Improving the mechanical properties of cement-based materials under high temperature: Reducing the C3S/C2S ratio

Aiming at the phenomenon of strength decline of cement stone at high temperatures, a new method was proposed to enhance its mechanical properties: the CaO/SiO2 ratio was pre-emptively reduced by decreasing the C3S/C2S ratio in the cement, which was then reinforced with an appropriate amount of silica powder. To verify the reliability of this new method, the hydration characteristics of the C3S-C2S system at 230 °C and 20.7 MPa were investigated via Vickers hardness, BJH, XRD, TGA, and SEM-EDS. Results showed no emergence of new physical phases with changes in the C3S/C2S ratio. Increasing the content of C2S facilitated the formation of additional xonotlite. Optimal Vickers hardness of the C3S-C2S system was attained at 27.69 MPa when the C3S:C2S ratio was 1:1. The compressive strength of compound cement, comprising G-class oil-well cement and low-heat cement, increased by 5–10 MPa when the C3S:C2S ratio in the compound cement was approximately 1.07:1. Both the C3S-C2S system and compound cement showed that their mechanical properties increased with increasing C2S content. Predictions suggest an optimal C3S:C2S ratio of 1:1 for the new low-calcium high-temperature-resistant cement. The future application of this new method promises material cost savings and reduced carbon emissions from cement production.