Microstructure-based simulation of time-dependent chloride diffusivity in saturated cement paste

For accurately predicting the service life and evaluating the durability of reinforced concrete structure exposed to chloride environments, it is highly desirable to determine the chloride diffusivity in cement paste. Because of continuous cement hydration and chloride binding during the process of chloride diffusion, chloride diffusivity varies with time. In this paper, a computational approacht for predicting the time-depending chloride diffusivity in cement paste is presented. HYMOSTRUC3D, a computer-based cement hydration model, is applied to generate the 3D microstructure of cement paste. Both of the cement hydration process and chloride binding are taken into account in the simulation of microstructure. Finite element method is applied to simulate the diffusion of chloride ions through the microstructure of cement paste and estimate the chloride diffusivity based on Fick's law. A series of statistical analysis are carried out to determine the representatieve elementary volume (REV) of cement paste. The dependences of chloride diffusivity on time and w/c ratio are investigated. Finally, the simulations are validated with the experimentally measured values obtained from the literature. The comparison indicates that the simulated values and measured vlaues are of the same order of magnitude. Moreover, the trend (shape) of simulated relationship (chloride diffusivity vs time, chloride diffusivity vs w/c ratio) fits very well with the experiments.