Experimental Study On Chloride Diffusion Into Concrete Specimens Considering The Effects Of Coarse Aggregate And Reinforcement

Under the marine environment,due to the corrosion of chloride salt,the performance of reinforced concrete is deteriorated,the corrosion of reinforcing steel bars is caused,which eventually leads to the decrease of structural carrying capacity and even failure failure.The process of chloride ion erosion in concrete has become a hot spot in the assessment of durability of concrete structures now.In the case of chloride salt attack on concrete,most of the chloride ion diffusion models obtained in the existing research results ignore the essential influence of the coarse aggregate and the reinforcing steel bar,and there is no systematic study on the chloride ion diffusion coefficient in the interface transition region.To sum up,this paper aims at the diffusion and transmission process of chloride ions in reinforced concrete composites,through the combination of physical test and numerical simulation to discuss the distribution and diffusion of chloride ions in the concrete with the effect of coarse aggregate and reinforcing steel.Combined with the experimental data,the variation of chloride ion diffusion coefficient in the interface transition zone was deeply studied.Finally,based on the three-dimensional spherical random aggregate model of reinforced concrete,numerical simulation research is carried out.The specific research contents of this paper are as follows:1.This paper summarizes the previous research results of chloride ion erosion mechanism in concrete.The differences between the chloride ion erosion models were analyzed and compared.The chloride ion diffusion model of the concrete used in this paper was proposed.2.The artificial tidal zone artificial simulation device independently developed by our group was used to simulate the real-time tidal fluctuation.Based on this,a test of chloride ion diffusion in plain concrete specimens was carried out.The effect of coarse aggregate content on chloride ion diffusion in concrete was discussed.By introducing the influence coefficient of the volume fraction of coarse aggregate,a prediction model of chloride ion diffusion in concrete considering the effect of coarse aggregate which is suitable for engineering practice is established.3.Based on the artificial ocean tidal simulation device above,the chloride ion diffusion experiment in reinforced concrete specimens was further studied.The effect of co-action of coarse aggregate and reinforcing steel on the chloride ion concentration distribution in reinforced concrete specimens was studied.During the test,the concentration of chloride ion and the distribution of the coarse aggregate in the front of the reinforcement were measured and obtained at each sampling point of the reinforced concrete specimens.After comprehensively considering the direct and indirect block effect of steel bars,the prediction model of chloride ion concentration in the steel front of concrete specimens considering the co-action of coarse aggregate and steel bar was obtained on the basis of the above model of predicting concrete.4.Through in-depth analysis of the measured data from physical experiments,the influence mechanism of interfacial transition zone on chloride ion diffusion in concrete is revealed.The effects of dilution,tortuosity and interfacial transition zone on the chloride diffusion coefficient were also discussed quantitatively.In this paper,the calculation model of chloride ion diffusion coefficient in interfacial transition zone is established by considering the influence coefficient of coarse aggregate volume fraction and interfacial transition zone thickness,which lays the foundation for the numerical simulation of chloride diffusion in concrete.5.According to the important parameters obtained from the above physical test results,a three-dimensional numerical model of reinforced concrete is established.The concentration distribution and diffusion characteristics of chloride ions in the same concrete and reinforced concrete specimens are studied by numerical simulation.The results of the numerical simulations and the measured data of the physical experiment are compared with each other to verify the correctness and rationality of the numerical simulation method.