Resistivity's Sensitivity to Concrete Mixture Design Parameters

This study aims to determine whether resistivity can be used as a quality assurance method to identify variations in mixture design proportions between a prequalified mixture and delivered mixture. Owner agencies expend significant effort qualifying concrete mixture designs, ensuring trial batching, and requiring mock-ups according to the concrete properties important for a project. After accepting a mixture design, however, the owner agency has few tests that ensure that the concrete delivered to the project site has the same mixture proportions of the mixture design approved for the project. At the batch plant due to measuring tolerances, enroute to placement due to water additions or water evaporation, and during curing due to environmental and human factors, the original concrete mixture can be modified. Literature has noted significant effects of paste volume and water-to-cementitious materials ratio on concrete strength, shrinkage, water absorption, and overall durability. This research proposes resistivity testing as a method sensitive to changes in concrete paste content and water-to-cementitious materials ratio between mixture acceptance and mixture delivery. Resistivity testing is increasingly used by concrete testing facilities and owner agencies for quality assurance and control purposes and can be performed on concrete cylinders intended for compressive strength testing. The study results demonstrate that resistivity displays the sensitivity needed to determine if a concrete mixture design’s parameters vary significantly from the intended concrete mixture design.