According to some cement manufacturers, making a kilogram of cement can produce almost another kilogram of carbon dioxide. 

Ange Therese Akono, an assistant professor at Northwestern University, considered doing something about that carbon emission – by stuffing more carbon into the concrete.

Making that mark

In a field defined by men, where research is usually a white preserve, Akono stands out. Originally from Cameroon in Africa, she did her bachelor’s in engineering from the highly selective Ecole Polytechnique in France and her Ph.D. from MIT.

“During my undergraduate studies, there were 20 percent female students in the engineering school,” she told Truly Curious. “I am glad to see that the fraction … has now increased to 30%. My hope is to further increase the representation of female scientists in nanotechnology.”

Indeed, nanotechnology is what the team used to increase cement strength. Many hoped that reducing the material needed could potentially reduce carbon emissions.

“Manufacturing is the primary reason for cement’s large carbon footprint,” Akono said. “The raw materials that you have to heat to yield a reactive phase — that is, cement — will release a significant amount of methane, and consume energy. The second aspect is the large amount of cement consumed worldwide annually.”

Nanotech to the rescue

The accepted way of testing cement strength involving dropping beams, an arduous process. Akono relies on scratch testing, which she developed as part of her graduate thesis at MIT. A series of pencils of increasing hardness produces a scratch, thus defining the limits of hardness. Among other things, the team has used that test to gauge bone hardness.

The next problem involved carbon-based nanomaterials. The electrical properties tend to make them clump. Traditionally, ultrasonic energy is used to agitate the solution to separate clumps and use a pore-forming agent (which makes the cement durable).

The Akono lab team reduced clumping by using ultrasonic sound to shake and separate the nanomaterials in water, then mixing it with cement at ultra-high speeds. By adding cement grains that can break up more clumps, stirring the mix for 24 hours during curing, and shaking it to remove large air bubbles.

If this effort to ultimately reduce concrete production seems too much, consider that 16 billion tons of concrete and cement are produced per year, accounting for 8 percent of carbon dioxide production.

Throttling carbon emission

“This number is on the rise because the world population is growing exponentially,” Akono said. “Moreover, most of this population is concentrated in cities. For instance, the United Nations predicts that by 2050, two-thirds of the world will be concentrated in cities. This absolute urbanization, coupled with population growth, leads to a significant release of greenhouse gasses. My analysis is conservative, as I am just focusing on concrete synthesis. I am not taking into account the amount of greenhouse gas released throughout the lifetime of the structure.” She adds, “If you have a material that is even 30 times stronger, then you’re significantly cutting down on the volume of cement.” “Not only do you cut down on cement consumption, you also increase the durability because the new cement will better resist harsh weather.”

Another concern is that cement’s raw material is also finite.

“In 30 years, going to the beach may become a privilege, because we may have used all the sand,” she pointed out. Reducing the amount of sand used could also help.

The way ahead

Akono is also studying whether old, recycled concrete can replace sand. That can reduce pressure on landfills and create new employment opportunities.

The team used one of four possible options for carbon nanoparticles: tiny fibers, multiwalled and spiral nanotubes, and graphene nanoplatelets. They all seemed to ensure better fracture toughness than standard cement.

Akron admits that, while potentially a great idea, “we are definitely at the level of laboratory testing. The next step is scaling it up to the structural level. We observed a significant increase of up to 30 percent for the resistance to cracking and up to 30 percent% for the strength. Finally, the water penetration resistance increased by up to 75 percent.” The last was a result of all that high-speed shaking during production.

Like anyone who understands how research works, Akron expresses both caution and cautious optimism.

“We are not there yet,” she said. “There is still a lot of testing to do, and a lot to do to re frame the current industry and create new ways of using cement. However, slowly but surely, we are moving toward green production of cement.”

Marileen Van Horne is doing her Ph.D. in child and family studies.

Click here for the original research article.

This feature first appeared in Truly Curious

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