Crushing concrete for new roads

PSI Technologies Inc. doesn’t mess around when it takes on a recycling project.

In a single day, the Saskatoon-based engineering company can crush and recycle as much as 2,500 tonnes of material that would otherwise be dumped in municipal landfills.

PSI specializes in recycling used concrete, mostly collected from demolished commercial and industrial buildings in Saskatoon and surrounding communities.

The material is crushed, sorted, stockpiled and sold to construction companies that use it primarily for road construction.

Last week, PSI employees crushed thousands of tonnes of concrete collected from a former hospital in Humboldt, Sask., and a pair of recently demolished churches.

PSI project engineer Duane Guenther said any construction project that uses gravel or natural aggregate can be built with recycled concrete at a similar cost.

Crushed concrete also functions as effectively as gravel or rock aggregate or better, said Guenther.

It has rough edges — also known as aggregate angularity — which improves adherence to other road building materials, including fresh asphalt.

The presence of residual cement in recycled concrete also improves adhesion, resulting in a more durable roadway.

“Using the crushed concrete gives us a better structure on roads because it’s is all fractured … and it holds together really well,” Guenther said.

“But when you’re talking about gravel or rock that’s been mined out of a gravel pit … you’ll often have rounded edges, which don’t quite have as much capacity.”

PSI got into the recycling business after it recognized an opportunity to acquire used concrete at a low cost, enhance its value and sell it as an alternative construction material to local contracting companies.

Demolition companies usually pay tipping fees to get rid of used concrete at local landfill sites.

PSI began testing the material and determined that crushed concrete was a viable alternative to gravel and rock-based aggregate.

The company now has a crushing site a few kilometres east of Saskatoon where material is trucked in, processed and stockpiled.

Equipment at the site includes the province’s largest mobile jaw crusher, which handles concrete, rock and other materials.

The crusher, one of several on site, was manufactured in Wisconsin by Lippman Milwaukee Inc.

One of the constant challenges facing PSI is convincing contractors that recycled concrete performs as well as natural aggregate.

Guenther previously worked as a project engineer with the City of Saskatoon and was involved in a trial known as the GreenStreet Project. It used crushed concrete and crushed asphalt to rebuild sections of 10 streets in Saskatoon.

Eighty-eight percent of the material used in the project was recycled.

The GreenStreet project showed positive results, confirming what PSI performance models had suggested.

A number of construction companies in Saskatchewan are now using the material, although acceptance by the public sector has taken longer than expected.

The City of Saskatoon recently indicated that it will begin using recycled concrete aggregate in some city projects.

PSI can produce more than 500,000 tonnes of crushed concrete aggregate per year, although annual tonnage is currently closer to 50,000 tonnes.

Sources of used concrete are numerous, although hauling the material can significantly increase processing costs.

PSI’s crushing equipment is mobile and can be relocated if necessary.

The company accepts deliveries of unset concrete, rock, used asphalt and other materials, which allows companies to avoid tipping fees.

“Concrete is probably the most common material that comes in,” said Guenther.

“As far as source material goes, it’s probably the most (plentiful).”

He said more material would be recycled in the province if tipping fees at municipal landfill sites were higher.

Tipping fees are relatively inexpensive in Saskatchewan, so the monetary incentive to keep material out of landfills is often too small to warrant the extra efforts associated with recycling.

PSI recently attempted to secure 15,000 tonnes of material from a demolished school, but the contractors in charge of demolition opted instead to truck the material to a landfill and pay tipping fees.

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