Performance of carbonated and plain steel slag powder as concrete admixtures

Due to its potential reactivity, steel slag (SS) is considered to be a promising supplementary cementitious material. In this work, wet carbonation was used to study the carbon dioxide sequestration (CDS) performance of modified steel slag (MSS). Carbonated modified steel slag (CMSS) and SS were used as cement replacements, and the workability, mechanical properties and durability of the blended cements were evaluated. At a carbonation pressure below 0.5 MPa, aragonite formed alone in aqueous solution. When the carbonation pressure was increased to 1.7 MPa, weddellite appeared on the surfaces of the SS. The CDS capacity of MSS first increased then decreased with carbonation pressure, peaking at 131.16 kg/t at 1.3 MPa. Residual soluble calcium salts in CMSS accelerated cement hydration by supplying Ca2+. The CMSS blends met standard requirements only at replacement ratios below 20%, with compressive strength up to 85.94% of that of the pure cement system. The optimal SS replacement was 15%, yielding 81.04% relative strength. At optimal dosages, the CMSS blends exhibited better carbonation, chloride and sulfate resistance than the pure cement system, while the SS blends showed reduced performance.