Influence Of Loading On The Diffusivity Of Chloride Ions And The Corrosion Initiation Time Of Steel Bar In Concrete

Much more reinforced concrete structures are widely applied inengineering, and there are much more durability problems of concrete. Inorder to solve the problems, much more researches are put in practice.Chloride ions erosion is a main influence factor of insufficient durability ofconcrete structures. Because the chloride ions in concrete will inducecorrosion to steel bars, then expanding and cracking to concrete protectivecourse, and may endanger the working safety of structures in shorter time.The most existing reinforced concrete structures are under loading andenvironment, and the influence of loading on diffusion coefficient isimportant.Based on the second Fick’s law, the Monte Carlo Method and thedatum of the chloride ions concentration of existing project and specimenof indoor simulation experiments, the theories of diffusion coefficient ofchloride ions and corrosion initiation time of steel bar in concrete underloading were studied. The main studies conclusions in the paper are in thefollowing: 1. Based on the progeny of the research in existence, the applicabilityof theoretic model of chloride diffusion in concrete was studied. And theconvection district was taken into consideration in the model. According tothe chloride ions concentration in concrete, the theoretic model withconvection course was validated.2. The most existing reinforced concrete structures are under loading,and loading has an important effect to the durability of concrete. Based onthe second Fick’s law, the ratio of diffusion coefficient of chloride ionsunder different levels of loading was deduced in the case that diffusioncoefficient of chloride ions is invariable. And the datum of indoorsimulation experiments validated the rationality of the model of ratio.3. Based on the Thomas model, another model of ratio of diffusioncoefficient of chloride ions was made in the case that diffusion coefficientof chloride ions was variable with the exposed times. And there were datumof5different exposed times of indoor simulation experiments. Set thediffusion coefficient of chloride ions of40days as a base, the ratios ofdiffusion coefficient of chloride ions of80days,120days,160days,200daysto the40days’ were calculated, it was proved that the model of ratio isrational. The results indicated that the ratio of diffusion coefficient waspreferably reflected the influence of loading level on diffusibility.4. Based on the second Fick’s law, took the influence of loading onthe boundry condition of diffusion eqution into consideration, the relation between surface concentration or interface concentration betweenconvection district and diffusion district of chloride ions was analyzed. Anda new diffusion eqution was deduced, the datum of indoor simulationexperiments validated it.5. The corrosion of steel bar in concrete is the efficient amse to thedamage of reinforced concrete structures. The corrosion initiation time ofsteel bar is related to the exposed time, protective course and loading.Based on the datum of indoor simulation experiments and the Monte CarloMethod, it was analyzed the influence of the above3factors of corrosioninitiation time of chloride ions. The results indicated that the influence ofbending loading was much greater.