Experimental Study On Chloride Corrosion Resistance Of Concrete Coated With FRP Sheets

Concrete structures such as wharf platforms and piers serving in the marine environment will be corroded prematurely by chloride ions,which will seriously affect the durability and long-term safety of structures.The method of strengthening concrete with FRP fiber sheet can improve the mechanical properties and durability of concrete structure.At present,the research of FRP reinforced concrete structures at home and abroad is mainly focused on the macro-scale structural and mechanical properties.There are few studies on the durability of FRP reinforced concrete structures against chloride ion penetration.Therefore,it is necessary to study the durability of FRP reinforced concrete structures against chloride corrosion.Moreover,strong ultraviolet radiation has aging effect on FRP materials.When hydraulic FRP concrete structures are exposed to this environment for a long time,the coupling erosion of chloride salt and ultraviolet radiation will bring serious dangers to structural safety.Therefore,it is of great significance to evaluate the durability of FRP reinforced concrete under such complex coastal environment,which is coupled by chloride and other factors.Based on the above problems,this paper foucses on concrete coated with FRP fiber sheets.A variety of reinforcement systems were designed.The chloride salt immersion environment,chloride salt coupled with accelerated ultraviolet radiation environment were simulated experimentally,which provided a reference for durability design of concrete structures coated with FRP fiber sheets under chloride ion erosion environment.The main research contents are as follows:Firstly,the chloride ion corrosion resistance of concrete with FRP fiber sheets under chloride solution immersion was studied.The time of chloride salt immersion erosion,the type of FRP fiber cloth,the number of fiber layers and the existence of epoxy resin coatings were investigated.The influence of these variables on the resistance to chloride ion penetration was discussed.The chloride concentration distribution in concrete strengthened with FRP in different test periods was measured,and the macro durability index was obtained.In addition,compressive strength tests were carried out on specimens with different time to study the effect of chloride corrosion on the mechanical durability.Secondly,the coupling effect of chloride solution immersion and accelerated ultraviolet radiation on the durability of FRP reinforced concrete was studied.The control variables included: environmental exposure type factors,coupling time,FRP fiber cloth types and number of layers.The chloride concentration distribution in concrete strengthened with FRP in different periods was measured and compared with the single factor chloride salt immersion test results.With the help of scanning electron microscopy(SEM),the micro-scale changes of concrete,FRP fiber and resin matrix before and after the test were analyzed.The macro-durability index was combined with the micro-structure changes,and the mechanism of the protective effect of FRP fiber sheets on chloride ion erosion of concrete was systematically revealed.Finally,the chloride diffusion model of FRP fiber reinforced concrete is established.Based on the existing theoretical model,an amendment is proposed.According to the experimental results in this paper,the equivalent influence coefficient of FRP is introduced and the piecewise equation is used to establish the chloride ion erosion model under chloride solution immersion.The analytical solution of chloride ion immersion concentration in FRP concrete is given.The predicted results of the model and the measured results are well verified.According to the prediction results of chloride ion concentration from 0.5 to 50 years of diffusion model,C2 and B2 have the best resistance to chloride ion.The effect of C1 and B1 D ranks second,while B1 is inferior to the former two.The effect of EP is inferior to that of all kinds of FRP,but it is better than that of OPC which is without protection.In the prediction of chloride ion concentration distribution,the value of damage factor ‘a' has a great influence on the results.In order to accurately predict the long-term chloride resistance and service life of FRP fiber reinforced concrete,it is necessary to consider the damage factor of FRP protective layer.