The New Miracle Concrete That Heals Itself
To continue with our series about one of the most versatile and widely used substances on the planet, concrete, today we’re going to take a look at microbial concrete. Microbial concrete is also known as bacterial concrete (bet you didn’t know that something as common as concrete has an AKA). Don’t be put off by the term “bacterial” – this is not concrete that carries germs and will make you ill. The correct term is actually “bio mineralised” concrete – it was developed by scientists who had the innovative idea that bio mineralising concrete could help to build stronger, more corrosion-resistant and even self-healing concrete. This is totally cool and futuristic construction technology.
Cracking is quite common in concrete structures due to natural processes such as weathering, land subsidence, earthquakes, faults and human activities. Without immediate treatment the cracks tend to expand and eventually need extensive and costly repairs. The remediation of cracks in concrete has been challenging researchers for many years – there are several products available to fix these cracks, such as structures epoxy, resins, epoxy mortar and other synthetic substances.
Now scientists have discovered that bio mineralisation of calcium carbonate using microbes (such as those in the Bacillus species) increases in the compressive strength of concrete by up to 36%. Microbial concrete absorbs six times less water than normal concrete which enhances the durability of the material. The addition of the microbes (which are abundantly present in soil) is entirely environmentally friendly and leads to a continuous self-remediating process.
Moreover, because traditional concrete is so prone to cracks, engineers often use a larger than necessary amount of steel reinforcement within concrete structures in order to prevent the cracks from becoming too large. In theory, the use of bacterial concrete could result in less steel being used to reinforce the concrete which adds to the environment friendly properties of the substance.
Bacterial concrete is produced by embedding the bacteria in the concrete so that they can constantly precipitate calcite – a phenomenon known as microbiologically induced calcite precipitation. The mineral precipitation involved in the process is natural and pollution free – an important consideration in these days of climate change when governments across the planet are committing to lower carbon footprints in accordance with the Kyoto Agreement. Under the most favourable conditions, Bacillus Pasteurian can continuously precipitate a new and highly impermeable calcite layer over the surface of an already existing concrete layer. However, the favourable conditions required do not directly exist in concrete – they have to be created.
A Costain highways site in south Wales, a trial structure on the Heads of the Valleys road is becoming a testing ground for self-healing concrete. A full scale wall structure is being built with a number of concrete panels. Each panel will feature a different combination of self-healing techniques so that they can be monitored to see how they react and recover over time. Testing starts at the end of September and will run for a minimum of six months. The trial will provide an insight into the feasibility of using the techniques in a full scale structure and the early stage effects on structural properties.