Cement is the cornerstone of modern construction, and enhancing its durability and safety has become crucial. An innovation may lead to buildings that are stronger and safer.
Princeton University’s latest research has turned its attention to humble oysters and the iridescent composite material that glitters within oyster shells – nacre, for design inspiration.
Nacre is a hard and resilient shiny material on the surface of pearls. By mimicking the properties of nacre at a microscopic level, researchers have successfully increased the toughness of cement by about 17 times, making individual cement blocks pale in comparison.
Scientists have been seeking ways to make inherently fragile materials like concrete or ceramics stronger, safer, and more durable. This time, they have found inspiration from the sturdy outer shells of oysters.
One of the most famous features of these marine bivalve mollusks is the nacre contained in their inner shells – also known as “mother of pearl”. It is made up of tiny hexagonal “tiles” composed of aragonite (a common form of natural calcium carbonate) and held together by flexible biological polymers, acting as a natural adhesive.
Aragonite provides the hardness to nacre, while biological polymers offer elasticity, giving mother of pearl excellent flexibility and crack resistance. Scientists from Princeton University Department of Civil and Environmental Engineering were curious if these characteristics of soft-bodied marine creatures, evolved over millions of years, could provide similar advantages for human building materials. Their research findings were published in the journal “Advanced Functional Materials” on June 10.
“The perfect combination of hard and soft components is the key to the outstanding mechanical properties of nacre,” said Shashank Gupta, co-author of the study and a graduate student at Princeton University. “By making concrete resistant to crack propagation, we can make it tougher, safer, and more durable.”
To achieve this goal, Gupta’s team made three types of beam materials with multi-layered structures, alternating layers of cement slurry and thin polymer layers. The first beam was made by stacking these two materials, while the other two had variations. The first one designed hexagonal grooves in the cement slurry, and the second one cut out hexagonal plates in the cement. These three beams were compared with a reference beam made of pure cement slurry (without polymer layers or hexagonal design).
Experiments showed that the reference sample’s beam was brittle and lacked ductility, but all three new types of beams exhibited significantly enhanced ductility and toughness. The most remarkable was the multi-layer beam with hexagonal plate design similar to mother of pearl. By mimicking the mechanical properties of microscopic nacre, this beam showed a 17-fold increase in toughness, a 19-fold increase in ductility, while maintaining a strength comparable to the reference sample.
“Our bio-inspired strategy is not just about mimicking the microstructure in nature, but learning from the principles behind it and applying these principles to the engineering design of artificial materials. The key to the strength of mother of pearl shells lies in the nano-scale layer sliding,” said co-author Reza Moini in a press release. “In other words, intentionally designing defects in brittle materials to enhance their strength.”
Stronger and safer cement is not only beneficial to the construction industry but is also crucial for the health of the planet, considering cement production accounts for about 8% of global greenhouse gas emissions. However, despite the promising research results inspired by mother of pearl, the multi-layer hexagonal plate technology needs further refinement before construction companies start abandoning traditional mortar in favor of using this new material.