Recycled concrete can turn waste concrete into resources,reduce the pollution of construction waste to the environment,and reduce the exploitation of natural resources.The service life of recycled concrete members is closely related to the penetration behavior of chloride ions in the environment.Chloride ions in the environment enter the recycled concrete member through its macro and meso defects and reach the surface of the steel bar.When the chloride ion concentration reaches the critical value,it will lead to corrosion and property degradation of steel bars,seriously affecting the durability of components.The numerical simulation method can directly reproduce the diffusion behavior of chloride ion in concrete and closely relate the microscopic behavior to the macroscopic performance.This paper uses PYTHON language to write four generation algorithms of recycled concrete with random aggregates of different shapes,and finite element software COMSOL transport of diluted species module is used to simulate the diffusion behavior of chloride ions in recycled concrete.The diffusion process of chloride ions in the meso model of five-phase recycled concrete under chloride environment is studied systematically.The influence of different aggregate shapes on the chloride ion diffusion performance of recycled concrete and the influence of each mesoscopic composition on the chloride ion erosion resistance of recycled concrete are compared and analyzed.Specific research work is as follows:(1)A mesoscale numerical model of chlorinated recycled concrete is proposed,which consists of five phase materials:aggregate,old mortar,new mortar,aggregate-old mortar interface zone(OITZ)and old mortar-new mortar interface zone(NITZ).Based on random theory,Fuller gradation theory and Walraven formula,an algorithm for generating and delivering four different shapes(circular,polygon,spherical,polyhedron)of random aggregate is written in PYTHON language.Based on the simulation analysis of different aggregate distributions(4 kinds),aggregate volume fractions(20%-50%)and recycled aggregate replacement rates(0%-100%),it is proved that the algorithm system of chlorine salt erosion of recycled concrete random aggregate is reasonable and accurate.(2)The mesoscopic numerical model of chlorinated recycled concrete is imported into COMSOL software,and four kinds of aggregate shapes of chlorinated recycled concrete are established respectively.The simulation calculation and analysis of chloride ion diffusion behavior under 20 different random models are carried out,and the simulation results are compared with the existing test results.It is shown that the simulation results are in good agreement with the existing experimental results,indicating that the method can simulate the diffusion behavior of chloride ions in the recycled concrete better,and the three-dimensional model is closer to the experimental results than the two-dimensional model.The stability of each model is as follows:polyhedral aggregate model>polygonal aggregate model>spherical aggregate model>circular aggregate model.(3)The mesoscopic numerical models of recycled concrete with random polygonal aggregate and polyhedral aggregate are designed.The diffusion process of chloride ions in recycled concrete under chloride environment is simulated.The concentration distribution of chloride ions is analyzed after five years of diffusion,and the distribution law of chloride ions in the recycled concrete is obtained.The results show that:The presence of random aggregate makes the diffusion of chloride ions in concrete uneven.When the chloride ion is blocked by the aggregate,the diffusion path is distorted and transferred around the aggregate,rather than the single linear direction of the heterogeneous material.When the aggregate volume fraction is small,the chloride ion diffusion in concrete is uniform because of the small proportion of aggregate.When the volume fraction of recycled aggregate increases,the tortuous and dilution effects caused by aggregate make the uneven distribution of chloride ions gradually obvious.(4)The calculation and analysis of chloride ion erosion resistance of recycled concrete under different working conditions are carried out to study the influence of each meso-component on the chloride ion erosion resistance of recycled concrete.The results show that:With the increase of the volume fraction of recycled aggregate,the content of old mortar in the interface zone between old and new increases,which promotes the diffusion of chloride ions.New and old mortar diffusion coefficients and interfacial diffusion coefficients have a certain influence on the internal diffusion of recycled concrete.The effect of the new mortar diffusion coefficient is more significant,and the effect of the interfacial diffusion coefficient is slightly less.Increasing the thickness of old mortar will weaken the resistance of recycled concrete to chloride ion erosion.The influence of the thickness of the interfacial zone on the chloride ion diffusion of the recycled concrete cannot be ignored.Selecting the appropriate thickness of the interfacial zone determines the accuracy of the calculation results.The macroscopic diffusion capacity of recycled concrete decreases with the increase of recycled aggregate replacement rate. |