Published on 10/6/2019
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What is curing of concrete
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What is curing of concrete?
Kavisha M. Desai, B. Tech Civil Engineering, Sardar Vallabhbhai National Institute of Technology, Surat (2017)
Curing of concrete is the last and one of the most important activities required to be taken in the process of concrete construction. This last step plays a very significant role in concrete performance and needs the full and minute attention of the persons involved in construction and those involved with quality assurance.
Curing is not the mere process of maintaining moisture on the concrete surface, but it helps to gain strength of concrete properly. Curing of concrete is the process of maintaining moisture in the concrete to ensure an uninterrupted hydration with a definite period to replenish the loss of moisture and to maintain favourable temperature for hydration process, in brief, the process of keeping the concrete moist to enable it to gain full strength is called. It is because of the process of hydration; the cement achieves its strength and binding properties. If this chemical process does not take place, it will remain a mix without any binding property i.e. without strength.
There should be sufficient water available in concrete so that the chemical reaction takes place between water and cement called “Hydration”. Because of hydration process, heat is generated called heat of hydration. Therefore, temperature increases inside the concrete and water evaporate from the concrete and concrete becomes dry. The object of curing is to control the temperature inside the concrete, continuing hydration process and to prevent dryness of concrete. It is necessary that sufficient quantity of water should be available in concrete till attains its full strength.
What are the methods of concrete curing?
Mallikarjun Kankanwadi, Pursuing B.E Civil
Basically, Curing is the process of keeping the concrete moist enough for the hydration of cement to be continued until the desired properties are developed.
Concrete releases high heat of hydration & affects the volumetric stability. The quickly drying surface of concrete results in the sudden movement of the moisture from the interiors to the surface. This steep moisture gradient causes high internal stresses which are responsible for internal micro cracks. Thus, to refrain the deformations & damages, Curing is quite essential.
Curing of concrete can be done by adopting following methods :-
- Water curing.
- Membrane curing.
- Curing by applying heat.
These methods are later subdivided into as follows :-
- Water curing :-
The precast members are immersed in curing tank for a certain period. Immersion in water is particularly important when the concrete has a low water-cement ratio.
2. Ponding -
Ponding is commonly adopted for curing of concrete slabs & pavements. This method consists of storing water at a depth of 50mm on the surface by constructing small ponds.,
3. Spraying -
Fogging raises the humidity above the curing concrete by spraying a fine mist of water regularly across it to maintain moisture. Vertical members of structure like column, walls, plastered surfaces, etc are cured by spraying water.
4. Wet covering -
Exposed surface of concrete is prevented from drying out by covering it with hessian, canvas or empty cement bags. These are periodically wetted. The interval of wetting will depend upon the rate of evaporation of water.
- Membrane curing :-
The process of applying a membrane forming compound on concrete surface is termed as Membrane curing. Membrane serves as a physical barrier to prevent loss of moisture from concrete. It's usually used if there's an acute shortage of water or the concrete's placed at an inaccessible site.
The various membrane forming compound are
- Bituminous & Asphaltic emulsion.
- Rubber latex emulsion.
- Emulsions of waxes & resins.
- Water repellent chemicals, viz. Silicon.
- Emulsions of paraffin.
- Plastic sheeting.
Note :- Curing compound must be applied on concrete before all the moisture/water content evaporates in order to obtain best results.
- Application of heat :-
The strength development of concrete not only depends on time but also on the temperature. Concrete is subjected to higher temperatures while the wetness is maintained to accelerate the hydration process for faster development of strength.
Following manners are adopted for applying heat :-
1.Steam curing -
Steam curing is used for precast concrete members. The members are heated up by steam either at a high pressure or low pressure.
Live steam, heating coils, electrically heated pads or forms are used for steam curing.
2.Curing by Infrared radiations -
This system is adopted in very cold climatic regions.
3.Electrical curing -
Concrete can be cured by passing alternating current through it using two electrodes eeitherburin or applied to the surface of the concrete.
These above methods are usually adopted for curing the concrete for the following period :-
As per the codes of IS 456 2000 & IS 7861 (part 1) - 1975, the minimum curing period of concrete made with OPC is 7 days for normal conditions and 10 days for dry & hot weather conditions.
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