Laboratory Wheel Tracking of Asphalt with Rubber Tires or Rubber Hoses

In recent years, wheel tracking of asphalt mixtures has gained considerable momentum, and the authors are evaluating the potential of standardizing a rubber-tire wheel tracking protocol which can enable direct decoupling of rutting and moisture damage by testing identical specimens in dry and wet conditions. Previous work has established the value of dry and wet comparisons; this paper specifically assesses the dry rutting component by comparing a rubber-tire wheel tracker known as the PURWheel-G2 with the asphalt pavement analyzer (APA), arguably the most well-known dry wheel tracking test. This paper has two main objectives: demonstrate that rubber-tire wheel tracking is capable of characterizing dry rutting in a manner comparable to the APA and recommend initial failure criteria for rubber-tire wheel tracking. The PURWheel-G2 was more variable than the APA with coefficients of variation nearly twice as large. Although there was variability, reasonable rut depth correlations were drawn between the PURWheel-G2 and APA, and an APA pass/fail criteria of 6 mm equated to 10 mm for conventional PURWheel-G2 testing using laboratory-compacted slabs. Using literature and available data, 6 mm was proposed as a rubber-tire pass/fail threshold when standardizing to typical APA compaction methods and boundary conditions (i.e., cylindrical specimens in confined molds). Ultimately, efforts are ongoing to improve limitations of the PURWheel-G2 prototype (e.g., variability) with modernized equipment, and the authors recommend agencies initially consider the same failure criteria already established for APA testing and be willing to adjust over time as data and experience dictate the need to do so.