What is Self-healing Concrete?

Table of Contents

What is Self-healing Concrete?

Methods of Self-healing in Concrete

Natural Concrete with the Ability to Heal Itself

Autonomous Self-healing Concrete

Method of vascular Self-healing

Capsule-based Self-healing Method

Embedding shape memory alloys (SMAs) method

Bacterial  or Microbial Self-healing Concrete

An Experimental Investigation on Bacterial Concrete

Choice of bacterial species

Reason for the choice

Summary of Process

Result Analysis

What is Self-healing Concrete?

Self-healing concrete is a specific type of concrete that can repair itself after the damage has occurred. Concrete's ability to mend itself when cracks appear is known as its self-healing or self-repairing property. The durability of concrete is the defining feature of these uses. Concrete's ability to withstand physical and chemical assaults is enhanced by its material characteristic of durability. There is a correlation between a decrease in durability and an increase in the likelihood of cracking.

Cracks in concrete can be classified 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, and poor construction all contribute to the problem.

There are a variety of causes for cracks to appear. For the sake of brevity, nevertheless, here are a few examples:

• Improper blending, agitation, and curing, resulting in a substandard product.
• Use of excessive force
• using low-quality components (Like reinforcements – easy corrosion)
• Consequences of unfavourable temperature
• Mixing flaws
• Too much moisture in the concrete and the ratio of water to cement was not kept at an adequate level.

Methods of Self-healing in Concrete

Multiple concrete self-repair techniques are presented. Some examples of this are:

Natural Concrete with the Ability to Heal Itself

There are self-healing characteristics inherent to concrete. In this technique, the unhydrated cement particles are used as a reparative substance. Minerals in the clinkers activate the healing process when they get hydrated.

By utilising the natural qualities of concrete and the dissolution of calcium, this reaction with water of cement aids in repairing fine cracks in the material.

Autonomous Self-healing Concrete

While the inherent autogenous self-healing approach is promising, it is limited to repairing very minor damage. This is where the self-healing, autonomous approaches shine. Here, additional exterior self-healing measures are provided for concrete restoration, boosting performance.

Method of vascular Self-healing

Vascular self-healing is an example of a multi-healing approach in which a web of hollow ducts containing a healing element is placed within the concrete. It is important to remember that the ducts are chemically inert when making your selection. These lengthy parallel tubes should also bind well with the surrounding concrete.

With clay ducts, inorganic phosphate cement (IPC) is the best option. Hydrostatic pressures, together with capillary or gravity forces, force the healing agent through a gap in the concrete, sealing the crack.

Capsule-based Self-healing Method

Microcapsules of either spherical or cylindrical shapes can be employed in this method. Ceramics, silica, glass, urea-formaldehyde and polystyrene are all viable options for the outer shell.

The cementitious matrix and capsule qualities determine the method's healing effectiveness. The multi-capsule system can be trusted as well. Healing components are released and the crack is repaired when these capsules break apart upon touch. Epoxy resins, polyurethane, or Methyl methacrylate monomers are all viable options for the healing agents (MMA).

Embedding shape memory alloys (SMAs) method

Context-Recalling Shapes Concrete can make use of alloys, a type of smart material with the unusual virtue of remembering its original shape after being distorted. Ultimately, they help in the process of introspection.

Putting Shape Memory Alloy wires through an electrical current to heat them up and then giving that heat to concrete beams has been studied by scientists. For this retrofitting project, we employed Shape Memory Alloys and pre-tensioned them before putting them through their paces. Midspan loading was provided during the test cycles so that cracking and deformation could be studied. The cracks were successfully repaired by the heated wires.

Bacterial  or Microbial Self-healing Concrete

Microcracking in concrete can be patched using the bacterial/ microbial self-healing technique, which is aided by the precipitation of calcium carbonate (CaCO3). The healing ingredients, which consist of microbial spores and calcium nutrients, are first created in batches and then mixed into concrete.

Researchers have observed fissures in concrete, such as those found in the side walls of a ship lock, repaired in as little as 60 days after experimenting with microbial concrete infiltration.

An Experimental Investigation on Bacterial Concrete

Here is a quick synopsis of what we learned by comparing the effects of adding bacteria to fresh and saltwater on concrete.

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Choice of bacterial species

Bacillus Subtilis BKH2, is a thermophilic anaerobic bacteria developed by genetic engineering (A genetically-enriched microbe).

Reason for the choice

• A user-friendly interface is provided, making this system excellent for self-repairing concrete.
• Constant, alkaline-thriving bacterial communities.
• Producing calcium carbonate crystals also help in mending concrete.
• The presence of bacteria aids in lowering the pH when cracking in concrete begins, to a range of roughly 10 or 11.
• An economically viable and ecologically sound choice.

Summary of Process

45-60 ml of bacteria is the recommended dosage.

Direct application of bacteria entails including bacterial spores and a calcium nutrient, such as calcium lactate, into the concrete mixture at the time of placement.

Now, after cracks appear in the concrete, bacteria become active (begin germinating by breaking spores) and consume calcium lactate, forming limestone that further aids in filling up the fissures.

Result Analysis

The compressive strength of concrete treated with bacteria is significantly enhanced during the curing process when ordinary water is used. The strength of concrete improves by around 40% after 7 days and by around 45% after 28 days.

Salt crystallisation during the first week of curing, as observed in experiments, appears to help boost strength by around 50%. This is presumably due to a high concentration of calcium chloride. On the other hand, after 28 days, the strength of cured lime in saline water gradually drops by roughly 40% due to the hydration of the lime.

That concludes this brief exploration of self-healing in concrete and the supporting evidence from experiments on self-healing bacteria.

I hope the blog provides you with a sound understanding of Self-healing concrete. 

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