Self Healing Concrete
Self-healing Concrete is an amazing invention in the building construction industry. Its use can solve the problem of deterioration well before the end of their service life.
Concrete is still one of the prime materials in the construction industry, from building a foundation to a structure like bridges, dams, retaining walls, and underground parking lots. Conventional concrete has a flaw, it tends to crack when subjected to tension.
In self-healing concrete is prepared with mixing healing agent or bacteria in the concrete convert nutrients into limestone has been under development at the Civil Engineering and Geosciences Faculty in Delft since 2006.
This research work has a wider perspective or goal to study the self-healing properties of plastics, polymers, composites, asphalt, and metals as well as concrete.
Hendrik Jonkers a dutch scientist has first produced self-healing concrete, a product that, despite its higher initial cost, could save money and work in the long run. Hendrik Jonkers has been nominated for the European Inventor Award of 2015 for his invention.
Cost of Self-healing Concrete
Unfortunately, Self-healing concrete cost is too high for normal construction use. Being innovative and useful construction material self-healing concrete cost is more than conventional concrete. It is about $33-44 per square meter.
Why the Need for Self-healing Concrete?
Concrete is still one of the most important construction materials from the time of its invention and will continue in the future also, but most concrete structures are prone to cracking.
Even a small crack on the concrete surface makes the whole structure Susceptible to deterioration because water seeps in to degrade the concrete and corrode the steel reinforcement, greatly reducing the lifespan of a structure.
Concrete can resist compressive force very well, but it is weak in resisting tensile force.
That’s why steel reinforcement is provided in concrete. In many concrete structures, an excessive tensile force can lead to crack and these can occur relatively soon after the structure is built. This crack is repaired by applying a concrete mortar that is bonded to the damaged surface.
Sometimes, for wider crack mortar is required to insert into the existing structure with metal pins to ensure that it does not fall away.
Repair or maintenance of any concrete is more time-consuming and it is often very difficult to gain access to the structure to make repairs, especially if they are underground or at a great height.
How Does Self-healing Concrete Work?
Self-healing concrete is a type of concrete that is made with mixing healing bacteria in it that will biologically produce limestone to heal cracks that appear on the surface of concrete structures.
Only some selected type of bacteria can produce healing limestone like genus Bacillus, along with a calcium-based nutrient known as calcium lactate, and nitrogen and phosphorus, are mixed with concrete ingredients while making concrete.
These select types of bacteria can be alive in concrete for more than 200 years.
However, when slef healing concrete element damage or crack and water start seeping through it, the bacteria spores are activated on contact with water and nutrients.
These activated bacteria start to feed on the calcium lactate available in concrete.
As bacteria consume oxygen and the soluble calcium lactate is converted to insoluble limestone.
The limestone gets solidified as come in contact with the atmosphere, thereby sealing it up. It represents the same process in which fracture in the human body is naturally healed by osteoblast cells that mineralize to re-form the bone.
During the bacterial conversion of calcium lactate to limestone has additional benefits that it consumes oxygen which is a major element in the process of corrosion of steel.
As this bacterial activity has consumed all oxygen, it increases the durability of steel-reinforced concrete constructions.
While making self-healing concrete two bacterial agents are feed name as the bacterial spores and the calcium lactate-based nutrients are introduced to the concrete as separate clay pallets.
These clay pallets ensure that the bacterial agent will not get active before cracking concrete.
This gets activated only when the concrete gets cracked and crack open up the pellets and incoming water brings the calcium lactate into contact with the bacteria do these become activated.
Self-healing Concrete is a successful test for this process and it is observed that the bacteria germinate and multiply quickly.
Bacterial agent converts the nutrients into limestone within seven days in the laboratory. But in the outside condition, it may take several weeks.
Finding the Right Bacteria For Self-healing Concrete PDF
For making self-healing concrete finding the right bacteria that can capable of surviving in an extreme alkaline environment is an essential requirement. As we know that, when water and cement mixed together have a pH value of up to 13, usually a hostile environment for life.
The majority of microorganisms will die at a pH value of more than 10. To make concrete that can self crack healing properties we require microbes that thrive in alkaline environments which can be found in natural environments, such as, carbonate-rich soils in desert areas of Spain, soda lakes in Egypt, and alkali lakes in Russia
Application in Small-Size and Medium-Sized Buildings (Residential and Public)
Small-size buildings are usually residential and located either in the suburbs, towns, or villages.
And like most buildings, concrete is one of the main building materials used, especially for foundation (slabs or columns), as small residential buildings rarely change function it is practical to want to increase their life-span, and hence self-healing concrete would be the better option.
Medium size structure generally uses more amount of concrete, unlike like skyscrapers that use more steel and small-size buildings which use more stone or wood.
Both residential and public middle-sized buildings seem to be eligible for the use of self-healing concrete, however, and especially in public buildings as the lifespan increases, designs must be flexible.
Therefore, instead of demolition, there will be re-modeling when the service held within the building is no longer needed in a particular area, which in turn has a positive effect in reducing the CO2 emission by avoiding construction.
Application in Large-Size Buildings and Roads (Residential and Public)
Self-healing concrete is used in the construction of bridges and all road constructions as they often experience small-sized cracks due to heavy loads and constantly need maintenance.
The use of this kind of self-healing concrete will reduce the maintenance cost significantly and will increase safety, therefore, it’s highly recommended to use due to its many benefits.
Self-healing concrete buildings will defiantly benefit from the use of this kind of concrete just as the infrastructure will be enhanced by providing safety and durability.
Advantages and Disadvantages of Self-healing Concrete
Advantages of Self-healing Concrete
- Self-healing concrete can get self-repair without any external treatment.
- Compare to normal concrete it has better compressive and flexural strength.
- It has good resistance against freeze-thaw attacks.
- Self-healing concrete permeability is low.
- Reduce corrosion of steel as crack self-repair which is a major reason starting corrosion.
- In self-healing concrete, bacteria used in this concrete-like Bacillus bacteria are harmless to human life and hence it can be used effectively.
Disadvantages of Self-healing Concrete
- Self-healing concrete cost is almost double compared to normal concrete.
- Growth bacteria can be affected by different environmental conditions.
- The clay pallets which mixed in concrete almost cover 20 % volume of concrete and This may become a shear zone or fault zone in the concrete.
Watch Video: Self-healing Concrete
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