With a staggering 70% of European infrastructure made using concrete, it is vital structures are not only durable, but sustainable too.
Concrete is a highly durable and resilient material that is relied upon across the world in urban and industrial spaces. However, even this robust and unique material can be susceptible to wear and environmental conditions and may require occasional maintenance. Early detection and repair of cracks is an important part of ensuring the longevity of concrete structures and reducing the costs and impacts of maintenance efforts is key to extending durability.
This is why scientists have been exploring ways of creating environmentally-friendly, self-healing materials, with a ground-breaking discovery made by Dutch microbiologist, Hendrik Jonkers, of Delft University of Technology (TU Delft).
As cement is the binding agent used to make concrete, Dr Jonkers added bacteria to a traditional cement mix, in order to create self-healing bio-concrete.
Bart van der Woerd, managing director of Green Basilisk, a spin-out company from TU Delft that makes self-healing concrete, explains: “The principle is that we add bacteria spores and nutrients to the concrete.
“Making 700 million m3 of concrete more sustainable is a realistic step forward” – Bart van der Woerd, managing director, Green Basilisk
“When a crack occurs, some water or moisture will enter the crack and will activate the bacteria spores. They transform into bacteria and the bacteria transform the nutrients into limestone, a material that already exists in ordinary concrete. The limestone then repairs the crack.”
The bacteria then die, but not before producing a spore, which will start the whole process again when a new crack occurs. When you consider that these limestone-producing bacteria can survive in concrete structures for up to 200 years, it is easy to see the potential long-term benefits for fast-growing European cities such as London and Rome, in increasing the lifespan of their buildings and lowering maintenance costs.
A sustainable alternative?
Dr Mercedes Sanchez Moreno is chair of SARCOS, a European network of researchers who explore different self-healing technologies and repair solutions that seek to extend the service life of new and existing concrete structures.
She says: “Self-healing concrete appears a promising, sustainable alternative for extending the service life of new structures, lowering maintenance costs and avoiding complicated repairs, by filling cracks at the earliest stage of damage and allowing the recovery of properties, whether physical or mechanical.”
Dr Moreno explains there are two main approaches for self-healing in concrete: autogenous healing and autonomous healing.
“Autogenous healing is a natural process, intrinsic to the properties of the material itself, mainly caused by the continuous hydration of cement and by the calcium carbonate precipitation. This process can be stimulated through tailored additions such as mineral, crystalline admixtures, superabsorbent (SAP) polymers and other non-SAP polymer additions.
“Autonomous healing, meanwhile, is an engineered process to improve the self-healing properties of a concrete element. There are different strategies for designing autonomous healing methods, depending on the method for incorporating the self-healing properties, or on the healing agent itself.”
On self-healing bio-concrete, Dr Moreno says: “It creates the potential for long-lasting and active crack repair, at the same time representing a potentially environmentally-friendly method.” The self-healing agent which is added to concrete mixtures is fully biodegradable, meaning there are minimal impacts when the concrete is crushed following the end service life of structures built using this technique.
Though a promising development, bio-concrete is still in its relative infancy, and it has a way to go before it becomes an economic choice. However, Van der Woerd says that as take-up increases, it will become more affordable.
“Self-healing concrete appears a promising, sustainable alternative for extending the service life of new structures, lowering maintenance costs and avoiding complicated repairs” – Dr Mercedes Sanchez Moreno, chair of SARCOS
In addition, as the technology evolves, it could potentially be introduced to more complex structures, such as dams, bridges, or indeed any structure exposed to water. It could also support infrastructure projects that involve structures exposed to extreme environments, such as cooling towers, off-shore turbines or industrial harbours.
Progress is being made in this area, says Van der Woerd, who explains that in 2019, Basilisk will expand and outsource its production to South Korea and Japan. He says his team is “putting effort in” to convince consultants, engineers and architects to get on board with the technology because “the demand starts with them”.
Van der Woerd concludes that bio-concrete has an important role to play in making long-term infrastructure more sustainable.
“The message is clear,” he says. “We do not own the world, we are just looking after it for our children. Let’s take good care of it – making 700 million m3 of concrete more sustainable is a realistic step forward.”