Effect of carbonation curing regime on strength and microstructure of Portland cement paste

This study aims to investigate the effects of pre-curing and carbonation duration on compressive strength and microstructure characteristics of Portland cement paste. Experimental results showed that 30-40% water loss of cement paste is ideal for CO₂ uptake. The combination of appropriate pre-curing and carbonation duration could increase compressive strength of cement mortar effectively, especially at early age. The optimal pre-curing duration decreases as the carbonation duration increases. Thermogravimetric analysis indicated that carbonation could retard hydration of cement paste and higher concentration of CO₂ increases crystallinity of carbonate. According to MIP results, the influence of hydration and carbonation on pore structure of cement paste is different. Carbonation could decrease large capillary porosity obviously while hydration fills small capillary first. In addition, it is observed from EDS point analysis that excessive carbonation lead to decalcification of C-S-H. Therefore, suitable pre-curing and carbonation duration is of significance to improve the strength and microstructure of cement pastes.