Abstract
The Superpave indirect tension (IDT) system was modified to determine the short-loading-time stiffness of asphalt mixtures from resilient modulus, creep, and strength tests. The idea was not only to provide a more accurate method to determine the resilient modulus, but also to determine whether reasonable measures of short-loading-time stiffness could be obtained from tests that provide other properties and thereby minimize the amount of testing needed to characterize asphalt mixtures. It was found that even when evaluated at very short loading times, the stiffnesses determined from the different tests were significantly different. Detailed evaluation indicated that the differences can be explained by the differences in loading rates between the tests. In general, stiffnesses from the different tests all appeared to be reasonable and followed the same trend. However, since the rheological behavior of asphalts and mixtures varies, stiffnesses from different tests were not directly related. Therefore, although the interpretation methods developed in this study for creep and strength tests appear to provide a reasonable alternative to the resilient or dynamic modulus, the short-loading-time stiffnesses determined from these tests are not directly comparable with the resilient or dynamic modulus or with each other. The work illustrates the sensitivity of stiffness to relatively small changes in loading rate and other variables, which emphasizes the need to precisely define load pattern, load level, and data interpretation methods to determine asphalt mixture stiffness at short loading times.
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