The study has been conducted on a large range of mix formulations, differing mainly by the nature of the binders used. Those were either pure or modified bitumens, so as to cover a wide range of rheological behaviours. The following tests have been performed on the mixes: (1) Gyratory Compaction according to the French method (PCG); (2) "Duriez" compression tests; (3) MARSHALL compaction followed by "Cantabro" tests performed at 18°C before and after water immersion; and (4) Vibrating compaction followed by "Cantabro" tests at 25°C. These simulation tests have enabled classification of mixes into several categories. It was however not possible to establish a full correlation (valid for all the tested formulations) correlation (valid for all the tested formulations) with any of the above listed "conventional" tests. These differences in behaviour are extensively discussed in relation to the rheological characteristics of the various binders. The damaging mechanisms seem to be dependent on both the chosen test procedure and on the mix formulation itself. This would explain why binders with different rheological characteristics can lead, via different failure mechanisms, to similar results in the "Cantabro" test whereas they are differentiated by the wheel-tracking test. This study is thus proposing some first elements for more rational approach in the design of open-graded drainage mixes. The choice of a test method, selection of operating parameters and finally the interpretation of results must always be guided by a careful analysis of the involved failuremechanisms. More particularly, this study shows that one cannot rely on a single criterion. A correct performance prediction can however be made from a cross-analysis of the results obtained through several different tests on the mixes.
Abstract