Engineers Discovered the Spectacular Secret to Making 17x Stronger Cement
While the modern world is build with cement, its creation is one of the biggest emitters of greenhouse gasses. As a result, finding ways improve its durability and safety is paramount.
In a new study from Princeton University, scientists turned toward the humble oyster and its iridescent composite material nacre for design inspiration.
Matching the characteristics of nacre at the microscopic level, the researchers were able to increase the toughness of cement some 17 times, as compared to a cement block on its own.
Scientists are always looking for ways to make inherently brittle materials, such as concrete or ceramic, tougher, safer, and more durable. This time, they found inspiration from one of the most unlikely of places—the extra-durable shells of oysters.
Once again, mother nature provides.
One of the most well-known attributes of these saltwater bivalve mollusks is the iridescent composite material nacre—also known as “mother of pearl”—that lines the animal’s inner shell layer. Although this material has long been featured in jewelry shops around the world, nacre is also an architectural wonder. It contains microscopic hexagonal “tablets” made of aragonite (one of the most common, naturally occurring forms of calcium carbonate) held together by soft biopolymer, kind of like an organic glue.
With the aragonite providing strength and the biopolymer providing flexibility, nacre is incredibly flexible and crack resistant—so much so that scientists from Princeton University’s Department of Civil and Environmental Engineering wondered if this mollusk maneuver honed by half a billion years of evolution could imbue similar benefits to human building materials. The results of their study were published earlier this month in the journal Advanced Functional Materials.
“This synergy between the hard and soft components is crucial to nacre’s remarkable mechanical properties,” Shashank Gupta, a co-author of the study and graduate student at Princeton, said in a press statement. “If we can engineer concrete to resist crack propagation, we can make it tougher, safer and more durable.”
To achieve this lofty goal, Gupta’s team crafted three types of multi-layered beams of material that alternated between cement paste sheets and a thin polymer layer. The first beam was made of these two ingredients stacked on top of one another, but the other two beams were slightly different. The first featured hexagonal grooves in the cement paste, while the second cut through the cement completely, forming hexagonal-shaped plates or “tablets.” All three beams were compared to a cast cement paste reference beam (i.e. no polymer layers or hexagonal markings at all).
The resulting experiments proved that, while the reference beam was brittle with no ductility, all three beams showed significantly increased ductility and toughness. However, according to the researchers, it was the multi-layered beam featuring those nacre-like hexagonal plates that was the most remarkable. By matching the mechanics of microscopic nacre, the beam delivered 17 times greater toughness and 19 times more ductility than the cast cement—all while maintaining as much strength as the reference beam.
“Our bio-inspired approach is not to simply mimic nature’s microstructure but to learn from the underlying principles and use that to inform the engineering of human-made materials. One of the key mechanisms that makes a nacreous shell tough is the sliding of the tablet at the nanometer level,” Reza Moini, a coauthor of the study, said in a press statement. “In other words, we intentionally engineer defects in the brittle materials as a way to make them stronger by design.”
Stronger and safer cement wouldn’t just be a boon for construction, but also the health of the planet, as the production of cement makes up roughly 8 percent of global greenhouse gas emissions. But while the study shows promising results for these nacre-inspired materials, this multi-layered, hexagonal-plated technique will need a bit more tweaking before construction companies start trading out mortar for mollusks.
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