Consider the humble concrete bridge. It's so common around the world that, when you pass over one, you probably don't think much about it. However, scientists and engineers are still working on improving concrete. Advances in technology hold the promise of bridges that last twice as long as those made out of traditional concrete mixes.
Concrete use dates back to ancient civilizations. The Romans, especially, used it for roads, aquaducts and buildings. It fell into disuse, but again became a common building material a couple of centuries ago. Reinforced concrete bridges date from the late 19th century. Since then, as various materials were added and new processes were developed, concrete itself evolved into something of a high-tech product. "It's a very complex system, it's one of the most complex chemical systems,? he says. ?We still don't understand it and very few chemists in the world can explain it."
Paul Tikalsky teaches civil engineering at Pennsylvania State University. His team studied the benefits of adding certain industrial waste products to the concrete used in bridges, both to recycle the waste material and to improve the lifespan of the structure.
"Bridges right now last maybe 25-35 years before we have to replace their decks or superstructures,? he notes. ?And in fact we could make them last 75 years and we wouldn't have to pay for them twice in our lifetimes. We would end up with paying less and getting more."
On the phone from Charlotte, North Carolina, where he was presenting a paper on his research to the Concrete Bridge Council Conference, Prof. Tikalsky explained that one of the industrial products he and his team have been experimenting with is fly ash.
"Fly ash comes from the combustion of coal,? he explains. ?So when you burn coal it would be the air pollution that goes up into the sky, but we collect it. And this particulate matter is almost exactly the same size and chemical composition as Portland cement and it's free."
Portland cement is a key ingredient in concrete and it's the most expensive part of the mixture, so replacing some part of the Portland cement with a low-cost industrial by-product is not only eco-friendly, it can also save money in construction. By substituting some of the cement in the mixture, the concrete and the critical reinforcing metal inside it are less susceptible to corrosion, which can shorten the life of a bridge.
Because part of Professor Tikalsky's research is funded by the federal government, the results will be available to anyone who's interested in the technology, not just engineers in the United States.
"The students we have at Penn State are from India, from China, from the Middle East and so forth, as well as from the United States,? he adds. ?We find this same technology. It's not proprietary. So all of the reports and all this kind of information is widely available and we actually find quite a bit of this technology transferred back to China, the Philippines, and throughout the world."
Paul Tikalsky and his colleagues at Penn State have identified 10 different concrete formulations that are the most promising for extending the life of a bridge. Their ability to outlast conventional concrete will be tested in real-world situations, by actually building bridges on highways in the state of Pennsylvania and equipping them with sophisticated monitors to evaluate bridge performance over the coming years.