SELF-HEALING CONCRETE
Self-healing concrete is the special type of concrete invented by a group of microbiology researchers under the head of henk jonkers. Bio concrete is also called as BACTERIAL CONCRETE or self-healing concrete. Its specially made to increase the lifespan or the durability of concrete structure by the self-healing action of that concrete
Nepal is a developing country, the consumption of the concrete is increasing every day. Concrete is the most used material in the building industry but the strength of the concrete is decreasing due to the Stress and weather conditions which are the main factors that slowly break the concrete. behind that Concrete is still one of the main materials used in the construction industry, from the foundation of buildings to the structure of bridges and underground parking lots. Traditional concrete has a flaw, it tends to crack when subjected to tension. it is possible to repair cracks, but this takes time and money, especially when the construction has to be closed down while the reparations take place.
when a crack is developed in the concrete it is will fail if we have not applied any remedies. Water will enter the cracks, in winter, there are chances that it freezes, causing the cracks to grow.When these cracks are deep enough to reach the steel reinforcement, this can corrode, causing serious damage.so we have to do some repair works in the cracked concrete. Repairs can be particularly time consuming and expensive because it is often very difficult to gain access to the structure to make repairs, especially if they are underground or at a great height. this is a serious problem which must be solved within a days if we have ignored this water seeps in to degrade the concrete and corrode the steel reinforcement, greatly reducing the lifespan of a structure.tensile forces can lead to cracks and these can occur relatively soon after the structure is built. Repair of conventional concrete structures usually involves applying a concrete mortar which is bonded to the damaged surface.in solving this problem which arises in the conventional concrete we can use Mineral-producing bacteria which could help mend micro-cracking in concrete. Self-healing concrete that can repair itself within three weeks and makes manual repairs superfluous. For this we just have to mix a genus Bacillus with healing agent capable of surviving in an extreme alkaline environment generally Cement and water have a pH value of up to 13.in this we mix a healing agent that works when bacteria embedded in the concrete convert nutrients into limestone.These bacteria are enclosed in pellets and can be dormant for 200 years.they start to work when they come into contact with water and oxygen, they wake up(This can only happen when the concrete is cracked or deconstructed).Fed by nutrients in the pellets, the bacteria will multiply and start to produce calcium carbonate (limestone), filling the cracks. The bacteria consumes oxygen during the bacterial conversion of calcium lactate to limestone, so the corrosional activity will decreases oxygen is an essential element in the process of corrosion of steel and when the bacterial activity has consumed it all it increases the durability of steel reinforced concrete constructions. Also when water seeps into the concrete, the bacteria germinate and multiply quickly.
The bio-concrete starts to produce limestone to heal cracks that appear on the surface of concrete structure. Genus Bacillus, along with a calcium-based nutrient known as calcium lactate, and nitrogen and phosphorus, are added to the ingredients of the concrete when it is being mixed. when genus bacillus comes in contact with water & nutrients the bacteria get activated. The activated bacteria feeds calcium lactate & consumes oxygen. The calcium lactate is converted into the insoluble limestone by the bacteria .The limestone solidifies on the cracked surface & get in the original condition.
In context of Nepal we should use the bio-concrete to decrease the re-constructional work. The bio-concrete increases the life span of the structure approximately 4 times, the life span of conventional concrete is 50-70 years whereas the life span of self- healing concrete is about 200-300 years. for the healing action of the bacteria the length of the cracks does not matter, only the breadth of the crack is considered .at one time the bacteria can fill up crack up to 0.8 mm. The material is repaired within 3 weeks, no matter the length of the crack. the liquid form of the bio-concrete which contain bacteria that can make ordinary concrete self-healing is also developed but clay pellets holding the self-healing agent comprise 20% of the volume of the concrete. That 20% would normally comprise harder aggregate such as gravel. The clay is much weaker than normal aggregate and this weakens the concrete by 25% and significantly reduces its compressive strength. While talking about cost it is very high to effort first time (about double that of conventional concrete (€80 euros per cubic metre) but If the life of the structure can be extended by 30%, the doubling in the cost of the actual concrete would still save a lot of money in the longer term
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