Effect Of Sulfate And Freeze-Thaw Cycle On Bonding Properties Of CFRP-Concrete Interface

Sulfate erosion is the main factor of concrete damage in saline environment.In the western saline environment,the sulfate-based corrosion ions are about 5-10 times that of seawater,and the winter in the western region is long and cold,and the temperature difference between day and night is large.The concrete structure suffers from the common erosion of sulfate and freezing and thawing in the outdoor,and the damage is e xtremely great.At present,CFRP reinforced concrete is an effective means to improve its strength and durability.The premise of CFRP working with concrete is to achieve load transfer through the bond stress between the two.Therefore,the core of CFRP reinforced concrete technology is the bond performance of CFRP-concrete interface.In this paper,the effects of sulfate on the bonding properties of CFRP-concrete interface under rapid freezing and thawing cycles were simulated by simulating the salting and freezing-thawing environment in western China.The experimental contents and research results are as follows:(1)The CFRP sheets were subjected to different freeze-thaw cycles in clear water and 5% sulfate solution respectively,the tensile test results of elongation,tensile strength and modulus of elasticity were compared with the sheet test results at room temperature.Tests show that CFRP is not affected by sulfate and freeze-thaw cycles.After 100 freeze-thaw cycles,the tensile strength is increased by 5%,the elastic modulus is increased by 10%,and the elongation is reduced by about 0.1%.(2)The effects of fresh water and 5% sulfate solution on concrete strength under different freeze-thaw cycles were studied by concrete strength test.The experiment shows that the concrete strength increases slightly and then decreases greatly with the increase of freeze-thaw cycles,and the lower the concrete strength,the more obvious the effect is.(3)The double-shear experiment was carried out to study the re lationship between the ultimate bearing capacity,stress-strain relationship curve and effective bond length of clear water and 5% sulfate solution after different freeze-thaw cycles.The test shows that the relationship between interface bearing capacity and stress-strain decreases with the increase of the number of freeze-thaw cycles.The same strength concrete is more obvious under the sulfate condition than the clear water condition;the lower the concrete strength under the same freezing and thawing conditions,the more obvious the decline.In contrast to the experimental results of effective bond length,the effective bond length formula considering the factors of sulfate freeze-thaw cycle was established by introducing the influence coefficient of sulfate freeze-thaw cycle.(4)Through the regression analysis of the change law of interface bond-slip curve,the expressions of interface characteristic parameters and interface ductility parameters are obtained,and the CFRP-concrete interface bond-slip model under the action of sulfate freeze-thaw cycle is established.Based on the regression analysis of the variation of interfacial bearing capacity,the bearing capacity model is established by introducing the influence coefficient of concrete strength and the number of freeze-thaw cycles under sulfate condition.