Multi-Scale Modification for Flexural Enhancement of Prestressed Recycled Concrete Beams Using Ceramic Waste Powder, Nano-Silica and Hybrid Fibres

To address the low mechanical performance and high carbon footprint associated with recycled aggregate concrete in structural applications, this experimental case study investigated the flexural behaviour of prestressed concrete beams incorporating 30% recycled coarse aggregate. A multi-scale modification strategy was adopted, combining ceramic waste powder (20%) and fly ash (10%) as cement replacements, 1.0% nano-silica for matrix densification, and hybrid fibres (0.3% steel and 0.2% polyester) for crack control. Ten beams were tested under four-point bending to evaluate cracking, yielding, ultimate loads, crack width and deflection. The optimal modified beam exhibited a 23.6% increase in compressive strength and a 22.8% reduction in maximum crack width compared to the reference beam. The test results were also compared with predictions from GB/T 50010-2010, ACI 318-19, and Eurocode 2, and a modified crack width formula was proposed to improve design accuracy for such sustainable concrete members. This study demonstrates that the proposed modification system effectively addresses the key limitations of recycled aggregate concrete, offering a viable solution for high-performance prestressed concrete elements in sustainable construction.