NRC develops more durable concrete – Ottawa Citizen

Researchers at the National Research Council in Ottawa have developed a new, more durable concrete that resists cracking -dramatically increasing the lifespan of structures like bridges and parking garages in Canada.

The new technology is slated to be used on the Seaway International Bridge near Cornwall, and industry professionals are calling it cutting edge.

“This is one of the most advanced concrete technologies,” said Felek Jachimowicz, vice-president of Research at W.R. Grace, a major U.S. construction research firm, and a partner in the project.

And while this new highquality concrete costs more up front than traditional alternatives, Jachimowicz said the low maintenance costs of the material will actually make it much cheaper in the long run.

The key, said lead researcher Daniel Cusson, is this new concrete doesn’t crack. Cracked concrete is a major problem in Canada and the Northern U.S., said Cusson, because it allows road salt and other corrosive materials to reach the metal reinforcements inside. “We’re very concerned about the durability of structures,” he said.

During their research, Cusson’s team came up with several ways to reduce cracking. The most successful was a process known as internal curing.

Concrete is made up of water and cement, as well as an aggregate such as sand.

Concrete with less water is stronger, said Cusson, but also dries faster. When concrete dries, it shrinks and when it shrinks, it cracks.

Typically, wet burlap is placed over concrete as it sets, keeping it hydrated in its early stages. Cusson said this process is less effective when the cement ratio is higher because water can’t permeate the material.

The solution is using porous shale, soaked in water, instead of sand. Once cement and water are mixed, the water trapped in the shale keeps the concrete hydrated from the inside-out.

Canada’s climate creates a unique challenge when building structures such as bridges, said Carleton University’s David Lau, a specialist in bridge engineering. The combination of hot summers, cold winters, high urbanization and road salt mean bridge and road decks need to be replaced regularly.

“That’s why, in the summer, we have all this road repair all the time.” he said.

New, high performance materials such as Cusson’s will always have better durability, he said, but added nothing is indestructible.

“There is no perfect concrete,” he said. “Even for brand new constructions, there are always some very fine hairline cracks.”

He said the key is to keep those cracks small, spread out and under control.

The Federal Bridge Corporation will be the first to use the new material during its $75 million improvement of the North Channel Bridge in Cornwall, which begins in May. The NRC’s concrete will be added sometime in 2012 and the bridge is slated to open in 2013.

“That’s going to be very exciting,” said Cusson.

Three other partners were involved in the research: the City of Ottawa, the National Capital Commission, the Quebec Ministry of Transportation and the Federal Bridge Corporation.

Claude Robert, chief engineer at the NCC, said the commission typically needs to replace bridge decks every 20 to 25 years. With the new concrete, he said, decks would only need to be replaced every 50 years.

He said the material could be used when the decks on the Champlain and Portage bridges are replaced in five to 10 years. He said the technology would also be well suited to the proposed Kettle Island bridge.

“That could be an application right there,” he said.

The City of Ottawa doesn’t have any firm plans for the material yet either. However, Jocelyne Turner, a spokesperson for the city, described the project as “promising” and said a pilot project may be considered in the future.

Cusson said he estimates that the material could mean long term savings of up to 40 per cent. He added that the technology would be applicable anywhere with a cold climate, such as Northern Europe or Russia.

Read more: http://www.ottawacitizen.com/develops+more+durable+concrete/4375241/story.html#ixzz1FeKbjwQN

 

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