Identification of a physical model to evaluate rutting performance of asphalt mixtures

Near-surface rutting has become a costly mode of failure for interstate highways. Even though the pavement is structurally sound, the hazard of water ponding and hydroplaning urges the transportation agencies to rehabilitate the deformed sections. This study was intended to identify a physical model that can provide reliable predictions about a mixture's ability to resist permanent deformation.; Analyses performed with the elastic layer analysis program BISAR and the FEM code ADINA provided information on the pavement's response to actual tire loading. The analyses provided evidence that stress states in the pavement are dependent on tire structure. Furthermore, it was found that radial truck tires induce severe near-surface stress states that have been identified as key factors in the mechanism of instability rutting.; The APA is a laboratory torture test that subjects a specimen to an accelerated loading sequence. The end result (rut depth) can be then correlated to the rutting performance of the mixture in the field. However, the ability of the test to replicate field conditions in the laboratory determines the reliability of the results. It was shown that the APA loading mechanism, the pressurized hose, was not capturing the critical lateral stresses found to be detrimental to HMA pavements.; Based on the tire study results, a new APA loading device was introduced to better replicate the stresses found under radial tires. Contact stress measurements under the two loading devices---pressurized hose and loading strip---showed that the loading strip was able to reproduce the lateral stresses found under individual ribs on a radial tire tread. Subsequent finite element modeling also showed that the loading strip appeared to generate similar shear stress patterns to those found under the modeled radial-tire load. A new method was developed to measure deformations, where a contour gauge is used to record and store the entire surface profile of the sample throughout the progress of the test. The area-change parameter was introduced to calculate the volumetric changes in the sample. Based on the area-change parameter we can calculate whether the specimen is failing primarily due to shear instability or because of excessive consolidation.; The introduction of the new loading device and the area-change parameter provided valuable information about the mixtures behavior. Test performed at low air void content, to control consolidation rutting, showed that both loading devices---loading strip and pressurized hose---were able to provide accurate predictions about the mixture's susceptibility to instability rutting.