Chloride diffusivity of pure cement paste

Abstract

A two-step scheme is presented for estimating the chloride diffusivity of pure cement paste. In the scheme, gel pores are included in the solid skeleton, composed of calcium hydroxide, unhydrated cement and calcium silicate hydrate, while capillary pores and the solid skeleton constitute pure cement paste. In combination with percolation theory, the effective medium method was modified to formulate the chloride diffusivities of the solid skeleton and pure cement paste sequentially. Detailed analysis was conducted to calibrate the percolation exponent for the high-diffusivity phase and the chloride diffusivity of the pore solution. Comparisons with various test results were made to verify the proposed scheme. Unlike existing analytical methods, the physical properties, volume fractions and morphological relationships of various phase constituents and the shapes, percolation behaviour and different roles of gel and capillary pores are all taken into account simultaneously. The calibrated chloride diffusivity of the pore solution was found to be considerably close to that derived by molecular dynamics simulation, suggesting that the scheme represents a more realistic pure cement paste. The scheme can reasonably evaluate the chloride diffusivity of pure cement paste at medium and long curing ages.