Search Content

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 Mn/ROAD materials showed the presence of viscoelastic properties even at temperatures well below freezing.

This report presents the results of a four-month research project on the use of the ignition method for determining the asphalt content and aggregate gradation of a hot-mix asphalt concrete mixture. The report includes a review of the available methods on asphalt content determination and the development of ignition method. This research expanded the knowledge in this area by focusing on Recycled Asphalt pavement (RAP) mixtures and providing ways to estimate the combined weight loss factor of RAP mixes and virgin mix made from multiple sources of aggregate. The conclusions drawn from this research are based on the laboratory results of 36 RAP and 36 virgin mixes. resting showed that regardless of RAP or virgin mix, as long as appropriate procedures are followed, the ignition method can accurately determine asphalt content and aggregate graduation of a mixture. The easy-to-use spreadsheet program written for estimating the combined weight loss factor can save the operator from repeating laboratory calibration on mixes made from identical aggregates but different proportions.

At the Minnesota Road Research Project (Mn/ROAD), asphalt concrete mixtures were used to evaluate both warm and cold temperature material properties with selected text methods and a wide range of testing parameters. These parameters were selected to approximate different levels of environmental conditions, traffic speeds, traffic loads, and, in certain cases, confining pressures. The underlying theories used to calculate stress and strain from various loading configurations also were rigorously evaluated to determine the appropriateness of comparing results from one testing configuration to another. Mn/ROAD mixtures were evaluated as the first step in linking laboratory measurements and test method selection to live traffic pavement responses and performance. A comparison of axial and diametral testing using harmonic loading showed that experimental results did not agree with theory. That is, the complex deviatoric modulus determined for diametral testing should have been less than the Young's modulus determined from testing axially loaded samples. This was not the case. This suggested that a further examination of the sample instrumentation, testing variability, and the possibility of anisotropic mixture behavior due to particle orientation during compaction are needed to resolve these differences. Other findings indicated that the influence of load duration is minimized as the test temperature decreases, there was little influence in rest period times in repeated loading tests on modulus, and confining pressure only had a significant influence on modulus above about room temperature.