The Loading Effect On Carbonation Of Concrete Beams

Durability of concrete structures is a common concern problem in civil engineering nowadays,and the carbonation of concrete is the preconditions of reinforced concrete structures durability failure in the general atmosphere.Most of the actual concrete structures are worked under load.So the study of concrete carbonization under the load has certain significance for the durability evaluation and design of concrete structures.This thesis combined theoretical analysis with numerical simulation,took Reinforced concrete beams as the research object,based on COMSOL FEM software and studied carbonization of concrete and concrete carbonization under the load.The main contents are as follows:1.Numerical model of concrete carbonation is established and verified,and then analyze the effect of water-cement ratio,cement content,ambient temperature,relative humidity,concentration of carbon dioxide on concrete carbonation depth with the carbonation model.2.Diffusion coefficient of carbon dioxide is obtained according to the diffusion theory of carbon dioxide with tensile（pressure）load,then establish carbonation model under the different levels of axial tensile（pressure）force and analyze the influence of tensile（pressure）load on depth of concrete carbonation depth and carbonation.3.Combined with the project example,carbonation of concrete beams under load is modeled,analysis the greatest depth of carbonation within the design lifeThe results showed that:the numerical model of concrete carbonation has high credibility.The relationship between water-cement ratio and concrete carbonation depth is approximately proportional,relationship between the amount of cement and concrete carbonation depth is approximately inversely proportional;Effect of temperature on the depth of carbonation is not particularly large;As the relative humidity increases,the depth of carbonation firstly increases then decreases,and depth of concrete carbonation is the biggest when relative humidity is 0.65;carbonation depth of concrete is approximately proportional to the concentration of carbon dioxide.The carbonation rate coefficient is 2.93 without the load;with axial tension increases,the depth of carbonation and carbonation rate are increased,carbonation rate coefficient and tensile load rate by the equation is k=k₀(1+0.039e^{（25P_t/8）}As increasing axial pressure,the depth of carbonation and carbonation rates are first decreased and then increased,carbonation rate coefficient and pressure load rate by the equation is:k=k₀（1-2.99P_c+4.51P_c²）,and when the pressure load rate is less than 60%,the pressure inhibit the carbonation of concrete.