Comparison of the use of the gyratory compactor in the French mix design method and in superpave level 1.

The gyratory compactor has been used in France for the design of bituminous mixes since 1975. A test standard and specifications have been published. The compactor is supplemented by a wheeltracking test. Mixes designed by this method proved durable and resistant to rutting, although French axle loads are very high (13 tons). SUPERPAVE has recently introduced use of the compactor for mix design by a purely empirical volumetric method in which compactor is not supplemented by any other mechanical test on the mix. Test conditions in the two methods are slightly different: the nominal angle in the French method is 1 degree against 1.25 degrees in SUPERPAVE; otherwise conditions are identical. It is interesting to compare these two methods. The French method is described first, SUPERPAVE is briefly outlined, the methods are compared and a tentative comparison is made between mixes produced by the two methods. Maximum binder content in SUPERPAVE is smaller than mimimum binder content specified in the French standard for wearing courses. For heavily trafficked pavements in the climate of South France, SUPERPAVE produces mixes with lower binder contents than mixes exhibiting good performance in France. SUPERPAVE takes no account of the thickness of the course; this could result in excessive voids content for wearing courses, particularly on very heavily trafficked pavements at high air temperatures.