Moisture determination of concrete panel using SAR imaging and the K-R-I transform

Moisture content inside concrete affects the properties and behaviors of Portland cement concrete. It also indicates the likelihood of structural damages (e.g., steel corrosion) in reinforced and prestressed concrete structures. While several laboratory techniques are available for moisture determination, it is a challenging task to estimate the moisture content of concrete in the field without using embedded moisture sensors. In this paper, synthetic aperture radar (SAR) imaging and the K-R-I (curvature-area-amplitude) transform were applied to a concrete panel specimen (water-to-cement ratio = 0.45) for moisture determination. A 10.5 GHz center frequency radar system was used to generate SAR images of the concrete panel at various moisture levels from 0% to 3.85% (by mass). Quantitative analysis of SAR images was carried out by the K-R-I transform to understand the simultaneous change of SAR amplitude and shape at different moisture levels. It was found that integrated SAR amplitude and average maximum SAR amplitude both increase nonlinearly with the increase of moisture content in the concrete panel. Spatial distribution of SAR amplitudes can be used to indicate subsurface moisture distribution in concrete. The area-amplitude (R-I) curve of SAR images quantifies the relationship between moisture content and its distribution. (C) 2018 Elsevier Ltd. All rights reserved.