Cut climate impact on masonry with moss bricks

cCement—the primary bonding ingredient in concrete, brick, and mortar—is a climate nightmare. To make it, you heat limestone and clay to extremely high temperatures using carbon-polluting fossil fuels. This leads to a chemical process that also releases massive amounts of carbon dioxide into the atmosphere. This process is carbon intensive and cement is used so widely that it accounts for about 8% of global carbon dioxide emissions. With the world’s construction stock expected to double by 2060, climate advocates are in dire need of alternative materials to bring them to market quickly.

A factory in Longmont, Colorado, may have the answer. By the end of this year, it will start producing concrete bricks made not of cement – but of sphagnum moss. Prometheus Materials, formed in 2021 from a research project at the University of Colorado, takes microalgae normally found in lakes or ponds and grows them in bioreactors. They add air, so the algae can feed on the carbon dioxide they contain, as well as seawater and light from LED lights. This allows the algae to produce a cement-like substance that is able to bind sand and gravel or stone together to make concrete. The method mimics the natural process by which organisms form hard corals and seashells.

Moss bricks are set to be commercially available in 2023. They were designed in partnership with and partly funded by American architecture firm Skidmore, Owings & Merrill (SOM) – best known for creating the Burj Khalifa in Dubai and New York. One World Trade Center.

The brick industry currently produces a tenth of the CO2 of conventional concrete block production, according to Prometheus Materials CEO Lauren Burnett. When the company finishes installing the solar panels to power its plant, that process will be carbon-neutral, and will be carbon-negative within three years, according to Burnett. “There is practically no CO2 emissions during the process, and we are actually capturing the CO2,” he says. “Because algae absorb it through photosynthesis, and then we include it in our building materials.”

Prometheus’ production schedule puts it near the forefront of a movement to replace traditional carbon-intensive building materials, such as steel and concrete, with materials derived from plants and other living things. The so-called “bio” sector is still in its infancy. But proponents say it has the potential to transform the construction industry from one of the world’s largest emitters – responsible for 11% of carbon dioxide emissions – to a carbon sink. That is, from the climate villain, to part of the solution.

A new era of plant-based buildings

Using nature in construction is nothing new. People have been taking plants and organic matter growing around them and turning them into structures for thousands of years. From South Africa to England to Afghanistan, straw has long been mixed with soil and water to make bread. Fast-growing, sturdy bamboo is a staple of much of traditional East Asian architecture. Timbers have retained their historical popularity in many countries, with 90% of new homes in the United States still made of wood frames. Over the past few decades, environmental activists have pushed for these carbon-absorbing materials to become the standard in homes and small-scale construction.

Traditional houses on stilts made of bamboo in Ban Muangkeo, a cultural heritage village on the Mekong River in Laos.
Wolfgang Kaehler – LightRocket / Getty Images

But it has proven difficult to build on a large scale using natural materials (although a few notable wooden skyscrapers have appeared in some cities). Therefore, scientists are working to develop a new generation of organic-derived materials that are strong and versatile enough to replace carbon-intensive steel and concrete. To spur these efforts, the US Department of Energy announced in June that it was awarding $39 million to 18 projects working on “technologies that can transform buildings into net-carbon storage structures.” The University of Colorado team behind the moss bricks is one of the recipients. Another benefactor is working on a fungus-based insulating material that can be used to retrofit homes. A third want to add microbes to wood to create a “living” material “as strong as steel”.

Read more: Homes made of straw or mold can now get a cheaper mortgage in the Netherlands

Only a few new bio-based materials have already been brought to market: bioMason, a Durham, North Carolina-based company that feeds bacteria with calcium and carbon dioxide to generate biocement, currently sells tiles in the US and Europe. Meanwhile, Dutch biotech company Basilisk sells concrete that contains limestone-producing bacteria, as well as a mixture that can be applied to existing buildings, allowing the concrete to self-recover from cracks, reducing the need for unnecessary demolition and rebuilding.

Most companies developing biomaterials face the same challenges as other climate-friendly technologies: They still struggle to scale lab successes to a commercial scale, at costs that can rival carbon-polluting alternatives. Some also need to know how to obtain large amounts of selected organic materials without competing for land with the agricultural industry, nature restoration projects, and renewable energy.

What does it take for moss bricks to become mainstream?

But Brant Coletta, a partner at SOM, who worked with Prometheus to design the bricks, claims that the technology’s “easy scalability” was the architecture firm’s main attraction. Initially, Prometheus will grow its algae — which can double in size every four to six hours — in its Colorado factory, produce its cement-like substance, turn it into bricks, and ship it to customers. Within 18 months, they will begin shipping a lightweight, dried version of the biocement, which customers can turn into briquettes — without expensive equipment or highly trained personnel.

Prometheus feeds microalgae with seawater, carbon dioxide and light to produce a cement-like substance
Brooks Freehill

To convince Coletta of this last point, one of the founders of Prometheus sent him some bricks in the mail with pictures of his young children making them in their backyard. “The quality control may not have been the strongest on this, but it shows how this product can find its way into the global market,” Coletta says.

Prometheus’ moss brick safety certification, by the American Society for Testing and Materials, must be completed by the end of the year, along with building the manufacturing plant, according to Burnett. He says the factory will immediately begin producing “tens of thousands” of bricks and soon reach a “significant” amount – although he has not disclosed expected quantities, citing commercial reasons. Burnett also declined to share the final price of the bricks before production began and the company could ascertain its costs. “Our goal is to have no green premium associated with our blocks,” he says.

Even if the cost of bricks proves to be comparable to traditional concrete blocks, it may take architects and developers a few years to be confident that they “will do their job and have little or no cost impact on projects,” Coletta says. There is not a lot of data on the prevalence of organic derived materials in the construction industry. Even in the Netherlands, which has emerged as a hub for sustainable building practices in recent years, experts say about 3% of the materials used are biological.

But SOM, which positions itself as a leader in green architecture and is keen to provide customers with low-carbon options, will add the bricks to its list of materials once safety certification is complete. “We’ve had clients come in and see us working on this and say they want it in their project right away,” Coletta says. “It’s hard for me to hold back my design teams.”

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write to Ciara Nugent at [email protected]

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