Researchers conducted eight large-scale laboratory tests to assess the combined impact of hot-mix asphalt (HMA) overlay mix and thickness on its performance to control reflective cracking. Bonding efficiency, flexibility, and stiffness of the HMA mix as well as overlay thickness significantly affect an overlay’s performance against reflective cracking. Researchers developed a generalized 3D finite-element model to predict an overlay’s reflective cracking potential and generated a database of 128 cases. They also developed a data-driven surrogate model to predict reflective cracking potential that engineers can easily use. Life-cycle cost analysis of overlay alternatives was performed using Illinois Department of Transportation’s unit prices from contracts between 2018 and 2019. The researchers identified optimal overlay configurations to control reflective cracking. An overlay composed of a 1.5 in (38.1 mm) SMA-9.5 or 1.25 in (31.8 mm) IL-9.5FG surface course and a 0.75 in (19.1 mm) IL-4.75 binder course had the lowest annual cost per mile among non-interstate projects. For interstate projects, an overlay composed of a 2 in (50.8 mm) SMA-12.5 surface course and a 2.25 in (57.2 mm) IL-19.0 binder course was the most cost-effective. The study concluded that to control reflective cracking and to reduce life-cycle cost, an overlay composed of an SMA-9.5 surface course and an IL-4.75 binder course is recommended for non-interstate projects. An IL-9.5FG surface course and an IL-4.75 binder course are suggested for low-volume and low-speed roads. For interstate projects, an overlay comprised of an SMA-12.5 surface course and an IL-19.0 binder course is recommended. A data-driven surrogate model may be used to design overlay thicknesses. The full text of this report is available from the University of Illinois web site at https://apps.ict.illinois.edu/projects/getfile.asp?id=10551
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