Self-Healing Concrete by Bacterial Mineral Precipitation

A team of microbiologists at The Delft University of Technology (TU Delft) in the Netherlands, headed by Dr. Henk Jonkers, Civil Engineering and Geosciences, Materials Sciences and Sustainable Construction—TUDelft, Water Resources Section, is researching how the self-healing capacity of concrete structures can be improved by using calcite-precipitating bacteria and what conditions are necessary for these bacteria to thrive.

Crack Prevention: Although concrete is the world’s most used building material, it can crack when under tension. If these cracks become too large, they will lead to corrosion of the steel reinforcement—[rebar within concrete pavements], which jeopardizes the structure’s mechanical qualities and is unattractive in appearance. That is why engineers often use a larger 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. Repairing cracks can be extremely difficult, so the ultimate solution would be “self-healing concrete”.

Bacteria: 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. They have mixed several of these bacteria into a cement paste, and after a month, found the spores of three particular bacteria were still viable.

Practical Use: 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. 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, they are also looking at 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 research is done at the TU Delft’s Microlab, and 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 collaborate with the TU Delft Biotechnology section at the Faculty of Applied Sciences and the South Dakota School of Mines, USA.

To read the entire TU Delft article, please click here.  To learn more about the research into “Self-Healing Concrete by Bacterial Mineral Precipitation”, please contact Dr. Henk Jonkers:  Email: h.m.jonkers@tudelft.nl
Telephone: +31 (0)15 27 82313   |   Internet: https://www.tudelft.nl

Additionally, the article, “The ‘Living Concrete’ that can Heal Itself”, by Andrew Stewart-CNN, explains that Dr. Jonkers, began working on “healing concrete” in 2006. “If you have cracks, water comes through. If this water gets to the steel reinforcements—steel rebars—if they corrode, the structure will collapse,” he said. Concrete is extremely alkaline and the “healing” bacteria must wait dormant for years before being activated by water. “The problem with cracks in concrete is leakage,” Jonkers explained. The bioconcrete is mixed just like regular concrete, but with the “healing agent” that remains intact during mixing—only dissolving and becoming active if the concrete cracks and water gets in.

To read the CNN article, please click here.

ISCP reported on “self-healing concrete” in 2012 and 2013, in two separate articles:

ISCP November 2012, page 2: “Concrete That Heals Itself to Undergo Testing in the Netherlands” describes how the team, headed up by Dr. Jonkers and Eric Schlangen, Concrete Technologist-TU Delft, showed that it is possible to mix special bacteria which release crack-sealing chemicals into concrete before it is poured—indeed keeping the concrete healthy only while they are alive. This experimental concrete contains limestone-producing bacteria that is said to “patch cracks by itself”, and is to undergo outdoor testing at TU Delft. To read this ISCP article, please click here.

ISCP April 2013, page 1-2: “Self-Healing Concrete Extended Through Polymer Capsules” stated that by contrast, Dr. Chan-Moon Chung, Professor of Polymer Chemistry-Yonsei University, South Korea, uses a chemical approach to create self-healing concrete. Dr. Chung’s group learned from laboratory tests that when the two substances “methacryloxypropyl-terminated polydimethylsiloxane” and “benzoin isobutyl ether” were mixed in the presence of sunlight, they were transformed into a protective waterproof polymer that readily adheres to concrete. The “healing balm” was placed inside tiny capsules made of urea and formaldehyde, keeping the chemicals safely stowed away from sunlight, until needed. When the concrete near the capsules cracked, the polymer capsules ruptured and released their contents, filling the cracks, solidifying in the sunlight, thus healing the concrete. To read this ISCP article, please click here.