Published in 2015
The results of dynamic modulus testing have become one of the primarily used performance criteria to evaluate the laboratory properties of asphalt mixtures. This test is commonly conducted to characterize asphalt mixtures mechanistically using an asphalt mixture performance tester as developed in NCHRP Project 9-29. The typical test specimen geometry consists of a cylinder having a 100-mm diameter and a 150-mm height. This geometry is practical for laboratory-prepared specimens produced using a gyratory compactor. However, the specimen scale is problematic when the test specimen is prepared from field cores and the investigator wishes to isolate the testing to a single asphalt mixture material/layer. This is because most asphalt mixture layers, especially surface and intermediate layers, are placed having a thickness less than 150 mm.
This study investigated the use of small-scale cylindrical specimens as an alternative means to conduct dynamic modulus testing of asphalt mixtures. To validate the small-scale approach, the dynamic modulus from small-scale specimens was compared to the dynamic modulus from full-size specimens (100 × 150 mm) using asphalt mixtures having a nominal maximum aggregate size (NMAS) of 9.5, 12.5, 19.0, and 25.0 mm. Small-scale cylindrical specimens having a diameter and height of 38 × 135 mm, 50 × 135 mm, 38 × 110 mm, and 50 × 110 mm were studied.
Based on the findings of the study, for 9.5- and 12.5-mm NMAS mixtures, any of the four small-scale geometry dimensions appears to be a suitable alternative to the full-size specimen when the full-size specimen cannot be produced. For 19.0- and 25.0-mm NMAS mixtures, the two small-scale geometries having a diameter of 50 mm appear to be suitable alternatives to the full-size specimen when the full-size specimen cannot be produced.
Benjamin F. Bowers, Ph.D., P.E.
Last updated: November 12, 2023