Ultra-Thin Whitetoppirig Ontarios Experience

Ultra-thin whitetopping (UTW) is one of the newest and most innovative applications of portland cement concrete. The technique entails bonding a relatively thin layer of concrete onto an existing asphalt pavement. This technique was conceived in the United States of America and the first experimental project was built in Louisville, Kentucky in 1991. The technology was first introduced to Ontario by the City of Mississauga in 1995. This first Ontario project was implemented to solve a severe rutting problem at a heavily truck trafficked intersection. A 100 mm concrete section was selected due to the high percentage of truck traffic and the significant braking action at this intersection. The project involved replacing two lanes with synthetic fibre reinforced fast track concrete and one lane with plain concrete. Performance of this ultra-thin whitetopping has been very good after 22 years of service. There are, however, some noticeable differences in performance between the plain concrete lane versus the fibre reinforced lanes. To date, there are approximately ten cracks in the plain concrete lanes and no cracks in the fibre reinforced lanes. This paper documents the performance differences on the Mississauga project. Cores were taken to assess bond performance and as constructed layer thicknesses. In addition, construction and design details are reviewed. This project has proven ultra-thin whitetopping is a viable rehabilitation option for rutted asphalt pavements in Ontario, and has lead to the construction of a larger project in 1997 in the City of Brampton. Construction techniques and design features for this project are briefly reviewed.