To further enhance the mechanical properties of CO2-cured sodium-doped calcium silicate (Na2Ca2Si3O9) compacts and promote sustainable low-carbon materials, this study analyzed the subsequent hydration hardening behavior after initial carbonation curing. The compressive strength evolution, pore structure, phase composition, and microstructure were characterized through strength tests, 1H NMR, XRD, TGA, FTIR, and SEM analyses. The findings reveal that subjecting carbonated Na2Ca2Si3O9 compacts to further water-saturated hydration curing enhances their hardening performance. The compressive strength of the 28 d subsequent hydration-cured samples exhibited a remarkable increase compared to the carbonated counterparts. Microscopic examination elucidates that sufficient water facilitates continuous reactions between carbonation products and unreacted Na2Ca2Si3O9, generating more prismatic pirssonite(Na2Ca(CO3)2·2 H2O), CaCO3, and (N)-C-S-H gels, leading to reduced porosity and superior compressive strength. The proposed mechanism offers insights into activating the subsequent hardening process of carbonated cementitious materials.
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