Roads & Bridges, October 2011
By: Tinu Mishra, P.E., and David Merritt, P.E.
California, like most states with densely populated areas, has many urban high-volume roadways, which are expected to last long, provide a smooth ride and require little maintenance, thereby minimizing inconvenience to the traveling public.
Rehabilitation of these roadways poses a tremendous challenge to Caltrans, as current work windows for road construction crews are sometimes as little as four to five hours, and typically at night. Yet, in these short work windows, Caltrans is required to maintain its highways at a high level of service under the constant wear and tear from high traffic volumes and varying weather conditions.
Currently, Caltrans rehabilitates concrete pavement through the use of rapid-strength concrete (RSC). The use of RSC is typically focused on projects where the highway facility is in relatively good condition, requiring spot rehabilitation of isolated areas. Typical RSC mixes achieve compressive strengths of around 2,500 psi in only 1.5 hours. It is common to add water-reducing admixtures, plasticizers and accelerators to a mix in an effort to maintain the workability of the mixture, while expediting the strength gain. However, the durability and long-term performance of such materials has come into question recently on many rehabilitation projects.