2008 Volume 6 Issue 1 Pages 143-155
For concrete structures exposed to salt environment, the microstructure and cracks play a crucial role in the ingress of chloride ions into concrete. In this study, concrete is simulated on the meso scale as a three-phase composite, i.e., aggregate particles, mortar and the interfacial transition zone (ITZ). Because of the advantages in predicting cracks behavior in concrete, Rigid Body Spring Model (RBSM) is employed to carry out the mechanical analysis to simulate the distribution and width of microcracks. And then, the truss network model is adopted to evaluate the chloride diffusivity of the cracked concrete. On the basis of the statistics analysis of diffusion coefficients of concrete and mortar determined experimentally, the diffusivity of ITZ is analytically clarified. The range of diffusion coefficient of ITZ estimated in this paper is approximately 3-16 times of that of mortar depending on the different assumed thickness, which agrees well with that of the previous experimental results. With the aim to validate the effect of microcracks on the diffusivity of concrete, a series of the chloride ions penetrating analysis is numerically carried out on the concrete specimen under different stress levels. The axial compressive and tensile loading conditions are investigated respectively and the effects of stress level on chloride diffusivity of cracked concrete are examined. Results indicate that the chloride diffusivity is significantly dependent on the stress level, but only considering the effect of cracks predicted by RBSM is not sufficient. So an empirical equation which can account for the microstructure variation of concrete under loading is proposed. With it, a reasonable estimation for chloride diffusivity of cracked concrete is achieved.