Concrete has been around much longer than most people think. Concrete-like materials have been used since 6500 BC. It is one of the most ubiquitous building materials in existence. It is used in building construction, roads, dams, fireproofing, and, of course, countertops to name a few. The problem is that concrete breaks. The old saying goes that there are two types of concrete: Concrete that’s cracked and concrete that will crack. There’s never been much we could do except replace it. Recent efforts in different parts of the world are trying to change that. Before long we will be using self-healing concrete.
At Delft University of Technology in the Netherlands, Scientist Henk Jonkers is developing a material he calls Bioconcrete that heals itself using bacteria. Bioconcrete is the same as regular concrete with one exception. It contains biodegradable capsules containing calcium lactate and Bacillus bacteria. Any crack in the concrete allows water to enter. The bacteria comes out of its dormant state and feeds on the lactate, combining calcium with carbonate to form calcite, more commonly known as limestone, which closes up the crack.
Researchers at the University of Bath, Cardiff University and the University of Cambridge in England are working on the same approach, driven by a national epidemic of potholes on British roadways.
Victor Li, a Civil and Environmental Engineering Professor at the University of Michigan has taken a different approach. His is based on material he developed in 1990 called Cementitious Composite. It’s similar to Portland cement, but the coarser parts of the mix have been replaced by microfibers. When stressed, the composite will bend without fracturing. If it is stressed to the point that it does crack, the cracks will be thinner than a human hair.
The way it heals itself is similar to the way our skin does. A crack exposes a dry composite to air moisture. The moisture is absorbed, and the composite grows, filling in the crack. Calcium ions in the concrete mix with the water and carbon dioxide to form calcium carbonate, the same material that seashells are made of.
The implications of self-healing concrete are staggering. Repair and maintenance of concrete structures cost billions of dollars a year worldwide. Self-healing concrete can extend the functional life of structures by years by significantly slowing deterioration. One of the most intriguing uses is in hazardous waste containment.
Self-healing concrete is still a few years from reaching the market. Considering the implications for multiple industries, it can’t come soon enough.
