Concrete gains its strength and durability through the process of hydration, where water reacts with the cement to form a hard matrix. However, hydration is a time-dependent and moisture-dependent process. For hydration to proceed effectively and for concrete to achieve its designed strength, it must be maintained in a moist condition for a certain period after placing and finishing. This process is known as curing.

The main objectives of curing are:
1. To maintain adequate moisture content in the concrete to enable complete hydration of cement.
2. To control the temperature of concrete during the early hardening period, especially in hot and cold weather.
3. To prevent shrinkage and thermal cracks that result from rapid drying or temperature variations.
4. To improve the overall performance of concrete, including strength, impermeability, and durability.

1. Environmental conditions – temperature, wind, humidity, and sunlight all influence evaporation rates.
2. Type of cement – faster-setting cements require more attentive early curing.
3. Water-cement ratio – low water-cement ratio mixes are more prone to rapid drying.
4. Size and shape of the structure – thin sections dry out quicker than massive ones.
5. Placement method – sprayed or pumped concrete may require different curing approaches.

Curing methods can be broadly classified into moist curing, membrane curing, application of heat, and miscellaneous methods.

This is the most effective and widely used method of curing.
Types of Water Curing:
1. Ponding:
• Water is retained on flat surfaces like slabs using temporary bunds.
• Provides continuous water supply.
• Suitable for horizontal surfaces.
• Advantage: Uniform hydration, effective temperature control.
• Limitation: Not suitable for vertical or inclined surfaces.
2. Spraying or Fogging:
• Water is sprayed or fogged over the concrete surface using nozzles.
• Suitable for vertical or irregular surfaces.
• Advantage: Easy to apply, economical.
• Limitation: Less effective in windy conditions.

When water is not easily available or continuous water curing is not feasible, membrane-forming compounds are used.
Types of Membrane Curing:
1. Liquid Membrane-Forming Compounds (LMFCs):
• These are sprayed or rolled on the concrete surface.
• They form a thin film that reduces moisture loss.
2. Plastic Sheets:
• Polyethylene or PVC sheets are laid over the concrete surface.
• The edges are sealed to prevent air ingress.

Used primarily in precast concrete production where fast strength gain is required. Types:
1. Atmospheric Pressure Steam Curing:
• Steam is applied at ambient pressure, typically within curing chambers.
• Temperature: 60–80°C.

• Reduction in strength by up to 40%.
• Surface shrinkage cracks due to rapid drying.
• Loss of durability due to permeability and poor hydration.
• Dusting and scaling of surfaces.
• Increased risk of corrosion of reinforcement due to low cover strength.

The minimum duration depends on environmental conditions and type of cement:
Cement Type Minimum Curing Period
Ordinary Portland 7 days
Blended Cement (PPC, PSC) 10 days
In hot/dry climates 10–14 days.
Steam curing 12–24 hours post placement (followed by air curing).

Condition Recommended Method
Hot, dry climate Water curing + white pigmented LMFC
Water-scarce regions Membrane curing or internal curing
Cold weather Steam or electrical curing
Precast concrete Steam curing
Massive pours Water curing (ponding or spraying).