Building crews will find one major difference between working with GFRP and steel rebar. “It’s one-quarter the weight of steel, so it’s easier to manage the bars around the site,” says John Amonett, general manager of infrastructure at Owens Corning. “We find the number of man hours required to install an equivalent length of fiberglass ends up being anywhere from one-third to one-half less than with steel.”
GFRP’s lighter weight also reduces the potential for workers to be injured when they lift the rebar or accidentally drop it. And, unlike epoxy-coated steel rebar, GFRP rebar isn’t slippery when wet.
Both Amonett and Bertz expect an increased use of GFRP rebar for bridge projects over the next few years. One reason will be the December 2018 release of the second edition of the LRFD Bridge Design Guide Specifications for GFRP-Reinforced Concrete from the American Association of State Highway and Transportation Officials (ASHTO). In both editions of the guidelines, bridge deck design is typically controlled by maximum crack width and shear limitations. However, the second edition increased the allowable maximum crack.
If Mannik & Smith engineers had been able to design the Anthony Wayne Trail Bridge using the updated specifications, they could have increased the bar spacing by ½-inch and thereby used less rebar. That, in turn, would have reduced the cost differential between GFRP and steel rebar.
Several other economic factors are helping GFRP rebar gain a foothold in infrastructure projects, including tariffs on imported steel, which have contributed to price increases for steel rebar. “ODOT released information that shows the cost of reinforcing steel has gone up 18 percent in the last year,” says Bertz. “So when you factor that in, we’re to the point where this [GFRP] product is going to be less expensive than reinforcing steel.”
Amonett points out that unlike steel’s volatile pricing, the cost of fiberglass has remained predictable and stable. This makes GFRP rebar a prudent option for contractors, who may prefer to choose a material with more stable pricing when they’re bidding projects that will continue for two or three years.
In addition, as contractors become more experienced and comfortable with GFRP reinforcements, they’re likely to lower their bids to more realistically reflect installation costs. And an increased demand for GFRP reinforcements could lower manufacturing costs due to economies of scale.
“We already know that on a life-cycle cost, GFRP will be a good savings, but for cash-strapped organizations – whether it’s a DOT or a local public agency – the first cost really matters. We are pretty confident that very soon that cost will be below the epoxy-coated steel,” says Bertz. “My belief is that 10 to 15 years from now, just as epoxy-coated reinforcing steel became the norm, GFRP and CFRP products will be more and more integrated and prevalent in bridge design.”