Microstructural changes in alkali activated fly ash/slag geopolymers with sulfate exposure
Sulfate attack is recognized as a significant threat to many concrete structures, and often takes place in soil or marine environments. However, the understanding of the behavior of alkali-activated and geopolymer materials in sulfate-rich environments is limited. Therefore, the aimof this stud...
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| Main Authors: | , , , , |
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| Format: | E-Article |
| Language: | English |
| Published: |
Springerlink
2013
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| Subjects: | |
| Online Access: | http://ir.unimas.my/id/eprint/15739/1/Microstructural%20changes%20in%20alkali%20activated%20%28abstract%29.pdf http://ir.unimas.my/id/eprint/15739/ https://link.springer.com/article/10.1617/s11527-012-9906-2 |
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| Institution: | Universiti Malaysia Sarawak |
| Language: | English |
| Summary: | Sulfate attack is recognized as a significant
threat to many concrete structures, and often takes place
in soil or marine environments. However, the understanding
of the behavior of alkali-activated and geopolymer
materials in sulfate-rich environments is
limited. Therefore, the aimof this study is to investigate
the performance of alkali silicate-activated fly ash/slag
geopolymer binders subjected to different forms of
sulfate exposure, specifically, immersion in 5 wt%
magnesium sulfate or 5 wt% sodium sulfate solutions,
for 3 months. Extensive physical deterioration of the
pastes is observed during immersion inMgSO4 solution, but not in Na2SO4 solution. Calcium sulfate dihydrate
(gypsum) forms in pastes immersed in MgSO4, and its
expansive effects are identified as being particularly
damaging to the material, but it is not observed in
Na2SO4 environments.A lowerwater/binder (w/b) ratio
leads to a greatly enhanced resistance to degradation
by sulfate attack. Infrared spectroscopy shows some
significant changes in the silicate gel bonding environment
of geopolymers immersed in MgSO4, attributed
mostly to decalcification processes, but less changes
upon exposure to sodium sulfate. It appears that the
process of ‘sulfate attack’ on geopolymer binders is
strongly dependent on the cation accompanying the
sulfate, and it is suggested that a distinction should be
drawn between ‘magnesium sulfate attack’ (where both
Mg2? and SO4
2- are capable of inducing damage in the
structure), and general processes related to the presence
of sulfate accompanied by other, non-damaging cations.
The alkali-activated fly ash/slag binders tested here are
susceptible to the first of these modes of attack, but not
the second. |
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