Synergistic Improvement in Setting and Hardening Performance of OPC-CSA Binary Blended Cement: Combined Effect of Nano Calcium Carbonate and Aluminum Sulfate

The combined effect and corresponding mechanism of nano calcium carbonate (NC) and aluminum sulfate (AS) on the setting and hardening performance of binary blended cement (ordinary Portland cement (OPC) and calcium sulfoaluminate cement (CSA)) were evaluated through multiple experiments, including setting time, calorimetry, compressive strength, X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP). The results showed that, as compared to OPC, OPC-CSA binary blended cement exhibited reduced setting time but decreased early strength, which could be caused by the depressed silicate phase hydration due to the fast supply of aluminate ions during the hydration of aluminate-contained phases contained in CSA. However, through the combined addition of NC and AS, the depressed silicate phase hydration was greatly promoted by NC due to its nucleation effect, and the reduced early strength was significantly improved. Further analysis indicates that the combined addition of NC and AS can promote the formation of C-S-H gel and decrease the porosity of the hardened OPC-CSA binary paste. In this way, one promising repair material with rapid setting and hardening properties was prepared by OPC-CSA binary blended cement with the combined addition of NC and AS.