Prediction of relative electrical conductivity of saturated cement paste

Abstract

Owing to its importance both in assessing the microstructural development and in computing the ionic diffusivity and permeability, it is of great practical significance to determine the relative electrical conductivity of saturated cement paste. This paper presents an analytical solution for the relative electrical conductivity of saturated cement paste. By modelling saturated cement paste as a two-phase composite material, consisting of capillary pores, and hydrated products and unhydrated cement grains, an analytical solution is derived for the relative electrical conductivity of saturated cement paste based on the general effective medium theory. Two parameters involved in the analytical solution are then determined by experimental calibration. After verifying the analytical solution with two sets of experimental results obtained from the literature, the effects of the water/cement (w/c) ratio and the degree of hydration on the relative electrical conductivity of saturated cement paste are evaluated in a quantitative manner. It is found that the relative electrical conductivity of saturated cement paste decreases with the decrease of the w/c ratio and/or with the increase of the degree of hydration. The paper concludes that the analytical solution presented can predict the relative electrical conductivity of saturated cement paste with reasonable accuracy. Notation aintermediate coefficient H(V 1 ÀV 1c ) Heaviside step function in terms of V 1 and V 1,c h 1 , h 2 coefficients between zero and one m percolation exponent in terms of n n parameter R cp relative electrical conductivity of saturated cement paste to pore solution t parameter larger than or equal to zero V 1 , V 2 , volume fractions of phase 1 (capillary pores) and phase 2 (hydrated products and unhydrated cement particles) V 1,c critical volume fraction of phase 1 V cap volume fraction of capillary pores V hyd volume fraction of hydrated products V unhyd volume fraction of unhydrated cement grains w/c water/cement ratio AE degree of hydration ó 1 , ó 2 electrical conductivities of phases 1 and 2 ó s , ó cp , ó 0 electrical conductivities of pore solution, saturated cement paste and hypothetical homogeneous medium