Effects of pore fluid type and ionic concentration on electrical conductivity of granular mixtures of electrically conductive graphite and nonconductive sand

Abstract

This study investigates the effects of pore fluid type and ionic concentration on the electrical conductivity of granular mixtures containing both insulating and conductive particles. Specimens with varying ionic concentrations were prepared, and we measured the electrical conductivity of mixtures of sand with varying graphite contents with increasing vertical stress. Results show that the percolation threshold appears to be at a carbon fraction around 20% and divides the tested mixtures into similar response groups. Normalized particle conduction Kp values reveal negligible effects of pore fluid type and concentration on Kp at a low applied stress level. However, at high stress levels, the Kp increases with increasing ionic concentration of pore water, and the Kp of the dry specimen was comparable to that of a saturated specimen with very low ionic concentration. Finally, the particle conduction estimating method for mixtures is suggested, and the relevance of pore water conduction is investigated.