Concrete Curing | Methods of Curing Concrete |Curing Time of Concrete
What is Concrete Curing?
Concrete Curing is the key process of maintaining moisture content and temperature in the concrete for a period of time, immediately following concrete pouring/placing. Curing of concrete plays a crucial role in concrete strength development and concrete durability.
Concrete Curing starts immediately after the process of concrete placing and finishing, and the process involves maintenance of recommended moisture and temperature conditions, both at the surface and in-depth of the concrete, and should be done for extended periods of time.
Why Concrete Curing is Important
Concrete that is cured properly has an adequate amount of moisture for continued hydration and development of strength, volume stability, resistance to freezing and thawing, and abrasion and scaling resistance.
The length of adequate curing time is dependent on the following factors:
- Specified strength
- Mixture proportions
- Ambient weather conditions
- Size and shape of the concrete member
- Future exposure conditions
Slabs on the ground (for example, pavements, sidewalks, parking lots, driveways, floors, canal linings) and structural concrete (e.g., bridge decks, piers, columns, beams, slabs, small footings, cast-in-place walls, retaining walls) require a minimum curing period of seven days for ambient temperatures above 40 degrees Fahrenheit.
Key Factors to Proper Concrete Curing.
There are 3 main factors the will ensure good curing:
- Temperature – Maintaining a sufficient temperature (≥10°C) to ensure that the chemical reaction continues
- Moisture – Having sufficient moisture to ensure the hydration process continues.
- Time – Maintaining both the moisture and temperature requirements for a minimum period of time (3 –7days)
Methods of Curing of Concrete
Concrete curing methods may be divided broadly into four categories:
- Water Concrete curing
- Membrane Concrete curing
- Application of heat
Water curing the best curing method because it satisfies all the key requirements of curing, which include the elimination of shrinkage, promotion of hydration, and absorption of the heat of hydration.
It is noted when the membrane method is used, and it is also desirable that a certain extent of water curing should be before the concrete is covered with sheet membranes. Water curing can be done in the following ways: ponding, sprinkling, and wet coverings.
Curing Concrete by Ponding Method
Ponding can be done on flat surfaces such as floors by enclosing the water within the floor surface. This ensures uniform curing by preventing loss of moisture from the concrete and maintaining a uniform temperature.
Sprinkling Concrete Curing
This frequent and continuous sprinkling of water on the surface but care must be taken to prevent the concrete damage by water. A fine spray of water applied continuously through a system of nozzles provides a constant supply of moisture.
Wet Covering Curing Method
Wet coverings are using a moisture-retaining fabric, and the coverings should be kept continuously moist. Care should be taken to ensure the surface is free from surface damage.
Membrane Concrete Curing
Sometimes, concrete works are carried out in places where there is an acute shortage of water. The lavish application of water for water curing is not possible for reasons of economy. Curing does not mean the only application of water; it also means creating conditions for the promotion of uninterrupted and progressive hydration.
It is also pointed out that the quantity of water normally mixed for making concrete is more than sufficient to hydrate the cement, provided this water is not allowed to go out from the body of concrete. For this reason, concrete could be covered with a membrane which will effectively seal off the evaporation of water from concrete.
Curing time of concrete
It is recommended for concrete structures to have a curing period of a minimum of 7 days at temperatures above 5º C (40º F) or until 70% of the specified flexural or compressive strength is achieved. The time can be reduced to three days when high early strength concrete is used and the temperature is above 10º C (50º F).
The complete curing period of the concrete takes about 28 days, but the concrete will be ready for use sooner. Every project will vary depending on the differences in the concrete mix, weather, placement, and finishing techniques.
Here is a summarized timeframes;
- 24 to 48 hours – after the initial set, forms can be removed and people can walk on the surface
- 7 days – after partial curing, traffic from vehicles and equipment is okay
- 28 days – at this point, the concrete should be fully cured