Key test for re-healable concrete

One of the issues with concrete is the formation of micro-cracks during hardening that can allow water to enter and eventually weaken the concrete.  Microbiologist Henk Jonkers and concrete technologist Eric Schlangen of Delft Technical University in the Netherlands have created a seal-healing concrete by incorporating spores of a bacteria that produces limestone along with the nutrient calcium lactate.  In the presence of water, the bacteria start growing. 

In the lab, the process has healed cracks up to 0.5 mm wide, significantly larger than the 0.2 mm cracks currently allowed by building standards.  Further research is underway to increase the ability of the spores and nutrients to survive the process of mixing the concrete.  Field tests are expected to start in six months. 

Although an example of bio-utilization or bio-assistance, the idea appears different from other approaches that use the analogy of capillaries to transport reinforcing materials to fracture sites.  I contacted Prof. Henk Jonkers and received this response:

In the late 1990 American scientists used bacteria to deposit a layer of limestone on concrete structures. We thought of the possibility to integrate such bacteria into the material to make it ‘self-healing’.

More info on our work you can read on our Blog:

According to Interview with Henk Jonkers on BBC, Prof. Jonkers applied his skills as a microbiologist to identify bacteria suitable for the alkali environment of concrete and worked closely with civil engineers to develop a viable solution.  It is intriguing that the activating agent (water) is also the the cause of concrete failing.  The system of concrete, bacteria and water is adaptive in a preventative sense - the micro-cracks self-heal before the water has a chance to widen the cracks and weaken the concrete.  

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