Field and Laboratory Investigation of Permeable Asphalt Mixes on Georgia Highways

The Georgia Department of Transportation (GDOT) investigated possible high permeability in asphalt mixes statewide in response to reports of prolonged wetness on pavements around the state after rainfall. In these locations, high permeability manifested itself as wet areas on pavement surfaces where wetness remained after natural conditions should have removed all moisture from the surfaces. Sixteen project sites were inspected for problem areas statewide, and core specimens were taken from six of the sites. Specimens were taken from areas considered representative of the problem areas in each project. The specimens were tested to determine the permeability, bulk specific gravity, maximum theoretical specific gravity, percentage of air voids, percentage of asphalt cement, and gradation of the mix. According to the findings of this investigation, some Superpaver; mixes that were designed in accordance with GDOT specifications exhibited undesirable permeability. The investigation determined that both mix design and construction contribute to permeable mixes; hence, permeability problems are to be corrected by a balanced adjustment to these processes, according to the following recommendations: (a) for each Superpave mix type used in Georgia, develop mix-specific acceptance criteria for maximum in-place air voids; (b) include evaluation of mix permeability in mix design; and (c) provide continued quality control during construction operations to ensure the success of the mix-specific acceptance criteria.