Mechanical properties and micro-mechanisms of polyurethane foam treatment of construction waste

The generation of construction and demolition waste (CDW) has been rising rapidly in recent years. However, the recycling rate of CDW remains low due to inherent challenges such as easy fragmentation, inadequate strength, and poor engineering properties of CDW particles. To address these issues, this study investigates the application of polyurethane foam adhesive (PFA) as a strengthening agent to enhance the mechanical and structural properties of CDW for use in civil engineering infrastructure. Unconfined compressive strength (UCS) tests and consolidated undrained triaxial compression (CU) tests were performed to evaluate the mechanical performance of PFA-modified CDW, while the microstructure was analyzed using Scanning Electron Microscopy (SEM). The results indicate a substantial increase in UCS with varying PFA content after 24 h of gelling. Specifically, UCS values increased by 123.7, 263.93, 497.78, and 737.18 kPa with successive increments in PFA content. Moreover, PFA exhibited a more pronounced enhancement of shear strength compared to UCS. At a PFA content of 6%, cohesion increased dramatically from 5.29 kPa to 868.96 kPa, while the internal friction angle rose from 35.83° to 39.53°. SEM analysis revealed that PFA improves the internal structure of CDW by cementing particles, filling voids, and forming cohesive aggregates. These findings propose a novel method for CDW recycling, offering significant potential for the broader adoption of PFA-enhanced CDW in engineering applications.