Compressive creep of reinforced polymeric piling

Reinforced polymeric piling (RPP) is a sustainable piling product that is gaining attention for use instead of timber piling in coastal and waterfront applications. However, unlike conventional construction materials that have well-documented creep behavior, there is virtually no reliable data on the compressive creep behavior of RPP. RPP is composed of a recycled plastic matrix made of high density polyethylene (HDPE) that is reinforced with steel or fiber reinforced polymer rods (FRP, E-glass, or fiberglass). In this study, an accelerated test method to predict the compressive creep of both recycled HDPE and FRP is employed. The method is based on the equivalence of strain energy density (SED) between conventional constant-stress creep tests and stress-strain tests, conducted at different strain rates. Test results indicate that the tested recycled HDPE exhibited a pronounced viscoelastic or viscoplastic response, at low strains, when loaded in compression. At room temperature, SED predicts that recycled HDPE will creep about 1.1 % in 100 years when loaded at an ultimate stress of 8.3 MPa (1200 psi). FRP exhibits a small viscoelastic tendency. SED predicts that the FRP loaded in compression will creep by less than 0.5 % in 100 years when loaded at an ultimate stress of 88 MPa (12 800 psi). The stress-strain behavior of RPP depends on strain compatibility of both HDPE and FRP. Creep of RPP will depend on the percentage of FRP reinforcement in the cross section. Creep of RPP is estimated to be on the order of 0.2 % to 1.8 % in 100 years under loading and reinforcement ratios employed for this research.