Research On Durability Of Bond Performance Of CFRP-fly Ash Concrete Interface Under Sulphate Erosion

In recent years,external viscose fiber reinforced composites(FRP)have been widely used in the process of strengthening and repairing concrete structures,such as convenient cutting,light weight,high strength,good durability,corrosion resistance,unaffected by magnetic media and good fatigue resistance.Through experimental study and engineering practice,the main failure modes of beams and plates reinforced by carbon fiber reinforced composite sheets are the interface stripping between the two CFRP and the concrete.Therefore,the key factor to ensure the quality of CFRP reinforcement is to make good bonding properties between the two.For most of the reinforced structures,their working environment is often in the outside,and more in extreme ultraviolet,high temperature,strong acid,strong alkali,cold,seawater immersion and so on extremely bad environment.If the reinforced concrete structures or components are exposed to one or more environmental coupling environment for a long time,the durability of the structure will decrease significantly,which reduces the bearing capacity of the structure and affects the reliability index of the structure.There are a lot of inland lake and saline alkali land in the northwest region.In the lake water or in the soil,the salt of the anion of sulfate root is contained in the lake.The sulfate ion,especially the Magnesium Sulfate is the typical salt,reacts with the cement stone in the concrete to produce the expansive material.In addition,the altitude and latitude are high,the climate conditions are cold and dry in winter,high temperature and drought in summer,the annual wind speed is large,the groundwater level changes with the season,the temperature difference between the day and night is large,the CFRP-concrete interface is often coupled with various environmental coupling effects,and its erosion damage is more serious.At present,domestic and foreign scholars have carried out a lot of experimental research on the durability of CFRP-concrete interface.It is mainly concentrated in the southeast coastal areas of China and the effect of chlorine salt on the durability of the interface,and the study of concrete is not treated with corrosion resistance,but the study on the durability of the western cold and dry areas under the effect of sulphate erosion is less.Based on the characteristics of the western region,on the basis of the existing equipment in the laboratory,the coupling action of high concentration sulfate solution and dry and wet cycle is designed.The durability of the interfacial bonding performance of carbon fiber sheet,rubber layer and concrete are studied.The concrete research aspects are as follows:(1)The changes of the modulus of elasticity,tensile strength and elongation of CFRP sheet after soaking with sodium sulfate solution in different days and different times ofdry-wet cycle of sodium sulfate solution are studied by using a universal test machine to destroy the CFRP sheet.(2)Through the double shear test of CFRP-concrete specimens,the damage type and failure process of the interface of different fly ash content after dry-wet cyclic erosion of sodium sulfate solution are studied.Under the action of different days of erosion,the strength change law of concrete specimens with different fly ash content,and the limit bearing capacity,strain distribution,bond slip constitutive relation,stress,local bond slip and effective bond length of the interface double shear under the action of dry-wet cycle of sodium sulfate solution are analyzed.(3)The measured values of different fly ash content and different dry-wet cycle were analyzed by regression analysis.Three important parameters were calculated.The effects of fly ash content and dry-wet cycle on the interface ductility,stress peak and critical slip were analyzed.Using the polynomial relationship between the assumed cycle times and the three parameters,the function relation of the three parameters with the dry-wet cycles is fitted.The functional relation of the three parameters is replaced by the Popovics model,and the bond slip relationship model is obtained under the conditions of this test.