Bacterial healing of cracks
Repairing cracks in concrete structures is a time consuming, costly but necessary business. Researchers are however looking into a new way of handling this, think of bacterial healing of cracks. A research is underway on how self-healing capacity of concrete structures can be improved by using calcite-precipitating bacteria and what conditions are necessary for these bacteria to thrive.
The process would involve putting spores of bacteria — which naturally produce calcium carbonate — in the concrete mix, which would be activated upon the formation of cracks.
Although concrete is the world’s most used building material, it has a serious flaw: it can easily crack when under tension. If these cracks become too large, they will lead to corrosion of the steel reinforcement, which not only results in an unattractive appearance, but also jeopardizes the structure’s mechanical qualities. That is why engineers often use a larger than necessary amount of steel reinforcement within a concrete structure in order to prevent the cracks from becoming too large. This extra steel has no structural use and is an expensive solution as steel prices are high.
Another way to deal with cracks is to repair them, but this can be extremely difficult in underground or liquid retaining structures. The ultimate solution would be self-healing concrete, which is exactly what TU Delft researchers are working on.
By embedding calcite-precipitating bacteria in the concrete mixture, it is possible to create concrete that has self-healing capacities. As the pH value of concrete is very high, only the so-called alkaliphilic bacteria are able to survive. We have mixed several of these bacteria into a cement paste and after a month found the spores of three particular bacteria where still viable.
The use of bacterial concrete can in theory lead to substantial savings, especially in steel reinforced concrete. It will also mean durability issues can be tackled in a new and more economical way when designing concrete structures. Bacterial concrete is ideal for constructing underground retainers for hazardous waste, as no humans would have to go near it to repair any occurring cracks. For residential buildings, however, it does seem the traditional repairing of cracks will remain the most economically attractive solution for now.
The researchers, TU Delft’s Microlab are currently looking focusing on creating the right conditions for the bacteria to produce as much calcite as possible and on optimizing the distribution of food for the bacteria.