Refined Numerical Simulation And Experimental Study On Coupling Effect Of Carbonation And Chloride Ingress For Concrete Structure

Concrete carbonation and chloride ingress are two major and hot problems in concrete durability field. The atmospheric carbon dioxide diffuses through concrete and reacts with hydration production. This process lowers pH value. As the value is lower than 9, the passivation film bounding steel would be dissolved, and then the corrosion initiated. Chloride has great penetration and power corrosion. When the concentration of chloride is reach the threshold, even though the pH value is larger than 11.5, the chloride can depassivate the steel, and then initiate the corrosion. Moreover, chloride can also react with iron. Therefore, the chloride ion penetrated can directly initiate corrosion and form point corrosion. The combine effect of carbonation and chloride ingress have not been got a consistent conclusion in the open literature, most of them are based on direct or indirect experiment evidence. But experiments have declared the sample under coupling of carbonation and chloride ingress is more serious corrosion. This thesis bases on the literature have pressed, and from the view of numerical simulation. There are two method-commercial software ABAQUS secondary development and compile finite element code using MATLAB-to predict the depth of corrosion under carbonation or chloride ingress. The parameter used in the mathematical model will be modified with compare to relevant experiment. The content and results in this thesis as follows:(1)Two dimensional partial differential equations of concrete components carbonation are established bases on the chemical dynamical balance of cement component carbonation and the mass balance Jaw of chemical reaction.Then the partial differential equations are solved by compiling two dimensional finite element codes with MATLAB, in which the multiscale aggregate model ("numerical concrete") is taken consideration. Therefore, the simulation gives us results under consideration of aggregate scale effective and coupling effect of multi-components carbonation reaction.(2)To model the process of atmospheric carbon dioxide diffuse through concrete and react with hydration product, the secondary development is conducted with subroutine UMATHT in ABAQUS. The subroutine is proved to be accurate comparing with relative experiments. The "numerical concrete" model algorithm is also developed using PYTHON software.(3)A partial differential equations model of chloride ingress in one dimension is established base on the experiment and theories that have done and proposed in open literature. The model is solved by compiling finite element code with MATLAB. An experiment of chloride ingress under different water-cement ratio in one dimension is conducted as well. The free, bonding, and total chloride concentration are detected after immerging into NaCl solution 60 days. The relationship between free, bonding, total chloride concentrations and water-cement ratio is plotted. The pH value on different water-cement ratio is plotted as well. The parameters in chloride ingress model are modified under comparing the results calculated in MATLAB with the result in experiment. As it is known, the present of carbonation retards the chloride into concrete by reduction in porosity. Then the model of combining carbonation and chloride ingress is established under this point of view. The ingressive depth combining carbonation and chloride is got by compiling finite element code with MATLAB...