Synthetic fibers have been recently used in a concrete mixture in an attempt to produce a new concrete pipe system, cheaper, lighter, and more flexible than conventional steel reinforced concrete pipes. However, no structural design codes have been introduced for synthetic fiber reinforced concrete pipes evaluation. Also, there is little in the literature regarding synthetic fiber applications in the concrete pipes. The effect of adding two types of synthetic fiber, polypropylene (PP) and polyvinyl alcohol (PVA) fibers, on the mechanical properties of concrete, including CTE, dynamic modulus of elasticity, and flexural strength, was investigated. Also, this study focused on the evaluation of the synthetic fiber reinforced concrete pipes performance in terms of ASTM requirements for strength, stiffness, and ductility, and developing design tables for synthetic fiber reinforced concrete pipe similar to those proposed in ASTM C76 standard using the numerical analysis. The performance of the synthetic fiber reinforced concrete pipes were evaluated under short- and long-term loading in accordance with ASTM protocols using different pipe diameters. Fiber dosages ranged from 4.75 to 18 kg/m3 (8 to 30 lb/yd3), and different areas of one steel cage layer were used to reinforce the concrete pipes. The finite element model of the three-edge bearing test was calibrated and validated using the experimental results. The linear and non-linear behavior of the synthetic fiber reinforced concrete material was characterized using the concrete damage plasticity (CDP) model. For input data representing the concrete material properties compression strength, tensile strength, and modulus of elasticity were determined for five fiber dosages 0, 4.75, 6, 7, and 9 kg/m3 (0, 8, 10, 12, and 15 lb/yd3). The results showed that adding fiber to concrete enhanced the flexural strength, increased flexibility, decreased the dynamic modulus of elasticity, and increased the CTE. Specimens reinforced with PP fiber showed more flexural strength and flexibility than those reinforced with PVA fiber. Using synthetic fiber increased the cracking load (produces 0.3 mm crack width), ultimate load, stiffness, and ductility of concrete pipes. Also, using synthetic fiber lowered the production cost as the reduction in the steel cage area ranged from 51 to 100%. Based on the experimental results, a new modified compression model was adopted to represent the compression behavior of fiber reinforced concrete in the finite element models. The tension behavior was defined using a model proposed by past research. A parametric study was conducted on four parameters: pipe diameter, pipe wall thickness, fiber dosage, and steel cage area. The parametric study results were summarized in tables that can be used as a reference for a new synthetic fiber reinforced concrete pipe standard.
Moreover, in response to sustained load, the tested pipes 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 the fibers adequately transfer the stress in the pipe wall and limit the crack width.