Creep study of FRP composite rebars for concrete

摘要

Fiber-reinforced plastic (FRP) rebars, long rods produced by the "pultrusion" process and containing by volume about 55 percent E-glass fiber and about 45 percent thermoset resin, have been successfully applied as concrete reinforcement in many construction applications. However, creep, fatigue, and corrosion from alkaline environment of concrete are areas of concern for any large-scale application. In this investigation the creep study was limited to determine whether the commercially available FRP rebars would creep under a sustained tensile load over a wide range of temperatures: low temperature (-23 deg C, -10 deg F), room temperature (21 deg C, 70 deg F), and high temperature (49 deg C, 120 deg F). Because these rebars have fibers generally oriented in the longitudinal direction 12.70, 15.88 and 19.05 mm (1/2, 5/8, and 3.4 in.), the load would be carried primarily by the fibers. Six FRP rebars in nominal diameters with a spirally wrapped glass fiber strand were instrumented with strain gages to measure both the longitudinal and diametral strains under dead weight loads adjusted to tension each of these rebars to about 50 percent of its yield stress. In order to monitor temperatures, a thermocouple was attached to each rebar. For the room temperature tests, strain was measured for 1800 hours (75 days) and over this period the strain did not show any trend to continue to increase. The low temperature tests was continued for 3,552 hours and again no discernible trend of increasing strain was observed. The high temperature test was performed for 3,792 hours (158 days). From the creep data in which a very small trend of increasing strain could be observed, the values of creep parameters m and n were determined as m chemical bounds 9.45, and n chemical bounds 0.297. These values closely match with published values for commercially available pultruded FRP WF beams.