days
2.5 mM CH sat/CH free – 20°C 14 / 28 / 60 / 90 / 120 days
5 mM CH sat/CH free – 20°C 14 / 28 / 60 / 90 / 120 days
10 mM CH sat/CH free – 20°C 14 / 28 / 60 / 90 / 120 days
15 mM CH sat/CH free – 20°C 14 / 28 / 60 / 90 / 120 days
20 mM CH sat/CH free – 20°C 14 / 28 / 60 / 90 / 120 days
CaCa
0.2/0.6 M Na
0.2/0.6 M Na
X mM Al
How does Al incorporate on SiO2 in paste pore solution conditions?
Fundamental study on silica
XPS on fused silica
Quantification
Binding typeSi-Al - Ca incorp.Structural energy
barrierBond strength
definition
How does Al incorporate on SiO2 in paste pore solution conditions?‐fct of alkalinity‐Ca saturated
Fundamental study on silica
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SEM on fused silica
Surface stateprecipitates -Dissolution
CaCa
0.2/0.6 M Na
0.2/0.6 M Na
X mM Al
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.0 5.0 10.0 15.0 20.0 25.0
Al/Si
incorp
[%at]
Al in solu on [mM]
60d 0.2 60d 0.6
M NaM Na
Aluminium incorporation
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Aluminium is incorporated on the surface of silica
Higher incorporationat lower pH (at 28 / 60 / 120 days)
+ 25%
Ca
0.2 / 0.6 M Na
X mM Al
Proposed Mechanism
Mechanism of dissolution of amorphous silica is similar to quartzif considered in term of chemical bounding
Dissolution of Q3 species make appears a Q2 surface, more reactive Q2 group retreat (step retreat like)
[Dove, 2008]
Proposed Mechanism
Al
Al(OH)-4 co-adsorb with Na+
deprotonated silanol groups are associated with Na+ sorbed in the outer-sphere plane
Al is incorporated in the silica framework
The Al ion stabilize the dissociated form of terminal silanol
[Labrid & Duquerroix 1991, Bickmore 2005]
[Koning, 2007]
[Trombetta, 2000]
[Dove, 2008]
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The aim of this test is to provide the same initial surface state for all the treatments
Differences on the 4 sizes were visible only after 90 days
Step 1:
Pre treatment:
30 mM Al / 0.2M Na
solution
90 days
The effect of aluminium on silica dissolution –« 4 sides test »
The aim of this test is to provide the same initial surface state for all the treatments
Differences on the 4 sizes were visible only after 90 days
Step 2:
Post treatment:28 /
60 / 90 / 120 days
0.6M Na solution
Step 1:
Pre treatment:
30 mM Al / 0.2M Na
solution
90 days
The effect of aluminium on silica dissolution –« 4 sides test »
Step 2:
Post treatment:28 /
60 / 90 / 120 days
0.6M Na solution
Step 1:
Pre treatment:
30 mM Al / 0.2M Na
solution
90 days
90 days post
treatment: Conclusion
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It was showed that the aluminium present in the C-S-H of blended pastes doesn’t
decreases the alkalinity of the system
Al incorporation and effect was successfully showed for concrete condition
The mechanism controlling silica dissolution in presence of Al was partially explained and
confirmed
Al is incorporated in the silica framework and probably stabilizes the step retreat
dissolution of the Q2 species
The alkalinity has an influence on the aluminium incorporated fraction. The lower
alkalinity present a higher aluminium incorporation
Aluminium effect has to be combined with an alkalinity reduction to be
more efficient (visible on expansion curves?)
Approximation of dissolution rate? prediction of gel formation rate expansion!
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Thank you