Development And Application Of A Testing System For Characterizing Loose Hot Asphalt Mixtures’"Rheological" Behaviors

Workability of asphalt concrete plays an important role in Asphalt PavementPerformance. How to assess accurately the rheological properties of asphalt mixture is the keyto ensure o the quality of the asphalt pavement. At present, researches about asphalt mixturerheology mainly aimed at the mechanical properties of compacted specimens in laboratory.The laboratory study process is complex, time-consuming and labor-intensive. Few researcheswere conducted about rheological properties of loose hot asphalt mixture, and all theresearches were mainly about the mixing workability or deformation and density changes inthe process of compaction tests. when using the same gradation and asphalt, aggregates, fillersand other materials, similar mechanical behavior and performance should be showed betweenthe loose hot mixture and compacted mixture from the Principles of material. Therefore, themixture in loose hot state could reflect performance in both pre-compaction and compactionstages. Therefore it is very meaningful to propose a new set of test system to study rheologyproperties of loose hot asphalt mixture.Rheological properties of the loose hot asphalt mixture were analyzed first in the text, theconcept of viscosity was proposed. A test system for rheological properties measuring of loosehot asphalt mixture was developed based on the viscosity property, and repeat experimentswere conducted to verify the stability of the test system. Rheological properties of asphaltmixture of different asphalt-aggregate ratio, maximum particle size and gradation type weretested with the self-developed testing system. According to the tests results viscous force Fand the fitting parameters k were used to evaluate rheological properties of loose hot asphaltmixture. Finally, the numerical simulation useing discrete element methods were conducted tointerpretate and validate the experimental results.The research results show that the test system was stable with coefficients of variation ofthe repeat test were within the range of±0.1, the maximum value do not exceed±0.2. Apower function was shown between the force and displacement of the loose hot asphaltmixtures. The loose hot asphalt mixture was a kind of pseudoplastic fluids according to theclassification of fluid. The viscous force F and the fitting parameters k showed a decreasingtrend with the increase of the amount of asphalt content; the greater the asphalt mixturelargest nominal particle size, the greater the viscous force F and the fitting parameters k;viscosity of SMA asphalt mixture was significantly higher than the AC asphalt mixture withthe same particle size and the amount of asphalt. Discrete Element Simulation results show that the average contact force increased with the maximum particle sizeincreasedof the type ofgradation; the average contact force of the SMA asphalt mixture was much higher than ACasphalt mixture when the maximum particle size was the same.