Volume 37, Issue 3 (May 2009)
Connected Air Voids Content in Permeable Friction Course Mixtures
Current hot mix asphalt (HMA) mix design procedures used to determine the optimum asphalt content for permeable or porous friction course (PFC) mixtures are based primarily on total air void (AV) content. Durability and functionality of PFC mixtures are also related to the total AV content. However, the connected AV content (defined as the proportion of AV that form connected pathways for air and water transport through PFC mixtures) may provide more insight into the mixture structure in terms of the AV content directly associated with functionality and durability properties and constitute an alternative parameter to conduct PFC mix design and evaluation. This study evaluated two laboratory methodologies (vacuum and dimensional analysis) for determining water-accessible AV content and two types of analysis to compute interconnected AV content based on X-ray Computed Tomography (X-ray CT) and image analysis techniques. Although both the interconnected AV content and water-accessible AV content constitute determinations of connected AV content, different nomenclature was used to differentiate the origin of the calculation. Dimensional analysis with application of vacuum and X-ray CT and image analysis with inclusion of surface AV are recommended for determining water-accessible AV content and interconnected AV content, respectively. Future work should focus on investigating the use of connected AV content as an alternative parameter to integrate in mix design and laboratory and computational evaluation of PFC mixtures.