Reconsideration of Required Studies on Predicting Long-Term Effects of AAR on the Performance of Real Structures

This paper is based on the hypothesis that expansion due to alkali-aggregate reaction (AAR) is caused by alkali-silica gel (ASG) constrained inside the aggregate, which is produced by the alkali-silica reaction (ASR) caused by high pH concrete porewater and reactive aggregates. An attempt was then made to describe the four points of studies required to bridge the gap between materials science fundamentals and engineering applications. 1) Petrographic diagnosis is essential for the analysis of the AAR, but its implementation has to be based on an assessment of what is not visible by polarized light microscopy, i.e. the presence of cryptocrystalline quartz and highly viscous ASG. 2) It is known that the trend of AAR expansion does not match that of accelerated tests and exposure conditions, and it is explained that this is due to the fact that the AAR expansion is affected by the change in the constraining conditions of the ASG due to the accelerated ASR. This can be a reason why the produced amount of ASG does not show a proportional correlation with the expansion. 3) It was then explained that this working mechanism can explain various complex pessimum phenomena (aggregate composition, aggregate grain size, total alkali content, temperature, and age of the evaluation). 4) The rate of ASR depends on the pH of the porewater, but the working mechanism by which the pH is determined and the process by which it influences AAR expansion was presented, explaining the necessity for long-term evaluation. One important suggestion of this study is that simply, slow ASR will result in more AAR expansion by the same amount of ASG.