OM-SEM analysis on a 10-year old concrete pavement in a bus stop have shown serious damage due to AAR. It turned out that the aggregates responsible for the formation of expansive products (both amorphous gel and microcrystalline phases) and the damage are serpentinite/greenstone/greenshist. There is clear evidence for reaction between the pore solution and some mineral phases (e.g. Ca-Mg amphibole, serpentinite, etc.). The reactions, however, are not fully understood so far, especially because some of the observed mineral phases are being stabile in high pH environment. Has anybody seen serpentinite, greenstone undergo to AAR (ASR)? Thanks!
Dear Mr. Pinter:
Please find attached a flow sheet demonstrating the supergene alteration of metabasic and metaultrabasic rocks to be published in Earth Science Reviews (2016) online and entitled:
Residual clay deposits on basement rocks: The impact of climate and the geological setting on supergene argillitization in the Bohemian Massif (Central Europe) and across the globe.
It may help you get a bit closer to a solution.
Viel Erfolg
Harald G. Dill
Dear Dr. Gill,
Thank you for the valuable information! I´ve already downloaded the full paper.
Best regards/Beste Grüße
F. Pinter
dear farkas,
Carbonation occurs when carbon dioxide from the air penetrates
the concrete and reacts with hydroxides, such as calcium
hydroxide, to form carbonates. In the reaction with calcium
hydroxide, calcium carbonate is formed:
Ca(OH)2 + CO2 → CaCO3 + H2O
This reaction reduces the pH of the pore solution to as low as
8.5, at which level the passive film on the steel is not stable.
Carbonation is generally a slow process. In high-quality concrete,
it has been estimated that carbonation will proceed at a
rate up to 1.0 mm (0.04 in.) per year. The amount of carbonation
is significantly increased in concrete with a high water-to-cement
ratio, low cement content, short curing period, low strength, and
highly permeable or porous paste.
There is a very interesting document recently published by RILEM 219-ACS :
Petrographic Atlas: Characterisation of Aggregates Regarding Potential Reactivity to Alkalis - RILEM Recommended Guidance for Use with the RILEM Petrographic Examination Method - Final draft report
Edited by Isabel Fernandes, Maria dos Anjos Ribeiro, Marteen A T M Broekmans, Ian Sims
You can acces to a pdf version with the link below
http://www.rilem.org/global/gene/link.php?doc_id=4973&fg=1
Regards
Maxime
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