Nondestructive observation of state of water in concrete using dielectric spectroscopy

Abstract

We present a method of observing the relaxation process reflecting the motion of water molecules masked by the contribution of electrical conduction. By using this method, we can observe the Cole–Cole-type relaxation process reflecting the motion of the bound water molecules in cement-based materials. The relaxation time and strength of this process increase with curing time, and both parameters saturate to a constant value. The curing time dependence of compressive strength can be described by a logarithmic function, and the change in compressive strength correlates strongly with the change in relaxation time. In the analysis using the τ-β CC diagram, the trajectory of the τ-β CC diagram shifts to the lower right as the curing progresses, and the feature of the trajectory of the τ-β CC diagram depends on the difference in the wetting environment. Our results indicate that the state of water retained in the pore structure can be used as a probe to obtain information on the curing progress of concrete.