Study On Damage Mechanism And Mechanical Properties Of Concrete Under Chemical Etching Environment

In the chemical corrosive environment of the concrete structure of industrial buildings,chlorine,sulfate,magnesium ion and other corrosive substances generally exist.The coupling erosion of chlorine,sulfate and magnesium salts is an important factor that causes the durability damage of concrete structures in industrial buildings.The corrosion mechanism of industrial concrete structure under the action of chlorine,sulfate and magnesium salt is the most complex,and the concrete damage is more severe.Therefore,this paper studies the corrosion mechanism and mechanical properties of concrete under the chemical corrosion environment of this type of concrete（chlorine,sulfate,magnesium salt coupling）,so as to provide reference value for the durability evaluation of industrial building concrete structures under the chemical corrosion environment.The field exposure test in actual engineering,this paper based on practical engineering conditions and natural soaking procedure specification design and natural air of indoor simulation test,the drying time for T/3,the soaking time is 2 T/3,microscopic detection by SEM,XRD analysis of the microstructure evolution of concrete after corrosion and erosion,reveal the industrial construction of concrete structure corrosion mechanism of concrete.Taking relative mass,compressive strength,relative dynamic elastic modulus and damage layer thickness as evaluation indexes,and combining with microscopic analysis results,the variation law of concrete mechanical properties was studied.The effects of soaking mode（half soaking,full soaking）,water-cement ratio（0.35,0.45,0.55）,corrosion solution concentration(C _chloride+C _sulfate+C _magnesium=0.5%,2.5%,5%),dry and wet period（3d,6d,15d）on corrosion mechanism and mechanical properties of concrete were discussed.The main conclusions are as follows:（1）The corrosion products of concrete are Friedel salt,ettringite and magnesium hydroxide.Corrosive ions enter the concrete in the order of reaction:chloride ion>sulfate ion>magnesium ion.The corrosion products in the initial stage of erosion are mainly Friedel salt and ettringite,and the magnesium hydroxide appears in the later stage of corrosion.（2）Within the range of factors in this paper,water-cement ratio,corrosion solution concentration and dry and wet period have little influence on the types of concrete corrosion products,which are all Friedel salt,ettringite and magnesium hydroxide,only changing the generation rate of corrosion products or extending the time node of magnesium hydroxide generation.（3）The concrete quality,dynamic elastic modulus and compressive strength are basically consistent,and generally show a trend of increasing first and then decreasing;The thickness of damage layer increases with the development of time,but the growth rate decreases.（4）When the corrosion time is consistent,the corrosion degree of semi-soaked concrete is much higher than that of fully soaked concrete.With the increase of the ratio of water to cement and the concentration of solution,the increment and decrease range of the mechanical properties of concrete increase,and the corrosion deterioration degree is higher.The smaller the dry and wet period is,the greater the degradation rate of concrete mechanical properties is in the later stage of corrosion,but the fluctuation range is less than the influence of water-binder ratio and solution concentration.The relationship between three factors affecting concrete corrosion is as follows:the concentration of>water gel is higher than that of>wet and dry period.（5）The development model of concrete damage layer thickness under such chemical corrosion environment is proposed,which can better predict the damage layer of concrete after corrosion.（6）A systematic indoor simulation test method is formed to establish the damage time relationship between the field exposure test and the indoor simulation test.1.367d of the indoor test under the same conditions is equivalent to 1d of the field test,which can more accurately realize the corrosion degradation of the field exposure test.