ABSTRACT

Flexible pavements are constructed with a binder course and a wearing course of asphalt mixture at the top. These mixtures have an initial air voids content of 6 to 8 %. When the pavements are subjected to repeated traffic loading, these materials deform and during that process densify. Such densification manifests in the form of depression along the wheel path. These depressions are normally called as ruts and signify the onset of the failure of the pavement. The current methods for quantifying rutting in the laboratory use repeated creep and recovery testing. In such tests, the material is subjected to loading conditions such that one gets a three stage creep curve. The cycle corresponding to the starting of the tertiary curve called as flow number is used for quantifying the expected "rut resistance" of the mixtures. In this presentation, we explore the issues related to repeated creep and recovery testing of asphalt mixtures and the so called "flow number". Experimental investigations were carried out with cylindrical samples of varying air voids subjected to a trapezoidal loading waveform under different confinement conditions. It is shown that it is possible for a material to reach the tertiary stage without passing through the secondary stage and this depends clearly on the testing conditions. Finally, the experimental test data is corroborated with an upper convected Burgers' model and it is seen that such models can at best predict up to secondary stage of the repeated creep and recovery curve.

ABOUT THE SPEAKER

Prof. J. Murali Krishnan is an Associate Professor in the Department of Civil Engineering, IIT Madras. His research interests are in the rheological and mechanical behaviour of asphalts, bitumen-like materials.