Properties Of Chloride Ions Transportion In Concrete Under Different Drying-wetting Cycles

The durability of concrete structures has attracted extraordinary concerns from thefield of civil engineering.Besides the using life and maintenance cost of concretestructures,it is also related to the protection of environment and the sustainabledevelopment of society.The durability of concrete structure due to choride ingress is thefocus of current research.The key study is the transportion mechanics of chloride rons inConcrete. The concrete structures in marine and salt lake envirnments are ingressed moreserious due to steels crossion which caused by cyclic choride penetration.It is morecompilcated of the chloride penetration under this effect of cyclic drying and wetting thanwhole soaking.Therefore,it is essential to study the penetration mechanics and influencefactors when concrete structures under these two conditions.Based on indoor experiments of chloride natural drying-wetting cycles,the chloridetransportion processes were studyed under8diffenert drying-wetting cycles through moremeticulous experimental method.It shows that: chloride contents of drying-wetting cyclesare larger than that of the whole soaking in a certain depth of surface,but smaller in deeperareas.There are apparent convection districts in range of0mm to2mm for the specimens ofdrying-wetting cycles,but specimen of the whole soaking has not.Surface chloride contentCsgrows and keeps stable as time with form of logarithmic function,There is a slightcontent increase for Csas growing of drying and wetting ratios.Convection depth△Xkeeps stable in range of2mm,△X will increase as growing of drying-wettingratios,otherwhiles,it will disappear gradually.The time-varying models of contents werefound through fitting methold.By the way of enforced fitting,chloride diffusion coefficients of different specimensin different periolds were obtained more convenient based on the form of FickⅡlawanalytical solution,and these diffusion coefficients equal the average values abtain by theway of stratifing. Diffusion coefficients decrease and keep stable as time with the powerfunction form.drying-wetting cycles have little influence on diffusion coefficients. G5S1(drying-wetting ratio5:1) has the highest transprotation efficiency in all specimens throughdiscussing their Cs, Cs,△Xand transportion depths.This way of drying and wetting cyclescan be used to indoor accelerated corrosion experiments.The accumulation processes of chloride ion and the mechanics of convection&diffusion were analysised based on experiments and existing achivements.It shows that:the key mechanism of chloride transportion into concrete is convection and diffusion for thespecimens of drying and wetting cycles.Besides,transportion and caculation models werefound based on FickⅡlaw analytical solution.Using the finite element software COMSOL,chloride transportion processes weresimulated,and simulation resulrs as well as models’ results show good similarities withthe experiments,which have certain practical significances for predicting the depth andcontent of chloride transportion in concrete.The simulation results indicated that:the speedof chloride transportion and accumulation will be increased as the growth ofdrying-wetting ratios.Meanwhile, the larger the ratios are,the higher the content willbe,and the more apparent the convection is.