Self-healing concrete is within reach

FM newsroom – innovation, construction. Engineers at Drexel University have created a new material that could help heal cracks in concrete by sending bacteria to the site of damage through a network of fibres.

Making concrete accounts for 8% of greenhouse gas emissions, but concrete structures degrade in as little as 50 years. Increasing the lifespan of concrete could be vital when it comes to reducing greenhouse gases. Fibre reinforcement in construction itself isn’t new – ever since the first masons mixed horsehair into mud, builders have been taking advantage of it to strengthen their materials, as the Institution of Mechanical Engineers points out.

Living, self-healing concrete

The team at Drexel have created ‘BioFiber,’ a polymer fibre encased in a bacteria-laden hydrogel and a protective damage-responsive shell. A grid of BioFibers embedded in a concrete structure improves its durability, prevents cracks from growing and enables self-healing. 

“We are seeing every day that our ageing concrete structures are experiencing damage which lowers their functional life and requires critical repairs that are costly. Imagine, they can heal themselves? In our skin, our tissue does it naturally through a multilayer fibrous structure infused with our self-healing fluid — blood. These fibres mimic this concept and use stone-making bacteria to create damage-responsive living self-healing concrete.” – Amir Farnam, PhD, an associate professor in the College of Engineering, and leader of the research team, told imeche.org.

Pioneering in research and development

The concept of bio-self-healing cementitious composites within the Advanced Infrastructure Materials Lab has been nurtured for several years. The team’s approach to creating BioFibers was inspired by skin tissue’s self-healing capability and the vasculature system’s role in helping organisms heal their own wounds.

 “The BioFiber project represents a collaborative, multidisciplinary endeavour, integrating expertise from the fields of civil engineering, biology, chemistry, and materials science. The primary objective is to pioneer the development of a multifunctional self-healing BioFiber technology, setting new standards at the intersection of these diverse disciplines.” – Mohammad Houshmand, a doctoral candidate in Farnam’s lab and lead author of the research, shares.

To make BioFibre, the team used a strong polymer core that supports concrete. They covered this core with a unique hydrogel full of tiny spores and enclosed it all in a tough polymer shell, like skin. The whole thing is just over half a millimetre thick.

“Selecting the right combination of bacteria, hydrogel and polymer coating was central to this research and to the functionality of BioFiber. Drawing inspiration from nature is one thing, but translating that into an application comprised of biological ingredients that can all coexist in a functional structure is quite an undertaking — one that required a multifaced team of experts to successfully achieve.” – Caroline Schauer, who led a team that collaborated on the research pointed out.

How does it heal?

Poured into concrete in a grid pattern, BioFibre helps strengthen it. But it really works when a crack breaks the outer shell. When water gets into the crack and reaches BioFibre, the hydrogel expands and fills the crack. At the same time, the spores become active and, with help from the concrete’s calcium, produce a material that fills the crack.

How long it takes to fix depends on the crack size and the spores’ activity. But it looks like the spores could do the job in just one to two days.

Farnam admits that there is much work to be done in examining the kinetics of self-repair; their findings suggest that this is a viable method for arresting formation, stabilizing and repairing cracks without external intervention.

BioFiber could one day be used to make a ‘living’ concrete infrastructure and extend its life, preventing costly repairs or replacements.

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