Overlays to the Rescue
Overlays are hot on both sides of the debate. Because public works departments may not have the funds to place new roads—either concrete or asphalt—many turn to overlays, which can be placed over either. The vast majority of roads in the United States are asphalt, but that does not limit what can be placed over it.
Four types of concrete overlays are currently in use: whitetopping, ultra-thin whitetopping (UTW), bonded overlay, and unbonded overlay. “Ultra-thin whitetopping is gaining in popularity because it can be done so easily,” said Haislip. UTW is used in situations where the existing asphalt pavement is full-depth (asphalt surface on asphalt base), and is ideal for normal traffic loads on residential streets and low-volume roads. It also can be used in asphalt intersections where pavement shoving and rutting are problematic.
Asphalt also offers many options. “There have been significant advances in asphalt overlay technology,” said New-comb. “When rehabilitating either a concrete or an asphalt road, an asphalt overlay is fast and cost-effective to construct. The result provides a smooth, safe, durable, quiet surface for many years.” There are several options to consider when rehabilitating an asphalt road: recycling, rubblization, mill and fill (the most popular today), thin overlays, modified mixes, open-graded friction courses, stone-matrix asphalt, Superpave, and Perpetual Pavements.
So which pavement option is better? Officials planning improvements on their local roads must take multiple factors into consideration, and have several resources to turn to. The Federal Highway Administration's procedure for performing life-cycle cost analysis is described in publication FHWA-SA-98-079, “Life-Cycle Cost Analysis in Pavement Design.” This publication, along with a host of others, can be combined with classroom knowledge and hands-on experience to give you the best pavement for your needs. Where environmental sensitivities are involved, the Building for Environment and Economic Sustainability (BEES) program from the National Institute of Standards and Technology can provide an even-handed comparison. The BEES software is available for free download.