Exploring the flow number (FN) index as a means to characterise the HMA permanent deformation response under FN testing
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abstract
Permanent deformation (PD), or rutting, is one of the common distresses occurring in hot-mix asphalt (HMA) pavements. As part of the HMA mix- and structural-design processes to optimise field performance, various laboratory tests, including the Hamburg wheel tracking test (HWTT) and flow number (FN), have been developed to characterise the HMA mix rutting resistance potential. With this background, this study was conducted to explore the potential of routinely using the FN test to characterise the PD response of Texas HMA mixes as a supplement to the HWTT. Towards this goal, a new PD parameter - the FN index - was developed to differentiate and screen the HMA mixes. The research methodology incorporated a two-phase approach, namely: (1) laboratory testing and (2) field correlations. Overall, the findings indicated that the FN index, computed from the FN test data, has the ability to statistically differentiate the HMA mixes evaluated, as well as promising potential to supplement the HWTT for routine HMA mixdesign and screening. In addition, the FN test has a practically reasonable test time (about three hours per specimen) and is cost-effective. However, the inability to readily test thin field cores and the need for field validation with long-term performance data remain some of the key challenges to be addressed with the FN test method.
