Scientists are developing ‘green’ alternatives to cement
Concrete is the second most used material in the world. We need it to support decks, buildings, patios, stairs, counters, etc., and its use has increased and tripled over the past forty years.
The essential building material includes water, coarse aggregates, such as sand and gravel, and a binding agent – where cement, a particularly carbon-heavy product, comes into play.
According to the International Energy Agency, the cement sector is the third largest consumer of industrial energy in the world, consuming 7% of industrial energy consumption. It is also the second largest industrial emitter of carbon dioxide, responsible for 7% of global emissions. Most emissions occur when raw materials, typically clay and limestone, are heated to over 2500 degrees Fahrenheit to become the super strong binder. Approximately 600 kilograms of carbon dioxide are released per tonne of cement produced.
But sustainable, “green” cement is becoming increasingly popular, especially given the environmental footprint of traditional cement. A recent example came out of the University of Tokyo last year, when researchers Kota Machida and Yuya Sakai made cement from food scraps. Food waste has been used as a filler in alternatives to cement before, but Machida and Sakai have developed the world’s first process for cement made entirely from food waste.
The duo spent months mixing food scraps with plastic to make the materials stick together. Finally, they found the right combination of temperature and pressure to make cement from food waste alone without additives. Using a “hot pressing” strategy typically used to make building materials from wood powder, they mixed the food waste powder with water and pressed it into a mold heated to 350 degrees Fahrenheit. The researchers say that the tensile or flexural strength of cement is more than three times that of ordinary concrete.
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“The hardest part was that each type of food waste requires different temperatures and pressure levels,” Sakai said in a press release. They used tea leaves, orange and onion peels, coffee grounds, Chinese cabbage and even leftover lunch boxes.
“Our ultimate hope is that this cement will replace plastic and cement products, which have worse environmental impacts,” Machida said in an interview with the AP earlier this month.
Engineers and researchers have been developing innovations for years to reduce the carbon footprint of cement and concrete. In 2021, scientists at the University of Tokyo created a process for making concrete that reuses old concrete products (which can often be thrown away), heats the materials to lower temperatures, and captures carbon dioxide from the ‘atmosphere.
In 2019, researchers from the Taipei National University of Technology in Taiwan and the Department of Water Resources in India found that natural wastes from agriculture and aquaculture can partly replace coarse materials and binders. green concrete. There are many other alternatives, and while these innovations are early in development, they bring building materials closer to carbon reduction goals.
But when it comes to scaling up food waste cement for use in buildings, Sohan Mone, a structural design engineer at multinational infrastructure company Ferrovial, says it could be difficult to convince companies to make the exchange.
“To completely change the way we use cement would require a lot of fundamental changes in our industry,” Mone says. “All the infrastructure is adapted to how cement works today, from how we install it to how we transport it, everything.”
That’s not to say it couldn’t be done or isn’t worth it, Mone adds. But one type of technology will not solve all the problems of the building industry.
One of Mone’s concerns is that cement workers and construction companies need to make sure everything is up to performance and safety standards. Most major infrastructure projects use concrete, which uses rebar – steel – to reinforce the cement. Cement alone, without additional structural support, acts like porcelain. Ceramic objects like sinks and toilets can withstand compression loads, but ceramic is not as strong as concrete.
“The second you apply a shearing force, like any tension or bending, [cement used on its own] breaks,” Mone says. “It’s not good for taking blood pressure.”
So using food grade cement or cement alternatives in concrete for more complex and demanding construction purposes would require significant safety and durability testing, Mone says. And the organizations that regulate the industry and the entrepreneurs themselves should be convinced of its viability.
“We’re heavily regulated, and rightly so, and we’re not very free as to what materials we can use,” Mone said. “The life cycle of these structures can last hundreds of years, and it’s an open question as to how some of these things work when exposed to the environment over time. There is always this fear of not knowing how something new will react. And the concrete itself needs a lot of maintenance.
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Green materials can also be expensive, which Mone says adds to the difficulty of convincing companies to use them. In large construction projects, it is more common to see developers choose the most economical plan. But switching to green cement could be worth it, especially when concrete use increases as developing countries ramp up construction projects and other countries update aging infrastructure.
Global cement production could increase by 23% by 2050, the Mission Possible partnership said in its concrete climate action plan. Just as cement and concrete shape our built environment, their impacts also shape our climate future.
The cement industry will have to reduce its annual emissions by at least 16% by 2030 to meet the standards of the Paris Agreement on climate change. And because cement and concrete will be crucial for future development, the researchers say making the material inputs of cement will be one of the fastest ways to reduce emissions and environmental impact.
“Given the urgency of the challenge and the time it has historically taken for technology systems to evolve, considerable effort will be required to get the next generation of low-carbon cements out of the lab and onto the market. Not all will succeed, but those that do could have significant decarbonization potential,” wrote Chatham House, a policy institute, in its 2018 report Making Concrete Change: Innovation in Low-carbon Cement and Concrete.
The growth of cities and the repair of infrastructure are certainly not slowing down anytime soon. But, with new developments in greener building materials, the carbon impact of revitalizing the built environment doesn’t have to be so heavy.