Steel is the world’s most recycled material. Its unique magnetic properties make it an easy material to recover from the waste stream, while its properties remain unchanged no matter how many times it is recycled.

Despite this, questions still remain whether structural steel can be safely reused in buildings and, if so, under what conditions.

The National Science Foundation’s Environmental Sustainability Program has given a team of researchers and engineers at the University of Delaware in the United States a three-year, $300,000 grant to answer these questions and establish guidelines for how and where structural steel members can be reused rather than recycled.

Although there isn’t a single convenient figure to answer the question “how much energy does it take to make steel,” because the answer depends on the exact combination of processes involved, the process of melting and reforming steel members is still an energy-intensive process with a sizeable carbon footprint. Eliminating the need for this and reusing steel members would have clear environmental advantages.

Structural Steel

Structural steel

“We hope to cultivate a cultural shift in how buildings are designed, constructed, deconstructed, and repurposed in order to have a more thoughtful regard for energy and natural resource consumption,” said Jennifer McConnell, associate professor at the University of Delaware’s Department of Civil and Environmental Engineering.

The researchers plan to generate evidence as to whether the structural integrity of structural steel members at the end of their service life would be acceptable for reuse applications.

“The reuse of structural steel is currently exceedingly rare, and reusing primary structural steel members as primary structural members is even less common,” McConnell said. “Our goal is to show that reuse of structural steel is generally acceptable, or at least to identify specific conditions in which reuse of structural steel is appropriate.”

The team includes Thomas Schumacher, assistant professor of civil and environmental engineering, and Erik Thostenson, assistant professor of mechanical engineering.

Thostenson pioneered the concept of carbon nanotube-based sensing skins for detecting deformation and damage in fibre-reinforced composites. He has examined many aspects of carbon nanotube-based sensing under a variety of loading conditions.

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His research introduced the concept of a composite layer bonded to concrete structures, which is capable of providing distributed sensing capabilities. Distributed sensing allows for increased detectability of forming or growing damage that cannot necessarily be captured with conventional point-type sensors such as strain gauges or accelerometers. Once developed, this sensing skin may be able to give real-time feedback on changes in strain, temperature effects, and formation and propagation of damage.

The research team will transfer this knowledge and expertise to investigate the use of smart sensing skins for monitoring construction-induced stresses in buildings.

“This research project provides an excellent opportunity to educate our students about sustainability issues in civil engineering,” says Schumacher, who teaches Sustainability Principles in Civil Engineering and whose research focuses on the development of novel sensing methodologies for non-destructive testing and structural health monitoring.

“The key to sustainability is to first reduce, then reuse, and as a last resort recycle.”