Investigation of asphalt concrete rutting mechanisms by X-ray computed tomography imaging and micromechanical finite element modeling

This paper systematically investigates the changes in asphalt concrete (AC) microstructure caused by full-scale accelerated pavement testing with a heavy vehicle simulator (HVS), using X-ray computed tomography images taken before and after HVS rutting tests. A viscoelastic micromechanical finite element modeling was also used to investigate effects of bitumen mastic and aggregate skeleton properties on shear resistance. The primary purpose was to determine the reasons behind the earlier failure of the rubberized gap graded AC mix used in the test compared to the polymer modified dense graded mix also included in the experiment. Shear related deformation appears to control the long term rutting performance of the test sections while densification was primarily an initial contributor at the very early stages of trafficking. A high concentration of aggregate interlock in the polymer modified mix, as a result of the dense gradation and larger aggregate sizes, appears to have resulted in greater dissipation of shear stresses and therefore greater shear resistance. The lack of this interlocking effect for the rubberized gap graded mix is proposed to have caused the earlier failure on HVS test sections.