Curing of concrete is defined as the process in which freshly cast concrete is kept in a sufficiently wet or humid state for a certain period of time after condensation so that the reaction of hydration is fully achieved.
There are different methods of treatment, but the common method requires at least 28 days of treatment.
Why the curing of concrete is important?
Concrete regains its strength through a reaction between cement and water, this reaction is known as hydration.
This is a very slow response and continues for years, after 28 days, the rate of reaction is negligible.
Thus it is necessary that water or moisture is available for at least 28 days for this reaction.
Moreover, the hydration reaction is the exothermic and large amount of heat is released during the reaction.
The treated water also helps to dissipate this heat; the need for treatment can thus be summarized as follows:
Curing is necessary to continue the reaction of hydration which gives concrete its strength.
It is necessary to avoid drying of concrete until full strength is achieved.
Also, dissipate the heat of hydration & reduces the shrinkage in concrete.
This prevents water loss by evaporation and helps maintain the hydration process.
Types of curing of concrete:
There are different methods of treatment used according to the situation, extent and nature of concrete.
In this method, after removing the shuttering or formwork, water is sprayed several times during each day through a hose or even bucket on the concrete.
This method is suitable for small tasks, requires a lot of supervision, and sprays fresh water as soon as the concrete dries.
Membrane curing of concrete:
This method is most suitable in areas with severe water scarcity.
It is observed that when preparing the fresh concrete, mixed water is generally sufficient for the entire hydration reaction.
It should not be allowed to escape through evaporation.
Membrane curing uses this fact and a sealing membrane is applied to the concrete that will throw water inside and avoid its escape through evaporation.
The membrane may actually be a sheet of polythene or it may be a membrane made by application of chemicals.
Various sealing compounds in use for membrane treatment are:
(A) Bituminous and asphaltic emulsion.
(B) Rubber latex emulsion.
(C) Emission of resins, varnishes, waxes, drying oils etc.
(D) Emulsion of paraffin or boiled linseed oil with stabilizer.
This type of curing is done for pre-cast concrete products manufactured in the factory.
Due to steam, the material is heated evenly and the strength is obtained at a very rapid rate.
Even in short intervals of stacked precast products, steam can penetrate and cure all pieces of all sides.
Low-Pressure Steam Curing:
In this method, steam is treated at atmospheric pressure about 70% of the 28-day power can be achieved in 16 to 24 hours.
A typical low-pressure cycle is given below:
Pre-steaming period of 3 hours.
Temperature rise period 4 hours, maximum temperature 4- 5 hours duration.
High-pressure steam curing:
If steaming is carried out at a pressure of 8 atmospheres, i.e., at about 800 kN /m2, it is called high-pressure steam curing of concrete.
The main difficulty in rapid steam curing is the loss of strength by the rapid rise of temperature.
This difficulty is overcome by the application of high pressure up to 8 atmospheres.
Curing by infra-red radiations:
This method is used in Russia and it is claimed that the strength loss due to rapid temperature rise does not occur in this method.
This is particularly suitable for hollow concrete products, where infrared heaters are placed in the hollow portion of precast components.
Curing by wet gunny bags:
This method is very useful for vertical surfaces of concrete-like columns.
Burlap or wet gunny bags made of jute are wrapped around concrete and kept continuously wet.
They retain moisture for a long time.
The material can be reused multiple times and therefore this method is very economical.
This curing of concrete method is particularly suitable for large slabs or road pavements.
The small dams are prepared with mud above the slabs and as a result, water is stored in ponds to a depth of 50 mm for 28 days.
The water used should be of good & potable quality.
Frequently Asked Questions:
What is concrete curing?
In the early ages, concrete has to maintain sufficient moisture content and temperature so that it develops the properties that the mixture was designed to achieve.
How many days is the curing of concrete?
Generally, it takes around 28 days to cure concrete, drying can take months.
What happens if concrete is not cured?
When concrete is not cured properly, its durability, strength and abrasion resistance are affected.
Why curing is needed to concrete?
Curing plays an important role in the strength development and durability of concrete
Concrete “cures” rather than “dries”.
Curing of Concrete means that instead of an evaporative process that causes it to harden, it is a chemical reaction that causes hardening.