Stone-on-Stone Contact of Permeable Friction Course Mixtures

Stone-on-stone contact of the coarse-aggregate fraction is one of the main characteristics of permeable friction course (PFC) asphalt mixtures that is required to provide adequate resistance to both raveling and permanent deformation. Currently, stone-on-stone contact is determined by comparing the air voids content in the coarse aggregate (VCA), assessed in both the dry-rodded condition (VCA(DRC)) and the compacted PFC mixture (VCA(mix)). The underlying assumption is that the coarse aggregate of a compacted PFC mixture with VCA(mix) equal to VCA(DRC) would develop a stone-on-stone contact condition equivalent to that existing in the dry-rodded aggregate. This study focused on proposing enhancements for the quantitative determination of stone-on-stone contact of PFC mixtures. The assessment supported on both laboratory testing and application of the discrete element method and image analysis techniques, led to recommendation of a criterion to determine the breaking-sieve size. In addition, verification of stone-on-stone contact using a maximum VCA ratio of 0.9 was recommended to ensure the design and construction of PFC mixtures with fully developed stone-on-stone contact.