Evaluation of Various Hamburg Wheel- Tracking Devices and AASHTO T 324 Specification for Rutting Testing of Asphalt Mixtures

Abstract

The Hamburg Wheel Tracking (HWT) device is a laboratory-controlled rut depth test that uses loaded wheel(s) to apply a moving load on asphalt mixture specimens to simulate traffic loading on asphalt pavements. Currently, different machines with various degrees of compliance with the current AASHTO T 324-14 requirements are used by highway agencies. The objective of this study was to assess the capabilities of commercially available and representative HWT equipment in the US and to evaluate different analysis and reporting methods for rutting and stripping performance assessment from the HWT test. After performing a comprehensive evaluation of HWT devices from different vendors, considerable discrepancies among different equipment were identified. Furthermore, the available HWT machines do not meet all the requirements set forth in AASHTO T 324 including those for the wheel position waveform, the temperature range, and the reporting parameters. Evaluation of the analysis methods was conducted by applying six analysis procedures to the test data of two asphalt mixes with contrasting rutting resistance and moisture susceptibility. For the poor-performing mix, substantial differences were observed among the different methods, especially in the reporting of the Stripping Inflection Point (SIP). For the good-performing mix, only two of the six methods successfully identified this mix as a non-stripping mix. It is recommended that an approach similar to the one adopted by Iowa DOT be implemented in the revised AASHTO T 324 specification.