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With the current trend toward developing mechanistic flexible pavement design and the need for more reliable design procedures, accurate characterization of hot-mix asphalt (HMA) properties is needed. Resilient and dynamic modulus tests were performed at five temperatures on two typical mixes used in the Commonwealth of Virginia to compare the test results. The dynamic modulus was measured at six frequencies at each of the testing temperatures, and the resilient modulus test was performed at one loading time. The study found that the size of the specimen statistically affected the measured resilient modulus value. Resilient modulus values obtained in the 100-mm-diameter specimens were higher than those obtained in the 150-mm-diameter specimens at all testing temperatures. No statistical differences were observed in the resilient modulus of the two mixes. However, statistical differences were found in the dynamic modulus of the two mixes. A strong relation between the dynamic modulus test performed at 5 Hz and the resilient modulus was found. Three different pavement structures were analyzed to estimate the variation of their bottom-up fatigue life when different moduli were used for the HMA layer. It was found that the measured dynamic moduli resulted in the highest fatigue life estimates for the three considered pavements. It is concluded that the dynamic modulus test provides a better characterization of HMA than the resilient modulus test because it provides full characterization of the mix over temperature and loading frequencies.

In this paper, the accuracy of ground-penetrating radar (GPR) for estimating pavement layer thicknesses is studied on the basis of the investigation of 17 pavement sites in Virginia. The considered sites have different types of pavement systems (flexible, continuously reinforced, jointed concretes, and composite) and different ages (0 to 5 years; 10 to 15 years; older than 20 years with a surface less than 10 years; and older than 20 years with a surface older than 10 years). Because of the diversity of the test sections considered, the accuracy of the GPR thicknesses was studied for pavement age for the same type of pavement and against pavement type for sites of the same age category. For flexible pavements, the GPR thickness error was found to increase as the pavement's age increased (4.4% error for pavements 0 to 5 years old versus 5.8% error for pavements older than 20 years with surfaces older than 10 years). Moreover, for the same age category, flexible pavements were found to have a relatively high thickness error (4.4%) compared with the continuously reinforced concrete pavements (3.0%) and with the jointed plain concrete pavements (2.3%) because of the relative homogeneity of concrete for electromagnetic wavelength when compared with the different dielectric profile of aged hot-mix asphalt layer.