The Effect of Aspect Ratio on the Frequency Response of Asphalt Concrete in Impact Resonance Testing

摘要

A comprehensive study was conducted to investigate the influence of aspect ratio (height/diameter) of laboratory specimens on the frequency response of asphalt concrete when tested with impact resonance (IR). Testing was conducted over a range of air voids and temperatures. The IR test, performed in longitudinal mode over 100 cylindrical asphalt concrete specimens, demonstrated that the test is repeatable and reproducible. It was observed that the test response was greatly dependent on the specimen length regardless of the aspect ratio, but the dependency was not noted for specimens with the same diameter of larger aspect ratios. Specimens with the same aspect ratio but different size delivered different resonant frequencies. The test results indicated that the frequency response increased as the aspect ratio increased approximately up to 0.7, and then it decreased with a nonlinear trend as the aspect ratio increased beyond 0.7, indicating the tendency of the frequency response reaching a plateau as the aspect ratio increased. It was inferred from test results that there was a threshold aspect ratio at which the fundamental longitudinal frequency mode was not the dominant frequency mode. Velocity calculations from measured resonant frequencies indicated that the true material properties could be attained at an aspect ratio of as low as 1. Based on the results of this study, testing specimens with a diameter of 150 mm and a height of 170 mm commonly used for producing dynamic modulus test specimens, provided proper size and aspect ratio for testing with IR.