Hydration of Portland cement with red mud as mineral addition

The use of red mud from Bayer process in association with Portland cement has been shown to be promising because of its good performance on the hardened state. However, the physicochemical interactions during the cement reaction have not been explored in depth in the literature. As the red mud is rich in iron, aluminates, silicate and, mainly, sodium components, the interaction with Portland cement is rather complex. Additionally, the large amount of finer particles can introduce another variable in the development of hydrated compounds. This work was aimed at evaluating the impact from partial substitution of Portland cement for different contents of red mud collected in an alumina production plant in the northeast of Brazil. The hydration reaction was monitored by isothermal conduction calorimetry and the setting time of cement by the Vicat test. The results indicate that the residue of bauxite ore affects the chemical reaction of cement, due to nucleation effects, packing and dilution, and the high amount of sodium and soluble aluminates from the red mud causes the formation of sodium silicoaluminate hydrate (NASH) and a greater amount of hydrated calcium aluminate, which had no effect on the setting time.