When a large crack appears in concrete, the obvious solution is to get some more concrete, or another patching material, and fill it in. But what if you could make sure these cracks don’t form initially? Or if they do, they are quickly sealed on their own on a microscopic level? It would certainly lead to a small carbon footprint for concrete plants, which contribute to roughly 7 percent of worldwide CO2 emissions worldwide.
For several researchers around the world, this is “self-healing concrete” is more science fact than science fiction, although it has yet to become commercially viable. Since concrete is used in all parts of the globe in nearly every permanent manmade structure, even a slight reduction in concrete demand by the elimination of crack repairs can have a significant impact on greenhouse gas emissions.
In the United Kingdom, researchers at three major colleges, Cardiff University, the University of Cambridge, and the University of Bath, are saying they are close to creating a self-healing concrete by the addition of calcite-precipitating bacteria that lies dormant in a concrete block and can produce limestone filler as soon as a micro-crack begins to form. The secret, the researchers say, is the seeding of concrete with microcapsules that contain bacteria in an inert form that activates as soon as water seeps in from one of these tiny cracks and mixes with calcium lactate and other nutrients.
According to the £3 million study, the type of bacteria that would be suitable to live in the highly alkaline environment is still being sought after. Also, the researchers need to find a way to produce huge amounts of spore quickly enough to make an effective seal. Once these hurdles are overcome, the study says, the widespread use of this prototype bio-concrete could lengthen the usable life of concrete structures by up to 50 percent and reduce to need to make expensive periodical repairs.
“Self-healing materials are particularly suited to situations where safe access for maintenance is costly, so the outputs of this extended research program could reduce the life cycle costs of infrastructure.” said Dr. Andrew Heath from the U.K.’s Department of Agriculture and Civil Engineering.
Another group of researchers in South Korea are talking a different tactic to create a low-cost concrete coating that will not break down into environmentally harmful materials. While this method does not use bacteria, it does involve microcapsules and chemical reactions that respond to conditions often experienced by concrete that is exposed to the elements.
In this Korean research, concrete is sprayed with a coating containing these micorcapsules. As soon as the tiny cracks begin to form as a result of water seepage and thermal stresses, the microcapsules are broken open, releasing sealant materials that react with sunlight and quickly solidify.
“Our self-healing coating,” the Korean report says, “offers the advantages of catalyst-free, environment-friendly, inexpensive, practical healing.”