Flexural Behavior Of High Strengthened Concrete Beams With Prestressed CFRP Under Salt Spray Dry-wet Cycles

The concrete buildings will appear structural damage inevitably due to aging,harsh environment and other factors in the long-term service.It is an economical and effective method to reinforce and strengthen the damaged buildings.Carbon fiber reinforced polymer provides an effective solution for the concrete repaired field due to its high tensile strength,corrosion resistance and convenient construction.In the actual reinforcement projects,CFRP also has the problem that the tensile strength can not be utilized completely,namely the low utilization rate.It can be solved by using prestressed CFRP to reinforce the concrete specimen.At the same time,salt spray erosion,dry and wet circulation and other harsh environment will also affect the CFRP reinforced concrete structure in the coastal areas of China,therefore it is necessary to study the durability of CFRP reinforced concrete.However,most of the researches are aimed at non-prestressed CFRP and ordinary concrete,and there are few studies on high strengthened concrete beams under salt spray dry-wet cycles that reinforced with prestressed CFRP.Supported by the National Natural Science Foundation of China,this paper studies the flexural behavior of beams that reinforced with different grades of prestressed CFRP under the erosion of salt spray dry-wet cycles.three prestressing grades have been designed,which are 0%,15%and 30%of the tensile strength standard value(f_cfk)of CFRP.the times of dry-wet cycles are set as 0,70,140 and 280 times.The research conclusions are as follows:?1?The flexural behavior of beams reinforced with different grades of prestressed CFRP.The results showed that prestressed CFRP had an obvious improvement on the flexural behavior of reinforced beams.And it improved the cracking and ultimate load of the specimen significantly,and the higher the prestressing level was,the bigger the proportion was.The ductility improved significantly as well.The length of the stripping stage of reinforced beams with 30%prestressing grade were increased obviously.The CFRP ultimate strain value was improved significantly,as well as the utilization rate of carbon fiber reinforced polymer.The improvement of prestressing level can enhance the bonding performance of the interface effectively.?2?The impact of the erosion of salt spray dry-wet cycles on the flexural behavior of beams reinforced with prestressed CFRP.The results showed that it had a significant deteriorating impact on beams'flexural behavior.After the high times of cycles,the cracking load and ultimate load and ductility coefficient of the specimens decreased significantly,and the stripping stage was shortened,the CFRP ultimate strain value decreased significantly as well as the interface's bonding performance.Furthermore,the destroy of 30%prestressing grade of reinforced beams were the fastest.?3?The effect of long-term dry-wet cycles on the flexural behavior of beams reinforced with prestressed CFRP.The results showed that NaCl solution made a more serious erosion on the CFRP-concrete interface of the reinforced beams with 30%prestressed grade after 280dry-wet cycles.And the bending capacity decreased more obviously,the destroy was more rapid.Furthermore,the brittle phenomenon of the reinforced beams were more significant.