Evaluation of Dynamic Modulus in Asphalt Paving Mixtures Utilizing Small-Scale Specimen Geometries

One of the primarily used performance criteria to evaluate the laboratory properties of asphalt mixtures has become the results of dynamic modulus testing. Using an asphalt mixture performance tester (AMPT), as developed in National Cooperative Highway Research Program (NCHRP) Project 9-29, this test is commonly conducted to characterize asphalt mixtures mechanistically. A cylinder with a 100 mm diameter and a 150 mm height comprises the test specimen geometry. For laboratory-prepared specimens produced using a gyratory compactor, this geometry is practical. When the test specimen is prepared from field cores and the investigator wants to isolate the testing to a single asphalt mixture material/layer, however, the specimen scale is problematic. This is due to the fact that most asphalt mixture layers are placed with a thickness less than 150 mm, especially surface and intermediate layers. The use of small-scale specimens as an alternative means to conduct dynamic modulus testing of asphalt mixture materials was investigated in this study. The dynamic modulus measured on small-scale cylindrical specimens was compared to the dynamic modulus measured on full-size cylindrical specimens (100 x 150 mm) using asphalt mixtures with a nominal maximum aggregate size (NMAS) of 9.5, 12.5, 19.0, and 25.0 mm, in order to validate the small-scale approach. An evaluation of small-scale specimens with a diameter and height of 38 x 135 mm, 50 x 135 mm, 38 x 110 mm, and 50 x 110 mm was conducted. For 9.5 and 12.5 mm NMAS mixtures, from the findings of this study, any of the four small-scale geometry dimensions tested appears to be suitable alternatives to the full-size specimen. The two small-scale geometries with a diameter of 50 mm appear to be suitable alternatives to the full-size specimen, for 19.0 and 25.0 mm NMAS mixtures.