Effect of applied vertical stress on the electrical conductivity of particulate mixtures containing both electrically conductive and nonconductive particles: experimental study on recovered carbon black

Abstract

This study aimed to evaluate the effect of applied stress on the electrical conductivity of granular mixtures containing small conductive recovered carbon black (rCB) particles and insulating large sand particles. The electrical conductivity (ECmix) of mixtures with varying rCB contents were measured according to vertical effective stress (σ′v) ranging from 11 kPa to 2.528 MPa, and the existing physical concepts of binary mixture and particle conduction were employed for the interpretation of test results. Results of this study demonstrate that the measured ECmix can be expressed as the power function of σ′v: ECmix = A·(σ′v/1 kPa)β. In the case where the rCB content was smaller than the threshold finer fraction (FF), A showed a measurable but limited increase with increasing rCB content, but β almost linearly increased with increasing rCB content. In contrast, in the case where the rCB content > FF, A showed an almost linear increase with increasing rCB content, while β showed almost constant values. Most notably, the results demonstrate that the maximum β could be observed when the rCB content ≈ FF. Finally, this study suggests A and β estimating formulas for ECmix based on the percolation theory.