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

• Published in: Construction & building materials 2015-07, Vol.88, p.10-19
• Main Authors: Le, Ha Thanh, Siewert, Karsten, Ludwig, Horst-Michael
• Format: Article
• Language: English
• Subjects: Aggregates; Aggregates (Building materials); Alkali resistance tests; Alkali silica reaction; Analysis; Ashes; Chemical properties; Concrete; Concretes; Construction materials; Mortars; Non-reactive aggregate; Paradoxical effect; Particle size; Reactive aggregate; Rice husk ash; Self-compacting high performance concrete; Silica; Silicon dioxide
• ISSN: 0950-0618
• DOI: 10.1016/j.conbuildmat.2015.04.005

•The effect of rice husk ash on ASR in mortar formulated from SCHPC was investigated.•The mortar containing reactive greywacke aggregate can be durable when SF and RHA5.7 are used.•SF was significantly more effective than RHA in mitigating ASR in mortar.•RHA had paradoxical effect on ASR especially when coarse RHA is used.•To mitigate ASR, RHA should be ground to very fine particle sizes of at least 5.7μm. 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.