Balance between carbonation and hydration: optimal timing of carbonation for enhancing the mechanical strength of Portland cement

Clarifying the influence of CO2 intervention timing on the mechanical and carbon sequestration properties of cement is of great significance for the low-carbon development of cement-based materials. In this study, CO2 curing experiments were conducted to investigate the effect of carbonation curing timing on cement strength and carbon sequestration performance. The results show that CO2 intervention curing enhances the early-age strength of cement-based materials but reduces their final strength. The optimal intervention timing for CO2 curing is at 7 d of cement hydration. When the degree of cement hydration is low or high, CO2 curing is detrimental to long-term strength development. The influence of CO2 intervention curing on cement strength is mainly reflected in the carbonated shell extending from the outer surface to a depth of 5 mm, with maximum strength changes of 20.98% (increase) and 30.52% (decrease), while the internal hydration process and strength development are almost unaffected.