| Carbonation resistance is one of the main performance of durability of cement based materials. Carbonization will cause the physical and chemical change of, as well as the interaction between, the internal temperature and humidity, the porosity and the carbonization material. A quantitative study on the coupling effect of heat-moisture-carbonation is very important for the prediction of the carbonization depth and the understand the carbonation resistance of cement based materials. This research conducted the following investigations on this scientific issue:(1) By the methods of determination of phenolphthalein, thermogravimetric analysis (TGA), X-ray phase analysis, infrared spectrometry and quantitative calcium carbonate analysis, the carbonation of concrete was evaluated through the quantitative and qualitative comparison between the experiment results. And a comprehensive analysis on the advantages and applicabilities of the determination methods of concrete carbonation was conducted.(2) Based on the size distribution function of cement particles, the periodic boundary conditions are applied to generate cement particles from big to small ones in the cubic simulated element. In considering the influence of the mineral compositions of cement, the particle size distribution of cement and water to cement ratio on cement hydration, three corresponding parameters were introduced to establish the three dimensional spherical cement hydration model. The experience selection on the parameters was replaced by a scientific derivation in the improved model. Furthermore, the whole cement hydration process was analyzed in view of microstructure and hydration products through the improved cement hydration model. Based on the reconstruction on the microstructure of cement paste, the analysis on hydration products and pore structure was simulated and verified using the hydration heat evaluation, thermogravimetric analysis and mercury intrusion method.(3) Based on the basic principle of multi-field coupling in porous media and the carbonation mechanism of cementitious materials, the parameters such as the materials content that can be carbonated, porosity, saturation at the first stage of carbonation were calculated with cement hydration model. Then, a theoretical model of carbonation deterioration of cement based materials was established. The model took the essential conversion between every two phases from gas, liquid and solid phases in hydrated cement based materials into account. Also the porous structure variation caused by volume expansion of carbonated products, and the interactions between temperature, humidity and carbonation were considered in the model. The established governing equation group on the carbonation of cementitious materials were in accordance with the mass balance in local coordinates, the chemical equilibrium, the ionic equilibrium and the porous media theory.(4) Based on the cement hydration model, the carbonation of both CH and CSH gel were taken into consideration to theoretically and experimentally investigate the calcium carbonate variation at different depth in cement paste. And the calcium carbonate generation at different depth in cement pastes with different water/cement ratios was also calculated. The experiment results agreed well with the numerical simulation which proved the reliability of the model.(5) The dilutive effect, boundary effect and the interfacial effect of aggregate were integrated into the theoretical model on the carbonation of cement paste to establish the carbonation model of mortars and concretes. The measurement on the calcium carbonate at different depth revealed the influence of water/cement ratios and carbonation ages on the development of calcium carbonate in mortars and concretes. The experiment results were compared with the model solution. Furthermore, the influence of environment temperature and humidity, concentration of carbon dioxide on the carbonation, as well as the porous structure variation of cement based materials due to carbonation, was analyzed through the theoretical model... |
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