Effect of macro-mesoporous rice husk ash on rheological properties of mortar formulated from self-compacting high performance concrete

•The effect of rice husk ash on rheological properties of mortar was investigated.•Rice husk ash/silica fume increased superplasticizer saturation dosage of mortar.•Rice husk ash predominantly increased the yield stress and viscosity of mortar.•Mortar formulated from SCHPC was a shear-thickening material.•Rice husk ash/silica fume decreased the shear-thickening degree of mortar. In the present study, effect of macro-mesoporous rice husk ash (RHA) on rheological behavior and flowability of mortar formulated from self-compacting high performance concrete (SCHPC) was investigated. For comparison, the investigation was also conducted on samples containing silica fume (SF). The results reveal that the incorporation of RHA/SF decreased mini-slump flow, and increased superplasticizer adsorption, superplasticizer saturation dosage, yield stress and plastic viscosity of mortar. The effect of RHA on yield stress and plastic viscosity is significantly stronger than that of SF, especially when the coarser RHA or the higher content of RHA is used. Interestingly, the increase in particle size or content of RHA predominantly increased plastic viscosity and yield stress rather than decreased mini-slump flow of mortar, especially 60min after water addition. Fresh mortar in this study is a shear-thickening material. The shear-thickening degree decreased over time. The incorporation of RHA/SF decreased the shear-thickening degree where the effect of SF is much stronger than that of RHA. It is suggested that the rheological behavior of mortar is attributable to the capacity and progress of the water adsorption of RHA.