Concrete curing is the practice of keeping concrete surfaces moist for a length of time after it has been placed in order to encourage cement hardening. It consists of temperature and moisture movement management from and into the concrete. Concrete curing is giving sufficient moisture, temperature, and time for the concrete to attain the appropriate characteristics for its intended use.
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1. Need for Curing of Concrete And Mortar
Cement hardening is a long-term process that involves a complex reaction with water. Curing in construction is done to prevent the water which has been mixed in the mortar or concrete from evaporating. It keeps moisture in the slab, allowing the concrete to continue to strengthen over time. Curing has a significant impact on all the characteristics of concrete, and therefore it should not be treated lightly.
Concrete that has been properly cured has a higher surface hardness and can resist more wear and abrasion. The chemical process of hydration is incomplete without proper curing. It will never be easy to achieve the desired strength of concrete without proper curing and there is no easy way to strengthen the poorly cured weak concrete.
2. The Purpose of Curing
Concrete's strength and durability are greatly influenced by curing. If concrete curing is not done, complete hydration of cement will not take place and the full strength will not be achieved. Proper curing results in:
Increased strength of concrete.
Improved wear resistant and weather resistant properties, and
Increased impermeability and durability.
3. Methods for Curing Concrete
Curing of concrete can be accomplished in a number of ways. The approach is different for different tasks. For instance reinforced cement concrete columns are cured by covering the columns with jute bags or straw to retain the water for longer time periods. The use of a particular approach will be determined by the nature of the task and the weather circumstances. The following types of concrete curing techniques are often used:
Canvas stretched on frames can be used to create shading. This method is generally used on big concrete surfaces, such as road slabs. In dry weather, this is necessary to protect the concrete from heat, direct sunlight, rain, and wind. The main purpose of shading is to retain the warmth of the heat of hydration of cement, in cold weather to prevent the concrete from freezing.
Using Gunny Bags to Cover Concrete Surfaces
This is a common process for structural elements like columns. It involves covering the exposed concrete surface with canvas, empty cement bags or gunny bags to stop it from drying out. Then, these bags are watered on a regular basis. The time interval between each session will depend upon the rate of evaporation of water.
Continuous sprinkling or spraying of water on the concrete surfaces ensures rapid curing of the concrete. The concrete should have set sufficiently before commencing the sprinkling process. For small scale curing, sprinkling can be done by hand, whereas for larger jobs sprays and hoses can be procured. This method is usually employed for curing floor slabs. Splashing water on top surfaces and allowing them to run down between the vertical and sloping surfaces, allows for both of them to be simultaneously wet. But, the amount of water required for this method of concrete curing is higher.
In this method of concrete curing, waterproof membranes like bitumen emulsion, wax, rubber latex emulsion, plastic films, and so on are applied to the concrete surface to prevent water loss.
This is the most effective way of curing. It can be used for curing horizontal surfaces like floors, roof slabs, road, and airport pavements. Ponding can also be done on the horizontal top surfaces of beams. In this process, the exposed surface of the concrete is first covered with moist gunny bags or canvas. These covers are removed after 24 hours, and little clay or sand ponds are constructed across and along the pavements, to divide it into segments. The water is poured between the ponds, and is replenished two to three times a day, depending on the weather conditions. Although this approach is incredibly efficient, it requires a lot of water. Ponds are readily broken, allowing water to flow out. Cleaning the clay after it has cured is also challenging.
Steam curing is accomplished by raising the temperature of the concrete in moist or wet conditions. This process enables the concrete to reach maximum strength in a short period of time. It is primarily used for precast components.
4. Important Points to Be Considered During Concrete Curing Process
Fresh concrete should not be exposed to sun, rain or dry winds.
Concrete should be covered with a tarpaulin while it is drying, if the weather is hot and dry.
The surface should be flooded with water for 24 hours after the concrete has been laid. For curing, the columns should be covered with gunny sacks.
Curing should continue for a minimum of fifteen days after the concreting is done.
Water used for curing should be of the same quality as that used for mixing the concrete.
Water used for curing should be clean and free from materials like oil, acids, alkalis, vegetable matter etc. Potable water is generally considered satisfactory for mixing and curing concrete, and other masonry works.
Water should not have dissolved chlorides or sulphates. The salinity of water should be checked. The best method is to taste the water. The pH of the water should be between 6 to 8.5, which is near to neutral.
Saltwater should not be used for curing or for any other construction purpose at all. Salt crystallization and rapid reinforcement corrosion are two issues that can arise.
5. Curing Period for Concrete
The final strength is dependent on proper curing. The curing of concrete should begin as soon as the concrete has reached its initial setting time or the formwork/shuttering has been removed. The process should be continued for a reasonable period of time, according to the specified standards, in order for the concrete to achieve its desired strength and durability.
Brickwork should be left to cure for at least seven days.
Reinforced cement concrete should be allowed to cure for at least 15 days.
During the rainy season, no curing is required.
It is a common practice that the curing of concrete is left to the discretion and comfort of the workers, and no measures are taken to ensure that it is done properly even though it has great importance in concrete construction. Site engineers and supervisors should take significant efforts to confirm that the curing is not overlooked on the job. Allowing the masonry, concrete, or plaster to dry slowly yields the best results. Alternate drying and wetting may be harmful. It is important to make arrangements for the necessary resources in order to maintain satisfactory levels of concrete curing by employing the best techniques available.
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