September 13, 2012

Pervious pavement is not concrete, explains Ready Mixed Concrete Association of Ontario

IAN HARVEY

correspondent

The Bard opined a rose by any other name would still smell as sweet but when it comes to pervious pavement, the last thing Ready Mixed Concrete Association of Ontario president John D. Hull wants to hear it called is concrete.

“It isn’t concrete,” he says. “It’s pavement. Or, what it used to be known as, no fines concrete.”

Calling it pervious concrete implies it can be mixed, laid and treated the same as concrete, he said, and that’s not only a misnomer, it’s a delusion.

Part of the battle to win acceptance of pervious pavement as a go-to solution in the right application is to classify it differently so people start treating it differently and, by extension, come to have different expectations over regular concrete.

Because pervious pavement has 25 per cent voids — to allow water to drain through unfettered — it doesn’t have the strength and durability expected of concrete.

Thus far, the road to acceptance for pervious is paved with questions. The Ontario Ministry of Transportation (MTO) added more doubts to the list with a technical paper, evolution of pervious concrete pavement at the MTO ,which was tabled at the 10th international conference on concrete pavement in Quebec City last July.

With two pilot installations under their belt, a commuter lot near Guelph, Ont. and a GO Transit parking lot at the Williams Parkway in Brampton completed in July 2011, the MTO is working with Simcoe County on another lot northwest of Barrie.

It remains a work in progress, according to the report.

“Pervious concrete pavement is a promising emerging technology that offers a functional ‘green’ option for light-duty pavements such as parking lots,” the report said but added further monitoring is needed to confirm the longer-term performance and quantify environmental benefits, chief among them, getting the slab poured right the first time.”

Front and centre among the reservations is the additional cost, the need for RMCAO-certified contractors who understand how to mix and apply the mix and the question of what specifications are best and finally, what testing equipment and procedures are required to ensure the finished product meets those specs.

Ravelling is also listed as an issue but there’s some discussion in the industry that it may be the result of inappropriate traffic using the surface.

Still, the MTO is “encouraged” and says it will continue on the learning curve.

“Putting greater emphasis on surface quality to improve lifespan and increase public acceptance of pervious concrete pavements and walkways and restricting maximum aggregate size to 13 mm or 10 mm in areas of high pedestrian traffic, will improve surface wearability and pedestrian walkability,” the paper said. It also noted adding height restriction barriers will limit heavy vehicles to prevent damage.

Laying pervious pavement should also be limited in high winds and high temperatures and more “investigation is needed to determine how to incorporate entrained air into the paste and assess its impact in providing freeze-thaw resistance.”

Hull finds the latter suggestion curious however: “There is no freeze-thaw issue because there is no water. Lots of other jurisdictions have shown that, including Michigan and Ohio.”

MTO’s concrete section head Hannah Schell, however, says the industry and pervious proponents shouldn’t be overly concerned. Pervious’ path isn’t much different from other innovations to pass through the scrutiny of MTO and it’s still on track.

“There have been some growing pains and I think we can borrow learning from other jurisdictions and we need to look at testing methods,” she said adding self-consolidating concrete, for example, while a different product, had just as a rocky ride.

As a product, she thinks pervious will find its niche, and as it gains more acceptance and better understanding may expand to other applications beyond parking lots.

“Certainly the U.S. Army Corps of Engineers and WalMart are using it a lot,” she said.

Hull says the industry is also committed to promoting pervious as a good option where water run-off is an issue and one which will pay for itself when other water containment systems are considered and priced.

“Water is the new gold,” he said adding that in new residential and commercial projects, the code requires installation of stormwater holding ponds which have to be dug, poured and configured with underground piping and maintained on an ongoing basis.

Weighed against the cost of the land alone for the containments, pervious is a winning formula, Hull said.

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