In a small section of road that passes over the Norfolk Southern railroad tracks, the Ohio Department of Transportation (ODOT) is looking to composite materials to replace traditional steel rebar.
Located just outside of Toledo, the Anthony Wayne Trail bridge was a crumbling section of a highway bridge in desperate need of rebuilding and expansion. The design firm tasked with replacing the bridge, Mannik & Smith Group, had originally specified using epoxy-coated steel rebar as is the norm in this type of project. As construction was getting underway, the firm was introduced to a new product from Owens Corning called Glass Fiber Reinforced Polymer (GFRP) as a potential replacement for steel rebar.
GFRP is made of high strength, corrosion-resistant glass fibres that are impregnated and bound by a highly durable polymeric epoxy resin. The surface is coated in sand to facilitate adhesion to the surrounding concrete. GFRP offers superior tensile strength, less weight and does not rust which gives the bridge a much longer service life. The increased longevity of the composite material is a particularly attractive feature when considering projects like the Anthony Wayne Trail bridge.
“The parameters that controlled the design were different than with conventional reinforcing steel,” said Richard Bertz, PE, CEO/president of Mannik & Smith. With steel rebar, the steel’s tensile strength affects the structure’s design. With GFRP reinforcements, crack mitigation or shear strength control dictates the design parameters.
Despite being more expensive than traditional steel rebar, the benefits of using GFPR so far have more than made up for the slight cost increase. Engineers found that with the stronger composite material they could space out the rebar by one-half inch. Even a small adjustment like a half-inch was enough to reduce the overall amount of rebar used, thus offsetting the higher cost. “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.”
Another benefit to using GFPR is the crews found it much easier to work with compared to heavy steel. “It’s one-quarter the weight of steel, so it’s easier to manage the bars around the site,” says John Amonett, GM 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.”