Curing of Concrete

Concrete curing is a method by which concrete is protected from moisture loss required for hydration and kept within the recommended temperature range. The curing will increase strength and decrease the permeability of hardened concrete.

In this process 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 curing of concrete is necessary:

• 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.

Methods for curing of concrete:

There are different methods of treatment used according to the situation, extent and nature of concrete which as follows:

1.Spraying water:

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 because it requires a lot of supervision and sprays with fresh water as soon as the concrete dries.

2.Membrane curing of concrete:

This method is most suitable in areas where severe water scarcity, when preparing fresh concrete, mixed water is generally sufficient for the entire hydration reaction.

It should not be allowed to escape through evaporation.

In membrane curing, 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:

1. Bituminous and asphaltic emulsion.
2. Rubber latex emulsion.
3. Emission of resins, varnishes, waxes, drying oils etc.
4. Emulsion of paraffin or boiled linseed oil with stabilizer.

3.Steam Curing:

This type of curing is done for precast 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 pieces of all sides.

4.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.

Also read: Durability of Concrete & Creep of Concrete

5.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.

6.Curing by infra-red radiations:

This method is used in Russia, it is claimed that the strength loss due to rapid temperature rise does not occur in this method.

This is particularly suitable for hollow blocks, where infrared heaters are placed in the hollow portion of precast components.

7.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 therefore this method is very economical.

8.Ponding method:

This curing of concrete method is particularly suitable for large slabs or road pavements.

The small dams are prepared with mud above the slabs as a result, water is stored in ponds to a depth of 50 mm for 28 days.

The water used must be of good & potable quality.

Also read: Compaction of Concrete, Workability of Concrete & Permeability of Concrete

Conclusion:

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.