Performance of Thin-Wall Synthetic Fiber–Reinforced Concrete Pipes under Short and Long-Term Loading

Abstract Synthetic fibers have been recently used as a replacement for conventional steel reinforcement in concrete pipes to enhance their durability, ductility, shear strength, and flexural strength. However, there is very limited understanding of the long-term performance of thin-wall synthetic fiber–reinforced concrete pipes, as synthetic fiber has material properties that may change with a sustained load over time. This research investigates the performance of polypropylene fiber–reinforced concrete pipe under short and long-term loads in terms of strength, deflection response, strain response, crack width, and crack patterns. Concrete pipes with diameters of 1,200 and 1,500 mm with respective wall thicknesses of 50 and 63 mm were subjected to the short-term three-edge bearing test. To ensure maximum fiber contribution to pipe strength, a 9 kg/m3 fiber dosage was used with different amounts of steel reinforcement. For the long-term three-edge bearing test, a pipe with a diameter of 1,200 mm reinforced with fiber dosage of 9 kg/m3 along with steel reinforcement with an area of 5.7 cm2/m was tested for 30 days at 40 % of the ultimate load (Load Stage 1) obtained from the short-term test, for another 30 days at 50 % ultimate load (Load Stage 2), and subsequently at 70 % ultimate load for a final 30 days (Load Stage 3). Short-term results showed that synthetic fiber was a viable replacement for the steel reinforcement cage, as some of the tested pipe achieved the strength requirement specified by ASTM C76-15a, Standard Specification for Reinforced Concrete Culvert, Storm Drain, and Sewer Pipe. In response to sustained load, the tested pipe initially exhibited a linear response, followed by a stable response with a slight increase in deflection over time. Fiber creep did not significantly increase the crack width or affect the time dependence of the strain, indicating that the fibers adequately transfer the stress in the pipe wall and limit the crack width. The cracks propagated longitudinally at the invert, crown, and springline, where there were high flexural tensile stresses.