Of the major carbon producers, aviation often gets the most attention. But underneath the soaring aircraft are the buildings, driveways, bridges, dams and sometimes roads that are made from an even bigger offender: concrete.

The building material accounts for at least 8 percent of the world’s total CO2 emissions. The aviation industry produces about 2.5 percent, although estimates vary.

Most of the concrete emissions are produced when limestone (calcium carbonate) is heated with clay to about 1,400 degrees C in a kiln to make cement, a key ingredient. The heating process fuses the calcium carbonates into calcium silicates, or as they’re known in the industry, clinker.

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Storing carbon in concrete

A better way to sequester carbon may be as close as your sidewalk. Read more›››

Two companies, Heirloom Carbon Technologies and CarbonCure, in early 2023 tested a process to inject recovered CO2 into freshly poured concrete. It was a small test, using only about 37 kilograms of carbon, but the process shows promise that, if scaled up, it could help the concrete industry reduce its footprint, they say.

“In the broader carbon-removal ecosystem, this is meaningful,” Anu Khan, of the environmental group Carbon180, tells the Washington Post. Finding a way to permanently store carbon is a major bottleneck, she says.‹‹‹ Read less

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Timber might be the new concrete

In the race for more sustainable building materials, wood is making a comeback. Read more›››

Of course, it isn’t old-style timber. Mass timber – engineered wood products created from layers of wood bound together – is being increasingly seen as a more environmentally friendly alternative to steel and concrete.

Proponents of the technology point to its aesthetics, structural strength and ease of construction. There’s also a lighter carbon footprint.

“The amount of energy to produce mass timber is a fraction of what it would be to produce the same materials in steel or concrete,” Antony Wood, director of Tall Buildings and Vertical Urbanism at the Illinois Institute of Technology and president of the Council on Tall Buildings and Urban Habitat, tells BBC.com.

And there’s another benefit. “While it’s producing itself, it’s sequestering carbon out of the atmosphere.”‹‹‹ Read less

Clinker is the binding agent that gives concrete its structural properties. But the process also produces CO2. And a lot of it. About 650 to 900 kilograms of carbon dioxide are produced and released into the atmosphere for every ton of cement in this process.

According to the International Energy Agency, cement production increased about 1.5 percent a year from 2015 to 2021, with demand expected to only increase worldwide. But for net-zero goals to stay on track, the agency says, the industry needs to see 3 percent annual declines by 2030.

An Innovative Material

Strategies for reducing those emissions include improving energy efficiency; using lower-carbon fuels; making the process more efficient so less scrap is produced; and switching to construction techniques such as pre-cast modules that reduce concrete use.

Another strategy: using innovative materials to make a better concrete.

One innovative material that is showing promise in the concrete industry is graphene, a single layer of carbon atoms that form a hexagonal lattice. Graphene is light, flexible, tough and has high resistance. It’s 200 times stronger than steel and five times lighter than aluminum.

And it passes many of those properties along when added to concrete, also reducing the amount of CO2-producing clinker needed without diminishing performance.

A team from the UK’s Exeter University in a 2018 paper found that such nanoengineered concrete showed “an unprecedented range of enhanced properties when compared to standard concrete. These include an increase of up to 146 percent in the compressive and 79.5 percent in the flexural strength.”

The researchers also reported a decrease in water permeability by 400 percent, suggesting that the composite material might be ideal for structures in areas subject to flooding.

And there was more.

“Including graphene we can reduce the amount of materials required to make concrete by around 50 percent – leading to a significant reduction of 446kg/ton of the carbon emissions,” co-author Monica Craciun said in 2018.

More recently, a team of researchers from French and Polish universities in 2021 concluded that integrating graphene-family materials into concrete could impart functions that might enable smart and multifunctional buildings. Used as a sensing material, graphene might help buildings monitor themselves for damage.

Overcoming obstacles

Although the Exeter team was bullish about the potential for graphene additives, it also encountered issues that made wide-scale implementation difficult. It found dispersing the material into the dry cement matrix expensive, complex and difficult to scale up.

