This 3D-printed, carbon-absorbing bridge is inspired by bones

By Rebecca Cairns, CNN

(CNN) — Affordable, versatile, incredibly strong and locally available, concrete is the world’s most used manmade material.

But it also has a huge carbon footprint, accounting for around 8% of global greenhouse emissions.

The concrete and cement sector has been trying to reduce its environmental impact for years through sustainable concrete mixtures or efficient designs.

Now, a research team at the University of Pennsylvania has combined both novel materials and a material-saving design, without compromising on strength and durability.

The project, called Diamanti, takes inspiration from nature and uses a robotic 3D printer to create complex, lattice-like patterns with a sustainable concrete mixture.

While most regular concrete absorbs carbon dioxide (up to 30% of its production emissions over its entire life cycle, according to some research), Diamanti’s enhanced concrete mixture absorbs 142% more carbon dioxide than conventional concrete mixes.

Its first design, a pedestrian bridge, uses 60% less material while retaining mechanical strength, says Masoud Akbarzadeh, an associate professor of architecture at the University of Pennsylvania and director of the lab that spearheaded the project.

“Through millions of years of evolution, nature has learned that you don’t need material everywhere,” says Akbarzadeh. “If you take a cross section of a bone, you realize that bone is quite porous, but there are certain patterns within which the load (or weight) is transferred.”

By mimicking the structures in certain porous bones — known as triply periodic minimal surface (TPMS) structures — Diamanti also increased the surface area of the bridge, increasing the concrete mixture’s carbon absorption potential by another 30%.

“The surface area, together with this material property, maximizes the reaction with carbon at the microscopic level,” says Akbarzadeh. “That contributes a lot to both (carbon dioxide) reduction and absorption.”

The project, launched in 2022 in collaboration with Swiss-headquartered chemical company Sika and with grants from the US Department of Energy, is now gearing up to build its first full-size prototype in France.

Concrete changes

Concrete’s strength, durability and safety, like fire resistance, “are fundamental to why it is used at the scale that it is globally,” says Andrew Minson, director of concrete and sustainable construction at the Global Cement and Concrete Association.

The cement industry has made significant efforts to improve sustainability, reducing its carbon emissions by 25% per metric ton between 1990 and 2023. However, the sector’s emissions are higher today than in 2015 due to increased demand, according to the International Energy Agency (IEA).

Most of its emissions — around 90% — come from cement, says Du Hongjian, a senior civil engineering lecturer at the National University of Singapore, who is not involved with the Diamanti project.

Cement is a binding agent that hardens when mixed with water, and is used in construction materials, including concrete, where it holds together aggregates like sand and stone.

The energy-intensive process to make cement involves breaking down limestone at temperatures up to 2,000 degrees Celsius (3,632 Fahrenheit) in a kiln, which generates carbon emissions. Additionally, limestone is a calcium carbonate that releases carbon dioxide at high temperatures, accounting for the bulk of cement emissions, says Hongjian.

Switching out some cement for other materials can help reduce its carbon footprint, and several companies and organizations are exploring more absorbent concrete mixes: Japan’s CO2-SUICOM states its concrete mix is carbon negative, and UK-based Seratech is one of several companies incorporating the CO2-absorbing mineral olivine into cement to make it more sustainable.

Diamanti’s concrete mixture, developed by Dr. Shu Yang at the University of Pennsylvania’s Material Science Department, uses diatomaceous earth (DE), a naturally porous, silica-rich material made from fossilized algae, to replace some of the cement.

This biomineral creates “channels” in the concrete that allow carbon dioxide to penetrate below the surface, says Hongjian. However, DE had a global production of 2.6 million tons in 2023 — so while Hongjian believes the material has potential, “the supply chain must be considered for future wider adoption” if it is to meet the huge demands for concrete, he says.

Minson agrees that supply could be an issue, but that where the raw material is available, it could provide a “niche solution.”

“There’s no silver bullet. We need to be doing all the different actions that we can to manage material demands and reduce carbon,” Minson adds.

Another innovative aspect of the research is the increased surface area: concrete absorbs carbon dioxide, but “only the surface concrete, which is exposed to the air, has this access to CO2,” says Hongjian.

Diamanti’s innovative two-pronged approach provides the sector with solutions that could be used together, or separately, says Hongjian, adding: “Even without the material innovation, the higher surface itself allows higher CO2 absorption.”

Bridging the gap

Before using Diamanti in the real world, the team had to test it, by creating a bridge prototype.

The bridge is modular, and each block printed by using a robotic arm and then connected with a tensile cable. According to Akbarzadeh, 3D printing reduces construction time, material, and energy use by 25%, and its structural system reduces the need for steel by 80%, minimizing use of another emissions-heavy material. He added that using the technique with Diamanti’s concrete significantly cuts greenhouse gas emissions compared to regular construction techniques, and reduces construction costs by 25% to 30%.

First, the team built a five-meter-long prototype to demonstrate feasibility, before constructing a larger 10-meter version with material provided by Sika Group Switzerland for load testing, which it passed with flying colors, says Akbarzadeh: “It exceeded all our expectations.” The prototype is currently on display at the European Cultural Center in Venice for the Venice 2025 Architecture Biennial.

Akbarzadeh and the team published their findings in Wiley’s Advanced Functional Materials journal earlier this year, and had initially hoped to build the project’s first full-scale bridge in Venice.

But, after the city changed its regulations regarding new large-scale structures, the team started looking for other iconic waterways in Europe. Akbarzadeh partnered with digital design studio Fortes Vision to create conceptual digital renderings that visualize the bridge over the River Seine in the center of Paris.

In September, the project secured approval to construct its first bridge in France, although the location is still being decided. Akbarzadeh is excited to test their designs in the real world, where they will continue to closely monitor and evaluate the structure.

Beyond bridges, the team is also exploring other architectural applications, such as prefabricated floor systems. It’s not a one-stop solution, says Akbarzadeh, but he hopes that Diamanti can create “a whole new world of possibilities” for concrete.

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