When it comes to strength, concrete certainly holds its own, and then some. Although it is perceived as rugged and durable and often stands the test of time, nothing lasts forever. Unsatisfied with “good enough,” researchers are looking to give concrete a longer life by helping it repair itself.
Concrete is ubiquitous. It is used in residential, commercial and infrastructure construction. Despite its popularity, there are drawbacks. It is energy and resource intensive to make and it is sensitive to damage. The formation of even a small crack can lead to extensive damage over time from freeze/thaw cycles, reinforcement (rebar) corrosion and compositional changes due to chemical leaching.
Concrete structures are typically in service for very long periods and can be difficult to inspect due to their size or location, such as underground structures. Researchers at the University of Cambridge are looking into mechanisms by which to enable concrete to take care of itself so that its lifetime can be dramatically extended.
As described in the University of Cambridge news, they are involved in a partnership with the Universities of Cardiff and Bath to develop self-healing concrete. Cambridge researchers are focused on microscale self-repair mechanisms through the use of microcapsules embedded in the concrete structure.
These microcapsules contain the necessary mineral ingredients to repair a crack if it forms. As the crack progresses it would break the beads open and release the healing agents. Micro and nanoscale cracks are of interest for this particular approach since the beads are not large enough to repair a more sizable crack.
Mid-sized cracks are a topic being addressed by Bath researchers. They will complement the microcapsules using, “…spore-forming bacteria that act as tiny mineral-producing factories, feeding on nutrients added to the cement and facilitating calcite precipitation to plug the cracks in the concrete.” Cardiff researchers are addressing the largest cracks using polymer “tendons” which stretch as the crack opens, but by application of heat can impose a compressive force on the crack to prevent further propagation.
For the Cambridge team, challenges include the successful integration of microscapsules into the concrete. The microcapsules have to be robust enough to last through the mixing process, but have to be sensitive enough to break open in the presence of a crack. Also, scaling up cost effectively will be essential to compete with traditional concrete structures.
They are already planning field tests in nonstructural components of the Department of Engineering’s James Dyson building currently under construction.
Image: Tanvir Qureshi, Department of Engineering, University of Cambridge