Evaluation of a Rutting/Fatigue Cracking Device

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CAIT project no.: FHWA NJ 2001 031

Fiscal Year: 1996/1997

Status: Final

Rutgers-CAIT Author(s): Thomas Bennert, Ali Maher

External Author(s): Leslie A. Walker III, Anthony Chmiel

Sponsor(s): NJDOT, FHWA-USDO


Rutting is one of the most critical failure mechanisms in New Jersey’s flexible pavement roadways. A current technology in the asphalt pavement testing industry involves the use of a loaded wheel-tracking device as a tool for predicting a pavement’s tendency for rutting. However, an industry-wide standardized set of testing criteria does not exist. Consequently, the state agencies and universities have experienced an array of conflicting results. Currently, the New Jersey Department of Transportation (NJDOT) is developing pass/fail criteria for asphalt samples tested in a loaded wheel-tracking device. Results from this study will be used to assist in the NJDOT project.

The objective of the study was to evaluate the effect of mix gradations, compaction methods, sample geometries, and testing configurations on rutting potential of hot mix asphalt (HMA) mixtures. The asphalt binder used in this study was PG 64-22. The testing matrix consisted of 143 samples with air voids of 7% (±1%). Four aggregate gradations were studied: 12.5 mm TRZ (through Superpave restricted zone), 12.5 mm BRZ (below Superpave restricted zone), 19 mm ARZ (above Superpave restricted zone), and 19 mm BRZ (below Superpave restricted zone). For each aggregate blend, two compaction methods were used: vibratory (bricks and pills), and Superpave gyratory (pills). The pill samples were tested both in traditional two-sample molds, as well as in center-cut one sample molds built specifically for this research project. Rut tests were conducted at both 64oC and 60oC with the Asphalt Pavement Analyzer (APA) under 689 kPa (100 psi) contact pressure and 45.4 kg (100 lb.) wheel load. Rut depths were measured at the end of 8,000 cycles.

Analysis of the test results indicates that mix gradation, compaction method, testing configuration, and temperature all have reasonably significant impacts on rutting in the Asphalt Pavement Analyzer. An asphalt pavement mix that violated the Superpave restricted zone showed slightly improved rutting resistance over a coarse (below the restricted zone) mix. Specimens compacted by the Superpave Gyratory Compactor showed less rutting than samples compacted in the Asphalt Vibratory Compactor. Further, there seems to be some accelerated loading effects near the end of the APA wheel path. Lastly, the increase of 4oC in testing temperature allowed a significant increase in APA sample rutting.