| Description |
The water-to-cement (w/c) ratio of concrete and mortar mixtures is an important parameter that affects its strength and durability. Present quality control/quality assurance procedure involves methods that require significant time and require samples to be taken off-site. Accurate and quick determination of w/c ratio before placing would ensure high-quality concrete construction. In this study, 17 concrete mixtures and 11 mortar mixtures were tested to obtain a relation between average dielectric constant and paste to aggregate content ratio using a handheld meter to indirectly determine w/c ratio within minutes after arrival on the job site by measuring capacitance. For concrete mixtures, significant variations in dielectric response with paste to aggregate content ratio were observed. Moreover, variations with time were minimal. For the limited data, quadratic and piecewise linear regression models were assumed and plotted between average dielectric constant and paste to aggregate content ratio. Quadratic and piecewise linear regression models were able to predict the paste to aggregate content ratio, water content, and w/c ratio of 16 and 10 concrete mixtures, respectively. When the quadratic regression model was used, most of the predicted paste to aggregate content ratio had a relative error within ± 11%. Most of the predicted water content and w/c ratio had a high relative error between 20% - 40%. When using a piecewise linear regression model, half of the predicted paste to aggregate content ratio had a relative error greater than ± 11%. Half of the predicted water content and w/c ratio iv had a relative error greater than ± 40%. As the predicted water content and the w/c ratio are very sensitive to the predicted paste to aggregate content ratio, the method cannot be used to predict water content and w/c ratio of concrete mixes. For mortar mixtures, the dielectric response was not too sensitive to the paste to aggregate content ratio. Also, significant variations in dielectric constant with time were observed. Significant variations in dielectric constant make the time of measurement an important factor and make it difficult to distinguish between two different w/c ratios. Therefore, the method does not apply to mortar mixtures. |
