Ductile Concrete Material Inspired by Mollusk Shells

Innovation: Academia

University of Michigan

2018

Image: Raimond Klavins / Unsplash / CC BY SA - Creative Commons Attribution + ShareAlike

Manage Tension

When a living system is under tension, it means there is a force pulling on it, like a person pulling on a rope tied to a horse. When applied to a living system, unless the system is completely rigid, the result is that it gets stretched. If stretching exceeds the strength of the living system’s material, it can damage it. Living systems manage tension using materials that are flexible and stretchable enough to survive most tension that occurs in their environment. The ocean’s intertidal zone offers a good example. The waves and incoming and outgoing tides put tension on soft-bodied organisms. Mussels resist tension with flexible threads that hold them onto rocks; in contrast, large algae have stretchy fronds.

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Manage Compression

When a living system is under compression, there is a force pushing on it, like a chair with a person sitting on it. When evenly applied to all sides of a living system, compression results in decreased volume. When applied on two sides, it results in deformation, such as when pushing on two sides of a balloon. This deformation can be temporary or permanent. Because living systems must retain their most efficient form, they must ensure that any deformation is temporary. Managing compression also provides an opportunity to lessen the effects of other forces. Living systems have strategies to help prevent compression or recover from it, while maintaining function. For example, African elephant adults weigh from 4,700 to 6,048 kilograms. Because they must hold all of that weight on their four feet, the tissues of their feet have features that enable compression to absorb and distribute forces.

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Concrete material from University of Michigan has tiny fibers dispersed within the concrete mixture that enhance the material's flexibility.

Benefits

Flexible
Resilient
Strong

Applications

Bridge design
Building design

UN Sustainable Development Goals Addressed

Goal 11: Sustainable Cities & Communities
Goal 12: Responsible Production & Consumption

The Challenge

Traditional concrete is brittle: When placed under stress, it is unable to move very far without fracturing. When concrete fractures, it eventually needs to be replaced, requiring more to be manufactured. Unfortunately, cement, one of the main ingredients in concrete, is one of the largest green-house gas emission sources. As a result, making more concrete increases its harmful effects on the environment.

Innovation Details

The concrete material is also called “engineered cementitious composite,”or ECC. The ECC has tiny fibers dispersed through the concrete mix, which contains gravel, sand, and cement. Under stress, the interfaces between the fibers and the cement have controlled slippage, which enables the concrete to bend and recover its original shape without fracturing. The material can deform up to 5 percent in tension before failing, which is approximately 500 times what typical concrete can endure.

Biomimicry Story

Nacre, or mother of pearl, forms the iridescent inner layer of the shells of some mollusks. It is a natural composite of plates of aragonite (a form of calcium carbonate) and natural s that coil around and through the plates. The polymer holds the plates together while allowing them to slip from side to side under stress, enabling the nacre to be both strong and flexible.

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close up photograph of purple, blue, pink and green shell

Biological Strategy

Interlocking Increases Material’s Toughness

Mollusks (Snails, Octopuses)

Plates in nacre increase toughness by interlocking

Biological Strategy

Weak Interfaces Make Material Tough

Black-lip pearl shell

Layers of weak and stretchy organic material between brittle mineral layers in nacre make the whole composite tough by managing cracks.

References

Journal article

Nacre-inspired composite design approaches for large-scale cementitious members and structures

ScienceDirect

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