The overall quality and compressive strength of concrete are dependent upon the water content of the concrete mixture. Detection of completion of the curing process is critical prior to application of surface finish or coatings. At present, there are few instrumental methods available for monitoring the concrete curing process, and no present method is sufficient for widespread application. To remedy this situation, American Research Corporation of Virginia has developed a noninvasive and nondestructive method of evaluating the moisture content of concrete slabs using a microstrip waveguide having resonance in the 300 MHz to 3 GHz range. The microwave resonance sensor (MRS) has been shown to respond to small changes in the dielectric coefficient of the concrete mix and of poured concrete slabs due to changes in moisture content. Moisture in the concrete interacts with the evanescent field of the circular microstrip waveguide to produce a change in the resonant frequency of the waveguide. A change in the resonant frequency on the order of 10 MHz is observable during the first month of curing, corresponding to a moisture content change on the order of 5%. Data will be presented on the use of the MRS to monitor the cure history of a range of concrete admixtures. Work on developing low-cost driving and detection circuitry for the MRS probe system will also be discussed.
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.full paper not received Publisher:Ashgate Publishing Company
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