Concrete Ideas for the Future
“The CFI grant is really the culmination of all our work.”
Dr. Amir Fam is talking about the $1.4 million grant the Canada Foundation for Innovation (CFI) awarded him and his colleagues this January. Together with other funding that he is waiting to hear about, the CFI money will go a long way towards his goal of building what he calls a “moving load facility” for testing bridges, a $3.5 million system, likely unique in the world. Having such a facility will help Fam, a professor of civil engineering and the Canada Research Chair in Innovative and Retrofitted Structures, realize what has long been one of the central goals of his research: finding new and better ways both to build concrete structures and to make sure that they last longer.
Conventionally, concrete is poured around rebar (i.e. reinforcing rods) and steel cages and shaped using wooden forms that hold the liquid concrete in place while it hardens. Removing the forms is time-consuming, potentially dangerous and disruptive – pulling them off a bridge can require blocking traffic for considerable amounts of time. Conventionally constructed concrete bridges have other problems as well. Heavy use and Canada’s harsh winter climate, with its repeated freezes and thaws, combined with water and road salt, damage them in the long run. Concrete cracks and breaks; far more seriously, the heart of all concrete structures, the steel rebar, corrodes, severely weakening it. Take a look at the crumbling and pitted older bridges passing over Ontario’s Highway 401 or Toronto’s deteriorating Gardiner Expressway, and it’s apparent that concrete can be surprisingly fragile.
Fam’s solution has been to create a new, different type of form, made from composites such as fibre-reinforced polymers. Designed to be left in place after the concrete hardens, speeding up and simplifying construction, they also act to reinforce the concrete, taking the place of corrosion-prone steel rebar.
Fam’s earliest work with fibreglass and other polymers relied largely on pre-made pipe developed for use in the oil and gas industry and suitable for what are called “closed forms,” those used for example in the pouring of bridge uprights. As well as speeding up construction and reinforcing the concrete, these fibre-reinforced polymer tubes protect the concrete against water and the damaging effects of salt and other chemicals. The first-ever bridge constructed using this technique was erected in Virginia in 2000. Such tubes have proven amazingly resilient. Fam has been working recently with colleagues at the Royal Military College to see whether similar columns might prove more blast-resistant than conventional concrete reinforced with rebar.
Tests carried out with high explosives at the Canadian Forces base at Petawawa have demonstrated that they are.
In the last six years or so, financed by Ontario’s Ministry of Transportation, Fam has turned his attention to developing fibre-reinforced polymer versions of the conventional wooden “open forms” currently used in bridge construction to shape and hold concrete in place when it is poured. Fam has used large flat plates that will form the underside of bridge decks, and corrugated fibreglass panels specially designed so that concrete will bond to them to serve as part of the roadbed.
What Fam has developed will revolutionize bridge construction. Yet it may well be years before we drive over bridges built using Dr. Fam’s latest techniques. Civil engineering, Fam will be the first to tell you, is a “very conservative profession.” With good reason – people’s lives depend on it, so nothing changes abruptly or before it has been carefully tested.
And that is where his new moving load facility for testing bridges comes in. Fam envisions building a sort of miniature railway in his lab at Queen’s. “It was inspired,” he says, “by the automatic car wash.” Models of future bridge deck components would travel on flat cars under a constantly pounding 200 ton hydraulic press, simulating the effect of heavy vehicles moving over them. The same track will then run them into a chamber where they will be sprayed with salt and other corrosive chemicals, and subjected to extremes of temperature before being hauled under the press again. The relentless pounding combined with extremes of temperature and constant exposure to corrosive chemicals would mirror the constantly changing real-life conditions a bridge endures over several decades, letting Fam test – and improve – his technology in the closest to real-world conditions possible. “It will be,” says Fam, “a structural engineering researcher’s dream come true.” The end result will be bridges that are stronger, easier to build, longer-lasting – and safer than what we have today.
Profile by Ian Coutts