Study of the possibilities of using Red Mud as an additive in concrete and grout mortar

Report, 2014

This report presents the results from a study of the possibilities of using red mud, a waste product derived from the digestion of bauxite with a versatile mineralogical composition, as additive in concrete, grout mortar and cement paste. Two types of red mud from China were used in the experiments. Concrete in which 0-30 % of the mass of the binder was replaced by red mud were cast for investigating the effect of red mud addition on the compressive strength and dry shrinkage of concrete. Grout mortars in which 0-30 % of the mass of the binder was replaced by red mud were cast for investigating the effect of red mud addition on the flexural and compressive strengths, dry shrinkage and water permeability of mortar. Cement paste in which 0-30 % of the mass of the binder was replaced by red mud were cast for investigating the effect of red mud addition on the capacity of Cs adsorption and ionic leaching. The results show that addition of red mud does not contribute to nor impair the strength of the concrete or grout mortar but instead acts as inert filler. The decrease in compressive strength of concrete with addition of red mud is mainly due to the increased water-cement ratio. There is no significant increase in dry shrinkage of concrete with addition of red mud, but there is a certain increase in dry shrinkage of grout mortar, especially when more than 20% of the binder is replaced by red mud. Addition of red mud in grout mortar significantly increases the water permeability of the mortar due to the increased water-cement ratio. Owing to the fluctuant results from the adsorption test, it is difficult to draw a conclusion of the adsorption capacity for Cs by addition of red mud in concrete. However, the preliminary results from a quick adsorption test indicated a good adsorption behavior of cement with the addition of red mud, especially at a low initial Cs concentration.