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Just as skin tissue is capable of self-healing with the help of the vascular system, an American research team has succeeded in producing “living” concrete structures that can self-repair their cracks using biological technology inspired by the human body.
The research team – from Drexel University’s College of Engineering – put a new twist on an ancient practice used by early builders to achieve this new concept of “living concrete” that uses bacteria that rush to the site of cracks to repair the damage.
In the past, the first construction workers mixed a type of fiber – “horse hair” – into the clay, which helped strengthen the building mixture. But a new method of construction takes this ancient mechanism to the next level by turning the fibers into a living tissue system that drives concrete-healing bacteria to the site of cracks to repair the damage. This technique was reported in patrol “Construction and Building Materials”.
Nature inspiration
The researchers called the bacteria-laden fibers “Biofibre,” and in the study they provided a detailed description of this system, noting that it is a polymer fiber covered with a bacteria-laden hydrogel and a protective shell that responds to damage. The bio-fiber network embedded inside the concrete improves its durability and prevents cracks from forming. Growth and self-repair.
Amir Farnam, associate professor at the College of Engineering at Drexel University and leader of the research team, says: a report Posted by the university’s website: “This is an exciting development that complements ongoing efforts to improve building materials using inspiration from nature.”
He adds: “We see every day that our old concrete structures are exposed to damage, reducing their functional life and requiring critical and expensive repairs. Imagine that they can repair themselves just as our skin tissues do so naturally.”
If skin tissue does this through a multi-layered fibrous structure filled with fibers with the help of our own self-healing fluid, blood, biofibres mimic this concept and use stone-making bacteria to create living, self-repairing concrete that responds to damage, Farnham explains.
Stone-making bacteria are natural living organisms that participate in many natural processes that contribute to the formation of stones or mineral deposits, including:
- Thiobacillus ferroxidans: These bacteria oxidize iron and sulfur compounds, leading to the formation of minerals such as iron oxides and sulfates, which can contribute to the formation of certain types of stones.
- Leptothrix discophora: These bacteria produce thin, filamentous sheaths that can become coated with iron or manganese oxides, contributing to the formation of mineral deposits.
- Cyanobacteria: Some species of cyanobacteria are known to be involved in the formation of “stromatolites,” which are layered structures formed by trapping and binding sedimentary grains by microbial mats.
- Lysinibacillus croicus: It is a bacteria known for its role in the formation of minerals, especially calcium carbonate.
Bacteria producing calcium carbonate
The research team worked with the bacterium Lysinibacillus croicus. This perennial bacterium, commonly found in soil, has the ability to drive a biological process called calcium carbonate precipitation to create a stone-like material that can settle and harden in a patch of exposed cracks in concrete.
The researchers found that when these bacteria are stimulated to form internal spores, they can survive the harsh conditions inside concrete, remaining dormant until called into action.
The formation of endospores, also known as “sporulation,” is a survival strategy used by some bacteria. It is a complex process that occurs when conditions become unfavorable for bacterial growth and reproduction. The steps involved in endospore formation usually include the following:
- the beginning: When environmental conditions become unfavorable (such as nutrient depletion or other stresses), the bacterial cell initiates the process of sporulation, in which the DNA within the bacterial cell condenses and becomes more resistant to damage.
- Barrier configuration: The bacterial cell undergoes asymmetric cell division, creating a smaller chamber known as the anterior spore within the parent cell.
- Development of mother cell and anterior spores: The mother cell engulfs the forespores and forms a double membrane around them, and the mother cell provides nutrients and protection to the developing spores.
- Composition of shell and coat: The anterior spore develops a cortex layer that provides resistance to environmental stresses, and a protein layer is synthesized around the cortex.
- Maturity and departure: A mature endospore forms within the mother cell. Eventually the mother cell disintegrates, releasing the endospores into the environment. The endospore remains dormant until conditions become favorable again, allowing it to germinate and resume normal bacterial growth.
Endospores are incredibly resilient and can withstand extreme conditions including heat, drought, chemicals and radiation, making them a highly effective survival mechanism for some types of bacteria. The Lysinibacillus croicus bacteria used by the researchers are known for their superior ability to form endospores, ensuring their persistence and potential reactivation when the environment becomes more suitable for growth and reproduction.
How does Biofibre work?
If bacteria are the primary factor in the Biofibre system, what distinguishes this work from previous attempts to employ bacteria is choosing the right combination of bacteria, hydrogel, and polymer coating, as explained by Muhammad Houshmand, a doctoral student in the Farnham laboratory who participated in the study.
“To assemble Biofibre,” says Houshmand, “we started with a polymer fiber core capable of stabilizing and supporting concrete structures. We then coated the fibers with a layer of hydrogel laden with endospores from bacteria, and encased the entire assembly in a polymer shell that responds to damage like skin tissue. The entire assembly is approximately “A little more than half a millimeter.”
Houshmand explains how the system works: “Biofiber is placed in a network throughout the concrete while it is being poured, and it acts as a reinforcement support agent, but its true capabilities are only revealed when the crack penetrates the concrete enough to penetrate the outer polymer layer of the fibers.”
He says, “When the water makes its way into the crack and eventually reaches the biofibres, it causes the hydrogel to expand and push its way out of the shell toward the surface of the crack. As this happens, bacteria activate from their internal form in the presence of carbon and a source of nutrients in the concrete, and the bacteria interact with the calcium present.” In concrete, it produces calcium carbonate that acts as a cementing material to fill cracks all the way to the surface.
The ultimate repair time depends on the size of the crack and the activity of the bacteria, a mechanism the team is currently studying, but early indications suggest the bacteria could do their work in as little as a day or two.
He adds, “Although there is a lot of work to be done in studying the kinetics of self-healing, our findings suggest that this is a viable way to repair cracks without external intervention, meaning that a living concrete infrastructure can be created and its life extended.” This prevents the need for costly repairs or replacements.
Facing the challenge…two unanswered questions
In a telephone conversation with Al Jazeera Net, Professor of Construction Engineering at the American University in Cairo, Mohamed Naguib Abu Zeid, expresses his admiration for what the researchers have achieved in their study of their ability to overcome one of the challenges that faced previous research teams that worked on using bacteria to repair cracks in concrete on their own, which is the challenge. Related to time, they observed the success of their method in getting bacteria to do the work in less than a day or two.
Abu Zayrad continues that two questions remain unanswered:
- the first: What type of cracks are bacteria good for? One of the important challenges that hindered the transfer of bacterial treatment to practical applications is that it works only with small cracks that occur in stages, and is not suitable for large and sudden cracks.
- Second: To what extent are bacteria able to work again after the cracks are repaired? If you succeed in repairing cracks once, can you work again?
However, even in the absence of an answer to the two questions, the results of the study remain, in Abu Zeid’s opinion, an important step on the way to moving this technology into application with the aim of extending the life of concrete, a breakthrough that will have material dimensions as well as more important environmental dimensions.
Extending the life of concrete is seen to help reduce greenhouse gases, as the process of making concrete components by burning a mixture of minerals such as limestone, clay or shale at temperatures exceeding 2,000 degrees Fahrenheit accounts for 8% of global greenhouse gas emissions.
Because concrete structures can decompose in less than 50 years depending on their environment, concrete is considered the most consumed and sought-after building material in the world, and producing concrete that can last for a longer period would constitute a major step in reducing its contribution to the phenomenon. Global Warming Global, not to mention reducing the long-term costs of infrastructure repair, as Abu Zeid explains.
