Aging infrastructure offers a potentially huge market for composite materials. According to a report by the coalition Transportation for America (Washington, DC, US), titled The Fix We’re In For: The State of our Nation’s Busiest Bridges, there are 69,223 structurally deficient highway bridges in the U.S. alone — 11.5% of all U.S. highway bridges — that require rehabilitation or replacement. These numbers have stimulated development of a number of composites-enabled technologies.
The early deterioration of concrete due to the corrosion and failure of steel rebar has been well documented. Conventional repairs could cost billions. In many locales, the useful life of corrosion-prone steel-rebar-reinforced concrete is limited to 25 years, rather than the 75 to 100 years once promised by its advocates. Therefore, the lifecycle cost advantages, not to mention the safety benefits, of using composite rebar continue to overcome resistance among change-averse municipalities. That said, once significant activity among composites fabricators looking to replace entire bridge structures has quieted, replaced by a more conservative focus on replacing vulnerable, corrosion-prone concrete bridge decks with robust composite replacements on steel truss bridges.
Progress is still halting. Faced with limited annual budgets, state and local transportation executives have the choice to replace a certain number of bridges with concrete that could last 30-40 years at best, or half as many using composites that could last up to 100 years. In both cases, their careers will be long finished before anyone will hold them to account, so the easy answer is twice as many low-cost bridges.
Scott Reeve, president of Composite Advantage (Dayton, OH, US), says the day cannot be won on the lifecycle-cost argument alone. Reeve, whose company is among the most successful fabricators of composite bridge decks, particularly for pedestrian bridges, confirms that the “upfront cost” problem still exists. “A composite vehicle deck is about twice the price of a concrete deck. Even accounting for lower installation costs, we are probably 1.8 times the traditional solution. Until we can get that differential down to around 15%, market penetration will remain slow.”
Although numerous contractors use composite wraps for remediation of concrete bridge decks and columns, it doesn’t help fabricators of composite structures, says Reeve. Composites can capture vehicular bridge deck replacements where composites bring immediate value over concrete — for example, being able to reuse the existing structural elements, which would not otherwise be able to support the weight of a concrete deck, or the addition of a sidewalk where one did not previously exist. Integrated properly, composites can enable replacement of a bridge over a single weekend, clearly a benefit in congested cities.
Despite the resistance posed by economics, Reeve is a long-term optimist regarding the potential for composite bridge decks. “It took 30 years for steel to replace wood in bridge structures, so the opportunity to change the mindset is still there.”