Numerical Simulation Of Freeze-thaw Damage Of Concrete

On the study of the freeze-thaw damage of concrete,the previous numerical simulation method always stays at the macroscopic level,and it is considered that the concrete is a homogeneous continuous material,resulting in large errors in the simulation results.In recent years,scholars at home and abroad have begun to establish concrete meso-scale models based on stochastic mathematical and statistical principles,but they are still quite different from actual concrete structures.Therefore,the establishment of concrete three-dimensional mesoscopic real model,has a certain significance in the numerical simulation of freeze-thaw damage.In view of this situation,this paper adopts the micro-focus industrial CT imaging technology to scan the concrete structure to generate a two-dimensional tomographic image.After a series of image preprocessing steps,the image is segmented by the local threshold segmentation method to separate and identify the set of concrete.Material,mortar,interface transition zone and porosity.In the medical image processing software Materialise Mimics,a concrete three-dimensional mesoscopic geometric model was reconstructed.The material parameters of each component in the model are determined by experimental methods.Fast freezing and thawing tests were performed on concrete specimens with different water-cement ratios and air contents.The changes in mass loss,relative dynamic elastic modulus,and compressive strength were measured.The three-dimensional meso-concrete model of concrete was imported into the finite element software COMSOL Multiphysics.Three control differential equations of Darcy seepage,heat conduction and dynamics for freeze-thaw damage were solved.Each attribute parameter was assigned,mesh was divided,freeze-thaw was set.The cycle simulates temperature and simulates the freezing and thawing process of concrete.The stress-strain distributions of the concrete model under different water-cement ratios and air contents were studied,and the change process and the influence of water-cement ratio and air content on the stress-strain distribution were analyzed.The variation of compressive strength and dynamic elastic modulus of each concrete model under different freezing and thawing times was simulated.Compared with the actual freeze-thaw test results,it was found that the numerical simulation results were slightly higher than the test results when the freeze-thaw times were the same in the same water-cement ratio and gas content,and the errors were generally within 10%.With different water-cement ratio and gas content,with the increase of freezing and thawing times,the change law of concrete compressive strength and relative dynamic elastic modulus simulation value is similar to that of experimental results.This numerical simulation compensates for the defects of the freeze-thaw test,and provides a new method for the analysis of the freeze-thaw damage of concrete to verify the feasibility and correctness of the numerical simulation method.