Experimental Study And Numerical Simulation On Coupling Penetration Of Chloride And Carbonation For Self-Compacting Concrete

Chloride penetration and carbonation are important reasons for the decline of performance of reinforced concrete structures during the service life,but the research on the coupling penetration of chloride and carbonation needs to be improved.At the same time,the application of self-compacting concrete?SCC?in engineering construction is more and more extensive,but the research on its durability has not been applied enough.Therefore,it is very important and urgent to study the durability of SCC.On this basis,the durability of SCC with coupling penetration chloride and carbonation was studied in this paper.Firstly,coupling penetration test for the ordinary SCC was carried out.The test designed two kinds of water-cement ratio SCC and three penetration environments.The coupling penetration environments alternates between chloride salt immersion and rapid carbonation cycle,and does not perform drying treatment in the test;single chloride penetration is only chloride salt immersion for the sample;single carbonation penetration is only rapid carbonation for the sample.Next,the chloride concentration,carbonation depth,pH value,microscopic morphology and compressive strength of the sample after penetration were examined.The results show that carbonation has little effect on coupling penetration due to the presence of water in pores of concrete and chloride penetration can inhibit the carbonation of concrete.Besides,the strength of concrete is improved in all three penetration environments.Then the experimental study on the effect of mineral admixture on the coupling penetration for SCC was carried out.The test group is SCC which is respectively mixed with three kinds of mineral admixtures,such as fly ash,blast-furnace slag and silica fume.The control group is SCC with the same water-cement ratio not blended with the admixture.And the above four groups were subjected to the coupling penetration of chloride and carbonation.Next,the carbonation depth,pH value,chloride concentration,pore structure and compressive strength of the sample were measured after penetration.The results show that the degree of carbonation of each group is from fly ash>blast-furnace slag?silica fume>ordinary self-compacting concrete and carbonation leads to an increase in the concentration of chloride inside the concrete.Under the coupling penetration the chloride ion binding capacity of SCC with blast-furnace slag and silica fume is significantly higher than that of SCC without mineral admixture.However,the binding capacity of SCC with fly ash is similar to that of SCC without mineral admixture.Finally,the numerical simulation of the process of coupling penetration for chloride and carbonation was carried out.According to the Bogue formula and the cement hydration kinetic equation,the content of each component in the concrete was determined.Then according to the influence of carbonation on the concrete pore structure,the concrete chloride adsorption curve and the chloride diffusion coefficient,and considering the time-dependent of the chloride diffusion coefficient,the Cl^-diffusion partial differential equation was modified.Next,the differential equations of CO₂ and each component were established according to the mass balance and diffusion law.Finally,the Euler formula and classical explicit format were used to solve the solution by Matlab.The validity and reliability of the model were verified by the model parameters analysis and comparing the simulated values with the experimental values.