First Graphene, a company that originated with support from the University of Adelaide in Australia, however, has been working to solve the issues identified by the 2018 research.

“We are advancing commercial-scale trials into strengthening cement/concrete and reducing the CO2 emissions,” Michael Bell, First Graphene’s managing director and CEO, tells KUST Review.

These trials are expected to show how much clinker reduction can be expected. That, combined with increased strength that might lead to thinner cement slabs and panels, will give better information about how much CO2  reduction the material can provide.

First Graphene also collaborated with Australia’s Wollongong University and an Australian municipal water authority to investigate how using graphene-enhanced materials might prolong the life of wastewater pipes. They published their results in 2022.

“This was positive in showing graphene’s strength-increasing capability and also improved resistance to sulphate and chloride erosion,” Bell says.

Challenges in the Middle East

Khalifa University in Abu Dhabi, UAE, is also looking at ways to improve concrete performance with graphene, and the material shows promise under the GCC region’s severe conditions of humidity, temperature and salinity, says Hassan Arafat, the senior director of the university’s Research & Innovations Center for Graphene and 2D Materials.

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The Romans did it better

While modern concrete can crumble in 50 years or less, Roman concrete construction has stood for thousands of years in a variety of climates and seismic zones. Read more›››

Some examples still hold up in direct contact with corrosive seawater.

A team of researchers wanted to know why. The team, with members from the United States, Italy and Switzerland, took samples from Italian archaeological site Privernum. They found that white chunks called lime clasts, previously dismissed as evidence of sloppy mixing or poor construction materials, may give the material the ability to heal cracks.

The findings suggest that using quicklime – rather than or in addition to the slake lime commonly used today – combined with a high-temperature process called “hot mixing” creates the lime clasts and a more durable material.

To test their theories, the researchers made two samples of concrete: one with the Roman-style formula, the other from a modern recipe. Each sample was deliberately cracked. Two weeks later, water passed through the modern concrete but was stopped by the Roman variety.

The researchers theorize that the lime clasts dissolve into cracks when exposed to water, then recrystallize, preserving structures over time.

They also suggest that adapting the formula for modern construction could lead to more durable, resilient and sustainable builds that could help shrink the carbon footprint of concrete around the world.”‹‹‹ Read less

“Graphene is known to be highly hydrophobic, which means it repels water and is not easily affected by high-humidity environments,” Arafat tells KUST Review. “This property makes graphene a promising material for improving the durability of concrete in high-humidity environments. In fact, research has shown that graphene-enhanced concrete has increased resistance to water absorption, which can reduce the potential for corrosion of steel reinforcement in the concrete.”

Temperature is also a factor, as concrete poured on hot days can shrink and crack. Arafat cites studies in Construction and Building Materials (2019) and Composites Part B: Engineering (2020) that suggest graphene can improve concrete’s performance at high temperatures.

“Overall, the potential benefits of using graphene in concrete are vast and could have a significant impact on many different industries,” Arafat says. “As research in this field continues to develop, it will be interesting to see which industries will be the first to adopt this technology and benefit from its unique properties.”

Among the industries he sees potential for:

Aerospace: Graphene-enhanced concrete could be used to construct lightweight and durable structures for spacecraft, satellites and other aerospace applications.”

Energy: “This could lead to the development of more efficient and durable infrastructure that is better able to withstand harsh environmental conditions.”

Infrastructure: The use of graphene in concrete could improve the durability and lifespan of roads, bridges and tunnels, he says.

More research is needed, Arafat stresses. “There are still challenges that need to be addressed in using graphene as a concrete additive, such as the cost of production, the potential toxicity of graphene, and the need to optimize the amount of graphene used in the mix to achieve the desired performance. These aspects are dependent on the region and its local conditions and applied concrete mixes.

“Our research center is working to explore the full potential of these materials and develop new applications that could have a significant impact on our Emirati society and beyond,” he says.