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Author | Elvira Esparza
Concrete is the most commonly used construction material, yet it also ranks among the most environmentally taxing substances. Self-healing concrete based on bioconstruction techniques, enables the material to repair itself, thereby preventing cracks from compromising the structural integrity of buildings.
According to a report by the International Energy Agency (IEA), the production of concrete is responsible for 8% of global CO2 emissions. This significant environmental impact has prompted the search for alternatives to reduce the material’s ecological footprint. In line with this objective, efforts are being made to develop various types of concrete with lower environmental impacts, such as fly ash concrete, recycled plastic concrete, low-carbon concrete, or self-healing concrete.
What is self-healing concrete
Concrete is renowned for its robustness and durability, yet it tends to deteriorate over time due to climatic conditions, stress, and overloads, which lead to the formation of cracks. Repairing these cracks, which compromise the safety of structures, is typically done on the exterior using surface treatments. However, self-healing concrete repairs cracks from the inside, preventing them from spreading.
Self-healing concrete projects
In 2015, Henk Jonkers, a microbiologist at Delft University of Technology in the Netherlands, presented the first self-healing concrete, featuring embedded bacteria. The technique involves introducing capsules containing bacterial strains and calcium lactate into the concrete, which serves as a nutrient for the bacteria. When cracks appear in the concrete and water enters, these capsules break open, allowing the bacteria to create solidified and insoluble limestone. These bacteria can remain dormant in the concrete for up to 200 years after construction. Given its unique characteristics, this building material, still in the experimental stages, is known as living concrete.
In 2021, researchers at Worcester Polytechnic Institute in Massachusetts developed a self-healing concrete incorporating an enzyme that reacts with CO2 in the air to produce calcium carbonate crystals that mimic the properties of concrete, effectively filling and sealing cracks. This model is inspired by the human body, where the enzyme carbonic anhydrase transfers CO2 from the cells to the bloodstream. This concrete can repair cracks in just 24 hours, whereas bio-concrete with bacteria takes approximately three weeks to achieve the same result.
In the United States, the Defense Advanced Research Projects Agency (DARPA) is working on the BRACE project (Bio-inspired Restoration of Aged Concrete Edifices) to develop technologies capable of self-healing cracks in concrete. This project draws inspiration from the vascular systems that facilitate continuous repair in living ecosystems and organisms. This concrete possesses the ability to self-heal similarly to how a cut on your arm would. With this project, they aim to reduce the time and cost of repairs while extending the useful life of infrastructures.
What are the benefits of self-healing concrete?
The advantages of self-healing concrete in construction are numerous:
- It extends the useful life of infrastructures, reducing the need for frequent maintenance tasks.
- It reduces carbon emissions by extending the life of the concrete, thus decreasing the need for new material production and consequently reducing emissions and waste.
- It improves safety by reducing the risk of structural collapse. By self-healing small cracks, the structure is secured, preventing the penetration of water that can corrode the steel reinforcement within the concrete.
- It reduces repair costs for structures, which in the EU alone amount to EUR 6 billion annually for infrastructure maintenance. Estimates suggest that self-healing concrete could reduce these costs by half.
How is self-healing concrete used in real life?
BRACE studies have been primarily developed in the military field. In the initial phase, the focus was on developing self-healing concrete for large and permanent structures such as nuclear silos. In the second phase, the development will expand to include temporary structures such as aerodromes. They also plan to extend their efforts to civil structures, including the repair of roads and highways, as well as the construction of homes.
Bio-concrete developed by Delft University is utilized in civil engineering projects, primarily in irrigation channels, bridges, and roads. It has been implemented successfully in the Netherlands, China, United States and in Europe.
Self-healing concrete is poised to revolutionize construction by offering a sustainable, durable, and environmentally friendly solution. However, its high cost compared to conventional concrete remains a significant obstacle to its widespread adoption.
Images | Tama66, Ricardo Gómez
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