Regulating High-Temperature Hydration Sensitivity of Calcium Aluminate Cement through CO2 Curing and MgO Modification

Calcium aluminate cement (CAC) exhibits severe strength regression due to the conversion of metastable hydrates ( CAH 10 / C 2 AH 8 ) and marked sensitivity to temperature variations. This study introduces a synergistic strategy that couples light-burned MgO modification (0–15 wt.%) with accelerated CO 2 curing (1 MPa, 4 h, 20°–50°C) to suppress phase conversion while simultaneously sequestering CO 2 . Comprehensive experiments combining X-ray diffraction (XRD), thermogravimetric and differential thermogravimetric (TG-DTG) analysis, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) analysis show that 10 wt.% MgO delays the transformation of CAH 10 into C 3 AH 6 through hydrotalcite stabilization and generates Mg-bearing carbonates (nesquehonite, magnesite) that densify the matrix. CO 2 curing at 35°C refines the pore structure (median diameter reduced from 308 to 6.94 nm; porosity from 26.6% to 16.4%), eliminating strength inversion and yielding 44.3 MPa at 90 days, matching the peak value of the uncarbonated reference. However, under elevated carbonation at 50°C, the long-term strength showed a moderate reduction, though it remained superior to untreated CAC. MgO modification coupled with accelerated CO 2 curing effectively mitigates the pronounced temperature sensitivity of CAC.