Since the first rooting or foundation of scientific researches or experiments, humans have been competitively improving to discover new technologies, one after the another in search of ultimate power in the planet. In the modern era of science and technologies humans have successfully developed various new and futuristic technologies like Self-Healing in various objects considering Glass or Concretes, Fast Charging Systems, 3D Printing technology, etc.
In the world with high pollution and decreasing sustainability, scientists or researchers have successfully managed a way for a complete sustainable future either by 3D Printing the concrete (building blocks of future) or providing it with a self-healing technology.
Self-Healing Concrete: An Overview
Concrete, the building block of any construction on the planet, had from the very beginning faced an issue of denting or cracking with time. However, scientists have found out an effective way to reduce this denting or cracking and moving towards a sustainable and human-friendly planet through the self-healing or self-repairing technology being all set to be implemented at a wider scale.
Self-healing concrete is defined as the ability of concrete to repair its cracked parts by itself. Some special materials which are made of fibers and capsules containing specific adhesive liquids are distributed into the concrete mix. When cracks happen, the fiber or capsule breaks apart and start the healing mechanism of the cracks by releasing adhesive liquid which is later dispensed into the material.
Cracks in concrete is a common phenomenon because of their relatively low tensile strength. In some tropical as well as equatorial countries it is very common to have cracks on concrete within very few years of construction due to the climatic condition. When concrete is exposed to direct sunlight accompanied by the rain water its durability decreases since water can penetrate into concrete. This has been a serious problem so far. Sometimes if microcracks grow and reach the reinforcement, not only it affects the concrete but also it corrodes the reinforcement steel bar.
The technology involves healing of dents and cracks either by autonomously or autonomically, either by triggering chemical reactions within the block itself or by using various other techniques like shrinkable polymers, specialized fibers or mineral or bacteria and other biological agents, etc. In general, this technology completely imitates the self-healing mechanism of human body wound healing by automatic release of collagens into the target spot, considering the cracks or dents to be the wound and the technique used as the collagen clotting.
How does Self-Healing Concrete Works?
The technology of automatically healing or repairing of denting and cracks in a concrete works in the two ways i.e. Autonomic and Autonomous healing of Concretes. The later are mentioned below: –
Autonomous self-healing technology is defined as the process of self-healing occurrence without any human intervention. The stimuli may be external such as heat, light, temperature etc. Autonomous crack healing capacity in cement best material relies upon the conventional constituent of the cementitious matrix and can also be stimulated through tailored addition.
Micro cracks can be cured with another method by using polymers in the concrete. The use of polymers which is reactive to heat as soon as the heat enters in microstructure cracks the polymers in response to heat it will shrink and heal the cracks. Polyethylene terephthalate (PET) is a type of shrinkable polymer which is activated with a heating system inside the build material to compress and close the crack enhancing autogenous healing process. This even increases the mechanical strength, durability, permeability and improvement in microstructure evaluation.
Fibers and Mineral Action
Fibers play a key factor in the blockage of cracks in the concrete due to its considerably low internal tensile force and subsequently decrease crack width, contributing to better self-repairing mechanism. According to some, fibers block the corroding chemicals to enter the crack and carry out several rounds of drying and wetting process to heal the cracked layers. However, the complete process of self-repairing using fibrous autonomous mechanisms is an effective process but costlier and a challenging process to carry-out in the external environment.
Other than fibrous technique of self-repairing, researchers are also working on a chemically equipped approach to the technology. These can be in the form of treated minerals called Supplementary Cementitious Powders that are mixed with cement. This mixture in return highly fertilizes and hydrates the mixtures improving the self-repairing as well as better binding of cementitious particles in the concrete.
Silica Fumes, Ash and Silicon Oxide, etc are popularly used to provide a better stability and rigidity along with improving the self-healing mechanism of the concrete. This mixture as well as fibrous technique provide almost 80% of the healing from cracks and dents emerging as one of the most efficient techniques for autonomous repairing or healing of cracks.
Autonomic Self-Healing Technology
Autonomic self-healing realizes the embedding of unconventional engineered addition in the matrix to provide self-healing function as discussed earlier. Autonomic has been considered the most useful technique of healing due to its situ repair. It acts directly at the location of damage with internal delivery or situ repair. The brooch for the autonomic healing agent is discrete and continuous. However, there are numerous factors upon which economic work such as from A development of autonomic capsule or bacteria which can repair concrete, mechanical characteristic, teaching and healing evaluation.
Autonomic healing of concrete can be done by using bacteria which are able to limestone which is Calcium Carbonate. And if we incorporate those into the cracks or around the cracks which are formed then the limestone will heal the cracks. Concrete is a hostile environment and the bacteria which releases Calcium Carbonate can survive in this environment of high alkaline pH and produces limestone at the same time. Research shows that bacteria can easily grow in alkaline conditions this makes them suitable for their use in concrete. The Bacteria is kept in a medium which contains calcium, and in presence of calcium and carbon dioxide they produce limestone that is calcium carbonate.
The cracks in concrete are then healed with bacteria and bacterial food which is Calcium, these bacteria will use calcium with carbon dioxide to precipitate calcite. There are some special types of bacteria like Bacillus which can produce limestone using calcium and carbon dioxide. This is also environmentally friendly.
Factors affecting Self-healing of Concretes
Since, the field involves mixture prior application to the victim concrete with dents. Hence, some factors need to be kept in mind as listed below.
Amount of Moisture
There is a general concept of science that bacteria and viruses can easily grow in wet and moist environments. So, moisture is a favorable factor for the growth of bacteria in Bio concrete cements. As there will be moisture the Bacillus family will grow and stay alive in bio-concrete for nourishment of formed cracks. Too high temperatures can kill them and they can clean sweep also. If this happens there is a meaning of bio-concrete. So the amount of moisture is directly related to the flourishes of the bacterial family and staying alive.
