Mechanical performance of spun-cast full-scale precast pipes incorporating hybrid conventional rebar cage and steel fibers

Precast reinforced concrete (RC) pipes are an important component of urban infrastructure for conveyance of stormwater and sewage disposal. This study investigates the mechanical performance of spun-cast precast fullscale pipes under three-edge bearing test (TEBT) and patch or point load tests for replicating the field loading scenarios. Six types of precast pipes incorporating various amount of conventional rebar reinforcement and local steel fibers were tested. Straight steel fibers of 25 mm length were cut from locally manufactured long steel wires. Two steel fiber dosages (i.e., 20 kg/m3 and 40 kg/m3) in concrete mixture were examined for mechanical behavior of pipes along with conventional rebar cage. It was observed that full-scale precast pipes without steel fibers and conventional rebar cage failed in an abrupt manner into various pieces. However, pipe made with concrete mixture incorporating steel fibers only without conventional rebar cage also failed into pieces but showed post-peak behavior and fiber crack bridging phenomena. Pipes having double conventional steel reinforcement ratio showed 60% higher ultimate load. Pipes incorporating 20 kg/m3 and 40 kg/m3 along with conventional rebar cage showed 10% and 30% higher ultimate load compared to that of identical pipe without steel fibers. Improved deflection softening and hardening behaviour were observed for pipes with fibers. Furthermore, multiple secondary cracks were observed during TEBT for pipe specimens incorporating fibers. Similarly, higher ultimate load and improved cracking behavior was observed under patch load for pipe specimens incorporating steel fibers. All the tested pipes incorporating steel fibers and conventional rebar cage satisfied the Class III and Class IV requirements of ASTM C76. It can be envisioned that the implementation of hybrid spun-cast pipes incorporating conventional rebar cage and local steel fibers lead towards the development of economical pipes for controlling the premature cracking and improved structural behaviour.