Bacterial Concrete: A Self-Repairing Biomaterial for Cracked Cement
Bacterial Concrete: A Self-Healing Material for Crack Repairs
Cracks are one of the most common problems in concrete structures, which can compromise their durability, strength, and aesthetics. Cracks can also lead to water infiltration, corrosion of reinforcement, and deterioration of concrete quality. To prevent these issues, various methods of crack repair have been developed, such as epoxy injection, grouting, sealing, and patching. However, these methods are often costly, time-consuming, and not very effective in the long term.
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Fortunately, there is a new and innovative way to repair cracks in concrete using bacteria. Bacterial concrete, also known as self-healing concrete, is a type of concrete that can automatically heal its own cracks by using the biological activity of bacteria. In this article, we will explain what bacterial concrete is, how it works, what are its advantages and disadvantages, and what are its applications and future prospects.
What is bacterial concrete?
Definition and concept of bacterial concrete
Bacterial concrete is a type of concrete that contains dormant bacteria and their nutrients embedded in the concrete matrix. The bacteria are usually spore-forming bacteria that can survive in harsh conditions for a long time. The nutrients are usually calcium-based compounds, such as calcium lactate or calcium acetate. The bacteria and the nutrients are either mixed with the concrete ingredients before casting or applied on the surface of the hardened concrete.
The concept of bacterial concrete is based on the natural phenomenon of bio-mineralization, which is the process of mineral formation by living organisms. Some bacteria can produce calcium carbonate (CaCO3), which is the main component of limestone and marble, as a by-product of their metabolic activity. Calcium carbonate is a hard and insoluble material that can fill up the cracks and pores in concrete and improve its properties.
Types and classification of bacteria used in bacterial concrete
There are various types of bacteria that can be used in bacterial concrete, depending on their ability to produce calcium carbonate and survive in different environments. Some of the most common bacteria used in bacterial concrete are:
Bacillus pasteurii: This is one of the most widely used bacteria for bacterial concrete, as it can produce a large amount of calcium carbonate in a short time. It can also tolerate high pH and temperature conditions.
Bacillus sphaericus: This bacterium can also produce calcium carbonate efficiently, but it requires more oxygen than Bacillus pasteurii. It can also survive in saline environments.
Bacillus subtilis: This bacterium can produce calcium carbonate at a moderate rate, but it has a high resistance to UV radiation and desiccation. It can also form biofilms that protect the bacteria from external factors.
Escherichia coli: This bacterium can produce calcium carbonate at a low rate, but it has a high genetic diversity and adaptability. It can also be genetically modified to enhance its performance.
How does bacterial concrete work?
Mechanism of bio-mineralization and calcium carbonate precipitation
The mechanism of bio-mineralization and calcium carbonate precipitation in bacterial concrete involves four main steps:
Activation of bacteria: When water enters the cracks in concrete, it activates the dormant bacteria and provides them with oxygen and moisture.
Consumption of nutrients: The activated bacteria start consuming the nutrients present in the concrete and produce calcium carbonate as a by-product.
Precipitation of calcium carbonate: The calcium carbonate precipitates in the form of crystals and deposits on the surface of the bacteria and the concrete.
Healing of cracks: The calcium carbonate crystals fill up the cracks and bond with the concrete matrix, forming a self-healing layer that restores the integrity and strength of the concrete.
The following figure shows the schematic diagram of the mechanism of bacterial concrete.
Source: [What is bacterial concrete? - The Constructor](^1^)
Factors affecting the performance of bacterial concrete
The performance of bacterial concrete depends on various factors, such as:
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Type and concentration of bacteria: The type and concentration of bacteria affect the rate and amount of calcium carbonate production, as well as the survival and activity of bacteria in different conditions. Generally, higher concentrations of bacteria result in faster and more effective crack healing, but they may also increase the cost and complexity of bacterial concrete production.
Type and dosage of nutrients: The type and dosage of nutrients affect the availability and consumption of calcium and carbon sources for the bacteria, as well as the pH and alkalinity of the concrete. Generally, higher dosages of nutrients result in more calcium carbonate precipitation, but they may also cause adverse effects on the setting time, workability, and strength of concrete.
Environmental conditions: The environmental conditions affect the activation and growth of bacteria, as well as the solubility and crystallization of calcium carbonate. Factors such as temperature, humidity, oxygen, pH, salinity, and UV radiation can influence the performance of bacterial concrete in different ways. Generally, optimal conditions for bacterial concrete are moderate temperature (20-30C), high humidity (80-100%), sufficient oxygen (5-10%), high pH (8-10), low salinity (<5%), and low UV radiation (<10 W/m).
Crack characteristics: The crack characteristics affect the accessibility and distribution of bacteria and nutrients in the cracks, as well as the amount and shape of calcium carbonate crystals. Factors such as crack width, depth, length, orientation, and location can influence the performance of bacterial concrete in different ways. Generally, optimal conditions for bacterial concrete are narrow crack width (<0.5 mm), shallow crack depth (<10 mm), short crack length (<50 mm), vertical crack orientation, and surface crack location.