Nondestructive testing of asphaltic laboratory samples through resonant tests

Knowledge of the dynamic modulus of bituminous mixtures is practical and theoretically meaningful in pavement design, construction, and monitoring. The tests in the laboratory for the determination of asphalt concrete (AC) moduli include the resilient modulus through the indirect tensile test (EN 12697-26), the complex modulus through the four point bending beam (EN 12697-26), the asphalt mixture performance tester (AMPT) and the simple performance tester (SPT) (AASHTO T342). Unfortunately, the tests above are time-consuming and quite expensive. On the other hand, the standard ASTM E1876 for resonant tests applies only to very thin (stocky) cylindrical samples (with a thickness-to-radius ratio, t/r, lower than 0.5) while the typical AC samples produced in the laboratory do not satisfy the ASTM E1876 requirements. Consequently, the main objective of this study is to set up and implement a tentative method to extend the range of applicability of the standard ASTM E1876 to common AC samples. The methodology was to carry out resonant tests on slender samples and to cut each of them into stocky samples (these latter complying with ASTM E1876 requirements in terms of t/r), deriving the master curve per material. These master curves allowed for deriving the value of the dynamic modulus for the given selected sample under its particular test conditions during the resonant test (i.e., temperature and frequency). Consequently, simplified formulae were provided for AC samples. Results were compared to Witczak's estimates. These formulae provide an approximate tool to carry out low-cost and high-speed inferences at the laboratory stage on common AC samples, whatever their thickness is. Additional studies are needed to investigate the reliability of the method further and reduce uncertainties.