How Self-Healing Concrete Works

Ordinary concrete is strong under compression but prone to cracking over time, and once a crack forms, water and chemicals can seep in and weaken the structure from the inside. Self-healing concrete addresses this problem by mixing in a special ingredient before the concrete even sets: dormant bacteria, sealed inside tiny capsules along with a nutrient source, and mixed directly into the wet concrete. As long as the concrete remains intact, the bacteria stay inactive and harmless, essentially asleep inside their capsules. But when a crack eventually forms and lets water seep in, that water reaches the capsules, breaks them open, and activates the bacteria inside. Once awake, the bacteria begin feeding on the nutrients packed in alongside them and, as a byproduct of that process, produce limestone. The limestone gradually fills the crack from the inside out, sealing it before water and air can cause further damage. This entire process can take a few weeks to fully seal a small crack, but it requires no outside intervention at all -- no inspection, no repair crew, and no additional material beyond what was already mixed in when the concrete was poured. Researchers have found that certain bacteria strains work especially well for this purpose because they can survive dormant inside concrete's harsh, alkaline environment for years before ever being triggered.