Evaluation of asphalt stabilized layer equivalency factors for use in airfield flexible pavement design
A California Bearing Ratio (CBR) design method has been used for Air Force airfield pavement design since the late 1920s. The procedures, calculations, and related nomographs have been updated to reflect developments in the pavement design, pavement analysis, and unique landing gear configurations and load levels introduced by new aircraft. Throughout these changes, the basic objective of CBR procedures is to design a pavement from the bottom up, through the consideration of the strength of a material (based on its CBR) and determining the amount of cover needed to protect that material. In a 1970s era update to the CBR procedure, equivalency factors were developed to allow incorporation of stabilized layers into the airfield pavement structure. The equivalency factor is a ratio which identifies the required stabilized material layer thickness needed to replace a specified thickness of traditional, unbound pavement. These equivalency factors were based on full scale tests performed by the Army Corps of Engineers at the Waterways Experiment Station. Current efforts to update and revise tri-service airfield pavement design guidance have focused on the established equivalency factors – with a desire to evaluate these factors to ensure their appropriateness, given new laboratory material testing methods and mechanistic modeling methods which have been developed in the last 40 years. This study outlines the process used to apply both linear and non-linear pavement evaluation techniques to determine the adequacy of established equivalency factors for asphalt stabilized base and subbase materials. Using material properties obtained from literature, various pavement structures containing both stabilized and unbound materials were evaluated under a standardized aircraft gear load. Load induced pavement critical responses were obtained using BISAR 3.0 and GT Pave. Analyzing these critical response magnitudes, the adequacy of established asphalt stabilized material factors can be determined and recommendations for more appropriate, yet still conservative, equivalency factors can be made.
Flexible Airfield Pavement, Asphalt Stabilized Layers, Bitumen Stabilized Layers, Equivalency Factors
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign