'Crack-Proof' Concrete Could Lead to Longer-Lasting Roads
A new kind of concrete made using nanotechnology is resistant to cracks and could be used to create roads that last for 100 years instead of 20, scientists say.
Engineer Surendra Shah of Northwestern University in Illinois and his team are adapting high-tech methods to improve a low-tech substance by infusing concrete with carbon nanotubes – strong, flexible pipe-like arrangements of carbon atoms too small to be seen by most microscopes.
About 12 billion tons of concrete is used globally every year, and that figure will almost certainly increase as countries such as China and India continue to develop.
But concrete needs to be replaced, and that can be costly. According to the Federal Highway Administration, the United States contains about 950 million miles (1.5 billion kilometers) of highway, but about 161,368 miles (260,000 kilometers) – or 17 percent – needs repaving. The figures do not include the more than 3 million miles of local roads that are also in need of repair.
That’s where Shah’s work comes in. At the atomic scale, concrete looks like a bunch of tennis balls packed together. Mixing cement and water creates spaces, or nonovoids, between the balls. This means that chips, cracks and potholes actually start at the subatomic level.
“If you want to make concrete more durable, then you want to make sure that those nanoscale-cracks are prevented,” Shah said. Adding nanotubes reinforces the concrete by filling the tiny voids between particles. Today concrete is reinforced with metal bars, but nanotechnology offers greater durability.
Paul Tennis, who works with the Portland Cement Association in Skokie, said that problems with traditional concrete occur during the freeze-thaw cycle in the winter months.
"Concrete is porous. Think of it as a sponge," Tennis said.
Water seeps into the pores, and when that water freezes, it expands, which can cause cracks. This gets worse during the winter months , when salt is used to keep roads from freezing. Salt works itself into the concrete and corrodes the steel reinforcement bars, further damaging the structure.
Using carbon nanotubes would make the concrete nearly impenetrable.
“If you can make concrete very impermeable, so that salt doesn’t go through, then you can extend the life to 100 years rather than 20,” Shah said.
Not surprisingly, this new technology isn’t cheap. But when that higher price tag is spread out over a much longer lifespan, it could become cost-effective. Shah expects nanotube-reinforced concrete to make its way into roads and buildings in five years.