For Self-Healing Concrete, Just Add Bacteria?

Posted: February 5, 2012 in Building Technology
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Concrete is one of the most widely used building materials in the world.  However, concrete is very poor in tension.  That is why steel bars are placed throughout concrete structures to create a composite material that will resist both tensile and compressive forces.  This is a very durable material but it still has a limited lifespan.  This limited lifespan occurs because of one main reason: water.

As already discussed, concrete is poor in tension, therefore, under loads that cause those forces, concrete cracks.  When concrete cracks, water can get introduced into the structure and compromise the integrity of the steel.

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Dr. Henk Jonkers, a faculty member of Civil Engineering and Geosciences at the Delft University of Technology in Delft, the Netherlands decided to approach this problem from a biological angle.  He searched for bacteria use water and calcium lactate to create calcite that is natural cement.  The problem occurred when trying to find bacteria that would survive in a very high pH environment (the typical pH of concrete is 11 or above on a scale from 0-14).  Jonkers and his collegues started looking in the soda lakes of Eygpt and Russia and eventually found a strain of Bacillus that thrived there.

Dr. Jonkers’ bio-concrete has the two key ingredients (the bacteria spores and the calcium lactate) introduced through separate expanded clay pellets. This ensures the ingredients will not come in contact during the mixing process.  Later, cracks will open the pellets and the incoming water will germinate the spores and mix the spore with the calcium lactate, producing calcite and filling in the cracks.

(Source)

Though clearly, the main advantage to this bio-concrete is a much longer lifespan of the structure and minimized repair, there are also some disadvantages.  The clay pellets that hold the bacteria and calcium lactate comprise 20% of the volume of the concrete mix.  However, these pellets are weaker than the components of the mix they are replacing, thereby reducing the overall strength of the concrete.  Cost is also a big disadvantage.  Currently, the cost of this self-healing concrete is double that of a standard mix, though Dr. Jonkers and his team are continuing to research better ways to introduce the agents into the mix all for a cheaper cost.

Currently, this product is still being tested.  Full scale testing just started this past year and the team is also trying to address concerns from the industry about lifecycle costs and performance of the product.
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Comments
  1. Hello just wanted to give you a quick heads up and let you know a few of the pictures aren’t loading properly. I’m not sure why but I think its a linking
    issue. I’ve tried it in two different web browsers and both show the same results.

    • Kim says:

      Thank you for letting me know. I am in the process of trying to roll my blog over to a new format and resurrect my writing (as you can see by the dates, I fell far behind). So I will add that to my list of things to look into. I’m sorry the pictures do not work properly for you, but if you click on the source link, you should be able to find the original article.

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