May 5, 2010
The devastation caused by recent earthquakes in Haiti and Chile, as well as by terrorist activities around the world, underscores the need for better construction materials and designs to protect critical public infrastructure against such extreme shocks.
Canada's core public infrastructure includes transport systems (roads, bridges and transit), public buildings that provide essential services, and municipal systems that deliver potable water and remove wastes. The foundation of our public infrastructure is a common building material: concrete. "Traditionally, we've designed our infrastructure to withstand natural disasters, not man-made events," says Dr. Zoubir Lounis, leader of the concrete structures group at the NRC Institute for Research in Construction (NRC-IRC) in Ottawa.
Steel can start to corrode after just 15 years of service in normal concrete.
In collaboration with the University of Ottawa, NRC is developing high performance structures that incorporate high performance concrete and advanced composite materials — consisting of fibre-reinforced polymers — to help make critical structures more shock-resistant. By adding a shock absorber, the new construction materials could improve the safety of critical infrastructure in Canada and around the world.
"Since it would be too expensive to protect all our public infrastructure, we're developing new technology as well as a risk management approach," says Dr. Lounis. This approach involves identifying public infrastructure that is critical both from a public safety and an economic standpoint. The goal would then be to incorporate shock-resistant materials into key structures at critical stress points — such as the load-bearing columns holding up a highway overpass — in order to provide adequate strength and safety margins, and extend their service life.
Statistics Canada has estimated the value of Canada’s core public infrastructure — including roads, bridges, drinking water, waste water and sewage treatment systems — at more than $286 billion.
The state of our roads, bridges, buildings and water/waste water systems is closely linked to our economy, safety and security, and quality of life. Consider the potential impact of disrupting traffic across an important trade route like the Ambassador Bridge, which links Windsor and Detroit, for even one day.
"The idea is not so much to protect these structures but to enhance public safety by ensuring that if an accidental or intentional shock does occur, the structure doesn't crumble but is only damaged — in other words, a ‘controlled and more ductile' failure," says Dr. Husham Almansour, the NRC project leader. "Our goal is to give people enough time to evacuate — depending on the size of the shock and the importance of the infrastructure."
"When we design a retrofit to resist extreme shocks, we want to make the structure more robust," adds Dr. Lounis. "Robustness means the structure has built-in redundancies, so external stresses are distributed between the different load-bearing elements and any damage that results is proportional to the shock or load."
NRC's new building materials and systems will undergo thorough testing that simulates the effects of blast or heavy impacts. "This is a huge undertaking with many private and public partners," says Dr. Lounis. After the shock-resistant materials and systems have been fully evaluated, they will be made available to Canadian companies and public infrastructure owners, giving them a competitive edge in world markets.
University of Ottawa shock-tube facility for conducting impact and blast tests.
Much of Canada's public infrastructure was built after the Second World War and is now approaching the end of its design life. "Instead of using the same conventional materials and doing the usual repairs, we're thinking about how to replace existing structures with new structures that will last twice as long," says Dr. Zoubir Lounis.
For example, most current bridges were meant to have a design life of about fifty years. High and ultra-high performance concrete (UHPC) could double their life span because it contains steel fibres and more cementing materials than normal concrete. "It is also more resistant to corrosive agents," says Dr. Lounis. "It will take up to 70-80 years for salt and water to reach the steel and corrosion to start, whereas with normal concrete, the salt could reach the steel after 15 years."
Concrete structures testing facility at NRC Institute for Research in Construction.
"UHPC can be three, four or five times more expensive than normal concrete," he adds. "But the entire life-cycle costs of a bridge made with UHPC will be much lower. Over a hundred years, the bridge will require very little maintenance, so you won't need to close it as often to repair or replace a component."
