Asphalt-Mix Studies: San Francisco International Airport

At the San Francisco International Airport, asphalt-concrete mixes in full compliance with the current FAA mix design criteria exhibited rutting on major taxiways subjected to heavy aircraft-wheel loadings during the period August 1995 through June 1996. Because of the high air traffic volumes at the airport, the heavy departing aircraft are subjected to slow moving, or stop-and-go traffic condition. To mitigate the problem, enhancements were introduced to the current FAA mix design criteria providing for a High Stability mix, which is performing satisfactorily. This provided an opportunity to use shear test equipment developed during the Strategic Highway Research Program (SHRP) for mix evaluations for airfields. The mix evaluation procedure using this equipment defines the propensity of a mix to rutting by means of a repeated simple shear test at constant height (RSST-CH). This procedure, and results of shear tests on cores obtained from the rutted sections and sections constructed with the High Stability mix are summarized in the paper. The results demonstrate that the shear test can be used to differentiate between the mixes that have shoved and rutted under the heavy aircraft wheel loadings and the High Stability mix, which has performed satisfactorily. This latter observation is supported by laser profilometer measurements as well as by visual observation. Based on the results of these tests as well as other experience with the RSST-CH, a mix design methodology is proposed for asphalt-concrete mixes to be used for asphalt pavements subjected to heavy aircraft wheel loadings.