Our world is filled with self-healing properties that can be observed in nature. From plants to the human body, every single living life is special for its self-mending properties. Have you ever wondered if this is possible in concrete also? Yes. It’s possible with the help of self-repairing concrete.
In today’s Brick & Bolt blog, you are going to explore more about self-healing concrete.
What is Self-Healing Concrete?
Concrete that can get repaired or mended by itself after any damage is called self-healing concrete. Often, there is a correlation between durability and cracking. There can be around 19 Types of Cracks in the Building, such as settlement fractures, expansion cracks, plastic shrinkage cracks, shear and flexural cracks, or any combination of these. Splits caused by reinforcing corrosion, weathering-related cracks, heat strains, concrete corrosion, and poor construction all contribute to the problem. In self-healing concrete, the ability to withstand physical and chemical damages is higher than that of other types of concrete. Thus, it can be a solution to these problems.
How Does Self-Healing Concrete Work?
There are numerous methods involved in the self-healing process. Some of them are:
Autogenous Self-Healing Concrete
In this procedure, unhydrated cement particles act as a healing agent. The hydration of the clinker minerals stimulates the healing process.
The intrinsic qualities of concrete and calcium dissolution aid in the repair of hairline fissures.
Autonomous Self-Healing Concrete
While the autogenous self-healing process is intrinsic, it is only effective for minor cracks. This is where autonomous self-healing approaches maintain their ground. Additional external self-healing provisions are provided to improve performance and facilitate concrete repair.
Vascular Self-Healing Method
Vascular self-healing is a multi-faceted healing technology in which concrete is embedded with a hollow tube network with a healing substance inside. When choosing tubes, keep in mind that they are chemically inert. Additionally, these lengthy parallel tubes should make a strong link with concrete.
Inorganic Phosphate Cement (IPC) is preferred in conjunction with clay tubes. When the healing agent comes into contact with a break in the concrete, it seeps due to hydrostatic pressures, capillary or gravity forces, and seals the crack.
Capsule Based Self-Healing Method
The healing efficacy of this approach is determined by the cementitious matrix and the characteristics of the embedded capsules.
Even a multi-capsule system can possibly be relied on. When these capsules come into contact with one another and split open, healing components are released, and the fracture is healed. Epoxy resins, polyurethane, and methyl methacrylate monomers(MMM) can all be used as healing agents. The microcapsule utilised in this method can be cylindrical or spherical in shape. The shell can be made of silica, ceramics, glass, polystyrene, or urea-formaldehyde.
Embedding Shape Memory Alloys (SMAs) Method
Shape Memory Alloys are a sort of smart material that can be used in concrete due to its unique ability to retain its original shape even after deformation. Essentially, they serve the purpose of self-centering.
Researchers explored the impact of heating Shape Memory Alloy wires with electrical currents before inserting them into concrete beams. The Shape Memory Alloys were utilised for retrofitting, and they were pre-tensioned before being tested. During the test cycles, loading was applied to the mid-span, and deformation and cracking were investigated. The heated wires proved to be successful in crack mending and closing the cracks.
Microbial or Bacterial Self-healing Concrete
Calcium Carbonate (CaCO3) precipitation can repair micro-cracks in concrete by microbial/bacterial self-healing. Microbial spores and calcium supplements containing healing agents are first manufactured in batches and then mixed into concrete. Researchers investigated microbiological intrusion in concrete, such as the side walls of a ship lock, and discovered that the fissures mended within 60 days.
Types of Self-Healing Concrete
There are two different types of self-healing concrete.
- Biotic
- Abiotic
Biotic Concrete
In biotic self-healing concrete, bacteria is used as a main ingredient. The bacteria that produce acid are added to this bacterial concrete. In this bio-concrete, bacteria act as catalysts for the crack-healing process. This is preferable when the concrete structure is in contact with water or moisture.
When cracks occur in concrete, water seeps in, and bacteria spores feed on calcium lactate, converting it to insoluble limestones. The insoluble limestone hardens and fills the cracks without external aid.
Different acid-producing bacterias are used in this bio-concrete. Such as:
- bacillus pseudofirmus
- bacillus halodurans
- bacillus cohnii
- bacillus pasteurising
- bacillus sphaericus
- escherichia coli
Abiotic Concrete
Abiotic self-healing concrete, as the name suggests, heals concrete cracks without the involvement of biological agents. Instead, it utilises various chemical compounds to fill and seal cracks that occur due to environmental stresses or mechanical wear. This reactive mechanism is often preferred in conditions where moisture accessibility is limited. It is a valuable alternative to biotic self-healing methods.
Some of the chemicals used in abiotic concrete are cyanoacrylate, epoxy, polyurethane (PU), methyl methacrylate(MMA), dicyclopentadiene(DCPD), Na2Sio3 etc.
Self Healing Concrete Applications
There are numerous applications of self-healing concrete in construction. Some of them are:
- Roadways and Pavements: Roadways made up of self-healing concrete could patch up minor damages by themselves when cracks occur.
- Bridges: The tiny fissures that usually form in bridge structures due to freeze-thaw cycles can repair themselves with the use of bacterial concrete.
- Residential and Commercial Buildings: Homeowners and builders can stay carefree, knowing that minor damages will mend themselves, extending the structure’s life.
- Tunnels: Autogenous healing in tunnels directs the concrete’s ability to repair its own cracks without external intervention, mainly through mechanisms such as the crystallisation of calcium carbonate and the hydration of unhydrated cement.
- Airports and Harbors: Airports and harbours are busy with heavy machinery and traffic. Over time, normal wear and tear can take its toll. Self-healing concrete employs healing agents such as autonomous self-healing, microencapsulation, and vascular healing to fix cracks and increase structural durability.
- Dams and Reservoirs: By using self-healing concrete in dams and reservoir construction, you can ensure longevity and greatly reduce the risks connected with concrete fractures and crevasses. Self-healing concrete contains an agent, such as dormant bacteria or capsule-based systems, that automatically repairs cracks and extends the life of the construction.
Advantages of Self-Healing Concrete
The following are benefits of self-healing concrete:
- It can span several decades or centuries. This is the primary benefit of self-healing concrete. This means that you will never need to replace your concrete surface again during its lifetime.
- Self-healing concrete reduces concrete upkeep. In regular concrete, cracks must be filled and sealed.
- Self-healing concrete improves compressive strength.
Challenges and Limitations
- One of the major downsides of self-healing concrete at the moment is its high cost. It is more expensive than conventional concrete. Perhaps in the future, the cost will drop down as self-healing concrete in construction becomes more popular.
- Many contractors do not yet know how to use this self-healing concrete in construction. Since it is a new product, many individuals have no idea how to utilise it.
- There is no existing code to standardise self-healing concrete in construction.
Self-healing concrete is a novel solution that takes us closer to sustainable, long-lasting construction. Its capacity to autonomously repair cracks opens up a wide range of applications in infrastructure, including roads, bridges, buildings, and tunnels. If research advances and its use becomes more common, self-healing concrete has the potential to dramatically cut maintenance efforts while also extending the lifespan of concrete structures and ultimately revolutionising current architecture.