Effects of sustained load and freeze-thaw exposure on RC beams strengthened with prestressed NSM-CFRP strips

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 three large-scale rectangular RC beams (sets BS-F and BS-FS) were tested. Each set consisted of one un-strengthened control beam, one strengthened beam with non-prestressed NSM-CFRP strips, and one strengthened beam using prestressed NSM-CFRP strips with 60% of the ultimate tensile strength of the CFRP strips. After strengthening, three beams from set BS-F were exposed to 500 freeze-thaw cycles (three cycles per day between +34oC to -34oC with a relative humidity of 75% for temperatures above +20oC). Also, the beams from set BS-FS were exposed to 500 freeze-thaw cycles (three cycles per day between +34oC to -34oC with fresh water spray for 10 minutes at a rate of 18 L/min at a temperature of +20oC while being subjected to a sustained load equal to 47% of the theoretical ultimate capacity of the non-prestressed NSM-CFRP strengthened beam. The beams were simply supported and tested under static monotonic loading in four-point bending configuration until failure. The damage done to the beams due to exposure was evaluated, and furthermore, the effects of sustained load and freeze-thaw exposure were elaborated on the load-deflection response, type of failure, ductility, and energy absorption. 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 NSMCFRP strips.