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Bending the rules to create a better infrastructure for our environment

Sugarcane bagasse ash collection in Louisiana’s sugar mill
Sugarcane bagasse ash collection in Louisiana’s sugar mill(LSU)
Updated: Jan. 14, 2021 at 12:51 PM CST
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BATON ROUGE, La. (WAFB) - The use of concrete is firmly cemented in human history with structural uses going back to ancient times. A research team is taking that ancient material into the future by creating a bendable product that will last longer and prove better for the environment.

Yes, bendable. You read that right. It goes against everything you think you know about concrete and the way it performs. The cracks in your house, the potholes in the road - those are all things that could become a distant memory with what’s being developed today.

“The lack of deformation capacity causes it [concrete] to crack,” explains Gabriel A Arce Amador, research assistant professor in the Bert S. Turner Department of Construction Management at LSU. “Because of the cracking, water and other detrimental agents can penetrate into the structure causing early deterioration such as corrosion of the steel reinforcement inside the concrete structures.”

Our concrete cities are crumbling around us. In fact, the American Society of Civil Engineers completed a study in 2017 that ranked the country’s infrastructure at a D – just barely passing. The process of fixing all that crumbling infrastructure isn’t cheap. And it’s a cost that doesn’t just come with dollars and cents.

“The process [of making cement] releases significant amounts of CO2 in the environment. CO2 is a greenhouse gas and the scientific community agrees that this gas can cause harm, so there’s a lot of interest in the community to make concrete more sustainable.”

The part of the process that creates most of the CO2 is in the production of cement.

“Concrete itself is a very ecofriendly material,” explains Arce. “It’s a mixture of sand, gravel, and water. If you mix that together, it’s going be mud. When you add cement, that’s the product that acts as glue and binds it together to make the rock-like material.”

Cement is made by calcinating limestone with other materials such as clay, silica sand, and iron ore at roughly 2,700 °F. This is the step in the process that is producing the majority of all that CO2.

“One of the key aspects is to reduce the use of cement or completely replace cement.”

So that’s what Arce and his teammates are working to do. And they’ve made some significant progress.

L-R: Dr. Gabriel Arce, Principal Investigator;  Dr. Marwa Hassan Co-principal Investigator;...
L-R: Dr. Gabriel Arce, Principal Investigator; Dr. Marwa Hassan Co-principal Investigator; Sujata Subedi, PhD student conducting the research work; Dr. Michele Barbato (Professor at University of California Davis).(LSU)

“We’re replacing cement with geopolymers,” Arce said. “These geopolymer binders can be made with clays calcinated at relatively low temperatures, which produce significantly less CO2 emissions than Portland cement.”

But that is only one piece of the puzzle. Remember when you were teased with the idea of bendable concrete? Let’s go back to that topic.

Bendable concrete is not necessarily new. Its invention is credited to Victor Li, a professor of civil and environmental engineering at the University of Michigan. In the early 1990s, he created what is called Engineered Cementitous Composites (ECC), which, to me and you, means bendable concrete.

“He came up with the innovative theoretical background,” Arce explained. “The way to do it was not to make it not crack, but to use its cracking ability as an advantage.”

Rather than an unintended crack that occurs over time, Li sought to create a material that would crack on purpose.

“The idea is to control the cracking,” Arce noted. “Instead of one large crack, you design the material to distribute the damage in multiple hairline cracks. When you control the cracking mechanism, you produce a concrete that will crack a lot, yet in a controlled and predictable manner exhibiting solely microcracks.”

These small cracks make the material more flexible. Also, the material increases its load carrying capacity after cracking, improving its strength.

“Most of the time you will not be able to clearly see the cracks with your eyes unless you use a microscope.” Arce said. “This is good for durability purposes as it makes the material impervious.”

Sounds great, right? Well, hang on, there’s a catch.

“Bendable concrete uses more cement than traditional concrete,” Arce noted.

Although it may produce a greater environmental footprint, it is better for infrastructure projects. That’s why it’s important to create bendable concrete using a cleaner form of cement.

“This is an exciting area of research that will develop significantly in the coming years,” Arce said.

Arce’s team has found a way to create a more sustainable product that has environmental benefits.

“For quite a long time now, it’s been common practice to partially replace cement with coal fly ash.”

Coal ash is the residue that is created when coal is burned. This typically comes from power plants. Fly ash is a very fine, powdery material that comes from the burning of finely ground coal in a boiler.

According to the EPA, the powerplants will dispose of all this coal byproduct in landfills, discharge it in the waterways, or recycle it in concrete or wallboard.

“A former LSU professor [Dr. Michele Barbato] started working on using sugarcane bagasse ash as cement replacement in conventional concrete,” Arce said. “We partnered to work on it together. When we were experimenting, we had the idea to use sugarcane bagasse ash in bendable concrete.”

Bagasse ash is a by-product of the processing of the sugarcane.

“When you’re processing [sugarcane], you crush it, and you end up with these fibers. Then, they burn it, and they produce energy from the burning process,” Arce explained. “The result is this fine black powder, and this is the powder that we’re using to add into our bendable concrete.”

What was once destined for the landfill is now a viable component to improve the process of making bendable concrete.

“It’s replacing sand,” he noted. “Sand in conventional concrete isn’t a problem, but when you make bendable concrete, you use a special kind of sand with fine particle size called micro silica sand.”

That special sand is manufactured, so that drives up the cost. Replacing this expensive sand with the sugarcane bagasse ash could bring the price down, which would make it more viable in the commercial market.

Sugarcane is already a vital part of Louisiana’s economy. According to the American Sugar Cane League, the industry employs roughly 17,000 people, is produced in 22 parishes, and has a $2 billion economic impact.

“It would be a very positive thing for the economy. You’re using a product that’s a waste and now it has value,” Arce noted. “It could create several jobs and would allow Louisiana to have a more resilient infrastructure.”

Additionally, making it more cost efficient will make it more attractive for those infrastructure projects.

“We can make infrastructure last longer. It should be significantly longer,” he noted. “Pavements, for example, we can significantly reduce the thickness, which means you use less, so now the cost isn’t as much.”

So, in the next 5 to 10 years, you could have a choice when hiring someone to add a concrete slab to your home. You could use traditional concrete, which may crack after a few years, or you could spend a little more to get something that is good for the environment and will last twice as long, if not longer, without any visible cracks.

A second project has the potential for even greater benefits, but will take a bit longer before it comes to market.

“It’s geopolymer based bendable concrete,” Arce explained. “This will allow for the manufacture of cement-free concrete with exceptional mechanical properties.”

This project is a collaborative effort with a team from Texas A&M, being led by Professors Miladin Radovic and Svetlana Sukhishvili.

“This is something that will develop significantly in the years to come. There is still plenty to explore,” he said.

What we do know is that there are better ways to fix the cracks of our crumbling infrastructure, and we can do so in a way that will minimize harm to the environment.

“This is a very, very sustainable product,” Arce said. “The main product that causes pollution is the use of cement. If you remove it, then you have a product that is very environmentally friendly and sustainable.”

Sources used in this report

https://www.infrastructurereportcard.org/

https://www.theguardian.com/cities/2019/feb/25/concrete-the-most-destructive-material-on-earth#:~:text=Half%20of%20concrete’s%20CO2%20emissions,the%20world’s%20industrial%20water%20use.

https://www.cement.org/cement-concrete-applications/how-cement-is-made

https://www.cement.org/docs/default-source/ga-pdfs/cement-industry-by-state-2015/louisiana.pdf?sfvrsn=2&sfvrsn=2

https://www.epa.gov/coalash/coal-ash-basics

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