SELF-HEALING OF CONCRETE BY BACTERIAL MINERAL PRECIPITATION

                                            -By Sanket Jain


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 the 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. 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.

Currently, the research focuses 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. In addition, the work is

being done at improving the self-healing ability of bacterial concrete and how this is affected by the

various deterioration mechanisms involved, such as sulfate attacks or temperature fluctuations.

The Self Healing Concrete project is part of the TU Delft wide Self-healing Materials research

program at the Delft Center for Materials (DCMat). Furthermore, they have collaborated with the

Biotechnology section at the Faculty of Applied Sciences and the South Dakota School of Mines in

the United States.