A three-step analytical scheme for estimating the steady-state chloride diffusion coefficient of mature cement paste

Abstract

The intention of this paper is to estimate the steady-state chloride diffusion coefficient of mature cement paste through laboratory test and theoretical analysis. In the test, the chloride diffusion coefficient of cement paste with water/cement ratios of 0.3, 0.4, 0.5, and 0.6 is measured at curing ages from 28 to 1800 days. The test results show that, for cement paste cured for smaller than 360 days, the chloride diffusion coefficient reduces quickly with the increase of curing age. For cement paste cured for larger than 360 days, however, the chloride diffusion coefficient decreases slowly with increasing the curing age. In view of the multi-phase and multi-scale characteristics of cement paste, a three-step scheme is developed to derive the chloride diffusion coefficient analytically. In the scheme, the chloride diffusion coefficients of the inner and outer hydration products and the solid phase are formulated with a two- and three-phase composite sphere models, respectively. Finally, for the bi-continuous cement paste system composed of a solid phase and capillary pores, the effective medium method is adopted to deduce the chloride diffusion coefficient. Eight sets of experimental data, obtained in this paper and collected from the literature, are used to verify the analytical scheme. It is concluded that the developed three-step analytical scheme can evaluate the chloride diffusion coefficient of mature cement paste with reasonable accuracy.