Effect of Aggregate Type and Size on Surface Resistivity Testing

Abstract

Surface resistivity testing has gained popularity as a nondestructive test method to assess the physical and chemical characteristics of concrete. This may be due to the fact that it is sensitive to variations in material parameters, especially cementitious phases. This experimental investigation concentrates on the effects of coarse aggregate type and gradation to determine whether they may be contributing factors in the variability of the resistivity measurements for a given cementitious binder. A total of 21 concrete mixtures designed with various aggregate type (limestone, dolomite, and gabbro), gradation (#67, #57, and #56), and binders (0.40, 0.45, 0.50 water-to-cementitious material ratios with Type I cement and Class C fly ash) were prepared and evaluated using surface resistivity testing. It was found that small changes in gradation may not necessarily influence the outcome of a resistivity test for a given mortar matrix. As for a change in aggregate type, there is minimal impact on the resistivity measurement for mixtures prepared with a Type I cement binder; however, the addition of fly ash seems to have a significant impact. The change in resistivity gain in time varied for all three aggregate types. Here, aggregate–paste interaction had a role in either diminishing or increasing the resistivity value, which may be consequential for concrete mixture classification with respect to ionic penetrability and misinterpretation of binder performance.