Asphalt Permeability Testing in Virginia

Because of high air voids, long-lasting damp spots on pavement surfaces, and problems that other states have had with permeable coarse Superpave mixes, the Virginia Department of Transportation (VDOT) decided to investigate the permeability of its Superpave mixes. As part of this study, VDOT also tested other asphalt mixes. Falling-head permeability tests were performed on pavement cores to determine the general permeability of the mixes. The permeability of some of the pavement cores was compared with the permeability of specimens made in the laboratory through the use of mixtures sampled during construction to determine whether laboratory specimens could be used to predict pavement permeability. The primary purpose of this investigation was to determine the general magnitude of permeability for mixes being used by VDOT, with an emphasis on Superpave mixes. A large percentage of the field cores contained excessive voids, resulting in excessive permeability. Each mix had a unique voids-permeability relationship. Mixes that were composed of large aggregates required fewer voids to achieve an acceptable level of permeability. In four of five cases, the results of laboratory tests were generally quite successful in indicating field permeability. The preliminary permeability testing demonstrates the importance of achieving low voids in the field and will help in the future development of density specifications and possibly in the establishment of permeability requirements. It is recommended that the permeability test continue to be used to help set such limits.