Unhappy with the performance of traditional overlays, researchers discovered an unlikely solution: thinner pavements cost less, ride smoother and are expected to have a longer lifespan.
What’s the Problem?
Roads don’t last forever. For decades, when a road was in need of rehabilitation, a two-inch overlay was placed on top of the original, worn-out surface. The new overlay would help fix the cracks and ruts and provide improved friction, at least for a few more years. But as costs have become a primary issue, these overlays have taxed the already-shrinking maintenance budget. Delaying the need to replace an overlay is fairly easy. By using better-quality ingredients (aggregates and asphalt binders), agencies can extend a road’s lifespan. Unfortunately, those better ingredients cost more than budgets allow. So was it possible to come up with an overlay that lasted longer and cost less?
What’s the Solution?
Researchers tested mixes that were thinner but included the higher-quality ingredients. In the laboratory, their experimental one-inch overlay passed all existing testing standards and also some additional severe performance tests. The new mixes in the laboratory by far exceeded the performance of the traditional two-inch overlays. Even though the ingredients cost 30 percent more per ton than the materials in the thicker overlays, fewer ingredients are needed and would amount to an overall saving of 30 percent per square yard. One additional benefit of the thinner lift—especially in cities with curbs and gutters—is that less preparation work is necessary, saving on construction cost and time. With the thicker lift, it is often necessary to mill and remove the existing materials.
Has It Paid Off?
Several years ago, maintenance crews installed test sections of one-inch and ¾-inch overlays at several locations around the state. Each of the sections held up to the traffic and showed no major problems. Since then, several TxDOT districts, including cities and counties, have begun using thin overlays on numerous projects. In the Austin District alone, 30 road rehabilitation projects have been completed with their thin overlay mix, at a cost savings of $17 million to date. Those savings mean that other roads—which would not have been repaired otherwise due to limited funds—can now be rehabilitated. Researchers have also developed a ½ inch overlay, which is also being field tested in some districts.
Project TitleDesign and Construction Recommendations for Thin Overlays in Texas
0-6615 and 0-5598
Texas Department of Transportation
Project Termination Date
For More Information
Thomas Scullion, P.E.Senior Research Engineer
Flexible Pavements – Dwight Look Engineering Building, Room 304C
Texas A&M Transportation Institute
The Texas A&M University System
College Station, TX 77843-3135
Ph. (979) 845-9913