Hydration and performances of ordinary Portland cement containing metakaolin and titanium slag

Metakaolin (MK) finds extensive use in cement, mortar, and concrete due to its exceptional pozzolanic activity, which has been found to significantly improve the long-term mechanical performance, impermeability, corrosion resistance, and other material properties. However, the high adsorption and low dispersion of MK lead to an increased demand for water and superplasticizers to achieve the necessary workability, which poses a challenge for the large-scale application of MK in cementitious materials. In this study, we propose the use of local solid waste titanium slag (TS) as a low-hydration-activity filler and water-reducing mineral admixture to mitigate the adverse effects of MK in Portland cement. The hydration process and performances of the blended cements containing ordinary Portland cement (OPC), MK and/or TS were analysed. Results showed that MK actively participated in the cement hydration process and refined pore structures of hardened pastes. However, the mechanical performance enhancement was accompanied by a dramatic reduction in fresh mortar fluidity. The addition of TS to the blended cement containing OPC and MK effectively improved mortar fluidity, and at the same time, resulted in slightly higher compressive strength compared to OPC. The addition of TS did not change the hydration products. However, it did enhance the filling and lubricating effects, resulting in a denser structure in the hardened paste.