Sustainable mix design of ultra-high performance concrete incorporating recycled brick powder: mechanical, durability, and microstructural effects

This study investigates the influence of recycled brick powder (RBP) as a partial binder replacement (10–40%) on the mechanical, durability, and sustainability performance of UHPC under standard and steam curing. Results indicate that increasing RBP reduced flowability but maintained workable consistency with proper superplasticizer dosage. Strength decreased slightly with higher RBP but remained above 100 MPa at 28 days; steam curing enhanced strength by 4–10%. The mixture with 40% RBP and 2% steel fibers (RBP‑40‑2) achieved optimal performance, with 28‑day compressive and flexural strengths of 118.3 MPa and 25.3 MPa, respectively. The chloride diffusion coefficient decreased from 0.799 × 10–12 m2/s (RBP‑0) to 0.377 × 10–12 m2/s (RBP‑40), attributed to pozzolanic hydration and micro‑filling effects. Sustainability assessment showed 37% lower embodied carbon and 38% cost reduction at 40% replacement. Overall, RBP proves to be an effective, eco-efficient binder substitute for UHPC, offering substantial environmental and economic benefits with minimal compromise in mechanical and durability performance.