In the aggregate

Two new types of concrete developed by a South Dakota School of Mines and Technology researcher will pave the way for the construction of better bridges in Rapid City and Sioux Falls.

The new concrete is expected to be stronger, more durable and more resistant to cracking than concrete currently used in bridge construction, according to Tech’s Dr. Venkataswamy Ramakrishnan, a distinguished professor emeritus in Tech’s Department of Civil and Environmental Engineering.

Concrete is made from a mixture crushed stone or gravel, sand, cement and water. Chemicals are added to make the concrete durable and more workable. The proportion of the sizes of the stone and sand, called gradation, has a major influence on the quality of concrete produced.

In South Dakota, all bridge decks have been constructed using a standard concrete specified by the state Department of Transportation.

Since 2002, Ramakrishnan has used $102,000 in research funding from the South Dakota Department of Transportation and United States Department of Transportation to investigate different gradations that would result in better concrete.

After two years of laboratory work, Ramakrishnan developed the two new concrete mixes. Both new types of concrete use less cement, which according to Ramakrishnan, “improves the overall durability and other desirable properties of concrete.”

One of the new types of concrete will be used in the three major bridges that will be part of the Southeast Connector in Rapid City. One of the bridges, located close to Interstate 90, was completed last month. The second type provided deck material for two Sioux Falls bridges on Interstate 29.

“This optimised concrete will considerably increase the service life of the bridges and save millions of dollars in repair and maintenance costs,” Ramakrishnan said.

During the six to nine months after construction, Ramakrishnan and Dr. Anil Patnaik, assistant professor in the Department of Civil and Environmental Engineering, will thoroughly investigate and document any cracking in the new bridges. They will compare the data to bridges constructed with standard concrete.