Effects of red mud on properties of self-compacting mortar

Abstract

Red mud is a waste material derived from alumina refineries through the Bayer process. In this paper, the red mud is used to replace fly ash at various replacement ratios in the production of self-compacting mortars. Two series of mix proportions (series I and II) are designed to investigate the fresh and hardened properties of self-compacting mortars (SCM). In series I, the replacement ratios of red mud range from 0% to 50% by weight; in series II fly ash is replaced by red mud at 0%, 25%, 50%, 75% and 100% by weight. The results show that the fluidity is reduced as red mud is used to replace fly ash; meanwhile, a trend towards mitigation of bleeding is observed due to red mud porosity. An increase in red mud content also brings a slight decrease of hardened density, an increase of water absorption and permeable voids. In the case of mechanical properties, red mud is effective in enhancement of the compressive and flexural strength; the compressive and flexural strength of SCM mixture samples prepared with red mud at 50% of replacement ratio are higher than those of other samples. As for the drying shrinkage and autogenous strains, all drying shrinkage values are increased as red mud is used to replace fly ash; however, a decrease of autogenous strains is observed with an addition of red mud, and the trend is more pronounced when the replacement ratio is 50%.