Optimization of the thermal and mechanical properties of concrete with steel slag coarse aggregates and waste glass replaced with cement

Waste glass (WG) and steel slag (SS) are industrial by-products with properties that benefit sustainable concrete production. This research aims to produce concrete with the highest compressive strength and lowest thermal conductivity for green buildings by using WG and SS as the cement and coarse aggregates, respectively. Such a combination is remarkable; furthermore, modeling and optimizing their effects on the thermal conductivity of concrete are an original contribution to this field. A response surface method (RSM) was used in the mix design by considering the most influencing factors (SS, WG, and w/b). The method assessed eighteen mixtures of multiple binders to examine the performance of SS and WG and their complementary roles in improving the desired properties. Substituting SS at high levels (up to 100%) significantly improved both desired properties. However, increasing WG and w/b positively influenced the thermal conductivity and negatively influenced the compressive strength, which decreased by more than 28% compared with the control sample. The implemented linear thermal conductivity effectively correlated the responses and considered factors with a high R-value of 88%. The multi-objective optimization approach determined that the combination of SS = 100%, WG = 30%, and w/b = 0.42 provides the highest compressive strength (71 MPa) and the lowest thermal conductivity (0.7 W/ m. K). Incorporating SS and WG into concrete improved its mechanical and thermal insulation properties and supported the green life strategies.