Research On Concrete Carbonation Model And Its Parameters

Corrosion of the reinforcement in concrete is one of the main factors affecting the durability of reinforced concrete structures. Concrete carbonation is precondition of reinforcement corrosion under ordinary atmospheric environment. The mechanism and influencing factors of concrete carbonation are studied, and the predicting model of concrete carbonation is investigated too. Especially, the concrete carbonation theory model based on the Fick's first law of diffusion is penetrated into.According to the law of conservation of mass, an equation that describes gas diffusion and transmission accompanied by chemical reaction is suggested, by which the real concentration of CO₂ in concrete is deduced and the theoretical argument for the assumption that the concentration distribution of CO₂ in concrete is a straight line is founded. On the basis of analysis of mechanism of concrete carbonation and hydration, an important parameter of the concrete carbonation theory model, which is the molar content of CO₂ absorbed by concrete when they react thoroughly is studied, also a more reasonable calculating formula is suggested. Still, the influence of different kinds cement to the parameter is analysed. Form the mechanism of gas diffusion in concrete, an effective gas diffusivity calculating model is proposed, which take concrete compressive strength as main factor and consider influences of environment temperature and relative humidity and the stress state and level of concrete. By the anterior work, a practical concrete carbonation depth predicting model is established. Through fly ash concrete accelerating carbonation test, the influence of water cement ratio, cement content, fly ash content, cast side and so on to concrete carbonation speed is analysed, using the test results validate the established concrete carbonation model.