Effect of Carbonation Curing on Mechanical Strength and Microstructure of Mortars Prepared with Steel Slag-Cement-MgO-CaO Blends

Steel slag powders were used as the main component of cementitious materials, and MgO, CaO and Portland cement were incorporated to prepare mortar specimens. The mortars were then exposed to CO₂ curing to test the compressive strength and microstructure and investigate the mechanism of improving strength of carbonation curing. The results show that the compressive strengths of mortars increase significantly after the carbonation curing, by 3.9-6.8 times after only 1d of carbonation. Prolonging the carbonation curing time facilitate the carbonation reaction, and hence increases the degree of carbonation and enhances the strength gain of mortars. The incorporation of CaO and MgO components increases the compressive strengths of mortars, and the highest compressive strength can reach 71. 6MPa after 14d of carbonation, when 5%(by mass) CaO and 15%(by mass) MgO are incorporated. The treatment of CO₂ curing decreases the total pore volume of mortar specimens due to the microstructure densification as a result of the formation of calcite CaCO₃(calcium magnesium Ca_xMg_1-xCO₃) and aragonite CaCO₃.