Inspired by the natural strength and resilience of oyster and abalone shells, engineers at Princeton University have developed a new cement composite that is significantly more crack-resistant and ductile than traditional cement. The research team, led by Assistant Professor Reza Moini, alternated layers of tabulated cement paste with thin polymer to create a material that is 17 times more crack-resistant and 19 times more able to stretch and deform without breaking. This innovative composite could potentially enhance the crack resistance and durability of various brittle ceramic materials, including concrete and porcelain.
The team drew inspiration from nacre, or mother of pearl, found inside shells, to develop the composite material. Nacre consists of hexagonal tablets of aragonite mineral bonded together by a soft biopolymer, contributing to its strength and flexibility. The aragonite tablets slide under stress, allowing nacre to dissipate energy and endure mechanical stress while maintaining structural integrity. By mimicking this structure, the researchers created composites using Portland cement paste combined with a stretchable polymer, polyvinyl siloxane, to enhance crack resistance and ductility.
In experiments conducted by the research team, three types of beams were produced to compare the crack resistance and ductility of the new composite with traditional cement. Beams with alternating layers of cement paste and polymer, as well as grooved sheets stacked with polymer layers, showed increased ductility and resistance to cracking compared to solid cast cement. The most significant results were observed in beams with completely separated hexagonal tablets, similar to the structure of nacre, which exhibited 19 times the ductility and 17 times the fracture toughness while maintaining strength.
The bio-inspired approach taken by the researchers focuses on understanding the underlying principles of natural materials such as nacre and using them to inform the engineering of human-made materials. By intentionally engineering defects in brittle materials to promote tablet sliding and enhancing the properties of the polymer-cement interface, the team aims to make stronger materials by design. While the findings are promising, further research is needed to develop techniques for practical application in construction materials beyond cement paste.
The researchers emphasized that their work is just the beginning, with numerous possibilities to explore in designing and engineering the properties of hard and soft materials, interfaces, and geometric aspects that influence the fundamental characteristics of construction materials. By understanding and replicating the mechanisms that make natural materials like nacre strong and resilient, engineers can create more durable and crack-resistant ceramics for a wide range of applications in the future.
Overall, the development of a new crack-resistant and ductile cement composite based on the structure of nacre represents a significant advancement in the field of construction materials engineering. By combining the strength of hard minerals with the flexibility of biopolymers, the research team at Princeton University has demonstrated the potential to improve the performance and longevity of brittle ceramic materials. Further research and development in this area could lead to enhanced durability and safety in construction applications, offering a promising solution for increasing the resilience of concrete and similar materials.
