Enhanced reactivity and CO2 mineralization of low-lime calcium silicate cement by incorporating nitric acid as an initial calcium leaching agent

This study proposed mixing HNO₃ solution with low-lime calcium silicate cement (CSC) to enhance the CO₂ capture and mechanical properties after CO₂-curing by increasing Ca²⁺ leaching at the initial stage. To clarify the influences of HNO₃ and the reaction mechanisms, various molar concentrations of HNO₃ (0, 0.01, 0.05, 0.1, 0.2, 0.5, and 1.0 M) were homogenized with CSC using a liquid-to-solid ratio (L/S) of 0.4 and CO₂-cured in a pressurized chamber for 24 h. The impact of HNO₃ on the initial reaction kinetics, Ca²⁺ leaching, phase composition after curing, CO₂ fixation capability, and mechanical performance were investigated. The findings revealed that the incorporation of HNO₃ had a pronounced influence on the degree of reaction, CO₂ fixation, and mechanical performance of CSC pastes. Nevertheless, the excessive incorporation of HNO₃ had a notable adverse impact on the reaction.