Spherical indentation behaviour of bitumen

The spherical indentation response of a 50 pen bitumen is investigated both experimentally and via an analytical model. The model for the indentation of a power-law creeping solid of Bower et al. [Proc R Soc London, Ser A 1993;441:97-124] is extended to account for the recovery behaviour of bitumen by employing the concepts of effective stress and effective strain under the indenter. An extensive experimental study of the monotonic, recovery and cyclic spherical indentation behaviour is reported for a range of temperatures. In line with the predictions of the model, the monotonic indentation response of the bitumen exhibits a power-law dependence on the indentation force, while the continuous cyclic response is primarily a function of the mean indentation load. The model is also successful in capturing the indentation recovery behaviour of the bitumen and is shown to be in reasonable agreement with periodic pulse tests over a wide range of test conditions.