Bone structures inspire stronger concrete

The internal structure helps to prevent cracks from spreading

Spotted: Building materials and construction are currently responsible for 11 per cent of the world’s total energy-related carbon emissions. To cut this figure, many manufacturers are turning to the most cutting-edge technologies to engineer greener materials. The natural world, however, can provide just as much help. In this spirit, scientists at Princeton University researching new ways to strengthen building materials, have sought inspiration from the human bone.

The manufacture of brittle construction materials, such as cement and concrete, often involves a trade-off between strength (the ability to sustain heavier loads) and resilience (resistance to cracking and degradation). By examining the architecture of the human cortical bone, the Princeton team discovered that the dense outer shell of human femurs provides strength and resists fractures and sought to replicate that structure in building materials.

Part of what makes the cortical bone so strong is that it contains elliptical tubular components, called osteons, that are embedded in an organic matrix and this unique structure deflects cracks around osteons. This stops cracks from propagating and lessens the likelihood that larger, more catastrophic breaks will occur. Using this logic, the team incorporated its own cylindrical and elliptical tubes into a cement paste and found that this encouraged a ‘crack-tube interaction’, whereby a crack gets trapped by the tube and delayed, dissipating the energy. This keeps cracks contained instead of triggering a wider structural failure.

Traditional methods of strengthening cement-based materials involve the addition of fibres or plastics. However, by shaping the internal structure of the material into cylindrical and elliptical tubes, Princeton’s geometric method enables strong and resilient materials to be created without the need for additives. According to the team, its new material is 5.6 times more damage resistant than existing counterparts.

As part of the research, the team also created a new framework to measure the inner arrangement of a material, or its ‘disorder’, which could help with the design of more, damage-resistant materials for larger-scale projects in future.

Written By: Duncan Whitmore and Matilda Cox