Experimental and GEP-based assessment of steel fiber-reinforced self-compacting concrete containing waste glass aggregate and silica fume

This study investigates the combined use of waste glass aggregate (WGA, 0–60% volumetric replacement of natural coarse aggregate) and silica fume (SF, 0–15% replacement of cement) in steel fiber-reinforced self-compacting concrete. The experimental program covered fresh, mechanical, and durability properties, along with production cost, embodied CO₂, and scanning electron microscopy (SEM) observations. The results showed that 15% SF improved strength and durability, whereas WGA contents above 45% reduced fresh performance. The optimum mixture, containing 15% SF and 30% WGA, increased the 90-day compressive, splitting-tensile, and flexural strengths by 23.72%, 28.90%, and 16.50%, respectively, compared with the control. This mixture also maintained surface water absorption below 7.81% and ultrasonic pulse velocity (UPV) values of 3532–3974 m/s. Even at 60% WGA and 15% SF, production cost and embodied CO₂ were reduced by 4.59% and 5.03%, respectively. SEM observations showed that high WGA contents increased voids, microcracks, and ettringite formation, which contributed to strength loss. Gene Expression Programming (GEP) models were developed using WGA, SF, and durability-related indicators as input variables. The models showed reliable predictive performance for strength, absorption, and water penetration depth. Overall, the findings support the practical use of WGA and SF for producing more sustainable and cost-effective self-compacting concrete.