Research On Flexural Performance And Durability Of Corroded Reinforced Concrete Beams Strengthened With CFRP

The corrosion of steel bars is caused by concrete carbonation,chloride penetration and other factors,which has become a major problem of influencing durability of concrete.The safety and durability of many structures have been damaged because of the corrosion of steel bars,and these structures need to be repaired or strengthened to continue in service.CFRP strengthening is a method widely used in strengthening of various structures as its advantages of light weight,easy construction,wide application and high durability.At present,scholars have made many researches on the reinforcement of corroded reinforced concrete members at home and abroad,and many achievements have been obtained.However,the study on the flexural behavior of corroded concrete beams strengthened with CFRP with different corrosion levels and the durability after strengthened is few reported in recent literature,and the number of specimens is not enough in existing studies.Eleven reinforced concrete beams(B0~B10)were designed and constructed in this study and B0 was the control beam(without corrosion).The corrosion of longitudinal rebars was accelerated with current,and the target corrosion levles were 2%,4%,6%,8%,10%,12%,14%,16%,18%,20%.All beams were strengthened with CFRP and tested with four-point loading,and the influence of different corrosion levels of longitudinal rebars on the failure modes,flexural bearing capacity and midspan deflection of corroded reinforced concrete beams strengthened with CFRP was investigated.The durability of corroded specimens strengthened with CFRP obtained from field and laboratory in salt solution was investigated through 100 days drying-weting cycles test on corroded specimens strengthened with CFRP.The main conclusions of this paper are as follows:(1)The failure modes of all corroded beams in this experiment strengthened with CFRP are all flexural failure.The ultimate failure of the test beam is due to the rupture of the bottom CFRP.From the distribution and width of cracks,the failure modes of reinforcing beams gradually change from the failure of the under-reinforced beam to the failure of the rare-reinforced beam with the increase of corrosion rate of steel rebars.(2)The flexural ultimate bearing capacity of the strengthened beams with different corrosion levels of steel rebars is lower than that of the non-corroded strengthened beam.Moreover,with the increase of corrosion level of steel rebars,the flexural ultimate bearing capacity of the strengthened beam decreases gradually,and the cracking load decreases slightly.The ultimate deflection of corroded strengthened beams has no obvious change with the corrosion level when the corrosion rate of steel bars is low and significantly reduced when the corrosion level of steel rebars is higher.The rates of strain change at different locations of the CFRP are not uniform,but increases rapidly when the load is about to reach its limit.(3)Based on the regression analysis of the test results,an expression for flexural bearing capacity of reinforced concrete beams with corroded longitudinal rebars strengthened with CFRP was proposed.The model was verified by the experimental data from other researchers.(4)The durability of corroded reinforced concrete members strengthened with CFRP in salt solution has increased significantly.Based on the previous study of our research group,a method for comprehensively judging corrosion state of the reinforcing bars of corroded reinforced concrete members through measuring the concrete resistivity and steel rebars half-cell potential was put forward and corrosion state of steel rebars in a strengthened bridge was evaluated.