An analytically based (mechanistic-empirical) procedure was conducted to estimate the development of rutting in asphalt pavements as a function of both traffic loading and environment as defined by pavement temperatures. The procedure uses permanent strain determined for a representative asphalt concrete mix as a function of load repetitions, shear stress, and elastic shear strain. It combines multilayer elastic analysis for determining key shear stresses and strains in the asphalt concrete resulting from traffic loading to be used in the permanent strain expression with a time-hardening procedure for the accumulation of permanent strain as a function of both traffic loading and environment. The WesTrack test sections were used to calibrate the methodology, with results of rutting predictions evaluated for four different test sections from that experiment. Based on the results of the regression analyses, an expression can be used to determine coefficients for use in the permanent strain expression that reflect the permanent deformation characteristics of a specific mix as measured in repeated simple shear test at constant height. In addition to the WesTrack examples, results illustrated the use of the approach to predict rutting development in a controlled loading condition at 50°C (122°F) using the heavy vehicle simulator.

The Heavy Vehicle Simulator (HVS) test results of the first experiment of the California Department of Transportation (Caltrans) Accelerated Pavement Testing Program, known as CAL/APT, are presented. The Goal 1 experiment was designed to validate the existing Caltrans pavement thickness design method for drained (containing an asphalt treated permeable base layer) and undrained (containing aggregate base only) flexible pavements. The pavement performance results include fatigue crack development, surface profile, and vertical deflections. The observed performance of the two types of structures is compared. The effects of construction compaction of the asphalt concrete, bonding between asphalt concrete lifts, the relative performance of the drained and undrained structures under the controlled HVS environment, and comparison of the observed performance and performance expected by the thickness design procedure are presented and discussed.

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A forensic study of asphalt mix performance at the San Francisco International Airport (SFIA) using the simple shear test developed by the Strategic Highway Research Program is described. The study examined taxi ways subjected to stationary and slow movements of heavy aircraft wheel loads and covered a period of about 2.5 years. The results of the study indicate the need to modify (or change) current FAA criteria for mix design of asphalt mixes for heavy-duty airfield pavements, particularly for taxi ways used for takeoff operations and subjected to stop-and-go operations of heavy aircraft like the Boeing 747-400. Information presented suggests that the simple shear test conducted in repeated loading while the height of the specimen is maintained constant (RSST-CH) can be used as a replacement for the current FAA mix evaluation procedure using the Marshall test. Mix design criteria are presented and are based on satisfactory performance of a high-stability mix introduced at SFIA for taxiways.