Estimating volume fraction of bound water in Portland cement concrete during hydration based on dielectric constant measurement

摘要

A study was conducted to estimate the volume fraction of bound water in Portland cement concrete (PCC) during hydration by monitoring changes of its dielectric constant using time-domain reflectometry (TDR). The travel time of an electrical pulse along the embedded probe was measured and the apparent dielectric constant K of PCC was determined. The experiment lasted for 206 days. The results showed that the decrease in dielectric constant was fast immediately after mixing with water. At day 28 the decrease was still significant. Only after 180 days did the decline become negligible. The decrease of K during hydration is the result of the transform of free water to bound water. Based on the dielectric mixing model, the dielectric constant of bound water (K_b) and its volume fraction at a different stage of hydration were estimated. TDR is a promising powerful tool to study small changes in dielectric properties of PCC during hydration.