Influence of steel slag on the hydration mechanism and thermal conductivity performance of alkali-activated steel slag-based foamed concrete

The application of steel slag to prepare foamed concrete has significant economic and environmental benefits. This paper investigated the effects of steel slag content on the hydration mechanism and thermal conductivity performance of the foamed concrete by preparing a type of alkali-activated steel slag-based foamed concrete (ASFC), which was prepared using an alkali‑activated ternary system of steel slag, fly ash, and desulfurization gypsum. The influence of steel slag content on the fluidity, setting time, stability, drying shrinkage, compressive strength, thermal conductivity, and microscopic structure analysis of ASFC was studied. The hydration mechanism was elucidated through microstructural analysis. The obtained results demonstrate that incorporating steel slag enhances the fluidity of the fresh mixture and prolongs the setting time of ASFC. Moreover, with the increase in steel slag content from 0 % to 30 %, the compressive strength of ASFC increased by 26 % (2.92–3.68 MPa), and thermal conductivity decreased by 24.6 % (0.325–0.245 W/(m·K)). However, increasing steel slag content marginally reduced volume stability. Microstructural analysis demonstrated that ASFC with 20 % steel slag content exhibited optimal pore structure uniformity, with smaller pore sizes and a dense matrix in which well-formed C-A-S-H gels encapsulated ettringite crystals. Steel slag enables effective dissolution of silicate glassy phases under alkaline activation (NaOH/Na₂SiO₃), facilitating C-A-S-H formation through enhanced raw slag hydration. • A novel alkali-activated steel slag-based foam concrete (ASFC) using is prepared using industrial solid wastes. • The hydration products and the microstructure of ASFC are analyzed through XRD, SEM, TD/DTG and MIP. • The synergistic hydration mechanism of ternary solid waste materials was elucidated. • Increasing steel slag content improves compressive strength and decreases thermal conductivity significantly.