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.
Benmokrane reached out to MTO, MMM Group (now known as WSP) and Buckland & Taylor to design 480 3 x 7-meter GFRP-RC deck panels, as well as sidewalks with 15- and 20-millimeter-thick GFRP-RC rebar. A total of roughly 350,000 meters of GFRP bars were used in the bridge deck. The GFRP was supplied by V-Rod Canada, which has supplied composite materials for hundreds of bridges for the MTO and other owners across the country. All of the panels were fabricated and cast at a precast facility (M CON Pipe & Products Inc., Ayr, Ontario, Canada) and then shipped onsite.
Two construction firms, Bot Construction and Ferrovial Agroman, accelerated construction by precasting the panels in pylons and connecting them with UHPFRC joints. After building the deck, Bot and Ferrovial drove 182 steel piles 50 to 70 meters deep for a cast-in-place substructure that is 75 meters high when measured from the bridge’s foundation footings. They then placed the precast, multi-beam center pier about 51 meters above the deck. The beams are connected to the bridge by 66 steel cables.
The bridge has been built in two halves. The westbound section was finished in November 2015, while the eastbound span is scheduled for completion this year.
Benmokrane and his research team at Sherbrooke have made recommendations to install fiber-optic sensors on critical parts of the bridge to measure strain and temperature data. The data, he says, will allow his team to assess the bridge under actual service conditions. The team will also conduct live field tests to assess the bridge’s long-term durability and serviceability in a wide range of environmental and traffic conditions.
Benmokrane believes the bridge is a landmark achievement for the composites industry as it looks to further expand into the infrastructure market. During the International Bridge Conference in National Harbor, Md., Benmokrane made a presentation on the design of the bridge and the benefits of FRP. He says he was happy with the feedback he received from engineers at the conference and is optimistic that applications like the Nipigon River bridge can open doors for many composites businesses.
“Based on the feedback I’ve been getting, I’m really expecting that in the future we will see many more bridges all over the world that use this kind of reinforcement,” says Benmokrane. “These bridges are very economic, elegant and have a great aesthetic.”
He says concrete bridges reinforced with GFRP rebars have an initial cost that is almost the same as concrete bridges reinforced with epoxy-coated or galvanized steel rebars. He adds stainless steel rebar is also two to four times more expensive than GFRP rebar.
“This is really bringing in millions of dollars to the industry with just one bridge,” Benmokrane said. “Can you imagine if the industry made 100 bridges of this kind per year?”
On Wednesday, September 13, Benmokrane will host an education session at CAMX on the technical details of his research and how the Nipigon River application demonstrates the potential for greater use of composites in bridges throughout North America. Next February, during ACMA’s annual Infrastructure Day, ACMA staff and representatives from its member companies will present applications like Nipigon River to members of Congress and their staff to advocate for composites in infrastructure.