Insight into mechanical properties and microstructure of concrete containing steel slag and ground-granulated blast-furnace slag

The impacts of steel slag (SS) and ground-granulated blast-furnace slag (GGBS) on the mechanical properties, hydration process, and microscopic characteristics of concrete were investigated in this study. The results show that substituting cement with SS has a negative impact on the strength; however, partial replacement of SS with GGBS could produce positive effect by facilitating the whole hydration of SS and cement. The improvement impact of GGBS on strength was small in early stages (3–28 days) and occurred mainly in the late stages (28–90 days). Meanwhile, the heat flow and cumulative hydration heat was decreased by the incorporation of SS and GGBS, in comparison to plain cement. The microscopic analysis results proved that replacing SS with GGBS could increase the whole hydration reaction degree, decrease the content of Ca(OH)2, enhance the compactness of the interfacial transition zone (ITZ), and refine the pore structure of concrete. Furthermore, a formula was established to estimate the splitting tensile strength according to compressive strength. The finding of this study provides valuable information on the practical application of the industrial wastes in concrete.