Using concrete as a medium, scientists at the University of Waikato have developed a new process to allow materials to heal themselves.
They have used a protocol called solid-state fermentation, and put it into practice with the help of nanobiotechnology, making concrete which regenerates to repair cracks as they develop.
Concrete is one of the world’s most versatile and widely used construction materials. Every year, billions of tonnes are used worldwide, but it is vulnerable to damage. Cracks accelerate a structure’s degradation, increase maintenance costs, and in severe cases lead to structural failure.
Scientists around the world have been working on the problem, but Waikato researchers Dr Aydin Berenjian and PhD student Mostafa Seifan are the only ones who have used a nanobiotechnological approach to address it. They believe their process will have a wide range of applications, including the oil and gas industry, medicine, environmental remediation, and construction materials.
They have made a kind of bio-concrete, introducing micro-organisms and nutrients into the initial mix, to create calcium carbonate when cracking occurs. Calcium carbonate is considered one of the most important materials on earth, crystallising in nature to produce things including chalk, shell, and rock. In this process it fills the cracks as they appear.
The performance of the material relies on many factors including the right bacterial species and nutrient ingredients, and the availability of oxygen. Dr Berenjian says the ability of bacteria to survive in a harsh concrete environment, and ability of cells to keep producing calcium carbonate over time are also crucial. “That is where the engineering came in. With the help of the unique fermentation system and nanobiotechnology, we have engineered a process that makes the calcium carbonate production very efficient even in a harsh environment like concrete.”
Testing in the lab indicates the bio-concrete is more durable than traditional concrete. However, to be industrially applicable the cost is an issue, as the product is more expensive than the standard ones in the market. Dr Berenjian says fixing concrete currently costs approximately $200 a cubic metre. “Fixing concrete manually also means cracks are sometimes missed, particularly if they are not visible. The return comes with the longer-term strength, and removing the cost of repairs.”
The new process is environmentally friendly, and producing more durable concrete it is also likely to be safer, for example in earthquake prone areas. Mostafa Seifan says they have taken a completely different approach to others working in the field, who are aiming solely to heal the concrete cracks. “We have developed a unique system by using nanobiotechnology to make the cells capable of inducing a high level of calcium carbonate in different fermentation conditions.”
Dr Berenjian is keen to see testing on a bigger scale, and he is particularly excited about future applications for the protocol itself. “We have had a lot of interest and our work has been thoroughly reviewed and published. It has huge potential for a range of other materials, industries and uses worldwide.”