Elastic Concrete Material Inspired by Sea Urchin Shells

Innovation: Academia

University of Konstanz

2017

Image: Nick Karvounis / 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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Manage Shear

The effect of shear stress on a living system is parallel internal surfaces sliding past each other. Slippage occurs in parallel with the force. Think about holding two wooden boards on top of each other and sliding one to the right and the other to the left. This may be easy until you add glue, which increases their shear strength and makes them harder or impossible to slide. Shear can occur in solids, liquids, and gases. Living systems must increase their shear strength to overcome these types of forces. For example, darkling beetles lock their wings together in flight to prevent lateral movement by using many small hairs on each wing. These hairs interlock to provide shear strength, just as two hair brushes put together would be difficult to slide past each other.

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Concrete material from University of Konstanz has an organized nanostructure that enables the material to bounce back to its original shape.

Benefits

Stronger
Resilient
Stable

Applications

Bridge and building design

UN Sustainable Development Goals Addressed

Goal 9: Industry Innovation & Infrastructure
Goal 12: Responsible Production & Consumption

The Challenge

Concrete is the second most consumed product on Earth besides water. Unfortunately, producing cement, an ingredient in concrete, has extreme environmental impacts that account for approximately 8 percent of annual global carbon emissions. Cutting down on carbon emissions from cement will involve investing in green cement technology and finding ways to build more efficiently with concrete. One major flaw with concrete as a construction material is its poor flexural strength, or lack of elasticity. This issue occurs because of the binder in concrete, calcium silicate hydrate (C-S-H); the random organization of C-S-H nanoplatelets limits the flexural strength of the material. When concrete is placed under stress, it is unable to move far without fracturing, and eventually, fractured concrete must be replaced.

Innovation Details

The elastic concrete material is made of C-S-H mesocrystals (a highly oriented assembly of numerous small crystals of similar shape and size) with highly aligned C-S-H nanoplatelets interspaced within a polymeric binder. The nanostructure has a ‘brick wall’ style architecture, in which the mesocrystals are the bricks and the polymeric binder is the grout. Due to this internal structure, during initial tests, a bent bar-shaped microstructure was able to return to its initial position without cracking or fracture. On a larger scale, this method could significantly reduce concrete fracturing in construction processes, improving the mechanical properties of future buildings.

Biomimicry Story

Sea urchins live at depths of the ocean that extend as low as 16,000 feet underwater. Pressure in this part of the ocean is very intense, but sea urchins can withstand such pressure, grow, and survive attempted attacks from predators without shell breakage. This biological wonder may be attributed to the organization of sea urchin spines. Each spine contains an array of calcite nanocrystals, forming mesocrystal structures. The highly oriented assembly of mesocrystals in the spine gives the material unique properties, such as incredible bending strength, making the shell durable and flexible.

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a variety of sea urchin skeletons are seen throughout the frame

Biological Strategy

Thin Shells Resist Impact Loading

Heart urchins

The hard outer coverings of some sea urchins, called tests, allow local deformation that may resist impact loading by incorporating collagen-swathed sutures.