September 18, 2006

Bridge Construction

Highway bridge construction turns to pre-casting

IRWIN RAPOPORT

correspondent

toronto

Signs are pointing to a greater use of pre-cast concrete components for building and rehabilitation of Ontario’s highway bridges by the province’s ministry of transportation.

“The ministry is going through a big change with our bridges,” said Rob Bradford, executive director of the Ontario Road Builders Association.

“We are not pouring them in place anymore; there is a huge program to switch that all over to pre-cast bridge components. The ministry believes you can build bridges faster that way and that is one of their key concerns.

“Pre-cast is a fine way to build bridges and it might even prove to be better than what we have been doing in the past,” Bradford added.

In theory, using pre-cast elements reduces work time and technical roadblocks.

By installing elements such as piers, slabs, bridge foundations and parapet walls, the pieces can be assembled and work can proceed on the next step once installation is complete.

The advantage is that elements can be pre-ordered and work schedules can be established based on delivery times.

Discussions have been held with ministry officials to determine whether the pre-cast concrete industry is ready for a shift to this type of construction.

“There will be some growing pains as we go into this,” said Bradford.

“They are not a huge issue at the moment, but the pre-cast industry is going to be very hard pressed to meet all the business and quality requirements.”

Bradford believes using pre-cast elements could reduce costs for the MTO by reducing work times for contractors, create additional opportunities for contractors to work on other jobs during the construction season.

Pre-cast construction is ongoing at the Mull Road structure at Highway 401, a lightly travelled road over Highway 401 in the Municipality of Chatham-Kent.

While timesaving was not a critical factor that outweighed the use of traditional cast-in-place technology, Mull Road was considered a suitable location to try an innovative approach for a deck replacement.

“There have been several previous ministry structures incorporating pre-cast elements,” said Bill Moore, MTO project manager for the Mull Road project, “but this may be the first application in Ontario to use full-width pre-cast panels that include the parapet wall. Other ministry regions have tried pre-cast deck panels spanning over two girders, and individual T-beams with an integrated slab.”

Moore believes pre-cast bridge construction is the future.

“We hope the pre-cast elements will decrease the onsite working time and reduce disruption with bridge closures,” he said.

The amount of work on the underside of the deck is decreased as the slab formwork is eliminated, lessening the workers’ exposure to traffic. While there is currently a premium cost associated with pre-cast elements, the cost is expected to decrease once the industry becomes more knowledgeable with its usage, explained Moore.

“While the usage of pre-cast within the ministry is still being reviewed,” he added, “it could be used on a project-specific basis when warranted, based on the experience gained in this project.”

John Hull, president of the Ready Mixed Concrete Association of Ontario, said the use of pre-cast elements can depend on many factors, including the span of the bridge, time for construction, how long one can restrict travel through a construction zone and the resources available to individual contractors.

“Pre-cast beams have been used in Ontario for a number of years,” he said, “but ready mixed concrete is still the choice of construction.”

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