- During the hydration of Portland cement concrete, free water reacts with the compounds of unhydrated cement to form the hydrated phases that make up concrete. The chemical reaction results in a reduction in the amount of free water and consequently produces hydration products. Thus, the estimate of free water content and other components in hardening concrete is very helpful in understanding the behavior of early age concrete and the ultimate quality of concrete that can be achieved. Although many properties of concrete are related to the volume fractions of its components, dielectric properties are a beneficial parameter for identifying characteristic components of hardening concrete over time. They can also serve as a useful and continuous nondestructive measurement technique applicable during the hydration process. This paper defines a volumetric relationship of fresh concrete and describes an approach to estimate the volume fraction of the different phases or components that make up hardening concrete. Additionally, the use of the approach was validated by comparing the results with the laboratory test data. 2012 American Society of Civil Engineers.