Development of novel mineral admixtures for sulphoaluminate cement clinker: The effects of wet carbonation activated red mud

In our previous work, an in situ wet carbonation method was proposed to enhance the activity of waste-sintering red mud (SRM) by producing large amounts of fine calcium carbonate and silica-aluminum gels. This paper further investigates the effect of carbonated SRM (C-SRM) dosing (0%, 5%, 10%, 15%, 20% and 25%) on the hydration-hardening properties of sulphoaluminate cement (CSA) clinker paste, such as flowability, setting time, reaction temperature, compressive strength, microstructure and pore structure evolution. The results show that the use of C-SRM as a new mineral admixture not only significantly improves early strength but also effectively compensates for the strength deficit of CSA clinker due to the conversion of AFt to AFm at a later stage. When the C-SRM content is 20%, the compressive strength reached its maximum at all ages, with the 1 d compressive strength increasing by 96.9% and the 90 d compressive strength by 19.8%. The microstructure analysis shows that the C-SRM has a good crystalline nucleation effect and can participate in the hydration reaction of CSA clinker, forming semi-carbonate aluminates and stabilizing ettringite, thus densifying the microstructure of the hardened paste. The above results open new possibilities for incorporating C-SRM as a novel mineral admixture into CSA clinker while further reducing CO₂ emissions.