Shrimp shells harnessed to strengthen cement

Reporting in Cement and Concrete Composites, a team of Washington State University and Pacific Northwest National Laboratory researchers created nanocrystals and nanofibres of chitin from waste shrimp shells to add to cement. As well as making the material stronger, the team found that the set time for the cement was delayed by over an hour, which is advantageous for long-distance transport and hot weather concrete work.

“The concrete industry is under pressure to reduce its carbon emissions from the production of cement,” said Somayeh Nassiri, an associate professor at the University of California, Davis, who led the research at WSU. “By developing these novel admixtures that enhance the strength of concrete, we can help reduce the amount of required cement and lower the carbon emissions of concrete.”

Cement production comprises about 15 per cent of industrial energy consumption and about five per cent of total greenhouse gas emissions worldwide. High consumption of the material is also partly driven by the challenge of durability — concrete cracks easily and must be repaired or replaced often, Nassiri said in a statement.

According to WSU, the global fishing industry generates between six million and eight million pounds of seafood waste annually. Most of that waste is dumped into the sea, said Hui Li, research assistant professor in WSU’s Composite Materials and Engineering Center and a corresponding author on the paper.

“In the current world, dealing with climate change through the circular economy, we want to use waste materials as much as possible. One person’s waste is another person’s treasure,” he said. 

Crab, shrimp and lobster shells are made up of about 20–30 per cent chitin with much of the rest being calcium carbonate, another useful additive for cement. At the molecular scale chitin has an additional set of atoms - a functional group - that allows the researchers to control the charge on the surface of the molecules and how they behave in the cement slurry.

“Being able to control the charge on the surface is an important piece to controlling how they function in cement. We could do that quite simply on the chitin because of the carboxyl group that sits in the chitin polymer,” said WSU Regents Professor Michael Wolcott, a corresponding author on the paper.  

The success in strengthening the cement paste was due to how the particles are suspended within the cement slurry and how they interact with the cement particles. 

“The chitin nanoparticles repel individual cement particles enough so that it changes the hydration properties of the cement particle within the system,” he said.

As they added the processed nanocrystals of chitin to the cement, they were able to improve and target its properties, including its consistency, the setting time, strength and durability. They saw a 40 per cent increase in strength in how the concrete can bend and a 12 per cent improvement in the ability to compress it.

“Those are very significant numbers,” Wolcott said. “If you can reduce the amount that you use and get the same mechanical function or structural function and double its lifetime, then you’re able to significantly reduce the carbon emissions of the built environment.”

The researchers are now hoping to scale up the work to begin producing the additive at large scales. The research also needs to continue to achieve the same level of enhancements seen at the cement paste scale at the concrete scale.