Effects of Testing Time and Confining Pressure on Falling-Head Permeability Tests of Hot-Mix Asphalt Concrete

Abstract

Superpave implementation has resulted in increased interest in the permeability of hot-mix asphalt concrete. Relatively open-graded Superpave mixes have given rise to concern about premature pavement failures due to increased water infiltration from the surface. Arkansas is investigating the use of a falling-head permeability test to evaluate Superpave mixes with respect to potential performance problems caused by increased permeability. The initial phase of the project concerns the development of laboratory testing procedures and equipment. Superpave field mixes from projects in Arkansas were sampled to investigate permeability testing parameters. In addition, compacted test specimens from a round-robin study of permeability were included in the testing matrix. For the Arkansas mixes, loose mix sampled at the hot-mix plant was compacted using the Superpave gyratory compactor. Field cores were also taken from completed pavement sections. Permeability tests were conducted on all samples to investigate the effect of testing time (15, 30, 45, and 60 min) and confining pressure (69 and 96.5 kPa) on the measured permeability values. Results of the testing suggest that neither the time interval used in measuring the head drop in a falling-head test nor the confining pressure used in the flexible wall testing apparatus significantly affects test results. These findings will greatly simplify testing methods and setup, making the test more attractive as a relatively routine tool for the mix design laboratory.