Influence of hydraulic cement substitutes on carbonation of calcium silicate cement☆

Enhancing the early-age carbonation efficiency and the setting time of calcium silicate cement (CSC) are crucial for its application as a nonhydraulic binder. This study investigates the carbonation efficiency of CSC blended with hydraulic cement substitutes, including Portland cement (PC), calcium aluminate cement (CAC) and calcium sulfoaluminate cement (CSA). Samples were made with 0 %, 10 %, 30 % and 50 % replacement with hydraulic binders and were cured in 20 % CO2 environment. The carbonation products were characterized microscopically using TGA, XRD and FT-IR, along with compressive strength test. The results revealed that hydrated CSC-PC is mainly characterized by amorphous content, primarily attributed to C-S-H. Meanwhile, samples incorporating CAC and CSA precipitated C2ASH8, C3AH6 and C4A$H12phases. However, carbonation destabilized these phases while precipitating significant CaCO3 content, a phase that ensures strength development in CO2-based binders. Incorporation of 30 % CAC and CSA has ensured precipitation of 14.5 g and 34 g per 100 g binder of CaCO3 after 6 h of carbonation, while the content was lower in pure CSC and CSC-PC samples. After 168 h of CO2-curing, the amount of unreacted clinker was nearly reduced by half when 50 % of CSC was substituted by hydraulic cement, increasing the compressive strength by 230 %, particularly for CAC-and CSAcontaining samples.