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 :-

1. Water curing.
2. Membrane curing.
3. Curing by applying heat.

These methods are later subdivided into as follows :-

1. Water curing :-

a) Immersion: 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.

b) 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.

c) 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.

d) 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.

2. 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.

3. 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.

a) 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.

b) Curing by Infrared radiations: This system is adopted in very cold climatic regions.