The U.S. Army Engineer Waterways Experiment Station (WES) was requested by the Middle East/Africa Projects Office (MEAPO) in April 1989 to provide technical assistance in analysing an unstable asphalt concrete (AC) airfield pavement. An AC overlay had been constructed on an aircraft parking apron and taxiway. The overlay had exhibited significant deformation and depressions under parked aircraft. The performance of the unstable AC pavement was unacceptable. The materials research and construction technology branch of the geotechnical laboratory at WES was requested to perform laboratory tests on AC specimens to determine asphalt cement, aggregate, and AC mixture properties. The purpose of this analysis was to evaluate the in-place AC material for compliance with specifications, determine possible causes for pavement failure, suggest procedures to avoid problems in the future, and recommend options for the repair of the airfield pavement. The laboratory evaluation of the AC material indicated that the poor performance was due to an improperly designed and produced AC mixture. Several factors contributed to the unstable mixture: (a) the aggregate gradations were consistently out of specification and were gap-graded, (b) the amount of natural sand in both the surface course and intermediate course was extremely high, and (c) the mix designs for the surface-course and intermediate-course mixtures did not meet the minimum requirements of the specification.
Abstract