Accelerated carbonation and performance of steel slag concrete with pressurized CO₂ curing

The carbonation of various alkali industrial wastes has been widely investigated owing to its potential permanent sequestration of CO₂. To make use of the carbonated products is of great significance, which may not only facilitate to cut the cost of CO₂ sequestration, but also economically utilize the industrial wastes. In this study, steel slag with relatively high contents of MgO and CaO was used as replacements of Portland cement or natural aggregates to cast concrete and the concrete was exposed to CO₂ curing with a CO₂ pressure of 0.10 MPa. The carbonation front, mechanical strength, microstructure, and carbonate products of the concrete were investigated. Results shown that the compressive strength of the slag concrete after CO₂ curing (0.1 MPa CO₂ and 14d) was significantly increased, obtaining an up to five-fold increase in comparison to that of the same concrete cured in normal moist curing condition for 28d. This may attribute to the densification of the concrete microstructure caused by the formation of Ca-bearing carbonates. According to the results obtained in this study, concrete with low-carbon emissions can be produced via the accelerated carbonation of steel slag.