Evaluation of Dilatancy Behavior of Asphalt Mixtures Using Partial Triaxial Compression Tests

Abstract

Dilatancy behavior plays a key role in the rutting of asphalt mixtures; therefore, it is important to study its behavior to better predict and mitigate rutting of asphalt pavements. In this study, a partial triaxial compression test (PTCT) was developed and employed to characterize the dilatancy of asphalt mixtures. On the basis of the analysis of the principles and the testing method of the PTCT, the parameters of the specimen and the pedestals were determined using the finite-element method to ensure that the specimen could provide a similar confining pressure to that in an actual asphalt pavement. The diameters and heights of the pedestal and specimen were determined to be 50×30 mm and 100×80 mm, respectively, by considering the aspect ratio of the specimen, actual pavement thickness, and numerical results. The test results were analyzed using the strain ratio and stress-dilatancy theories, considering the coupled effects of dilation gradient, distortional strain, and volumetric strain of the asphalt mixtures. It is shown that the degree of dilatancy changed with the strain ratio, which is sensitive to the air void content and loading rate. The stress-strain relationships of the asphalt mixtures indicate that dilation is related to the air void content and testing time. The asphalt mixtures contracted at the beginning of testing and then dilated after the peak stress, and the dilation increased continuously with increase of the axial strain. The specimen contracted when the dilation parameter d (d=1−volumetric strain increment/axial strain increment) was less than 1.0 and dilated if d was greater than 1.0. The dilation gradation was strongly correlated with the factors, including the stress-strain relationship, air void content, loading rate, and testing time. This study demonstrated that PTCT is a good and accurate test method to evaluate the dilation of asphalt mixtures.