Volume 37, Issue 1 (January 2009)
Effects of Densification on Permeable Friction Course Mixtures
Compaction of permeable or porous friction course (PFC) mixtures is generally considered a process without major issues, and field density requirements (or corresponding total air voids [AV] content) are not currently specified for this type of hot mix asphalt. However, proper densification is one of the most important aspects to control during construction to prevent raveling, the distress most frequently reported as the cause of failure in these mixtures. This paper presents an evaluation of the effect of densification on PFC mixtures. This evaluation included both the study of the internal structure of compacted mixtures and a comparison of performance based on macroscopic response. Results from this study showed that differences encountered in the internal structure of road cores and specimens compacted using the Superpave Gyratory Compactor limit the use of these laboratory compacted specimens in durability and functionality evaluations of PFC mixtures. In addition, changes in densification, after reaching stone-on-stone contact, modified the mixture properties and performance. The magnitude of these modifications provided evidence of the ease of verifying not only stone-on-stone contact during mix design, but also of the importance of controlling the density during construction to ensure an equilibrium density that guarantees the balance between mixture durability and mixture functionality.