Durability Study Of High Strengthened Concrete With Prestressed CFRP Under Freeze-thaw And Wet-dry Cycles

With the development of the national economy,a large number of buildings fail to meet the demand of the current requirements due to natural aging,corrosion,functional changes,etc.Compared with reconstruction,the reinforcement of the damaged building has important social and economic benefits.Carbon fiber reinforced polymer has brought new opportunities for the development of concrete reinforcement project with the advantage of high specific strength,corrosion resistance,convenient construction etc.The durability of CFRP reinforced concrete is an urgent topic to be studied for the hostile environment(such as freeze-thaw cycles,wet-dry cycles,wet-thermal environments,high temperature environments,etc.)it still exposed in service.Supported by the National Natural Science Foundation of China,the four point bending test was performed on the high strength concrete specimens strengthened with prestressed CFRP under freeze-thaw cycles and wet-dry cycles.The effects of freeze-thaw cycles,wet-dry cycles and prestress on the durability of the specimens were analyzed in present paper.The main research results are as follows:(1)The impact of prestress on CFRP reinforced high strength concrete were studied.As the results show that prestressed CFRP significantly increased the cracking load and ultimate load of the specimen.The higher the prestress level is,the stronger the carrying capacity is.Besides,the generation and development of concrete cracks were inhibited,the deformation extent was decreased and the flexural rigidity was improve effectively for the high strength of the prestressed CFRP.When the debonding failure occurs,the higher the prestress level,the thicker the concrete layer on the CFRP.(2)The durability of high strength concrete strengthened with prestressed CFRP under freeze-thaw cycles was studied.The results reveals that freeze-thaw cycles lead to the decrease of the carrying capacity of all the specimens.And the effect is gradually increased with the increase of the prestress level.The failure modes of specimens with the maximum level of prestress transformed from the debonding of interface between CFRP and concrete,caused by central flexural-shear crack,to shear modes.After the freeze-thaw cycles,the location of the failure surface of the specimen gradually transformed from the concrete surface to the resin-concrete interface and the resin layer.Prestress increased the deterioration degree of the interfacial bonding performance.The durability of resin and fiber-resin interface directly impacted the durability of the bonding performance between CFRP and high strength concrete under freeze-thaw cycles.(3)The durability of high strength concrete strengthened with prestressed CFRP under wet-dry cycles was studied.The results show that the carrying capacity of specimens are not obvious in the early stage of wet-dry cycles.The carrying capacity of specimens decreased in different degrees after 120 cycles.And the higher the prestress level is,the faster the carrying capacity load decreases.The location of the failure surface of the specimen is gradually transformed from the concrete surface to the interface between resin and concrete.With the increase of the prestress levels,the interfacial bonding performance deteriorated significantly.The degradation of the resin is the main reason of the degradation of the interfacial bonding performance during the wet-dry cycle.