VOLUMETRIC COMPOSITION CONTROL DURING DESIGN AND PRODUCTION OF ASPHALTMIXES

The Dutch Heavy Duty Asphalt Pavement Working Group (HDWRG) organised a performance testing program to evaluate the permanent deformation based on a tri-axial testing technique. A square wave vertical loading was applied to specimens of 10 different Asphalt mixes together with a square wave horizontal confining stress to simulate exactly the stress pattern as can be expected in the road itself. By varying the confining stress level the conditions at several depths can be simulated. From experience it is known that a uni-axial test is not capable of predicting the permanent deformation performance of stone skeleton mixes such as Porous Asphalt (PA) and Stone Mastic Asphalt (SMA). During the tri-axial testing with confining stress it was found that the Porous Asphaltmix showed the behaviour as known from practice; hardly sensitive to any deformation! The SMA mix however showed a strong tendency to creep. Calculations based on a new volumetric mix design method showed that the SMA had an overfilled stone skeleton. The composition of the mix was corrected by applying the new volumetric approach and the volumetric corrected SMA showed no excessive permanent deformation anymore. In this paper recommendations are given to further develop a volumetric based design method and also to develop a method to control the volumetric composition of the asphaltmix during the production phase with the available aggregates at the time. If recycled material is added to the asphaltmix a volumetric based production control method is even more necessary. It is also recommended to determine asphaltmix performance under tri-axial test conditions; the confining stress level depending on the depth of the layer in the construction. (A) For the covering abstract see IRRD 885061.