Mechanism of ASR reduction by reactive aggregate powders

This study aimed to evaluate the effectiveness of a mechanism responsible for the mitigation of expansion when reactive aggregate powders (RAP) were used in concrete containing the same reactive aggregate. In the first part, it was shown that RAP were efficient in reducing the expansion of concrete by 35 to 95%. The most efficient powders were those coming from aggregates having high active silica contents (glass, opal). Powders of siliceous limestone were less effective. In a second part, experimental evidence of the pozzolanic activity of RAP was obtained. It was shown that RAP were similar to pozzolan, since they consumed lime and produce calcium–silicate–hydrate (C–S–H) having a lower calcium/silica (C/S) ratio than normal C–S–H. The third part showed experimentally that these low C/S C–S–H could increase the redistribution of alkalis of the pore solution, thus reducing the alkalinity of the pore solution to a level that was sufficiently low to limit the attack of coarser reactive aggregates. In the final part, numerical simulations using a modified version of the hydration model CEMHYD3D were carried out to support this assumption.