UC Berkeley

The water-to-cement (w/c) ratio is one of the most important parameters determining the quality of cement-based materials. Currently, there is no practical way to accurately determine this ratio after all the ingredients of concrete have been mixed, posing a significant quality control problem for the construction industry. A new method has been developed to address this challenge whereby an electrical resistivity probe is immersed in fresh concrete, providing an instantaneous and accurate measure of a concrete’s water-to-cement ratio. Experiments were conducted on eight concrete mixtures designed according to the ACI 211.1 procedure, with varying w/c ratios (0.30, 0.40, 0.50, and 0.60) and fly ash percentages (0% and 25%). The results demonstrate a strong direct correlation between the resistivity of fresh concrete and the water-to-cement ratio. Average w/c ratio estimates based on measurements using the resistivity probe were within ±0.01 of the actual values for all mixes tested.