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November 2, 2018

The surprising construction materials that could help save Ontario’s green space

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Whether it’s a road, a sewer, or the foundation walls of a new gleaming tower somewhere in the GTA, every major new building or infrastructure project starts in a quarry somewhere in rural Ontario. That’s where the sand and gravel that eventually become concrete are blasted out of the ground with explosives before being loaded on a truck, on their way to becoming part of something new and shiny in the city.

But the material, referred to as “aggregate” in the construction industry, can also be reclaimed from infrastructure and buildings that have been demolished and replaced. That’s not done as often as it could, though — thanks to rules in such places as Mississauga, Niagara, and Windsor that insist fresh “virgin” aggregate be used in municipal projects.

“Our industry’s looking at ways to get greener — there’s a lot of pressure on us for that,” says Rob Bradford, executive director of the Toronto and Area Road Builders’ Association. “And this stuff (reclaimed concrete and asphalt) is piling up in our yards … it’s all going to end up in landfill once there’s no room left, and that’s not a good thing.”

A report released by TARBA earlier this month shows that some Ontario municipalities have adopted much stricter rules on public projects than provincial policy requires. Under provincial rules, builders can use recycled aggregate as long as they follow standard procedures for checking its quality and, when necessary, mix it in with new stuff to ensure its strength. The Ministry of Transportation uses reclaimed aggregate in provincial highways.

The province says one thing, but municipalities say another. City rules that restrict the use of recycled aggregate are motivated by quality-control concerns: stuff fresh from the quarry is a known quantity and has predictable strengths and characteristics. Municipal building officials don’t have the same confidence in aggregate that might once have been part of a busy road or held up a building for 40 years, and it’s not like the original builder can vouch for it.

But recycled aggregate can also be used for pretty humble jobs — filling trenches dug for water mains or buried power lines, for example, or creating gravel shoulders on the sides of highways, where material strength is less of a concern.

Some municipalities have adopted rules that encourage the use of recycled aggregate: Toronto allows it to be used either in part or in full for all but three of the possible uses TARBA surveyed. Right next door, though, Mississauga prohibits the use of reclaimed aggregates for anything other than paving bike paths or access roads.

“For communities that say they’re about building a green city and longer-term thinking, this is an opportunity to signal that those things are important, even when they’re working on contracts for road work,” says Kate Graham, the report’s author and a political-science professor at Western University.

It’s not just road builders who want to see more use of recycled materials: even quarry owners and operators — who, in theory, could see it as competition — are in favour of it.

Keep reading on


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