Road Science Illustrated: Thin-Lift Hot Mix Asphalt Overlays Done the Right Way

This article presents an illustrated guide to thin-lift hot mix asphalt (HMA) overlays. Pavements must first be evaluated to determine if HMA overlays are appropriate. Pavements exhibiting structural distresses such as alligator cracking or potholes will not benefit from HMA overylays. A cold milling or leveling course is recommended prior to HMA overlays if pavement distress is severe. Sweeping the pavement in advance of thin-lift placement is critical. In addition, a tack coat application of liquid asphalt, designed to promote adhesion between old and new pavement layers, should be applied prior to a thin overlay. The next step involves the application of the thin overlay. The grade of asphalt binder used and aggregate quality depends on the climate and type of traffic. Micro surfacing, which is a type of slurry seal, is then applied to achieve a durable surface texture, fill minor ruts, and seal the pavement surface. Thin HMA overlays are an effective method for restoring pavement rideability and improving pavement surface friction.