Issues pertaining to the permeability characteristics of coarse-graded superpave mixes

In order to evaluate the relationships between in-place air voids, lift thickness, and permeability, 23 on-going HMA construction projects were visited and field permeability tests conducted. Field permeability tests were conducted at 15 randomly determined sites for each project. Cores were taken at each of the 15 locations to determine pavement density using AASHTO T166. In addition, for some of the projects, the cores were tested with the Corelok device and a laboratory permeameter. As agencies begin to include permeability specifications, mix designers need tools they can use during the mix design process to evaluate the permeability characteristics of a given aggregate structure. Two techniques were evaluated: laboratory permeability measurements on samples compacted using the Superpave gyratory compactor and water absorption determined with AASHTO T 166 or the Corelok device. Results, of testing within this study indicated a good relationship between permeability (measured in the field and laboratory) and pavement density. Both the gradation nominal maximum aggregate size (NMAS) and the lift thickness placed in the field were shown to affect the permeability-density relationship. Increasing the NMAS requires higher densities to ensure an impermeable pavement. Also, as the lift thickness of a given pavement (and mixture) increases, permeability decreases at a given density level. Some reasonable relationships were found between the permeability of samples compacted using the gyratory compactor and field samples. Reasonable relationships were found between permeability and water absorption regardless of nominal maximum aggregate size.