Effects of Sustained Load and Freeze-Thaw Exposure on RC Beams Strengthened with Prestressed NSM-CFRP Strips

Abstract

An experimental program was conducted to investigate the combined effects of sustained load and freeze-thaw cycling exposure on the flexural behaviour of reinforced concrete (RC) beams strengthened in flexure using prestressed Near-Surface Mounted (NSM) Carbon Fibre Reinforced Polymer (CFRP) strips. Two sets of five large-scale simply supported rectangular RC beams (sets BS-F and BS-FS) were tested. Each set consisted of one un-strengthened control beam and four beams strengthened using NSM-CFRP strips prestressed to 0, 20, 40, and 60% of the CFRP ultimate tensile strength. After strengthening, the beams from set BS-F were exposed to 500 freeze-thaw cycles. The beams from set BS-FS were exposed to 500 freeze-thaw cycles; simultaneously, each beam in this set was subjected to a sustained load representing 47% of the theoretical ultimate capacity of the non-prestressed NSM-CFRP strengthened beam. Thereafter, the beams were tested at room temperature under static monotonic loading in four-point bending configuration until failure. The damage done to the beams due to environmental exposure and long-term loading was evaluated, and furthermore, the effects of sustained load and freeze-thaw exposure were discussed on the load-deflection response, type of failure, ductility, energy absorption, and strain in CFRP strips. Analysis of the results revealed the significant effects of the sustained load and freeze-thaw cycling exposure on the flexural performance of RC beams strengthened with prestressed and non-prestressed NSM-CFRP strips.