Article originally published in the Spring-Summer 2016 edition of the Colorado Public Works Journal
As noted in the May 2014 “Guide to Concrete Overlays” published by the National Concrete Pavement Technology Center (CP Tech Center), shrinking budgets and ever-increasing traffic volumes have necessitated the immediate need for engineering strategies to preserve and maintain the nation’s roadways. One such approach is an unbonded concrete overlay.
Unbonded concrete overlays are used to restore structural capacity to existing pavements ranging from moderately to significantly deteriorated. The term “unbonded” simply means that bonding between the overlay and the underlying pavement is not needed to achieve desired performance. Thus, the overlay performs as new pavement and the existing pavement provides a stable base.
There are several benefits of using unbonded concrete overlays, including the solution’s cost-effectiveness. According to the CP Tech Center, “dollar for dollar, they are one of the most effective long-term pavement preservation and major rehabilitation options for existing pavements.” Other benefits of unbonded concrete overlays include their quick construction, ease of maintenance, and sustainability assets.
In general, unbonded resurfacing is highly reliable, offering longer design life than road rehabilitation with asphalt. It has been used successfully by several states, providing on average more than 30 years of good-to-excellent performance, according to the CP Tech Center.
Innovative methods of construction are continuously being explored, and Route D south of Kansas City, MO was the first in the nation to use a fabric bond breaker in 2008. The 3.7 mile long unbonded overlay was constructed in 50 days with a 5” minimum concrete thickness and 6’ x 6’ jointing on a 24’ wide road carrying 9,300 ADT (5% trucks). The new surface has now been serving the traveling public for 8 years, and a 2015 visual distress survey demonstrated that it is performing extremely well.
The NW Chapter of ACPA can provide further education on material considerations for long-lasting concrete overlays, and will gladly review potential projects to identify which option(s) are best for your situation. For more information, please contact us.