Theoretical And Experimental Investigation On Durability Of Concrete Structures In Coastal Substation

Substation is an important infrastructure,which can contribute economic growth and social stability.Moreover,the concrete frame in substation,which is subjected to various non-load factors in addition to load in service,is the most important civil infrastructure.As the reason,it is necessary to study the durability of substation concrete frame.In this paper,through the substation investigation and testing in coastal areas,it was found that the stray current will affect the durability of concrete frame in substation.Then,the deterioration of steel and concrete in stray current environment,the erosion of concrete by chloride ions in coastal substatio n environment and the durability life of concrete frame of coastal substation were discussed and studied,and the main research achievements were shown below:(1)After investigating,testing and assessing 136 substation,the manifestation of main diseases of concrete frame was analyzed,the reliability test statistics of substation frame members were carried out.Then,the durability damage of concrete member in stray current environment and environment without stray current were compared,and it was found that the stray current is an important factor to decrease the durability of concrete frame.Moreover,the formation principle of stray current in concrete frame of substation was analyzed,the calculation formula of corrosion rate of steel bar caused by stray current is presented and the mechanism of resistance deterioration of reinforced concrete frame caused by stray current is further studied.(2)According to the Nernst equation and First law of Faraday Electrolysis,the corrosion of steel bar was calculated and the theoretical model of steel corrosion under stray current is established.Moreover,according to the law of conservation of mass and energy conservation law,the corrosion efficiency of steel bar under electrification accelerates corrosion was obtained,and the corrosion correction model of steel bar based on the conservation of mass and energy is established.Further,the corrosion mechanism of steel reinforcement under the coupling of stray current and chloride ion was studied,and the corrosion model of steel reinforcement under the coupling of stray current and chloride ion was established.(3)The corrosion test of steel bar under the coupling of stray current and chloride ion was carried out.The experiment and its test equipment are designed based on the law of conservation of mass and energy conservation law.Moreover,the corrosion law of reinforcement under the coupling of stray current and chloride ion was tested and studied.The experimental results illustrate that the applied current wil l accelerate the corrosion rate of the steel bar,and the accuracy of the calculation method proposed in this paper is verified.(4)Based on theoretical and experimental analysis,the performance degradation of concrete frame under stray current environment was studied.The time varying model of rust swelling stress and corrosion depth was obtained,based on First law of Faraday Electrolysis and internal force balance analysis.The whole process of development of rust swelling stress of steel bar before and after concrete cracking was studied to get the critical rust swelling stress and the corrosion depth of the steel bar.Furthermore,The time varying model of compressive strength and modulus of elasticity of concrete from generation of rust swelling force to cracking was established.(5)The chloride ion concentration on the concrete surface in the environment with stray current and without stray current were analyzed and experimentally studied respectively.Moreover,the influence regularity of stray current,environmental chloride ion concentration,time and concrete strength on the accumulation of surface chloride ion concentration were got and the relationship between chloride ion concentration on concrete surface and stray current,chloride ion concentr ation in coastal atmosphere,time and concrete strength were established.A time-varying model of chloride ion concentration on concrete surface in coastal atmosphere was established,a time-varying model of chloride ion concentration on concrete surface of coastal substation was established,and a time-varying formula of chloride ion concentration on concrete surface based on existing concrete structures was established.(6)Based on the time-varying analysis of chloride ion erosion process in coastal environment and Fick’s second diffusion law,the time-varying models of chloride ion erosion under steady state and unsteady boundary condition were established respectively.Moreover,the time-varying models of chloride ion erosion in steady state and unsteady state of diffusion process were established respectively.As the result,the time-varying law of chloride ion erosion and chloride ion diffusion coefficient in concrete in coastal atmospheric environment were obtained.Moreover,It is found that the time-varying law of chloride ion concentration on concrete surface is correlated with the time-varying law of chloride ion diffusion coefficient,and based on the correlation,the time-varying law of chloride ion diffusion coefficient of concrete was obtained.(7)Based on the nernst equation and time-varying analysis of chloride ion n process in stray current environment,the time-varying models of chloride ion erosion considering the time-varying process of chloride ion diffusion was established.Furthermore,a time-varying model of chloride ions erosion in a stray current environment considering both boundary and diffusion instability is proposed.As the result,the time-varying law of chloride ion erosion and chloride ion diffusion coefficient in concrete in coastal atmospheric environment were obtained.The relationship between the influence coefficient of stray current on chloride ion diffusion and current voltage intensity is obtained.(8)The durability life of substation concrete frame system and its comp onents is studied.Based on various failure modes,the formulas for calculating the weakest chain model of durability life of component or component section were established.The durability life relationship between frame system and component is establishe d,and the durability life analysis theory of system is established.The calculation method of durability life of structure in different systems proposed.The life prediction model of concrete member based on chloride ion erosion in stray current environment was established,the life prediction model of concrete members based on steel corrosion is established and the life prediction model of concrete members is established based on the rust swelling stress.