Durability Of Reinforced Concrete Beams Strengthened With CFRP Under Sustained Loading And Environmental Conditions

In virtue of great advances in its production techniques,high strength concrete has been widely used in civil engineering,including skyscrapers,bridges,ports,and wharfs.Affected by external environments and human factors,concrete structures usually require reinforcement before the end of the designed life owing to overloads and environmental factors.Recently,carbon fiber reinforced polymer(CFRP)has been employed for concrete structures reinforcement owing to their low mass,high strength,and good corrosion resistance.In freezing marine environments in northern China,the concrete structures during service reinforced by CFRP are exposed to various adverse factors such as freeze-thaw cycles and tides,besides sustained loads.Based on the engineering background mentioned above and supported by National Natural Science Foundation of China(51378089),we propose a study of durability of CFRP reinforced high strength concrete under combined effects of sustained loads,freeze-thaw cycles,and wet-dry cycles via the four-point bending test using self-designed sustained loading equipments.The following conclusions can be drawn:(1)Effects of sustained loading(single factor),freeze-thaw cycling and wet-dry cycling(dual factors),and sustained loading,freeze-thaw cycling,and wet-dry cycling(triple factors),on the durability of CFRP reinforcement beams were investigated using 15 test beams.The effects of different level sustained loads,freeze-thaw cycles,and wet-dry cycles on bending capacity of reinforcement beams were investigated by analyzing failure mode,bearing capacity,mid-span bending,strains of steel and CFRP of the sample beams.(2)The results indicated that failure modes of reinforcement beams under different environments are highly consistent and the debonding initiates from the concrete surface.Exposed to harsh environments,cracking loads and debonding loads of reinforcement beams degraded to different extends.The freeze-thaw and dry-wet coupling environment brings a negative effect on shear strength of the CFRP-high strength concrete interface,while the presence of sustained loading further reduce bending capacity of the sample beams.Meanwhile,it has also been demonstrated that damages on reinforcement beams induced by freeze-thaw cycles in early stage exacerbate degradation effects by following dry-wet cycles on the CFRP-high strength concrete interface.(3)Based on the Chen and Teng Equation,we propose an environmental damage coefficient that can effectively predict debonding bearing capacities of CFRP reinforcement beams under different environments.Meanwhile,CFRP reinforcement beams under sustained loads were modeled using ABAQUS and the simulation results were highly consistent with the experimental results.