It has been shown that stiffness and relaxation ability of binders can not rank bitumen (especially polymer modified bitumen, PmB) according to their real cracking properties on site. Considering that cracks in pavements occur most of the time in the binder, it would be useful to determine these properties in order to select bitumen in a more accurate way. Tests using fracture mechanics theory could be interesting for this purpose. The test proposed in this study is inspired by fracture mechanics: the three point bending test on a pre-notch bar. The paper describes the procedure used to mould the sample and to perform the test. Results on different binders are then presented. It appears that the shapes of the loaddisplacement curves are not the same for pure binder and PmB. However, the same intrinsic properties have to be determined whatever the bitumen is. The effects of viscoelastictity and crack propagation have so to be evaluated. Indeed, it is necessary to understand what leads to the deviation from the linear behaviour: viscous flow or crack growth. In order to answer to these questions, results from acoustic emission during the three points bending experiment are presented. It is so possible to link the load-displacement curve to the crack initiation and grow. Moreover, the test is modelled by finite element with a viscoelastic stress-strain relation. (Author/publisher)
Abstract