Under the right conditions, concrete decays with alarming speed. One tiny crack can quickly become larger due to the freezing and thawing action of infiltrated water. Researchers around the world are closer to creating self-healing concrete with the addition of various microcapsules. One team of scientists is working on a low-cost concrete coating containing microcapsules that would break open, releasing sealant materials that react with sunlight and quickly solidify, effectively sealing the cracks as they appear. Another team is studying microcapsules containing calcite-precipitating bacteria that lies dormant in the concrete but would produce limestone filler as soon as water seeps in from a micro-crack. (Limestone is an ingredient in concrete.) An effective bacteria that can live in the highly alkaline environment is still being sought, but the widespread use of such “bio-concrete” could lengthen the usable life of concrete structures by up to 50% and reduce the need to make expensive repairs.