Microwave Reflection Properties of Concrete Periodically Exposed to Chloride Solution of 3% Salinity and Compression Force
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Corrosion of steel rebar in a concrete structure compromises its structural integrity and hence its performance. Chloride intrusion into concrete can lead to depassivation of the steel and initiation of corrosion. Methods exist to detect chlorides in concrete, but the practical use of many of these may be problematic because they are destructive and time consuming, and cannot be used to analyze large structures. Microwave nondestructive evaluation techniques applied to mortar have proven successful for detecting mixture constituents, chloride ingress, and cure-state monitoring. In this paper several concrete samples are cyclically soaked in distilled water and saltwater while also experiencing compression force. Compression force, simulating in-service loading, results in increased microcracking and permeability, which promotes chloride ingress. The daily microwave reflection properties of these samples were measured at 3 GHz. The results show the capability of these microwave measurements for detecting the increased level of chloride permeation as a function of increasing number of soaking cycles. In addition, comparisons between the reflection properties of mortar and concrete cubes soaked in distilled water exhibit similarity in trends, indicating that the various phenomena that occur within them are systematically similar.