Mechanical Performance of Modified Polyurea Lining for Rehabilitation of Aging Urban Underground Concrete Drainage Pipes

Aging and deterioration of urban underground drainage pipelines frequently trigger road collapses, urban waterlogging and groundwater contamination, posing critical challenges to the operation, maintenance and disaster prevention of urban underground infrastructure. Conventional rehabilitation solutions, including cement-based linings and traditional polymer liners, suffer from inherent limitations such as reduced effective flow cross-sections caused by excessive lining thickness, unsatisfactory corrosion resistance and durability, and high construction disturbance. In this study, a modified polyurea (MPU) material was applied to the trenchless rehabilitation of drainage pipelines via spray-applied pipe lining technology. The mechanical properties and interfacial bonding performance of MPU were systematically characterized at the material scale; full-scale external pressure tests were conducted to investigate the effects of 3–8 mm thick MPU linings on the bearing capacity and failure characteristics of structurally damaged concrete pipes; and the anti-seepage repair performance for local perforation defects was evaluated through void-crossing testing. The results demonstrate that MPU lining can meet the engineering performance requirements for pipeline rehabilitation when applied with matched interfacial primer following standard construction procedures. Even the baseline bond strength tested without primer remains sufficient to ensure stable cooperative load bearing between the lining and the host concrete pipe. The 3–8 mm thick linings increase the cracking load of damaged pipes by 61.7–145.7% and the ultimate load by up to 162.2%, while transforming the failure mode from brittle fracture to ductile failure. For local perforation repair, the 3 mm thick MPU lining achieves a critical hydrostatic failure pressure of 1.23 MPa, maintaining favorable structural integrity and interfacial bonding stability under the test conditions. With a well-balanced combination of thin lining thickness, rapid curing and high structural strengthening efficiency, as well as favorable inherent corrosion resistance, the MPU lining provides novel material alternatives and fundamental experimental evidence for the green trenchless rehabilitation of aged underground pipelines and offers technical support for the safe operation and maintenance of urban underground infrastructure.