Influence of rice husk ash on strength and permeability of ultra-high performance concrete

This paper aims to investigate the effects of rice husk ash (RHA) on strength and permeability of ultra-high performance concrete (UHPC). RHA was manufactured by calcining rice husk at temperature of 500 °C and incorporated in UHPC mixture to replace different ratio of silica fume (SF) by weight. Flowability and air content of fresh mixture and the compressive and flexural strength at different curing ages were measured. Permeability before and after loading were assessed by water absorption and chloride ion penetration. The pore structure was also evaluated for selected samples by using mercury intrusion measurement. The results show that the addition of RHA to replace SF decreases the fluidity of fresh UHPC mixture and entraps more air bubbles. The addition of RHA enhances the compressive strength and impermeability of UHPC due to the refined pore structure. The permeability of cylindrical specimen increases notably with the increasing vertical loading and the lateral loading has an insignificant influence on the water absorption. When the loading level is lower than 70% of ultimate strength, the RHA added sample presents a lower water absorption and chloride ion penetration than the control one. Therefore, RHA is a promising substitute for SF in UHPC production.