Numerical Simulation Of Freeze-thaw Failure And Chloride Penetration Resistance Of Concrete

Cement concretes is widely used,so its durability has always been the focus of research.In the three north area of our country,the concrete was severely damaged by freeze-thaw cycles due to the cold environment.At the same time,due to the use of deicing salt,the concrete is eroded by chloride ions in the case of freeze-thaw damage,which accelerates the destruction of the concrete and reduces the life of the concrete.In the past,the experimental method was used to study,which will inevitably consume certain resources.In this paper,the method of numerical simulation can save certain resources,and it has a certain significance for studying the freeze-thaw cycle damage of concrete and chloride ion penetration.This paper utilize the relevant theory of concrete structure and the randomness of Monte Carlo method to establish a three-dimensional mesoscopic random aggregate model of concrete through MATLAB.At the same time,the nuclear magnetic resonance technology is used to obtain the pore structure information inside the concrete,making it more complete.The three-dimensional meso-concrete model of concrete was imported into the COMSOL Multiphysics finite element software.With the Darcy seepage field,temperature field and mechanical field in the software,solving the control differential equation of the freeze-thaw process,and then assigning the parameters of each phase of the concrete to simulate the freeze-thaw cycle process of concrete.Besides,the chloride diffusion coefficient of each phase of concrete is considered to simulate the diffusion process of chloride ions in concrete Through the dilute substance transfer module included in the software.The simulation results show that,with the increase of air content,the and the loss of relative elastic modulus of concrete have decreased,which meas increasing the air content could result the decrement of the compressive strength but improve the frost resistance of concrete.At the same time,the simulation value of the initial compressive strength of concrete is close to the test value,and the error is about 10%,which shows the feasibility and correctness of the model.This numerical simulation provides a new idea and method for studying the free ze-thaw cycle damage of concrete.After analyzing the results of previous studies,it is believed that the width of the micro-cracks generated by the freeze-thaw cycle is so small that it has little effect on the diffusion coefficient of chloride ions.Therefore,this paper assumes that the diffusion coefficient of chloride ions in the cracks caused by the freeze-thaw cycle is constant,and then numerically simulates the diffusion process of chloride ions inside the concrete under the freeze-thaw cycle.The results show that after the chloride ion diffuses to a certain depth inside the concrete,it is difficult to conti nue to diffuse into the inside.But with the increment of the number of freeze-thaw cycles,freeze-thaw failure to concrete internal structure gradually increases and the depth will gradually become larger.