When a 12-story condominium building suddenly collapsed last June in Surfside, Florida, one reason was was hiding deep inside the structure. Within its concrete foundation, walls, and floors was a critical but risk-prone building material: steel reinforcing bar. In the aftermath of the collapse, investigators found this material to have extensive corrosion—enough to cause the massive building to simply fall apart.

Steel reinforcing bar, or rebar, is a key part of the way buildings like that condo tower are built, and it is critical to their structural integrity. But steel rebar is also susceptible to the moisture that can wind its way through concrete, causing largely invisible corrosion that can lead to structures collapsing almost without warning.

A team of researchers at Rensselaer Polytechnic Institute (RPI) has an alternative. Instead of using steel to reinforce concrete, they’ve developed a composite reinforcing material made of surprisingly strong hemp fiber. Their hemp-based rebar uses the hearty fibers of the hemp stalk in combination with a resin or bioplastic to form bars that can safely replace steel rebar in concrete construction.

“There are some natural fibers that have a similar strength to steel for the same weight,” says Alexandros Tsamis, a professor of architecture at RPI. Synthetic materials like carbon fiber and fiberglass have such strengths, and so does hemp. When combined with plant-based bioplastic, hemp rebar could be an all-natural alternative to steel rebar. “Instead of extracting it from the earth, you grow it,” Tsamis says.

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