Carbonate Depth Prediction Model For Concrete Components Under Freeze-thaw Environment And Experimental Study

From the perspective of the concrete carbonation mechanism,the carbonizable material in the concrete will continue to react with CO₂ in the atmosphere,resulting in a gradual decrease in the basicity of the protective layer and the destruction of the steel passivation film.In the northern area,the concrete structure freezes and thaws from winter to spring,and carbonization takes place during the rest of the year.In view of this alternate phenomenon,based on the theory of pure carbonation of concrete,the effects of freeze-thaw and stress are increased,and the carbonization results of concrete under the coupling of freeze-thaw,carbonization and stress are analyzed,which has certain practical value.The durability of concrete structures has been recognized from the beginning of the last century,and many achievements have been made.In terms of carbonization of concrete,it mainly stays at the material level.Qualitative conclusions or empirical formulas are given based on tests.Few scholars consider both freeze-thaw cycles and load actions,and analyze the influence of load on the components from the theoretical aspect.In this paper,the freeze-thaw environment is taken as the premise,and the effects of freeze-thaw cycles and stress levels on the carbonization of concrete is studied.This paper starts with the influence mechanism of load on concrete pore structure,analyzes the effect of stress level on the permeability of concrete,and combines the change of concrete porosity with freeze-thaw cycles to establish a prediction model of carbonation depth of concrete.The carbonation-freeze-thaw alternate test of a concrete short beam under stress status was carried out.Numerical model and test results verify each other.The research contents and conclusions of this article are as follows:（1）.The effects of freeze-thaw cycles on the carbonation depth of concrete were studied,and a modified numerical model of concrete carbonation under freeze-thaw conditions was established.（2）The load changes the characteristics of the pore structure of the concrete,and then affects the permeability of the concrete.The correction of the diffusion coefficient of carbon dioxide considering the load and freeze-thaw cycles is established.（3）Based on the existing theoretical models,combined with the effects of freezing-thawing-load on the diffusivity of concrete,a prediction model of carbonation depth of concrete considering the stress under freeze-thaw environment was established.（4）The influences of load patterns（tensile pressure）and different stress levels on the concrete body strain,porosity and carbon dioxide diffusion coefficient were analyzed.The three laws of change are found similar.（5）The carbonation-freeze-thawing alternation test of the concrete beam under load state were carried,and COMSOL Multiphysics multi-physics software were used to analyze the simulation solution.Comparing the theoretical and practical results,it was found that the two have good agreement.