Ultra high performance concrete made with rice husk ash for reduced autogenous shrinkage

Abstract

Ultra High Strength Concrete (UHPC) is generally made with low w/c mixtures and by adding silica fume. Low w/c mixtures, however, exhibit high autogenous shrinkage, while a high amount of silica fume increases the price of these mixtures. For designing ultra high strength mixtures with low autogenous shrinkage and lower costs the possibility of using rice husk ask (RHA) as alternative for silica fume has been studied. The use of RHA as replacement of cement is well known, but the application of this material for (ultra) high strength mixtures has hardly been considered yet. In this paper the results are shown of an extensive study of the compressive strength of UHPC made with partial replacement of cement by RHA. The mean size of the RHA particles varied from 3.6 ?m and 9 ?m. Samples with a combination of 10% RHA and 10% SF showed higher compressive strength than the control samples with either 20% RHA or 20% SF as cement replacement. This blend proved to be the optimum combination for achieving maximum synergic effect. Due attention is given in this paper to the observation that the use of RHA resulted in a substantial reduction of autogenous shrinkage compared to UHPC mixtures made with silica fume.