Research conducted during 1999-2000 for the California Department of Transportation (Caltrans) by the Pavement Research Center (PRC) at the University of California, Berkeley (UCB) provides the most recent, relevant findings on the performance of asphalt treated permeable bases (ATPB). Pavement sections were constructed at the Richmond Field Station near Berkeley, California and tested by use of accelerated pavement testing (via the Heavy Vehicle Simulator (HVS)).
Caltrans has used ATPB layers as a standard component in new flexible and rigid pavements for about 20 years. Over this time span, various changes were made to the ATPB layer such as increasing the asphalt binder stiffness and content, and percent of crushed aggregate in the mix. In the Caltrans design process, the ATPB layer is placed between a granular base course and the overlying HMA layers.
During the early 1990’s, it was noted that ATPB layers were stripping or clogging with fines for some in-service projects. This led to the study at UCB. The conclusions of the PRC research showed that (Bejarano and Harvey, 2002):
The bottom line is that Caltrans is re-evaluating the use of ATPB layers. One option is to discontinue their use and another is to modify the ATPB layer and the filter requirements. Further, Caltrans has placed renewed emphasis on achieving higher HMA densities with lower air voids. This reduces the amount of water that can enter the pavement structure and thus the need for the ATPB layer.