Modelling the synergistic effect of waste glass and inert slag aggregate on ultrahigh-performance concrete tensile strength

The recycling of electric arc furnace slag (EAFS) and waste glass powder (WGP) into ultrahigh-performance concrete (UHPC) is an eco-friendly and cost-effective sustainable method. In this study, the synergistic effects of using EAFS and WGP as weight replacements with fine aggregates (reaching 70%) and with cement (reaching 40%) on the tensile strength and durability characteristics were investigated. The technical complementary roles of WGP, EAFS and nanosilica (NS) as blends of binary and ternary binders were evaluated using design of experiment and response surface methodology (RSM) to improve the properties of UHPC. Accurate correlations between the independent variables and the targeted responses were determined by the generated second-order models. Multi-objective numerical optimisations were performed using the maximum flexural and splitting strengths and uppermost replacement levels of WGP and EAFS to attain a sustainable mixture with a compressive strength greater than 150 MPa. The inclusion of 15.36% WGP, 49.61% EAFS, and 2.48% NS were predicted to reach maximum 180-day flexural and splitting tensile strengths of 35 MPa and 17.44 MPa, respectively. These two combinations optimised different parameters, including a minimum water absorption (WS) of 0.99% and a minimum volume of permeable air voids of 2.63%. Moreover, these ideal proportions reduced cement consumption significantly and led to the production of eco-friendly UHPC, fulfilling the specification requirements at the lowest cost and minimum cement content.