SELF HEALING CONCRETE

Concrete healing bacteria

MOHAMMED HASIM BEEDULLAH

PHD COURSE / STRUCTURAL
Concrete healing bacteria are a type of self-healing technology that involves the use of bacteria
to repair cracks in concrete. This bio-based approach mimics natural processes to restore the
integrity of concrete structures, improving their durability and lifespan.

How It Works

The principle behind concrete healing bacteria is relatively simple: certain bacteria can produce
minerals, particularly calcium carbonate (CaCO₃), when they are activated by water and
nutrients. When cracks form in concrete, water can infiltrate these cracks, providing the bacteria
with the moisture needed for activation. The bacteria then "activate" and produce calcium
carbonate, which fills the cracks and repairs the damage.

Key Components:

1. Bacterial Strain: Specific strains of bacteria are used, commonly Bacillus species (e.g.,
Bacillus subtilis). These bacteria are known for their ability to survive in dormant states
(spores) for extended periods and can withstand harsh environments.
2. Encapsulation: The bacteria are often encapsulated in materials such as calcium lactate
or other nutrients that keep them dormant until activated. This encapsulation ensures that
the bacteria can survive for long periods within the concrete without prematurely
"activating" and producing minerals.
3. Crack Formation: When cracks form in the concrete, water infiltrates the cracks and
dissolves the nutrients or activates the bacteria, allowing them to produce calcium
carbonate, which then fills the cracks and restores the structural integrity.
4. Self-Healing Process: Over time, the bacteria "heal" the concrete by precipitating
calcium carbonate crystals that seal the cracks, preventing further water infiltration and
reducing the potential for further damage.

Benefits:

1. Durability: Self-healing concrete can significantly extend the life of concrete structures
by reducing the need for repairs and preventing the spread of cracks.
2. Sustainability: This approach can reduce the environmental impact of concrete, as it
minimizes the need for extensive maintenance and repairs, reducing material
consumption and waste.
3. Cost-Effectiveness: Over time, the ability of concrete to self-heal can reduce the costs
associated with repairing or replacing cracked structures.
4. Improved Safety: By preventing cracks from worsening, self-healing concrete reduces
the likelihood of structural failure.
Applications:

 Infrastructure: Concrete used in roads, bridges, tunnels, and buildings can benefit from
the self-healing properties of bacterial concrete.
 Marine Structures: Concrete used in underwater structures, which are especially
vulnerable to cracking and degradation due to the corrosive effects of water, can benefit
from the healing process.
 Long-Term Durability: Any concrete structure that is expected to have a long lifespan
can benefit from the ability to self-heal, such as dams, parking garages, and even certain
residential or commercial buildings.

Mechanism of Action:

 When cracks form in concrete, the introduced bacteria become activated in the presence
of moisture and oxygen.
 They metabolize nutrients and produce enzymes, leading to the precipitation of calcium
carbonate (CaCO3).
 This calcium carbonate forms a layer that effectively seals the cracks.

Types of Bacteria:

 Ureolytic Bacteria: These are the most effective for concrete healing. They can convert
urea into ammonia and carbonate ions, which facilitate calcium carbonate precipitation.
 Common examples include species from the genera *Bacillus* and *Sporosarcina*.

Environmental Adaptability:

 These bacteria thrive in alkaline conditions, which correspond to the pH typical of

concrete.
 They can also exist in spore form, allowing them to survive for extended periods until
activated.
Case Study: Self-Healing Concrete Using Bacteria

 Project Overview:

In various civil engineering projects, particularly in Japan and the Netherlands, researchers have
implemented the use of Bacillus bacteria in concrete to enhance its durability and self-healing
capabilities.

 Objective:

To investigate the effectiveness of using bacteria in concrete to create a self-healing mechanism

that can automatically repair cracks, thereby increasing the lifespan of structures and reducing
maintenance costs.

 Methodology:

1. Material Preparation:

- Concrete mixtures were prepared using standard Portland cement with the addition of
Bacillus pasteurii or similar ureolytic bacteria.

- The bacteria were encapsulated in a calcium carbonate carrier to protect them until activation.

2. Concrete Curing:

- The concrete was cured under controlled laboratory conditions, ensuring optimal moisture
and temperature levels to support bacterial growth and activity.

3. Crack Induction:

- Upon curing completion, controlled cracks were created in the concrete samples to simulate
damage.

4. Healing Process:

- Samples were exposed to moisture to activate the bacteria.

- The healing efficiency was evaluated over several days through visual inspection and
measuring crack width.

5. Performance Evaluation:

- The self-healing efficiency was tested by monitoring crack reduction through microscopy and
mechanical tests to assess the impact on tensile strength and load-bearing capacity.
  Results:

- After a fixed period, the concrete samples containing bacteria demonstrated significant healing
with observable reductions in crack width.

- In some cases, cracks of up to 0.5 mm were completely sealed within a week due to calcium
carbonate deposition, improving the structural integrity of the concrete.

 Conclusion:

This case study confirmed that integrating bacteria into concrete effectively enhances its self-
healing properties. The findings show that such bacteria can be a sustainable solution for modern
civil engineering challenges, offering longevity and resilience to concrete structures and reducing
the frequency and cost of repairs.

Challenges and Considerations:

1. Effectiveness: The full effectiveness of bacterial self-healing concrete depends on factors

like the types of bacteria used, the crack size, the environmental conditions, and the
concentration of nutrients.
2. Cost: While the initial cost of bacterial concrete might be higher, the long-term savings
in maintenance and repairs could offset this.
3. Environmental Concerns: There may be concerns regarding the long-term survival and
ecological impact of bacteria in the environment, especially if cracks are sealed in
locations exposed to extreme weather conditions.

Research and Development: While promising, research into concrete healing bacteria is
ongoing, and further testing and optimization are needed to ensure that the bacteria can work
effectively in a wide range of environments and under varying conditions