Effect of carbonation curing on mechanical strength and volume stability of steel slag concrete

Currently the utilization ratio of steel-making slag is relatively low, and hence there is a need to seek for new economical ways to use the steel slag. In this study, steel slag concretes were prepared by using ground steel slag powders as partial replacements of Portland cement at different levels and/or using the coarse steel slag directly as aggregates as substitutions of river sands and coarse aggregates. The steel slag concretes were then exposed to CO₂ curing to investigate the influences of carbonation on the compressive strength and volume stability of the concretes. The results show that the compressive strengths of steel slag concretes increased significantly after the carbonation curing, which increased by 3.2-5.3 times after 14 d of carbonation and moreover the highest compressive strength reached 65.3 MPa. Prolonging the carbonation curing time facilitated the carbonation reaction, and hence increased the carbonation depths, decreased the pH values and enhanced the strength gain of steel slag concretes. The treatment of CO₂ curing decreased the water absorption of concrete specimens due to the microstructure densification as a result of the formation of calcite CaCO₃ (calcium magnesium Ca_xMg_1-xCO₃). Steel slag aggregates might also be carbonated, which is beneficial for the compressive strength development and the volume stability improvement.