Single-Pipe Model of Oxygen Diffusion in Unsaturated Cement Pastes: Comprehensive Analysis of Surface, Knudsen, Bulk, Transition, and Water-Curtain Diffusion

Abstract

One of the most important factors affecting the durability of concrete structures is reinforcement corrosion, which is caused by oxygen concentration. Therefore, it is important to investigate oxygen diffusion in cement pastes. However, current research on oxygen diffusion models of unsaturated cement pastes has led to unclear conclusions. In this study, we propose a single-pipe oxygen diffusion model that considers five diffusion mechanisms: surface, Knudsen, transition, bulk, and water curtain. Further, a three-stage method is used to set up the model, and the division mode of this method is based on the mean free path (MFP) and the Mohycan model. The accuracy of the model is verified by comparing the calculated results with the experimental data. The proposed single-pipe model can be used to further analyze the durability degradation of reinforced concrete structures caused by steam, carbon dioxide, and other gases in the atmospheric environment.