Evaluation of alkalinity of pore solution based on the phase composition of cement hydrates with supplementary cementitious materials and its relation to suppressing ASR expansion

Yuichiro Kawabata, Kazuo Yamada Journal of Advanced Concrete Technology, 13, 538-553, 2015 A model to evaluate quantitatively the alkalinity of pore solution based on phase composition of cement hydrates with SCMs was proposed and was compared with suppressing effect of ASR expansion. The model is devised from the per-spective of alkali sorption by C-S-H gel, and the parameters for calculation can be evaluated thanks to phase composition analysis such as XRD/Rietveld analysis and selective dissolution. The experimental results have shown that ASR ex-pansion is strongly correlated to the alkalinity of the pore solution, which can be calculated with the proposed model. Based on the results, the ASR suppressing effects of SCMs are converted to the reduction in total alkali content as available alkali content. Finally, the required replacement level of SCM with the proposed model was compared to the CSA A23.2-27A standard based on numerous experiments and field experiences in Canada. The calculated result was well consistent with the minimum replacement level of SCMs specified in CSA A23.2-27A. A subsequent interpretation of this study supports that the dominant mechanism of SCMs for ASR suppression is a reduction of alkalinity of pore solution.

The contents of this paper are very useful especially for cement chemists and concrete engineers who are at present concerned about the ASR problem in Japan and its suppression measures by using SCMs such as fly ash, blast-furnace slag and silica fume. This paper is written in a polite English with good figures and tables. The reviewer also agrees with the authors that SCMs such as fly ash and blast-furnace slag can contribute to the mitigation of ASR expansion of concrete mainly due to the reduction of alkalinity of pore solution in concrete, and that the low C/S ratio CSH formed around fly ash and slag particles can effectively absorb the Na and K ions and fix them in the texture of CSH. (Reviewer B)