After the surface of a busy asphalt intersection in Mississauga, Ontario, Canada, failed, city and public works officials opted for concrete pavement to provide a more permanent solution.
The city fixed the intersection of Courtney Park and Kennedy with asphalt in 2007 and 2010 and intended to repair it with asphalt again in 2012. The asphalt already had up to 100 mm, or 4 inches, of rutting in just two years since the last resurfacing. There were two options:
1. Asphalt: Mill 140 mm, HDBC - 100 mm (two lifts), HL-1 - 40 mm.
2. Concrete: Remove asphalt (225 mm), 32 MPa (4600 psi) Class C-2 concrete.
The solution: Due to the severity of the rutting and the two previous failed asphalt repairs, the City of Mississauga chose the concrete option.
There would be only eight days between identifying the problem and the reconstruction, so a full engineering study could not be conducted. Since the in-place cross section of asphalt was 225 mm, it was easiest to completely remove the asphalt and replace it with concrete. This would assure durability and provide a very conservative design for this fast-tracked project.
Rain was forecast for the night of the concrete pour, so the start time was moved to an earlier time. High early strength, 5000 psi concrete with macro-synthetic fibers was ordered and the first load of concrete arrived at the jobsite at 3 p.m. Placement, finishing, and testing were completed by 6:30 p.m. In addition to standard testing, maturity meters were installed in the concrete to determine when the pavement could be opened to traffic. This testing showed that 2200 psi was attained in less than eight hours and 2900 psi was attained in 14.5 hours.
For such a small section of concrete pavement, the actual and future potential paybacks to the city and the environment were substantial. If concrete was first considered five years earlier, the city would have saved 14 hours of traffic delays at the intersection.
There were also significant potential life-cycle cost savings and reduction in the amount of time the road had to be closed due to frequent asphalt repairs over a 20-year period.
Over the expected 20-plus-year life of concrete, asphalt would have needed to be replaced several times. Due to the conservative design, concrete is expected to last more than 100 years as constructed. Athena Sustainable Materials Institute determined the several environmental impact savings (see chart above).
With the growing trend toward life-cycle cost and environmental impacts being required, this project highlights how concrete pavements can address significant pavement performance issues in a very short time, while also addressing several cost savings and road safety issues in municipal pavement infrastructure. TCP
Submitted by the Ready Mixed Concrete Association of Ontario. For more information, visit www.rmcao.org . To see a video of the project, visit here .