For those of us who live in the eastern half of the United States, it was a pretty tough winter. Many cities, including Detroit and Indianapolis, set records for snowfall and saw exceptionally cold temperatures. Inevitably, the snow melts, the temperatures warm up, and spring arrives, bringing with it longer days, sunshine and flowers. Spring also brings some things not as pleasant, such as roads with a lot of new potholes and bridges deteriorated by road salt and freeze/thaw cycles — and the inevitable “construction” season.
While I navigated rough roads around the U.S. Midwest over the Easter weekend, I came across an article in the April 16 Txchnologist Blog about a new “superhydrophobic concrete,” doped with copious amounts of siloxane-based additives to repel water, and augmented with polyvinyl alcohol (PVA) fibers to impart flexibility. (See http://txchnologist.com/tagged/concrete.) Developed by a team of researchers at the University of Wisconsin (Madison, Wis.), laboratory testing of the formulation suggests this advanced concrete could last more than a century, compared to 30 years for conventional concrete roads.
I was reminded of an experiment conducted by the Utah Department of Transportation in 1989 when I lived in Salt Lake City. A 4-mile/6.4-km stretch of the busiest portion of Interstate 15 through Salt Lake City was coated with a 0.75-inch/19-mm layer of a material called Syn-crete, a polymer-modified concrete. The idea was to prolong the life of the highway for at least 10 years, delaying reconstruction and its associated costs. Within days, large chunks of the topping cracked and disbonded from the underlying roadway, breaking windshields and causing other damage to vehicles. The topping was completely removed soon after, at considerable expense. A decade later, I-15 through Salt Lake City was completely rebuilt in preparation for the 2002 winter Olympics. To my knowledge, this was done with conventional techniques.
The new superhydrophobic concrete from Wisconsin is being tested in a university parking structure to see if the results seen in the lab can be replicated in everyday use. The inventors say the product costs more than conventional concrete, but, in time, would “pay for itself with diminished maintenance.” Hold on! Are we talking lifecycle costs? I think I’ve seen this movie before, as it relates to composites in infrastructure. And the evidence is in — lifecycle costs just don’t matter unless the price premium is fairly small.
There are more than 600,000 bridges in the U.S. and it is estimated that almost 26 percent are either structurally deficient or functionally obsolete. This represents a huge potential market for repair and/or replacement. Faced with limited annual budgets, state and local transportation executives have the choice to replace a certain number of bridges with concrete that will last 30 to 40 years, 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.
I contacted Scott Reeve, president of Composite Advantage (Dayton, Ohio), to see if any progress has been made in winning the lifecycle-cost argument. Reeve, whose company is among the most successful fabricators of composite bridge decks, confirmed the 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,” he noted. “Until we can get that differential down to around 15 percent, market penetration will remain slow. The existing government procurement structure does not value life cycle costs in infrastructure.”
Numerous contractors are using composites for remediation of concrete bridge decks and columns. While this is good for material suppliers and the reputation of composites as a whole, it doesn’t help fabricators of composite structures, says Reeve. Composite Advantage has established a strong reputation in pedestrian bridges and has been able to capture vehicular bridge deck replacements where composites bring immediate value over concrete — for example, being able to use 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.” I hope he’s right, and I hope that the new super concrete — which is, after all, a fiber-reinforced composite — succeeds as well. I certainly wouldn’t mind seeing a few less potholes every spring.