Study of Carbonation-depth Prediction of Unsaturated Concrete Considering Carbonation-produced Water

Carbon dioxide can react with alkaline carbonate substances in cement-based materials, which harms the durability of the concrete structure. The carbonation reaction is a process of releasing water, resulting in an increase in pore water saturation, which was always neglected by previous studies. In this paper, a transient pore water saturation equation is proposed and introduced into the classical carbonation reaction kinetic model, which is simulated by finite-element software with a typical ordinary Portland cement. The model was verified by two classical empirical equations for carbonation-depth prediction. The simulation results indicated that the increment of pore water saturation originated by carbonation-produced water will weaken the CO2 diffusivity and enhance the carbonation resistance. Besides, the growth rate of carbonation depth is slightly faster without considering the produced water and with higher initial saturation, the difference will be more significant. If the influence of carbonation water is ignored, the predicted carbonation depth of unsaturated concrete may be less accurate. This study can provide some reference for theoretical and experimental studies on concrete carbonation. However, future work is still needed including more realistic effects in the model such as the mesoscale modeling of concrete and the integration of stress states. KEYWORDS: Ordinary Portland concrete, Carbonization reaction, Carbon-dioxide transport, Finite-element method, Pore saturation.