Comparative study of the efficacy of fly ash and reactive aggregate powders in mitigating alkali-silica reaction

Abstract

This study investigates the ability of reactive aggregate powders to mitigate alkali-silica reaction (ASR) in comparison with fly ash using the accelerated mortar bar test (AMBT). ASR expansion results confirm that the reactive aggregate powders can mitigate ASR, although fly ash still has better mitigating efficacy. Microstructural characterization post-AMBT shows presence of extensive cracking in the plain OPC mortar, few cracks in the mortar with 25% reactive aggregate powders and negligible cracking in the mortar with 25% fly ash. Elemental analysis shows that the reactive aggregate powders are able to increase the Si/Ca and Al/Si ratio of C–S–H composition similar to fly ash. 25% fly ash replacement however results in much higher Si/Ca and Al/Si ratio which likely explains its better efficacy in mitigation. Thermogravimetric analysis results demonstrate that the reactive aggregate powders are pozzolanic like fly ash and that a reactive aggregate powder with better pozzolanic properties has better efficacy to mitigate ASR. The reactive aggregate powders however unlike fly ash do not contribute to compressive strength development of the mortars.