Experimental Study on the Bearing Capacity of Fiber-Reinforced Geopolymer Pipes

To investigate the mechanical behavior and failure mechanisms of fiber-reinforced geopolymer drainage pipes under three-edge bearing loads, three-edge bearing tests were conducted on unreinforced engineered geopolymer composite (EGC) and polyvinyl alcohol fiber-reinforced engineered geopolymer composite (PVA-EGC) pipes, as well as glass fiber-reinforced polymer (GFRP)-reinforced EGC and PVA-EGC pipes. The effects of different matrix materials and reinforcement types on the bearing capacity, crack development, and strain field evolution were systematically analyzed based on the load–displacement response, crack evolution, and distributed fiber optic monitoring. The results show that the unreinforced pipes exhibited brittle failure with four-lobe cracking. The bridging effect of PVA fibers delayed crack propagation and improved the post-cracking bearing capacity and structural integrity. The ultimate bearing capacity increased from 2489.38 N for the EGC pipe to 3088.98 N for the PVA-EGC pipe, representing an increase of 24.1%. For the reinforced pipes, the cracking load increased from 7215.18 N for the GFRP-reinforced EGC pipe to 15,339.56 N for the GFRP-reinforced PVA-EGC pipe, corresponding to an increase of 112.6%. The ultimate bearing capacity increased from 18,123.94 N to 24,855.69 N, representing an increase of 37.1%. The GFRP-reinforced PVA-EGC pipe exhibited a more gradual decrease in post-peak bearing capacity and improved deformation resistance and structural ductility. Crack analysis showed that PVA fibers effectively restrained crack localization. The cracking mode changed from through-cracks to multiple fine and uniformly distributed cracks, significantly improving the crack control capacity of the pipe. In addition, the combined action of PVA fibers and GFRP reinforcement reduced strain concentration and promoted more uniform stress transfer. This delayed crack propagation and the development of the GFRP reinforcement toward its ultimate stress state, thereby improving the overall bearing performance of the pipe.