Accurate strength prediction models of ordinary concrete using early-age complex permittivity

Early determination of correct cement dosage for concrete mixes and prediction of their compressive strengths are very valuable in construction industry. This article presents a few compressive-strength prediction models for ordinary concrete using early-age measurements of relative complex permittivity. Both the dielectric constant and loss factor of the first-seven-day concrete with four types of mix proportions were measured for building the mathematical models composed of exponential functions at 6 GHz, whereas the measured dielectric data at 28 d were used for model validations. The proposed models not only have high regression accuracy with R2-values of greater than 0.97 but also the low prediction errors of within 10%, which significantly outperform the existing models of the same kind. Through Cole–Cole plot analysis, this article reveals an interesting finding that a minimum loss factor was located at 3 GHz regardless of the age of concrete, which would be useful for wireless network design and planning inside a building. The average loss tangents of various concrete mixes have also been verified to have the same value (~ 0.33) regardless of concrete age, which explains the confidence in use of early-age dielectric properties. Moreover, this article also initiates a precise prediction method of using loss factor and dielectric constant simultaneously in a 3-dimensional plot, wherein no explicit mathematical model is required.