Alkali silica reaction in mortar formulated from self-compacting high performance concrete containing rice husk ash

Abstract

In the present study, the resistance of mortar formulated from self-compacting high performance concrete containing rice husk ash (RHA)/silica fume (SF) and reactive/non-reactive aggregates to alkali silica reaction (ASR) was assessed.For the mortar containing greywacke reactive aggregate, SF is significantly more effective than RHA in reducing expansion of the mortar under accelerated testing conditions (NaOH 1M at 80°C). The increase in particle size of RHA increased the expansion of mortar. Surprisingly, the mortars containing coarse RHA, i.e. 15.6 and 7.7μm, were disrupted after 28 and 56days of immersion. However, the increase in the fine RHA (5.7μm) content decreased the expansion of mortar.For the mortar containing non-reactive basalt aggregate, the incorporation of RHA increased the expansion, and the samples containing the coarse RHA (15.6μm) cracked substantially. This indicates that RHA had paradoxical effect on ASR. The results from microscopic investigations show that RHA particles cracked substantially. The cracks also radiated from the RHA particles into the matrix, and ASR gels formed inside the RHA particles. It is suggested that to mitigate ASR by using RHA, RHA should be ground to very fine particle sizes of at least 5.7μm.