Optimal Formulation and Characteristics of Lightweight Foamed Concrete Constructed Using Surface-Activated Waste Polyurethane

The massive generation of waste polyurethane (WPU) poses a significant environmental challenge, while the development of energy-efficient building materials demands sustainable solutions. This study presents a novel approach for repurposing WPU through surface activation combined with physical foaming technology to produce lightweight, high-strength WPU-based foamed concrete (WFC). Using single-factor and response surface methodology experiments, the optimal formulation of WFC was determined. The resulting material exhibited a dry density of 455.8 kg / m 3 and a water absorption rate of 29.5%, meeting the specifications for grade A05 foamed concrete (dry density ≤ 525 kg / m 3 ) and grade W30 (water absorption ≤ 30 % ). Notably, the incorporation of surface-activated WPU significantly enhanced the material’s performance, yielding a 25.9% increase in compressive strength and a 17.2% reduction in water absorption compared to the control. Microstructural analysis revealed that the surface activation treatment improved the interfacial bonding between WPU and the cement matrix and promoted the formation of dense hydration products (C–S–H gel), which collectively contributed to the enhanced mechanical properties and water resistance. This study demonstrates the feasibility of utilizing WPU in foamed concrete and provides a scientific basis for its engineering applications.