Reassessment of Diametral Compression Test on Asphalt Concrete

This report examines the diametral compression test, as described in ASTM D4123-82 (1987) and SHRP Protocol P07 (1993) procedures. The test helps determine the resilient modulus of asphalt concrete, and less frequently its Poisson's ratio, both mechanical parameters of an ideally elastic material. However, the actual behavior of asphalt concrete is not elastic, but viscoelastic. The viscoelastic behavior of asphalt concrete under traffic-induced loads can be described by the phase angle and the magnitude of the complex compliance or complex modulus. These can be determined from the diametral compression tests that subject the specimen to haversine load history, and from the viscoelastic data interpretation algorithms derived in the current research. To avoid inaccuracies in the data interpretation, the vertical deformation should be measured over a 1/4 diameter central sector of the cylinder by means, for example, of the in-house developed displacement gage. A series of tests on specimens with various asphalt binder viscosity verified the validity of the viscoelastic data interpretation. Specimens from MnROAD materials showed the presence of viscoelastic properties even at temperatures well below freezing.