Internal structure of compacted permeable friction course mixtures

Durability and functionality (i.e., noise reduction effectiveness and drainability) of permeable friction course (PFC) mixtures depend on the characteristics of the air voids (AV) contained in the mixture. This study analyzes the internal structure of PFC mixtures, assessed in terms of AV characteristics; determined using X-ray Computed Tomography and image analysis techniques. Corresponding results showed: (i) heterogeneous distributions of AV in the horizontal direction of both field-compacted mixtures (road cores) and specimens compacted using the Superpave Gyratory Compactor (SGC) and (ii) limitations to compare their vertical AV distributions. Recommendations to reduce the horizontal heterogeneity included using road cores with a minimum 152.4 mm diameter and coring SGC specimens to 101.6 mm in diameter. Implementation of field-compaction control and future analysis of mixtures prepared accordingly was recommended to determine the pattern of vertical AV distribution that should be reproduced in SGC specimens and corresponding modifications required for fabrication of these specimens.