Composite Materials for Infrastructure
New materials that replace or improve the performance of traditional materials – wood, steel, iron, and concrete – are now becoming available for architects and engineers to incorporate into new buildings or to use to repair and retrofit deteriorating structures. With these new materials, it is possible to tailor properties to provide for greater strength, toughness, or ductility – the ability to be easily drawn into wires or hammered into thin sheets. With the availability of new composite materials, architects are able to design structures that are lighter, stronger, and more energy efficient, in new styles and organic shapes that were previously unthinkable.
“Rather than what we have traditionally done in civil engineering, which is to design our structures to accommodate the strengths or deficiencies in the materials, now we are in a position to decide how the materials should perform and design the materials to meet the needs of the structure,” says Maria Lopez de Murphy, an assistant professor of civil engineering who studies the performance and longevity of composite materials for infrastructure. “I see architects and structural engineers teaming up to take advantage of these new materials, but it is happening slowly,” Lopez admits. “Many of these new ideas are coming out of universities and research centers, because that’s where you have the freedom to experiment. You need to be a little more conservative when you bring such ideas into, for instance, the Department of Transportation.”
As she makes her way through the cavernous facilities for civil infrastructure testing and evaluation built inside a former refractory building at Cato Park, near the University Park campus, Lopez (photo on previous page) points out large concrete girders studded with sensors, fiber reinforced polymers that can be nailed onto an existing structure to provide strength, and small steel fibers that can be mixed into concrete to replace much of the steel rebar that currently supports concrete structures. Improving traditional building materials such as concrete, can be just as important as developing new materials. “Regular concrete is strong in compression but weak in tension,” Lopez remarks, indicating a massive concrete beam radiating fracture lines. “If cracks are too wide, you can get corrosion of the reinforcing rebar. The benefit of short fibers is that you take the properties of rebar and put it in the tiny capsules in concrete so that cracks are smaller and more distributed, so you can use less rebar.”
The fibers can range in size from microscale to a couple of inches in length, and be made of steel or synthetic polymers. The initial difficulty in using the fibers was in uniformly mixing the fibers into the concrete. That problem seems to have been solved with the use of self-consolidating concrete, a concrete that flows almost like water. The goal of her current research is to determine the theoretical amount of fiber to provide the greatest toughness and flexural strength while maintaining the flow properties.
“Our aging infrastructure is in need of repair and retrofit,” remarks Lopez, “and there is not enough money out there to turn all our old bridges into new bridges. We need to have many tools in our toolbox to decide which can be restored and which need to be replaced. That’s the niche I’m working in.”