Concrete Solutions

By Matt Shipman 

People are always looking for ways to make something less expensive, longer lasting or more environmentally friendly – and a team of researchers at NC State is figuring out how to do all of those things at once for some of the largest, most common buildings found anywhere: parking garages.

These advances are important, because parking garages seem to be everywhere. Whenever a new shopping center, office or apartment building is built, you can bet a new garage is being built too. And now those buildings can be made for less money and will last longer.

Dr. Sami Rizkalla explains how carbon fiber could take the place of steel in concrete beams. Rizkalla tests his ideas to the limit in the Constructed Facilities Lab.

For example, the researchers have figured out a way to use 30 percent less steel in the manufacture of the concrete beams, or spandrels, used in the construction of parking garages. Steel is incorporated into the spandrels for reinforcement purposes, but the new design curtails the use of steel without sacrificing safety. Dr. Sami Rizkalla, one of the leaders of the research team, says the new spandrel design, "simplifies construction for precast concrete producers." In addition to using less steel, the new design cuts labor and manufacturing time in half, significantly decreasing costs.

The researchers not only come up with new designs, but test them in NC State's Constructed Facilities Lab (CFL),  applying enormous forces on experimental structures to see if the designs can function in the real world. Greg Lucier, the CFL manager and a doctoral student at NC State, says tests at the lab show that the new design guidelines include a significant margin for safety. For example, Lucier says the spandrels could handle two to three times the maximum weight they would be expected to bear.

At the same time, Rizkalla says, his research team is also studying ways to remove steel entirely from precast concrete structures by replacing it with advanced composite materials. Using composites, such as carbon fiber, in place of traditional steel can give parking structures a much longer service life. Lucier explains that the steel reinforcement can actually become the most vulnerable part of a concrete beam over time as it is exposed to water and begins to rust. Thus, designs that rely on advanced composite materials in place of steel could last longer because composites are not susceptible to corrosion.

The success of the research program is drawing interest from the concrete industry, with individual companies coming to NC State to get input on how to improve their products and manufacturing processes. Some are even looking to collaborate on research and development projects.

The researchers will be presenting an overview of their new designs that minimize the use of steel at the spring convention of the American Concrete Institute in San Antonio this March.

Link:

• Constructed Facilities Lab