Research On Degradation Law And Mechanism Of CFRP Sheet-Concrete Interfacial Bonding Performance Under Sulfate Environment

Carbon fiber reinforced composite materials(CFRP)have been widely used in the reconstruction and reinforcement of existing structures due to its advantages of high strength,light weight,non-magnetic properties,good durability,and easy construction.The CFRP reinforced concrete structure is through the bonding force of CFRP-concrete interface to realize the load transfer between two materials,so that the two materials work together in combination.Therefore,the bonding performance of CFRP-concrete interface is the key to the technology of CFRP reinforced concrete structure.In practice,many CFRP-reinforced concrete structures are often exposed to harsh environments.The durability of CFRP-concrete interfaces under harsh conditions is directly related to the long-term stress performance of CFRP-reinforced concrete structures.At present,the research on the durability of CFRP-concrete interface is still not sufficient.This article combines the National Natural Science Foundation of China’s “Research on degradation law and mechanism of FRP sheet-concrete interfacial bonding performance under the coupling effect of sulfate environment and load in cold and drought regions of western”(51368053),using sulfate continuous soaking and sulfate dry-wet circulation two kinds of accelerated corrosion test to simulate the sulfate erosion environment.The mechanical properties of various components of the CFRP-concrete interface under sulfate attack were investigated,and the degradation regularity and degradation mechanism of CFRP-concrete bond properties under sulfate environment were discussed.The main research contents and conclusions of this paper are as follows:(1)Through the tensile tests of CFRP sheets at room temperature,continuous sulfate soaking,and sulfate wet-dry cycle,the effects of sulfate attack on the failure morphology,stress-strain relationship,tensile strength,elastic modulus,and elongation of CFRP sheets were investigated.The test results show that sulfate erosion has little effect on the mechanical properties of CFRP sheets.(2)Through the durability test of concrete under the effect of continuous sulfate soaking and sulfate wet-dry cycle,the degradation law of concrete compressive strength with erosion time under sulfate attack was studied,and the influences of concrete water-binder ratio,fly ash content and sulfate concentration on the compressive strength of concrete were analyzed.The test results show that proper reduction of concrete water-cement ratio and increase of fly ash content can improve the durability of concrete in sulfate erosion environment.Through the analysis and fitting of the experimental data,a concrete compressive strength attenuation model considering the influence of sulfate erosion was established,which provided a key reference for the study of the interface durability of CFRP-concrete.(3)Using double-sided shear specimens,the interfacial bondability of CFRP-concrete under room temperature,continuous sulfate soaking and sulfate wet and dry cycles were tested.The effect of sulfate erosion on the failure modes,ultimate bearing capacity,distribution of stress and strain,and effective bond length of CFRP-concrete interface were analyzed.The effects of concrete water-binder ratio,fly ash content and interface bonding length on the interface mechanical properties were discussed.The test results showed that: a)After the sulfate erosion,the interface failure mode has changed.As the erosion time increases,the interface failure gradually changes from the failure of the concrete layer below the interface to the destruction of the CFRP-concrete interface;b)After sulfate erosion,interface parameters such as interface ultimate bearing capacity,CFRP maximum strain value and interface maximum shear stress all decreased with the increase of erosion time,and the rate of decline was accelerated with the increase of erosion time;c)With measures such as reducing the water-cement ratio of concrete and increasing the amount of fly ash to improve the sulfate resistance of concrete,the durability of CFRP-concrete interface in the sulphate attack environment can be improved;d)After sulfate erosion,the effective bond length at the interface increases with the sulfate attack time.(4)Through the regression analysis of the change law of interface bearing capacity with erosion time,the comprehensive influence coefficient of bearing capacity in sulfate environment was introduced(taking into account the influence of water-binder ratio,fly ash content,and sulfate solution concentration),and the interface capacity model of CFRP-concrete considering the effects of continuous sulphate soaking and sulfate wet-dry cycle was established.(5)Through inductive analysis of the interface bond-slip curve,the expressions of the interface eigenvalues(the interface shear stress peak and its corresponding interface slippage)and the interface ductility parameters are obtained.Based on this,a CFRP-concrete interfacial bond-slip relationship model considering the continuous immersion of sulfate and the wet-dry cycle of sulfate was established.