A concrete future for road repair
March 1, 2013 by Staff Report
Road-maintenance projects are certainly not an uncommon site around the Greater Toronto Area, so the work that was done in September 2012 to repair the intersection of Courtney Park and Kennedy Road in Mississauga, Ont. would not seem unique to the average commuter. But in truth, this lane improvement project raised plenty of interest. Enough for the project to be nominated for—and win—the 2012 Ontario Concrete Award for Specialty Concrete Products, as well as an Ontario Public Works Association award in the field of disaster and emergency construction repair (under $2-million category).
Why would a lane-improvement project garner so much interest? Two reasons—it was done with concrete and it was done fast.
The City of Mississauga decided to go with concrete to repair a severely rutted section of asphalt pavement in a turning lane at the intersection of Courtney Park and Kennedy Road. The asphalt in the turning lane had been previously repaired in 2007 and 2010, so the city decided to try going with a concrete repair.
The city was looking for a material that would offer longevity for the turning lane, which was next to a truck shop that produces high levels of truck traffic that create additional strain on the lane, according to Dave Morris, geotechnical and materials testing coordinator with the City of Mississauga’s Transportation & Works Department.
“It seemed that for the last six years we were in there every other year, grinding and overlaying and nothing seemed to work,” said Morris. “Why go in there every few years and do asphalt repair?”
A tight time frame
One hesitation the city had with using concrete for road repair was the potential for long closure times, particularly in high-traffic areas like Courtney Park and Kennedy Road, so this project had to be completed relatively quickly. The city proposed starting the reconstruction at 10 p.m. on Friday, Sept. 7 and reopening the road in the morning on Monday, Sept. 10.
The city repair contract was awarded to Royal Ready Construction Ltd., which used its partner division, Royal Ready-Mix, as its material supplier.
Due to time constraints a full engineering study could not be performed, so conservative designs were used for the project. It was decided that the entire 225 mm of asphalt would be removed and replaced with 35 MPa fibre-reinforced concrete.
Royal Ready-Mix proposed using macro-synthetic fibres in the concrete mix design as an added safety factor. The effect of the fibres on the mix design was verified through the use of Street Pave 12 software, developed by the American Concrete Pavement Association. The use of the fibres had the same effect as reducing the concrete cross-section to 200 mm. The reduction was not made but the fibres were still used to increase the concrete pavement’s structural capacity.
“It gave [the concrete] an early increase of strength for the first three days. If there’s a crack, it holds the crack together, ” said Morris. “After 28 days, they don’t help increase the strength—the concrete takes over. But they do help keep the pieces together.”
Tony Capobianco, president of Royal Ready Construction, said his company had previously used the fibres in commercial concrete paving projects. The tight time frame for the project proved to be the most challenging aspect, especially since the weather refused to cooperate. Rain was expected on the day of the concrete pour so the start time was changed from 10 p.m. on Friday, Sept. 7 to 10:30 a.m. the same day.
“We did tie [traffic] up for that one period, but they don’t have to worry about that now for 20 to 30 years,” he said.
Excavation of the asphalt sections took place from 10:45 a.m. to 3 p.m., with the concrete placement, finishing and testing
performed from 3 p.m. to 6:30 p.m.
Maturity Meter wires were installed for the last three loads of the concrete to establish when the lane could be reopened, in addition to the standard testing of temperature, slump and air content.
The maturity testing concluded that 15 MPa was achieved at the eight-hour mark and 20 MPa at the14.5-hour mark.
Capobianco said he was excited to hear that his company exceeded all expectations, especially after two separate testing companies performed strength tests.
“The two independents strength tests they did were identical,” he said. “We were glad to hear the mix was consistent throughout.”
Even though the concrete reached the necessary strength to open the lane ahead of schedule, the city elected to wait until Monday morning to open the lane since the traffic flow is lower on weekends and it wouldn’t affect traffic.
Although the macro-synthetic fibres played a vital role in accelerating the strength of the concrete, it wasn’t the only important factor.
“Two things have to come together,” said Capobianco. “Your labour force has to work in an expedited manner and the integrity of the concrete mix has to be right.”
Not requiring help from outside sources for supply also helped, he added.
Morris said the contractor’s knowledge and experience were a great benefit to the project. “They understood what had to be done and they adjusted their time and procedures and manpower to fit the project.”
Morris said he hopes that this project will encourage the use of concrete in road-maintenance projects by municipalities.
“This project may encourage future projects,” said Capobianco. “I think being able to turn the job over to them the next day is the key. I think it’ll help municipalities make their decisions in the future.”