| description abstract | To effectively evaluate the contact characteristics of a particle system, an aggregate contact-slip tester was developed in this investigation on the microscopic level. Contact indexes, including the maximum slip force, number of macropeaks, and number of micropeaks, were proposed to quantitatively evaluate the contact characteristics of the particle system. The contact tests were conducted on single-file-size particle systems and three graded particle systems of aggregate. By comparing and analyzing the variation coefficient of parallel tests for different speeds and particle sizes, the key test conditions were determined such as loading rate, sampling interval, and test distance. The validity of proposed indexes was verified adopting the ANOVA method by selecting the six-file-size aggregates and three typical graded mixtures. The results show that the appropriate test conditions of this method are loading rate of 10 mm/min, test distance of 80 mm, and sampling interval of 1/45. Each index has little discreteness and shows a good discrimination to the contact characteristics for the materials with different gradations. The maximum slip force reflects the structure stability of the particle system, and the contact effect of the single-file-size particle system enhances with the increase of the aggregate size. The contact among particles of a graded particle system is more frequent, and the system is in an unstable dynamic microadjustment state under the action of external force. The structure stability of the particle system improves with the increase in the number of coarse aggregates, especially particles with a size of 9.5 mm, which is affected by the interference of fine aggregates adversely. The macropeak number and micropeak number, respectively, reflect the particles’ contact characteristics when the particle system is in a stable state and a metastable state. The more frequent contact does not mean that the structure of the particle system is more stable. According to the ability to form and maintain the stable structure of asphalt mixture, the order of three gradations is open-graded friction courses (OGFC)-13 > stone matrix asphalt (SMA)-13 > asphalt concrete (AC)-13. | |