The width of cracks is the most important factor on which the self-healing concrete technique depends. The healing speed, as well as the healing quality, is directly proportional to the width of the cracks. If the cracks are smaller, it is easy to repair and they last for longer since there was very less damage. Sometimes the cracks are so wide that getting self-healed does not even fix the problem. Tests have shown that the occurrence of crack is a function of temperature between 20degree to 80degree the width differs about 0.05mm to 0.20mm.
Water Cement Ratio
The water to cement ratio mainly affects the two properties that are strength and workability of concrete. As the increase in water to cement ratio comprehensive strength decreases and the workability increases and vice versa. A high water-cement ratio includes more unreacted cement particles and this is proved that earlier crack formation is a sign of imbalance of water and cement ratio. The self-healing process increases and even works more effectively as well as accurately when the right number of ratios of water and cement is.
Pressure is one of the key factors for the formation of cracks in the cementitious matrices. If there is tremendous pressure then it won’t be helpful for self-healing agents to do their work because the amount of crack formation will be more than its healing speed. Since cracks can form very easily due to high pressure there should be proper use of cement/ steel pillars, so that it can handle the stress of weight of infrastructures.
Use of Nanotechnology in Self-Healing Concrete
From the very initial days, nanotechnology was aimed to be used as a tool for manipulation of structures at a nanoscale (roughly one-billionth of one meter). It is regarded as the best technology that would help better understand the planet at a minute phase. The same intention pulls the use of nanotechnology under the newer technology i.e. self-healing concrete. This collaboration might help Concretes to attain better flexibility as well as durability.
In comparison to the traditional techniques suggested by the researcher regarding self-healing or repairing technology i.e. autonomous or autonomic, nanotechnology can completely change the game by simply rearranging and recombining after any type of dents or cracks with a better efficiency rate, rather than going through a lengthy process.
In other words, in my opinion, Use of Nanotechnology for Self-healing technology can provide a robust and reliable solution with quicker action response time. On the one hand, it can provide a modern-day answer to the rising demands of customized housings with strong hold capacity. On the other hand, Increased prices of Nanotech items leads to shattering of further research upon the technology. The same has resulted in a decline in the testing and experimentation of compatibility checks between different binders and nanotech products to be used.
Some of the basic challenges for the development of Self-healing technology are listed below: –
Manufacture of Materials
The manufacture of required elements for the technology i.e. Fibers or Supplementary Cementitious Powders, etc requires proper cultivation of customized chambers. This results in low volume production of the same which leads to price hike of the material for the laboratory experiments of Self-healing technology. Despite the price of the materials, the same had subsequently failed to deliver satisfactory results in the experiments.
The researcher working on Self-healing technology had failed to provide enough efficiency in repairing the system.
Lack of Proper Machineries
The technology involving the self-repairing of the cracks and dents in a concrete is in very initial stages but the researchers are expecting the coming decade for mass scale global deployment. One of the biggest challenges for the same involves lack of efficient and cost-effective machinery for large scale production of the elements for the final product. However, the scientists are expecting the challenge to be solved as we move closer to retrieve a final product out of the current experimental stage for the technology.
Self-healing of cracked structures or concrete, doesn’t that sound revolutionary? Infact, the concerned technology is itself another revolutionary step of science toward sustainability with various applications showing up to date.
Concrete, the fundamental building blocks of developing planet Earth. However, the same are expelled out of the construction site if found dented or cracked leading to generation of tons of construction waste. Self-healing technology has the potential of repairing dented structures automatically. This invention is expected to increase building blocks more efficiently and increase life-span. This might decrease the generation of construction wastes in the coming years by limiting fresh production rather than reusing the same.
Reduce Wear & Tear
Developing nations like India, regularly face the issue of wear and tear on the roads or highway leading to giant holes in the mid-path. This technology can deliver an effective way to tackle the giant holes by healing or repairing without the need of starting with the re-manufacture of the same. This is the best use case where these technologies can outplay others without any misconceptions.
The plants or factories producing cements or binders contribute almost 12% of the total greenhouse gas budget. Self-healing technology can dramatically reduce fresh production which can later deliver a better and pollution-free environment.
Some of the backlogs of the technology are mentioned below.
The ingredients or elements needed for completion or working of Self-healing of Concrete i.e. Nanotechnology, bacteria, etc are today found at a cost much higher than expectations. Until the prices of the same are under the expected band, it is tough to implement on a mass scale.
Among the elements, Nanotechnology is of special significance for its higher price and lesser supply.
Lack of Standardization
The technology is comparatively newer; hence this doesn’t have a proper standardization or a code of implementation. Local standardization is however available for some, but a global standardization is absent which is necessary for better as well as efficient application.
Need of Specialized Labor
Very few contractors accept these types of construction across the planet. Like India being an underdevelopment country has very few or more or less none skilled and highly educated labor across the construction industry. This technology demands proper implementation in requisite quantity.
Recent technologies or inventions by the modern-day researchers aim to provide a better and sustainable life on the planet, either be it 3D Printing, Nanotechnology or may it be Self-healing Concretes, etc. On the one hand, 3D Printing delivers the matched copy as designed in the software, on the other hand, Nanotechnology provides artificial intelligence-based arrangements in the form of a concrete. Apart from the above two, Self-healing is yet another technology that in short, works as a binder between a crack in a concerned block or concrete.
The use of Nanotechnology in the construction industry can trigger the remote use of these particles, either to change the configurations or appearance using cloud processing.