Residual tensile properties of GFRP reinforcing bars after loading in severe environments

The long-term behavior of glass fiber-reinforced polymer (GFRP) reinforcing bars is one of the most critical issues for the acceptance of these materials as reinforcement for concrete structures. There is a high demand for experimental studies to investigate the stability of the tensile strength, ultimate elongation, and elasticity modulus. GFRP reinforcing bars inherently have a low elasticity modulus, which must not significantly decrease over time under loading or the serviceability behavior of the concrete element containing them will be jeopardized. This paper evaluates the residual tensile properties of three sizes of sand-coated GFRP reinforcing bars in alkaline and water environments combined with sustained loading and elevated temperature. Bar diameters of 15.9 (No. 5), 12.7 (No. 4), and 9.5 mm (No. 3) were loaded for different durations, then tested in axial tension for residual tensile properties. The test periods varied from 1 to 4 months under elevated temperature to hasten degradation and simulate extended service periods. The reduction in tensile strength was found to be 7-13% of the guaranteed strength for the three bar sizes under elevated temperature, which is at least 26% higher than the specified design strength as recommended by ACI 440. IR-03. More importantly, no significant change in the elastic modulus was observed.