Quantification of stone-on-stone contact in permeable friction course mixtures based on image analysis

The main features that differentiate permeable friction course (PFC) mixtures from dense-graded asphalt mixtures are the high total air voids content-18 to 22%-and stone-on-stone contact condition in the coarse-aggregate fraction of the PFC mixtures. The main purpose of ensuring these features is providing improved functional properties to the PFC mixtures, including high drainability, surface texture, and noise reduction capacity. In this context, the research objective was to evaluate the PFC mixture internal structure, in terms of the quantification of stone-on-stone contact based on the analysis of digital images. PFC mixtures fabricated with both asphalt rubber and polymer-modified asphalt were characterized. Corresponding analyses of the relationship between the microstructure- and macroscopic-parameters used to characterize the stone-on-stone contact supported the importance of verifying both the voids in the coarse aggregate ratio and Cantabro loss to properly screening the PFC mixture performance. In addition, controlling the compaction process is required to fully develop the stone-on-stone contact condition and consequently ensure adequate resistance to both mixture disintegration and permanent deformation.