As a part of the Federal Highway Administration's (FHWAs) Accelerate Loading Facility (ALF) experiment, asphalt pavement lanes were built with six different asphalt binder types and two different thicknesses and tested for rutting and fatigue cracking. Loose asphalt mixtures were taken from each lane at the time of construction and compacted in the laboratory. These plant produced (PP) laboratory compacted specimens and other lab produced (LP) specimens were subjected to dynamic modulus and flow number tests using Simple Performance Tester (SPT). Field rutting measurements of the ALF lanes were conducted during and after the loading. A good agreement between permanent strains measured by the flow number test and the ALF rutting measurements were observed for the initial rutting. The rutting of asphalt mixture layers of the ALF lanes were also predicted using Level 1 and Level 3 analysis of Mechanistic Empirical Pavement Design Guide (MEPDG) software utilizing the detailed data that is available for the ALF lanes. Comparison of the predicted rutting with the ALF rutting measurements indicated that MEPDG level 3 predictions, based on asphalt stiffness equation, somewhat agreed with the actual ALF rutting. However, the level 1 rutting prediction, based on the actual SPT measured |E*|, significantly over-predicted rutting. NCHRP 1-37A permanent deformation prediction models used in MEPDG were also utilized separately to predict rutting of the ALF lanes using predicted and measured stiffness values. Similar results as with MEPDG level 1 and level 3 was obtained. The over-prediction of rutting by level 1 MEPDG may be related to the calibration of NCHRP 1-37A permanent deformation equation. The model seems to have been calibrated using predicted stiffness from NCHRP 1-37A equation, which is proven to over-predict stiffness at high temperature, rather than tested SPT stiffness and thus can only provide reasonable rutting estimates for level 3 (using predicted stiffness).
Abstract