This paper investigates the quasi-static permanent deformation (rutting) behavior of two asphalt mixtures commonly used as asphalt base course mixtures on national highways in Pakistan. These asphalt base course mixtures are denoted as gradation A (coarser -Mix A) and gradation B (comparatively finer -Mix B) in the National Highway Authority's (NHA) general specifications of 1998. The permanent deformation behaviour is assessed using simplified quasi-static uni-axial laboratory tests performed over a range of temperatures and stress levels. Analysis of results from a standard repeated load uni-axial test often used as a practical tool to assess the permanent deformation resistance of bituminous mixtures shows that, due to the lower applied stress levels, and high temperature, mixture-B was observed to resist permanent deformation better than the coarser mixture-A. At high stress levels and at high temperature, the shift in behaviour of both mixtures was observed. Mixture-A was noticed to be less susceptible to permanent deformation. It was assumed that the interlocking mechanism, of the coarse aggregate at low stress levels could not be initiated which resists further deformation over the temperature regimes tested. Binder-fines mortar exhibited a more dominant behaviour. However, at higher temperatures the "Interlock" mechanism was found to play a dominant role making the coarser mixture less susceptible to permanent deformation. (a) For the covering entry of this conference, please see ITRD abstract no. E214938.
Abstract