Durability Of Reinforced Concrete Beams Strengthened With CFRP Under Load And Dry-wet Conditions

With the rapid development of China's economy,the application of high strength concrete is extensive.Due to the effect of external environment,the problem of reinforcement of concrete structures gradually becomes significant.In recent years,carbon fiber reinforced polymer(CFRP)has been widely used in concrete structures reinforcement for its high strength-weight ratio and excellent corrosion resistance.In addition to chloride ions and dry-wet cycles,reinforced concrete structures are usually under load conditions during their service in coastal areas.Such conditions have a great impact on the performance of structures.Therefore,it is particularly important to correctly evaluate the durability of the CFRP reinforced concrete structures.Financed by National Natural Science Foundation of China,this paper adopted self-designed loading device to exert sustained load on the strengthened beams and dry-wet cycle tests were carried out.3.5% salted tap water was used for dry-wet cycles which included 0,40,80 and 120 times.Three loading levels were 0%,30% and 60% of the ultimate load of the unreinforced concrete beam.The main contents and conclusions of this paper are as follows:In this experiment,the strength class of concrete was C60.The high strength concrete beams strengthened with CFRP were firstly subjected to dry-wet cycles and sustained load.Their long-term performance and the failure mechanism were investigated by four-point bending test,regarding capacity,failure mode,deflection,CFRP strain,steel strain,concrete strain,and crack development.The experimental results show that the performance of the strengthened beams were deteriorated after dry-wet cycles and sustained load.The ability of CFRP to retard the development of cracks was also weakened.The fracture gradually developed from the concrete surface to the bonding between adhesive layer and concrete.The ultimate load,mid-span deflection and ultimate strain of CFRP decreased at the end of test.And the stiffness of specimens decreased significantly at the later stage of loading.Moreover,the degree of deterioration was further aggravated with the increase of the load level.Based on the analysis of the constituent elements of strengthened beams,dry-wet cycles had no obvious adverse effect on the concrete and the steel bars.The deterioration of epoxy and the decrease of bond strength were the main factors which led to the performance degradation of strengthened beams.