Inspired by oyster and abalone shells, Princeton engineers have created a cement composite that's 17 times more crack-resistant and 19 times more stretchable than standard cement, potentially improving brittle ceramics like concrete and porcelain.
Introduction
Fracture toughness is a property of construction materials that determines how well they can resist fractures under external pressure. Along with toughness, ductility, and durability, Fracture toughness is a crucial factor in ensuring the safety of construction structures. Across the world, several research programs have been initiated to estimate the fracture toughness of different materials that can be used for construction. Recently, a team of researchers at the engineering labs of Princeton University has proposed a cementitious composite that displays high fracture toughness and ductility, thus offering a ground-breaking alternative to concrete.
The results of the research initiated by Shashank Gupta, Hadi S. Esmaeeli, and Reza Moini at the Department of Civil and Environmental Engineering of Princeton University have attracted considerable attention from ConTech experts as it can transform the construction industry.
Summary
• Recently, a team of engineers at Princeton University has created a nacre-inspired cementitious deposit that is 17 times more fracture-resistant and 19 times more ductile than traditional cement.
• The new material imitates the inherent architecture of natural nacre to achieve high fracture toughness.
• The Princeton team has used laser technology to introduce the nacre-like structure into a composite of cement and polyvinyl siloxane (PVS).
• The newly developed nacre-like cementitious composite can withstand high pressure and can prove to be a game-changer in the construction materials industry.
A construction material inspired by nature
The new nacre-like cementitious composite of the Princeton labs is inspired by the myriad designs and forms existing freely in nature. Nacre, commonly known as mother of pearl, is a naturally occurring resilient material that has served as the primary reference for this experiment. This lightweight natural material is composed of brittle material and yet shows high fracture toughness. According to scientists, the secret of nacre’s toughness and ductility lies in its inherent design.
Nacre is composed of both hard aragonite and soft biopolymers. The structure consists of hard aragonite tablets arranged in a brick-and-mortar pattern and held together by the biopolymer compound. The engineers at Princeton have tried to recreate this architecture in their new cementitious composite to achieve maximum fracture toughness. This experiment is distinct because it utilizes design principles, and not just amalgamation of compounds to achieve a durable construction material.
Nacre-like cementitious composite: Key features
Even though there have been experiments on nacre-like formations in lab settings, they have had partial success in creating construction material with high fracture toughness. The team of researchers credited with the development of the new material has utilized advanced laser technology at the Princeton labs to transform simple cement into nacre-like formations. Cement tablets replace Aragonite in this new design, and instead of biopolymer, the brick-and-mortar pattern is held together by polyvinyl siloxane. Using a focused pulsed laser, the cement is fabricated into hexagonal tablets with grooved patterns and laminated with the elastomeric polyvinyl siloxane matrix.
The bio-mimetic design results in the high fracture toughness of the nacre-like cementitious composite. The hyper-elastic polymer matrix allows the polygonal cement tablets to slide over it and endure external pressure. The planned fabrication of grooves also allows scientists to control the path of the crack propagation, further strengthening the material against fractures.
So far, the Princeton team has tested three variations of the microstructure. The three variants were put through a bending test to assess their strength. Of these, the structure that most closely resembles natural nacre proved to be the variant with the highest fracture toughness. As predicted, the new design is 17X more fracture-resistant and 19X more ductile than conventional cement. Test results have also shown that the nacre-like composite is as tough as engineered cementitious composite (ECC) and ultra-high-performance concrete (UHPC).
The future of nacre-inspired construction materials
According to the triumphant team of engineers, this is only the beginning. The nacre-like cementitious composite may have achieved the desired results under lab conditions but its real test lies in practical use. However, this is a significant breakthrough in developing construction materials that can withstand catastrophes. The major scientific turnarounds in this project are the implementation of design principles inspired by nature, inducing micro-architecture through laser, and the introduction of polyvinyl siloxane (PVS) as the intervening layer.
While the development of micro- and nanostructured materials and their application in industry have been well-established, construction materials require assembling microstructures on a macroscopic scale. This is what the laser-built nacre-like cementitious composite project aspires for. This ingenious bio-mimetic invention is an important milestone in the development of damage-resilient infrastructure projects with extreme loading conditions or those that require materials with high impact and blast resistance.
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