The less cement used, the better because cement manufacture is a significant source of carbon emissions.
We’ve seen researchers make cement stronger with unrecyclable glass and others with recycled tire waste. We have also seen cement made with food waste to help fight climate change. Pacific Northwest National Laboratory and Washington State University scientists are using a material derived from shrimp shell waste to make stronger cement.
In a recent study, the scientists—led by Assoc. Prof. Somayeh Nassiri—started by extracting a compound called chitin from shrimp shells that would have otherwise been thrown away.
The food industry generates six to eight million metric tons of shrimp, crab, and lobster shell waste every year. Depending on the region, those claws and legs largely get dumped back into the ocean or landfills. However, these shells are not garbage! Instead, they are a rich source of chitin and chitosan – both are biodegradable materials with possible applications in eco-friendly food packaging and beyond.
Chitin, a natural biopolymer, is found in crustacean shells and is the second-most common biopolymer in the world (behind cellulose). Chitin (and chitosan) offers many of plastic’s desirable properties minus its destructive quality; it takes only weeks or months to biodegrade, rather than centuries. It has recently been utilized to create compostable food wrap, gardening pots, nanoparticles that kill mosquitoes, and an antibacterial covering, among other things.
In their most recent investigation, the scientists obtained chitin nanocrystals and nanofibers, each of which was only a thousandth as wide as a human hair. These were added to regular cement paste at a weight percentage of 0.05, and the resulting hardened cement was up to 40% more flexible when bent and 12% more compressible.
Additionally, it took a little longer to set than conventional cement—about an hour longer. This characteristic is desired in some circumstances, such as when delivering wet, premixed concrete over great distances to construction sites. The longer setting time is likely caused by the chitin fibers and crystals’ ability to reject individual cement particles, which alters the cement’s hydration characteristics.
However, more research is still required, and the team is particularly interested in how the cement impacts the performance of the concrete in which it is employed. In the end, it is believed that by making cement stronger, less cement will need to be used, lowering the carbon footprint of the construction sector.
The study was published on June 9, 2022, in the journal Cement and Concrete Composites.