Time-dependent behavior of synthetic fiber-reinforced concrete pipes under long-term sustained loading

This study presents the long-term behavior of synthetic fiber-reinforced concrete pipe (SYNFRCP) in actual field conditions. Conventional reinforced concrete pipe (RCP) was tested for comparison purposes. The research program was twofold. First, the short-term relationships between the applied loads and the deflections of SYNFRCP were obtained on the basis of the ASTM C497 three-edge bearing test. Second, the changes in the deformations of the buried RCPs and SYNFRCPs under sustained loading were monitored for up to 4,200 h. Two fiber dosages of 8 lb/yd³ (4.8 kg/m³) and 12 lb/yd³ (7.0 kg/m³) were used during the pipe production. Two 24-in. (600-mm) and two 36-in. (900-mm) pipes were buried in trenches with a sustained load of 1,350 lb/ft/ft (65 kN/m/m). The pipes were initially backfilled with native soil up to 2 ft (600 mm) and 4 ft (1,200 mm) over the top of the pipe and then backfilled with 14 ft of pea gravel above this to simulate the maximum fill height sustained by a Class 3 Wall B precast concrete pipe on the basis of ASTM C76. Two displacement transducers were installed from the crown to the invert at two sections along the length of each pipe. All buried pipes were precracked until the first visible crack was observed. The precracking was done to evaluate the long-term performance of SYNFRCP in which fibers are engaged after cracking. The strength, the crack width, and the change in the vertical deformation of the buried SYNFRCP and RCP are compared and presented in this paper.