Techniques and methods
In 1998, guidelines for the thickness design of thin whitetopping were developed for CDOT by Construction Technology Laboratories Inc. in Skokie, Ill., with basic parameters and techniques unique to concrete overlays. The guidelines require a minimum asphalt thickness of 5 inches, after milling or grinding, for a resurfacing project to qualify for thin white-topping. A hot-mix asphalt base is required to avoid cracking, especially in areas with heavy traffic.
In urban areas, where CDOT has placed most of its thin whitetopping, the department has developed a couple of ways to overlay existing curbs and gutters. One process covers the curb face with a mountable (angled) profile; the other removes a section of the curb face before the overlay. By removing the original curb, the contractor can reduce its vertical profile by 4 inches.Roadblocks to adoption
CDOT has overcome some of the most common barriers that can discourage states and municipalities from trying thin whitetopping.
Noise control. Transverse tining has historically been the most popular way to texture concrete overlays. Although the technique meets Federal Highway Administration safety guidelines, it often results in noise complaints. Since 2003, CDOT has tested alternatives, including tining with sinusoidal waves, burlap, and diamond grooving and grinding. The agency's preferred method is now Astro Turf: rough enough to add skid resistance but low-noise. If the pavement is designed for speeds of 50 mph or greater, it must have a macrotexture; if speeds are lower, CDOT specifications don't require texturing.