Delft University of Technology, Netherlands researcher, Henk Jonkers, is working towards creating a self-healing concrete. Researchers are experimenting with calcite-precipitating bacteria to create a “living concrete.” Due to concrete’s high pH value, only alkaliphilic bacteria can survive. Several of these bacteria have been isolated by researchers and put into cement paste for a month and three bacteria types were still viable.
Self-healing concrete would make the need for steel reinforcement unnecessary. Steel and rebar do not give any structural support and will save significantly on construction costs.
The next step in the quest is to find conditions in which the bacteria can thrive. Ideally, the mixture needs enough, well-distributed calcite as food. There are also variables to consider, such as sulfate attacks and fluctuation in temperature.
Concrete is the most popular building material there is in the world. The Romans built the Pantheon with it 2,000 years ago. Since then scientists have been researching ways to make it stronger.
Until now, no matter how concrete was reinforced, or mixed, it would crack. Under certain conditions, these cracks can create a collapse.
Professor Henk Jonkers, says that the issue with cracks in concrete is the leakage. Wherever there are cracks, water will come through. Also if the water gets to the steel rebar, it will cause corrosion and the structure will collapse.
Jonkers’ lab in the Netherlands at Delft University, has created bioconcrete. This is a concrete that uses bacteria to heal itself. The “healing agent” is only active when it gets wet.
Microbiologist, Jonkers, started working on this idea in 2006, after a concrete technician asked him if it was possible to make self-healing concrete with bacteria. It took Jonkers three years to figure out how to make it possible. However, he did experience some challenges along the way.
The bacteria used, must be able to survive the concrete environment, very dry. It is high in alkaline too and the “healing” bacteria must be able to lie dormant for many years before water activation. Jonkers used Bacillus bacteria, because it can thrive in high alkaline conditions, and produces spores, which can live for decades without oxygen or food.
Then Jonkers needed the bacteria to actually repair the concrete material, limestone. To produce limestone, the bacilli would need a food source. Jonkers chose to use calcium lactate. He put the bacteria and the calcium lactate into biodegradable plastic capsules and then put the capsules into the wet concrete mixture.
Now, when cracks form in the concrete and water leaks through, it opens the capsules, releasing the bacteria. The bacteria will germinate, multiply, and eat the lactate. In doing all of this, the bacteria combines the calcium with carbonate ions to form limestone and seal the cracks.
By Jeanette Smith
NY Daily News: Concrete May Soon be Able to Fix Itself, Thanks to Bacteria
CNN: The “Living Concrete” That Can Heal Itself
Photo courtesy of Hanna Sorensson’s Flickr Page – Creative Commons License