Better Roads Magazine, 12 November 2011
by Daniel C. Brown, Contributing Editor
Thin asphalt overlays: Valuable versatility
For a host of reasons, thin asphalt overlays are proving to be one of the most useful road treatments in the tool boxes of state and local transportation departments. Budget restraints have pressured agencies to make their road dollars cover more square yards, and thin overlays can do that. Plus, agencies want to add the maximum life to a pavement – preserve it for as many years as possible.
Again, thin overlays answer the bell.
“We’ve been pretty steady on thin asphalt overlays,” says Aric Morse, a pavement engineer with the Ohio DOT. “Smoothseal is a tool that our districts like to use very much.” He is referring to a trademarked thin overlay product that comes in two varieties, Type A and Type B. Both of them go down at about 1-inch thick; sometimes Type B is placed a bit thicker, at 1.25 inches. The Type A overlay has 8.5-percent polymer-modified binder and is typically placed on low- and medium-truck-volume roads. The Type B overlay has 6.4-percent polymer-modified binder and is placed on medium- to high-truck-volume roads.
“Thin overlays give us a new surface course; and the Smoothseal overlays are a little richer in binder content,” says Morse. “They should last 12 to 15 years, if they’re placed on the right pavement.
“You get some economy by placing these overlays a little bit thinner. But they cost somewhat more per ton because there is more asphalt in them.”