A paper towel in a public washroom? It’s made from recycled paper. Pick up a coffee from your local drive-through? The cup is made from recycled plastic.
The desk calendar in front of me as I write this has a line on every page telling me it’s made from recycled material.
Recycled materials seem to have taken over our lives — except for building materials. Recycled concrete is almost unheard of, but shouldn’t we be able to use it in new buildings?
Now a team of researchers from the University of Notre Dame in South Bend, Ind., is asking the same question.
Concrete is the most commonly used construction material in the world, but it is also the biggest in terms of environmental impact, says Yahya "Gino" Kurama, a professor of civil and environmental engineering and earth sciences at Notre Dame.
"Coarse aggregates, such as crushed rock and gravel, make up most of a given concrete volume," he notes. "The mining, processing and transportation operations for these aggregates consume large amounts of energy and adversely affect the ecology of forested areas and riverbeds."
Kurama cites a recent paper in the journal Science, which stressed the environmental impact humans have had and pointed out that more than half of the concrete ever used was produced in the past 20 years. He says that, in his research, he wants to contribute to efforts to reducing the demands we’re making on our natural environment as we manufacture so much concrete from virgin materials. Instead, he wants to use recycled concrete to reduce at least some of the aggregates.
"Especially in years to come, the renovation and replacement of our nation’s aging infrastructure will result in both an increase in the supply of old concrete rubble and the demand for new concrete," he says. "We need to be better prepared to utilize this growing resource at a higher level."
That, he says, is the thrust of his research. The variability and the uncertainty about the quality and properties of recycled concrete has been a barrier standing in the way of its use. We haven’t known how its variabilities affect strength, stiffness and durability when used as part of the mix in reinforced concrete structures.
Kurama’s team is trying to understand how using recycled concrete will affect the behaviour of reinforced concrete structures so that using the material won’t result in unintended and undesirable consequences.
Much of the research to date, he says, has centred such industrial byproducts as fly ash, slag and silica fume as partial replacements for some of the cement in the mix.
"In comparison, conservation of coarse aggregates has been largely ignored in the U.S.," he says.
That’s why we still know relatively little about the properties of recycled concrete.
Kurama’s group so far has investigated recycled materials from a large number of sources, studying the inherent variability in material quality and properties. They also addressed the problem of deflection behaviour — how much the structure would continue to deform over a long period of day-to-day loading. And they have studied the potential for using recycled aggregates in precast concrete.
The team studied variability from 16 recycled aggregate sources in the U.S. Midwest, and figured out ways to pre-qualify the material for structural applications.
Now the team is extending its reach by forming partnerships with researchers in the eastern, southern and southwestern U.S.
"We are also looking at durability and lifecycle cost, in comparison with natural aggregates and the effects of recycled concrete aggregates in pre-stressed concrete."
The ultimate objective, Kurama says, is to provide a body of information that could be used by engineers to design concrete structures that incorporate varying amounts of recycled concrete aggregates that have less impact on the environment than concrete structures made using natural aggregates.
Korky Koroluk is an Ottawa-based freelance writer. Send comments to firstname.lastname@example.org.