'U' scientists create bendable concrete

BY ANKIT SUR
For the Daily
Published May 15, 2005

Cracks and potholes have plagued our roadways for years, but they may become a thing of the past because of University scientists who have created concrete that bends.

Dr.. Victor Li, civil engineering professor at the University and his team have developed “bendable concrete,” also known as Engineering Cement Composite. ECC is much stronger and is also more resistant to crack and other anomalies that have plagued the traditional concrete used today. Using ECC to build roads would result in roads that may be able to last for ten years without repair in some areas, Li said.

The Michigan Department of Transportation has wasted no time enlisting the help of Li’s team in order to build a more resistant bridge – this summer they will use bendable concrete to repair a bridge in Ypsilanti.

“We are employing the use of ECC to save money and to make our bridges last longer,” said Bill Shreck, a MDOT spokesperson. “This is a good opportunity for us to examine the effectiveness of the material. If it holds up it has the potential to (be) used across the state.”

According to Shreck, with over 10,000 bridges in the state, bendable concrete could save the state of Michigan thousands of dollars on bridge repairs. and millions of dollars on road repairs.

While traditional concrete has impressive strength when compressed, it is extremely weak under tension. In the past, scientists and engineers have reinforced concrete with steel bars or mesh. While these efforts proved to be effective, they did not end the engineers’ battle against road decay.

In the 1970’s, scientists introduced fiber-reinforced concrete, which contained special fibers like nylon or polypropylene and others to improve the tensile strength of concrete. However, scientists soon discovered that the addition of these fibers not only increased the tension strength but also made it more flexible.

The flexibility exhibited by fiber-reinforced concrete is due to the nature of the fiber. Nylon and other polymers can stretch when pulled apart — that’s why when you pull on a plastic bag, it does not rip, but stretches. When these materials are used to reinforce concrete, they absorb some of the energy during tension, giving concrete flexibility.

Li’s engineering team built on this idea, using the concept of adding a special polymer fiber to make concrete not only more flexible, but to make it 500 times more resistant to cracks and 40 percent lighter, Li said.

Even though fiber-reinforced concrete has been around since the 1970’s, Li’s team has been able to alter the internal structure of concrete itself. They arranged the polymer fibers inside concrete in such a way that when the load on the material is high, the fibers absorb energy very efficiently, giving it high tensile strength.

Well before the bridge in Ypsilanti was planned, bendable concrete was used in Japan’s Mihara Bridge, reducing the road-deck’s thickness from 230 millimeters with typical concrete to 50 millimeters, Li said.

“Even though ECC costs three times more than traditional concrete, the material saving leads to an overall cost saving,” Li said.

Modern concrete is a mixture of cement, sand, rock and water. Traditional concrete can contain other substances, such as industrial ash, which alter its properties.