Correlating APA to Field Permanent Deformation for HMA Mixes at the NCAT Test Track

Abstract

This paper presents the findings from a study in which a common type of Loaded Wheel Tester (LWT), the Asphalt Pavement Analyzer (APA), was used to evaluate the rutting characteristics of HMA mixtures at the Oval Test Track at the National Center for Asphalt Technology (NCAT). Mixtures from twenty six test sections were tested by APA. The specimens used for APA tests included the laboratory compacted cylindrical samples through the Superpave Gyratory Compactor (SGC) at four and seven percent air voids. The results from this study indicated that APA rutting at 500 cycles correlated strongly to the final APA rut depth at 8,000 cycles. Regression analyses revealed that the APA rutting for SGC-compacted specimens at seven percent air voids correlated reasonably well (R2 = 0.64) to the field measured rut depths; whereas the APA results from lab-compacted specimens at four percent air voids had a weak correlation (R2 = 0.20) to the field rutting measurement. Based on the results from this study, it was suggested that for QC/QA purposes, the number of cycles in APA rutting tests might be significantly reduced from the current 8,000 cycles. Specimens at seven percent air voids were recommended for rutting evaluation.