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article imageUsing bones and shells to make super-concrete

By Tim Sandle     May 30, 2016 in Science
Concrete is a strong material, essential for most construction projects. It is, however, prone to cracking over time. Can concrete be made stronger? It seems so by adding bones and shells.
Technologists working at the Massachusetts Institute of Technology have looked to nature for inspiration to "re-design" concrete. Concrete is not a well-defined material; concrete is a somewhat random assembly of crushed rocks and stones held together with paste, a fluid cement which hardens over time. The structure of concrete, especially at the micro level, will vary from one batch to another. It is also influenced by the types of rocks and stones used in the preparation. The extent to which concrete cracks comes down to the number and arrangement of pores. Here the more porous the end product, the more vulnerable it is to fracturing over time.
To do this the researchers began examining the physical and biological structure of bones, shells, and deep-sea sponges. The reason for doing so is because these natural formations are strong and durable. The durability is a facet of the geometric interweaving of molecules.
The examination has taken place at the so-termed “mesoscale”; this is a "space" between the microscale and the macroscale. The outcome is that much comes down to arrangement, connection and length. Variations of these lead to materials having different mechanical properties. For example, a sea sponge is strong because it has overlapping onion like layers of silica. The material properties have been drawn out from the use of such techniques as nuclear magnetic resonance, scanning electron microscopy, and X-ray diffraction.
From this, the scientists have developed a framework that can be followed in order to boost the strength and consistency of concrete. This is a work in progress, with the steps of the framework being tested via conventional compression and nanoindentation experiments.
The findings from this inquiry have led to a ‘bottom-up’ re-examination of concrete, inspired by the micro-mechanical formation of bones and shells. This involved the use of computer programs.
It is hoped that the insights into material configuration will lead to more durable roads and stronger buildings and bridges.
The research outcomes are described in the journal Construction and Building Materials. The paper is titled “Roadmap across the mesoscale for durable and sustainable cement paste – A bioinspired approach.”
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