Characterization of Moisture Content in a Concrete Panel Using Synthetic Aperture Radar Images

Abstract

Moisture content in concrete structures is commonly associated with many durability problems (e.g., steel corrosion and freeze-thaw) and can be used in structural health monitoring and nondestructive testing of concrete structures. In this paper, the use of synthetic aperture radar (SAR) imaging for characterizing subsurface moisture content and distribution is proposed, using a concrete panel specimen as an example. A 0.3×0.3×0.05-m concrete panel specimen cast and conditioned in laboratory was air-dried for almost 5 months and simultaneously monitored for its moisture variation by SAR imaging. From the analysis of its SAR images at different moisture contents, it was found that SAR images can not only qualitatively capture the moisture distribution inside concrete but can also quantitatively correlate with the overall moisture content inside concrete. Higher SAR amplitudes indicate stronger electromagnetic scattering response, suggesting greater values of dielectric constant. A critical contour in SAR images is proposed as an insightful measure for the subsurface sensing of concrete. An approach for determining the critical contour in each SAR image is proposed.