Concrete is everywhere in our daily lives - from buildings to roads - but it can crack over time and with increased stress. These cracks, even tiny ones, can let water and air in, eventually causing rust and weakening the steel reinforcements hidden within. Repairing these cracks is dangerous and expensive, especially on bridges and highways.
For years, scientists have been trying to use bacteria to automatically repair these cracks. But most methods require external nutrients to maintain the bacteria's normal function.
That's the idea behind new research from Dr. Congrui Grace Jin, whose recent research explores a self-healing concrete system powered by microorganisms.
Jin points to this major obstacle, saying, "Microbial-mediated self-healing concrete has been extensively studied for more than three decades, but it still suffers from an important limitation—all current self-healing methods are not fully autonomous, as they require external nutrients to sustain the repair agent to continuously produce repair material."
Her solution draws inspiration from nature, achieved by reinventing lichen. Lichens are simple organisms composed of fungi and cyanobacteria that survive solely on air, sunlight, and water. Kim's team designed a synthetic version that uses nitrogen-fixing cyanobacteria (which absorb carbon dioxide and nitrogen from the air) and filamentous fungi (which help collect calcium ions and generate calcium carbonate (CaCO₃) - a mineral that can fill cracks in concrete).
They tested three combinations of microorganisms: Trichoderma reesei with Anabaena inaequalis, Trichoderma reesei with Nostoc punctiforme, and a mix of three. All three combinations grew well in a laboratory environment with just air and light (without any added nutrients). To understand how the microbes were performing, the team used five methods: densitometry (to check light absorption), biomass dry weight, resazurin (an indicator to detect metabolic activity), selective media fungal inoculation, and phycocyanin testing (to check the health of the algae).
The results showed that the paired microbes were healthier and more efficient than growing them individually. They are even able to form calcium carbonate (CaCO₃) in concrete samples, which bodes well for their potential in practical applications. What stands out about this approach is its ability to repair cracks without human assistance, potentially reducing the need for costly manual inspections and maintenance in the future.
Dr. Jin is also working with social scientists at Texas A&M University to understand public feelings about the use of "living" organisms in construction and explore the ethical and legal issues involved. The research, funded by the U.S. Defense Advanced Research Projects Agency's (DARPA) Young Faculty Award Program, combines biology and engineering to solve real-world problems that impact millions of people.