Study On The Transport Mechanism Of Chloride Ion In Concrete Under High Temperature

The mechanical properties and durability of concrete structures are closely related to their environment.For high performance concrete serving in the marine environment,it will be harmed by high temperature and chloride erosion,which seriously affects the service life of concrete.The relocation project of Shougang is located in Caofeidian Industrial Zone in Tangshan,Hebei Province.the flue of the coking project in this project has been immersed in seawater for a long time,suffering from the erosion of chloride salt from the marine environment,and accompanied by the harm of high temperature.So the mechanical properties and durability of the structure are facing a huge test.Combined with the project case,the transport mechanism of chloride ion in concrete under high temperature is explored in this paper.The C80 high performance concrete specimens were soaked in high temperature and chloride solution,and then the compressive strength test,chloride ion penetration test(electric flux method),chloride ion titration test and micropore structure test were carried out.The changes of compressive strength,electric flux,chloride ion penetration depth and pore structure characteristic parameters of concrete after high temperature and immersion in chloride solution were studied.The permeation behavior of chloride ion in concrete is simulated and analyzed by using COMSOL software,and the following conclusions are drawn:(1)When the temperature rises from 20℃ to 300℃,the electric flux of C80 high performance concrete increases rapidly,with an increase of 285%,that is,the resistance to chloride ion permeability of concrete decreases.With the increase of immersion age,the compressive strength and chloride penetration depth of concrete increased at different temperatures,and with the increase of chloride solution concentration,the compressive strength of concrete increased at first and then decreased,and the penetration depth of chloride ion increased continuously.(2)After 20℃ room temperature and 300℃ high temperature,with the increase of immersion age of 3% chloride solution,the porosity and total pore volume of C80 high performance concrete decrease,and the most probable pore diameter and average pore diameter become smaller and smaller.the characteristic parameters of concrete pore structure have obvious time variation,which is the most fundamental reason that affects the chloride ion diffusion coefficient.After high temperature,the porosity and average pore size of concrete will increase,and the proportion of harmful holes will increase.(3)The chloride ion diffusion correction model and random aggregate model of concrete are established.The chloride ion diffusion process of concrete is numerically simulated and analyzed by using COMSOL software,and the simulation results are compared with the experimental results to verify the correctness of the simulation model and method.