Candidate for fully permeable shoulder retrofit validation site
Caltrans Thin Bonded Concrete Overlay of Asphalt (BCOA) Pilot Project. First Caltrans thin bonded concrete overlay of asphalt (BCOA) has been recently built in SR113 at Woodland, District 3. Thin BCOA, formerly known as thin whitetopping, is a pavement rehabilitation technique that consists of placement of a 4 to 6 in. thick concrete overlay on an existing flexible or composite pavement.
Caltrans thin BCOA pilot includes two stretches of SR113: PM 11.8-12.8 and PM 14.7-17.6. The latter was paved on October-November, 2018, while the former was paved on April-May, 2019. The design section of the project includes 6 in. thick concrete overlay on the milled asphalt base, 6 ft transverse joint spacing, and widened slabs. The overlay was built with a rapid strength concrete that was designed to provide 450 psi flexural strength (requirement for opening to traffic) in 24 hours. The pilot project includes also the use of new rubberized asphalt mix as a base.
The early field performance of the thin BCOA pilot is being monitored as part of Caltrans 3.39 Partnered Pavement Research Center project. The monitoring is focused on slab cracking, longitudinal unevenness, and transverse joint faulting and load transfer efficiently. To help the monitoring process, the pavement has been instrumented with a total of 110 sensors, which will be measuring concrete and asphalt strain, concrete and asphalt temperature, and concrete internal relative humidity.
It is expected that the monitoring of the construction and the early field performance of this pilot project will help to identify best and improved practices and standards applicable to California’s climate, materials, and construction work zone practices.