Cost-effective and sustainable ultra-high-performance concrete with electric arc furnace slag and calcium carbonate: a multi-objective optimization and experimental validation approach.

Ultra-high-performance concrete (UHPC) delivers exceptional performance, but it is still largely a high-clinker material, which drives up both cost and embodied CO₂. Here, we present a low-clinker UHPC matrix that incorporates electric arc furnace slag (EAFS) and calcium carbonate powder (CaC), with quartz flour fully replaced by CaC. The mixtures were proportioned using the Modified Andreasen & Andersen particle-packing approach and then explored through a central composite design to quantify how cement dosage, water-to-binder ratio, and high-range water-reducer (HRWR) dosage control fresh flow and strength development. A desirability-based optimization was finally used to minimize cement content while maintaining self-compacting workability (240–260 mm slump flow) and UHPC-level 28-day strength (≥ 150 MPa). Relative to the control mixture, the optimized formulation reduced cement from 852 to 598 kg/m³ (− 29.8%), which corresponds to an approximate ≈ 30% reduction in cement-related embodied CO₂ (≈ 127–178 kg CO₂/m³ avoided on a cement-only basis). Under ambient curing, the optimized mix achieved a slump flow of 252 mm and compressive strengths of 151.1 ± 7.9 MPa at 28 days and 158.9 ± 3.1 MPa at 90 days (+ 5.1% from 28 to 90 days). Young’s modulus increased from 40.1 ± 1.5 GPa at 7 days to 45.0 ± 1.4 GPa at 90 days. RCPT charge passed decreased with age (281 ± 11 C at 28 days to 78 ± 7 C at 90 days), indicating improved resistance to chloride-ion penetration over time, although values remained higher than the control. Overall, the results show that UHPC-level strength and self-compacting flow can be achieved with a substantially reduced clinker demand using a particle packing-theory and statistic-guided mixture design strategy.