A new technique was developed to measure the moisture content inhot-mix asphalt concrete. The technique involves measuring the dielectric properties of the hot-mix asphalt concrete using electromagnetic waves in the microwave range of 12.4 To 18.0 Ghz. Using the dielectric property measurements, the moisture content can be calculated. This study used piedmont gravel and limestone aggregates in dense-graded and open-graded cases. One type of asphalt cement was studiedexclusively because three types of asphalt were found to have almost the same dielectric properties. Asphalt content, surface smoothness, and specimen thickness were also found to have no effect on the measured dielectric properties. The study considered the different void ratios that had noticeable effects on the microwave reflection measurements. However, the presence of water in the mixes overshadowedthe effects of all other factors on the dielectric properties of the mix. Regression models were developed to predict the volumetric moisture content. The study suggested a model that was found to be a function of the dielectric properties of dry and wet hot-mix asphalt concrete. Therefore, in practice, several cores are essential to obtain the in situ dry dielectric properties of hot-mix asphalt concrete. This paper appears in transportation research record no. 1317, Asphalt mixtures: design, testing, and evaluation 1991.
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