Within the past two decades or so, the asphalt paving industry has responded positively to increasing global concerns over shrinking natural resource reserves and worsening environmental conditions through the development and deployment of warm-mix asphalt technologies. Such technologies make it possible to produce and place asphalt concrete at reduced temperatures compared to conventional hot-mix methods. Several studies have reported on the potential of warm-mix asphalt with regard to improved pavement performance, efficiency and environmental stewardship. This paper reviews several of those studies in the context of pavement sustainability. Overall, warm-mix asphalt provides substantial sustainability benefits similar to or, in some cases, better than conventional hot-mix asphalt. Sustainability benefits include lower energy use, reduced emissions, and potential for increased reclaimed asphalt pavement usage. Growth in utilization of warm-mix asphalt worldwide may, in the not-too-distant future, make the material the standard for asphalt paving. Regardless, there are concerns over some aspects of warm-mix asphalt such as lower resistance to fatigue cracking, rutting and potential water-susceptibility problems, particularly with mixes prepared with water-based technologies, which require further research to address.

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The validity of backcalculation results partly depends on the pavement cross section used in the procedure. However, the development of a backcalculation cross section is challenging, particularly for an unconventional pavement (subgrade stiffer than base). The unconventional stiffness profile poses challenges to backcalculation, including compensating layer effects. This study presents a systematic investigation to determine an optimum backcalculation cross section for seven unconventional pavements at the National Center for Asphalt Technology pavement test track. Apart from the unconventional stiffness profile, the granular materials had different stress sensitivities: the subgrade was stress independent, whereas the aggregate base material exhibited some stress sensitivity. Falling weight deflectometer testing provided 2,268 deflections for backcalculation, which was executed with Evercalc 5.0, and 126 deflection tests on embedded gauges for forward calculation, which was accomplished with WESLEA 3.0. Nine candidate cross sections were evaluated. The study converged on a three-layer backcalculation cross section that provided an overall good deflection basin fit, a balanced match between measured and predicted stresses, and reasonable moduli. A key lesson is that the as-built cross section of an unconventional pavement may not necessarily yield valid backcalculated moduli, although there may be a good deflection basin fit. A working knowledge of the pavement materials is useful for developing an optimum backcalculation cross section, which should be validated through field instrumentation when available.