New Concrete Less Dangerous During Earthquakes
Following the devastating earthquakes in Turkey this summer that killed as many as 20,000 people and injured another 27,000, images of survivors trapped beneath the rubble of collapsed buildings appeared daily in news reports worldwide.
Now a North Carolina State University engineer is developing a new type of concrete to help prevent such scenes from happening again. Because it's reinforced with mats made of thousands of stainless steel fibers injected with a special concrete slurry, the new material, called Slurry Infiltrated Mat Concrete (SIMCON), can sustain much higher stress loads and deformations than traditional concrete.
Tests show that concrete buildings or bridges reinforced with SIMCON are far more earthquake-resistant and less likely to break apart in large chunks that fall off and cause injury to people below.
"The high-performance concrete we are developing has a great potential to revolutionize the way concrete structures are built and used," says Dr. Neven Krstulovic-Opara, assistant professor of civil engineering. Because it's comparatively easy to use and economical, SIMCON can be used in new construction or to reinforce existing structures, he says.
If extreme stresses cause SIMCON to fail, its mass of fibers and concrete doesn't collapse in the same way traditional concrete does, Krstulovic-Opara says. Instead of large chunks breaking and falling from a structure, the material crumbles into small, harmless flakes.
This controlled form of failure is a key advantage of SIMCON, the NC State engineer says. Because failure is inevitable in all structures, engineers must design buildings and bridges to fail in the safest way.
In conventional concrete structures, this is achieved through the use of steel reinforcing bars -- rebars -- which give the concrete tensile strength it would otherwise lack. For safety and design reasons, the concrete is designed so that the rebars will fail before the concrete does. Unfortunately, many structures have not been designed to sustain the powerful stresses caused by earthquakes. When such extreme stresses occur, the concrete can crack, explode and break away from the rebars, causing the structure to collapse.
By contrast, failure of SIMCON would present little danger to people or property below.
Currently, Krsulovic-Opara is working with a team of NC State researchers to develop new structural systems that would best employ the advanced features of SIMCON -- high strength, durability, low cost and ease of construction. The project is funded by the National Science Foundation. NC State faculty taking part in the project include Dr. John Hanson, Distinguished University Professor of civil engineering, and Dr. Paul Zia, Distinguished University Professor Emeritus of civil engineering.
Contact: Dr. Neven Krstulovic-Opara, Jenny Weston