Thin-walled flexible concrete pipes with synthetic fibers and reduced traditional steel cage

Abstract

Structural classification of buried pipes depends on their inherent response to external loading and interaction between the pipes and the surrounding soil. There are mainly two classified types of pipes, rigid pipes and flexible pipes. This study focused on performance evaluations of a proposed new class of concrete pipes, semi-rigid pipes, which are flexible concrete pipes that are reinforced with synthetic fibers and have thinner walls relative to standard concrete pipes. The innovative flexible concrete pipe system has the advantages of simplified structural design, thinner pipe walls, lighter weight, improved durability due to the use of non-corrosive reinforcement (synthetic fibers), and potentially lower production cost due to reduction of steel reinforcement and wall thickness. Based on the three-edge bearing test in accordance with ASTM standard C497, 44 thin walled concrete pipes (flexible concrete pipes) with diameters from 760mm (30in.) to 3050mm (120in.) were tested with different fiber dosages (ranges of 1.2–14.3kg/m3) and reduced steel reinforcement (ranges of 35–50% reduction).Test results show that discrete synthetic fibers increase the shear capacity of the thin walled concrete pipes and delay the shear failure mode, significantly enhancing the load carrying capacity with the reduced steel reinforcement. Moreover, thin walled concrete pipes with 50% reduction of steel reinforcement and the addition of synthetic fibers maintained bending stiffness up to 5% deflection of the inside diameter for small diameter pipes [760mm (30in.), 910mm (36in.) and 1370mm (54in.)], and bending stiffness up to 3% deflection for large diameter pipes [1830mm (72in.), 2130mm (84in.) and 3050mm (120in.)].