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Concrete is the most used material in the construction industry and dates to the Roman Empire. Engineers at the University of Pittsburgh (Pitt, Pittsburgh, Pa., U.S.) are now re-imagining its design for the 21st century.

New research introduces metamaterial concrete for the development of smart civil infrastructure systems. The paper, "," presents a new concept for lightweight and mechanically tunable concrete systems that have integrated energy harvesting and sensing functionality.

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“Modern society has been using concrete in construction for hundreds of years,” says Amir Alavi, assistant professor of civil and environmental engineering at Pitt, who is the corresponding author on the study. “Our massive use of concrete in infrastructure highlights the need for developing a new generation of concrete materials that are more economical and environmentally sustainable yet offer advanced functionalities. We believe that we can achieve all of these goals by introducing a metamaterial paradigm into the development of construction materials.”

Alavi and his team have previously developed and explored their use in applications like . This new study introduces the use of metamaterials in the creation of concrete, making it possible for the material to be specifically designed and tailored in its attributes such as load-bearing capability, flexibility and shapeability. These can be fine-tuned in the creation of the material, enabling builders to use less material without sacrificing strength or durability.

“This project presents the first composite metamaterial concrete with super compressibility and energy harvesting capability,” said Alavi. “Such lightweight and mechanically tunable concrete systems can open a door to the use of concrete in various applications such as shock absorbing engineered materials at airports to help slow runaway planes or seismic isolation systems.”

The material is also capable of generating electricity — not enough to send power to the electrical grid, but more than enough to power roadside sensors. The electrical signals self-generated by the metamaterial concrete under mechanical excitations can also be used to perform structural health monitoring (SHM), measuring damage inside the concrete structure or to monitor loads and stresses during earthquakes.

Eventually, these smart structures may even power chips embedded inside roads to help self-driving cars navigate on highways when GPS signals are too weak, or when LIDAR is not working.

The material developed at Pitt comprises reinforced auxetic polymer lattices embedded in a conductive cement matrix. The composite structure induces contact-electrification between the layers when triggered mechanically. The conductive cement, which is enhanced with graphite powder, serves as the electrode in the system. Experimental studies show that the material can compress up to 15% under cyclic loading and produce 330 microwatts of power.

Alavi and his research team are partnering with the Pennsylvania Department of Transportation (PennDOT) through the at Pitt to develop this metamaterial concrete for use on Pennsylvania roads. The project also included researchers from Johns Hopkins University, New Mexico State University, the Georgia Institute of Technology and the Beijing Institute of Nanoenergy and Nanosystems.