In Canada, thousands of commuters rely on the TransCanada highway – a continuous highway system that travels through all 10 provinces of Canada from coast to coast. Like many highways in America, TransCanada has a lot of bridges made with steel-reinforced concrete structures. However, when the steel corrodes, bridges are left with major durability problems that lead to structural degradation and costly repairs. One bridge over the Nipigon River on the Highway 11/17 corridor east of Thunder Bay, Ontario, has become proof that composites can be a viable alternative to steel.
In 2013, the Ministry of Transportation of Ontario (MTO) began a $106 million project to replace the Nipigon River bridge with two parallel spans carrying four lanes. The result was the first cable-stayed bridge in the Ontario highway system and the world’s first cable-stayed bridge with glass fiber reinforced polymer-reinforced concrete (GFRP-RC) deck panels. The GFRP features vinyl ester resin and boron-free E-glass fibers.
According to Brahim Benmokrane, Ph.D., a civil engineering professor at the University of Sherbrooke who helped the project come to fruition, the use of GFRP-RC for the 252-meter bridge deck was as much a matter of necessity as it was innovation. Since the bridge is the only way to travel from eastern to western Canada by car, a shutdown for repair would force cars to take a southbound detour through the United States. Therefore, instead of using piers to secure the bridge, engineers opted for a cable-stayed design.
However, cable-stayed bridges are much harder to design than traditional bridges from an engineering standpoint due to their exposure to compression forces up to 9,000 psi. Those forces, Benmokrane says, make it logistically impossible to repair a cable-stayed bridge deck in the event the concrete starts to deteriorate.
That’s why, he adds, it was important for the MTO to approve a design with a structural component like GFRP that would prove extremely durable and would not need any major repairs for more than 100 years. “Even if there aren’t any problems [with GFRP], the declination can come from the concrete itself,” Benmokrane says. “So you really have to choose composite materials.”
Last year, Benmokrane and his team published a study about the specific combination of materials that went into the bridge. They constructed eight panels – six GFRP-RC panels and two steel-reinforced panels – and tested them for cracks. They concluded GFRP rebar connected by a 220-millimeter-wide ultra-high performance fiber-reinforced concrete (UHPFRC) joint did not show significant cracks because of their very high tensile strength and modulus of elasticity.