Revisiting Ancient Roman Cement: The Environmental-Friendly Cementitious Material Using Calcium Hydroxide-Sodium Sulfate-Calcined Clay

This study proposes an environmental-friendly cementitious material using calcium hydroxide-sodium sulfate-calcined clay based on the idea of ancient Roman cement. The pozzolanic reaction characteristics of calcined clay are studied by adjusting the ratio of calcined clay and calcium hydroxide in both experimental and thermodynamic modeling methods, which demonstrate that 70% calcined clay and 30% calcium hydroxide are the optimal ratio for the pozzolanic reaction of calcined clay to promote the formation of hydration products. Furthermore, the effect of sodium sulfate on the microstructure and mechanical properties of the cementitious materials are also investigated. Results indicate that 5% sodium sulfate (relative to the total mass of the binder) can accelerate the pozzolanic reaction of calcined clay and optimize its mechanical properties. Overall, this study provides a non-clinker cementitious material with high utilization of calcined clay to reduce energy consumption and CO2 emissions.