Evaluation and Recommended Improvements for Mix Design of Permeable Friction Courses

This project focuses on the improvement of the mix design and the development of guidelines for construction and maintenance of permeable friction courses (PFC). The study started with an information search documented in Technical Report 0-5262-1 that summarizes information from a worldwide literature review and Texas Department of Transportation (TxDOT) district interviews focused on performance, maintenance, and construction of PFC. The information gathered was used to define an experimental design directed to evaluate four main aspects of PFC mix design: volumetrics, functionality (or drainability), durability, and aging. These aspects were evaluated for mixtures fabricated with both TxDOT asphalt types: PG-76-22 and asphalt rubber. Dimensional analysis and calculation of the theoretical maximum specific gravity of the mixture were recommended for evaluating total air voids (AV) content and water accessible AV content. The computation of water accessible AV was suggested for future application in design and performance evaluations. In addition, the density specification was modified (from 78-82 percent to 76-80 percent) to ensure adequate drainability. Field evaluation of drainability during construction was recommended to ensure adequate initial functionality properties in terms of permeability. For durability, the draindown test and the Cantabro loss test (conducted in both dry and wet conditions) were recommended. In addition, density requirements for field compaction were suggested to improve the control of functionality and durability. Technical Report 0-5262-2 constitutes the second interim report and documents construction and maintenance guidelines for PFC.