Utilization of red mud derived from bauxite in self-compacting concrete

Red mud derived from alumina refineries through the Bayer process is a waste material with a density of 2187 kg/m3. The particle size distribution of the red mud is similar to fly ash. In this paper, the physical and chemical properties of the red mud including oxide and mineral contents are studied by XRF and XRD. The potential use of the red mud as a pozzolanic material to replace fly ash in self-compacting concrete (SCC) is assessed by conducting a range of fresh and hardened properties test (such as slump flow, density, porosity, compressive strength, splitting tensile strength, elasticity modulus and drying shrinkage). The XRF and XRD results show that the oxide forms in the red mud are mainly SiO2, Al2O3 and CaO at 45.76%, 40.69% and 4.98% respectively, and the crystalline phases are mainly gismondine, goosecrekite and epistilbite which belong to the zeolite family. The results show that the strength activity indeces (SAI) of the red mud are 79.60 and 88.46 at 7 days and 28 days respectively, which are approximately equal to that of a common Class F fly ash. Meanwhile, with the use of the red mud to replace fly ash in SCC, the compressive strength, splitting tensile strength and elasticity modulus are enhanced. Moreover, with the addition of the red mud, the drying shrinkage decrement is observed in SCC, which might be due to the red mud's internal curing. Therefore, the feasibility of utilizing the Bayer red mud in SCC is demonstrated.