Contribution of calcium-containing minerals on the mechanical properties of alkali-activated materials: A study of carbonation steel slag

Not only capture CO₂, the carbonated steel slag (CSS) can be used as supplementary cementitious materials to exhibit excellent physical and chemical properties. In order to understand the mineral phase evolution and hydration mechanism of CSS in alkali-activated materials (AAMs), the contribution of calcite and calcium-containing minerals (Ca-minerals) to the hydration degree was deeply investigated, and the microstructure and mechanical properties of AAMs were explored. The results showed that AAMs prepared by CSS exhibited stronger early mechanical properties and lower drying shrinkage than AAMs prepared by steel slag (SS). The compressive strength of AAMs prepared by 30 % CSS and 70 % fly ash was 54.2 % greater than that of AAMs prepared with SS in the same conditions. The EDS test suggested that the carbonation product calcite possessed a higher specific surface area and provided more nucleation sites. Both calcite and Ca-minerals could provide Ca^2 + into the silica-aluminate network. The decomposition reaction rate of calcite stabilized at around 30 % when FA was incorporated in paste, and the remaining calcite could fill the pores to improve the strength. Interestingly, 87.6 % of calcite mainly produced pirssonite when only CSS existed in paste. Besides, the Ca-minerals (srebrodolskite, brownmillerite, and all mayenite) in CSS possessed higher reactivity compared with SS, and underwent rapid decomposition under alkali activation conditions. Carbon footprint analysis showed that AAMs prepared with CSS resulted in the lowest carbon emission of 308.4 kg CO₂-eq, providing a novel approach for the application of CSS.