Research on transversely isotropic permeability of asphalt pavement: Laboratory tests and computational simulation

Moisture infiltration in asphalt pavement shows strongly transverse isotropy due to its inherent microstructure and paving process. However, there is no accurate measurement of transversely isotropic permeability, due to the limitation of the existing test device. Consequently, the precise quantification of its effect on dynamic responses within asphalt pavement remains unknown. This investigation is aimed, firstly to get the authentic horizontal and vertical hydraulic conductivity in asphalt mixture by developing a novel permeameter, secondly to illustrate the influence that transverse isotropy has on time history and spatial distribution of dynamic responses in asphalt pavement through finite element simulation. In this research, Hollow Marshall specimens, corresponding compaction device and custom-made permeameter were utilized. Two types of asphalt mixture: asphalt concrete and open graded friction course with gradient porosity of 4±1% and 20±2%, respectively were used. The hollow diameters of all specimens were controlled to be 15 mm or 20 mm. Experimental results show that permeability in both types of asphalt mixture presents transverse isotropy and this characteristic is fiercer in asphalt concrete. Computational simulation illustrates that transverse isotropy of permeability plays a different role in affecting pore pressure compared with changes in its amplitude. Vertical hydraulic conductivity's effect is more distinct on response duration and spatial distribution, compared with horizontal conductivity. In summary, these results suggesting an underestimation of transversely isotropic permeability characteristic in previous researches on predicting mechanical behavior of fully saturated asphalt pavement.