Curing Concrete | Method of Curing | Purpose of Curing | Minimum Curing Period of Concrete
The article will clearly explain the Find out the secret behind curing concrete and learn all about the different types or methods of curing, cure time for concrete, and the purposes of cured concrete. Read our guide to understand how long time or curing period you should let it cure, and what types of curing are best for your project.
What is Curing?
Curing is a process that occurs during which a chemical or physical reaction takes place, resulting in a harder, tougher or more stable linkage or substance. Some curing processes require maintenance of certain temperatures and/or humidity levels, while others require a certain pressure.
Curing of Concrete:
Curing is the process by which concrete hardens. When you add water to a concrete mixture (cement, sand and aggregate), an exothermic reaction takes place (oxygen combining with carbon dioxide) that helps the concrete harden. This happens very quickly, but it takes a long time for the concrete to actually become dry. So, the concrete is kept moist until the hydration reaction in concrete completes. This process is called “Curing of Concrete.”
Curing is the process that keeps concrete moist to protect it from loss of moisture due to atmospheric temperature and hydration reactions.
Purpose of Curing of Concrete:
Hydration describes the relationship between water and cement. This reaction is exothermic (which releases heat). Hydration begins when water is added to the concrete mixture, which causes the concrete to start drying out quickly. In order to prevent concrete from drying out before reaching its maximum strength, concrete is maintained moist via curing.
HOW LONG DOES CONCRETE TAKE TO CURE?
After hardening, concrete doesn’t reach its full strength instantly. It has to go through the curing process first. As a result, you have to wait a little longer before putting any weight on it – so if you’ve just laid a driveway, keep your car away from it:
Curing Time of Concrete:
The concrete mix actually gets stronger as time goes on, but to reach practical strength, most industrial concrete mixes have a 28 day curing period or cure time for concrete
After seven days, the concrete will have gained around three quarters of its compressive strength. However, you should refrain from driving vehicles or heavy machinery over the surface until after 28 days.
For concrete that you’re going to use in your driveway, it should set within 24-48 hours. But if you want to park the family car on it for 28 days, be sure to let it cure for that long before driving over it. You might think your concrete is strong enough after taking a test walk on it, but overloading it before it’s fully cured could undo all the hard work you’ve put into its construction.
Minimum Curing Period of Concrete:
As per IS 456 – 2000 | Concrete should not be cured under 7 days for ordinary Portland Cement and at least 10 days for concrete with mineral admixtures or blended cement. In case of hot weather and arid temperature conditions, the curing should not be less than 10 Days for OPC and 14 days for concrete with blended cement & mineral admixtures.
Concrete Cure Time Based on Cement Types:
The minimum curing period of concrete structures is dependent on the type of cement used.
Table-A: Cure time of Concrete Based on Types of Cement
|Types of Cement
|Type I, ASTM C 150—When the special attributes listed for any other type are not necessary, use this type.
|Type II, ASTM C 150—When a moderate sulphate resistance is necessary, for general use, but especially.
|Type III, ASTM C 150— When a high level of early strength is wanted, utilise.
|Type IV, ASTM C 150—For used when a low heat of hydration is desired.
|Type V, ASTM C 150—For used when high sulfate resistance is desired.
|Hydraulic Cement, Blended Hydraulic Cements, Expansive Hydraulic Cement
Minimum Curing Time of Different Concrete Constructions:
Table-B: Minimum Concrete Cure Time for Different Types of Construction
|Curing period, days
|Pavement and other slabs on grounds
|Highway pavement, airfield pavements, canal lining, parking lots, driveway, walkways, and floors
|Refer to Table-A
|Buildings, bridges, and other structures
|Cast-in-place walls, columns, slab, beams, all other portions of buildings except slab-on-grade, small footings, piers, retaining walls, tunnel linings, and conduits.
|Refer to Table-A
|Unreinforced huge portions not incorporating crushed granulated blast furnace slag or pozzolan
|Massive unreinforced sections that comprise pozzolan or ground-granulated blast furnace slag
|Reinforced mass concrete
|Colored concrete floor and slabs
Concrete Compressive Strength Development V/S Curing Time:
Factors Effecting on Concrete Curing:
The cure time or period of concrete is dependent on the following factors:
- Specified Strength of Concrete
- Grades of concrete
- Temperature – The chemical reaction between cement and water in concrete creates heat, which requires constant adding of water to complete hydration. In summer, fifty percent of the water evaporates from the mixture. So, more water is needed during sunny days.
- Size and Shape of the Concrete member
- Material availability
- Labor force
- in situ versus plant concrete production
DIFFERENT TYPES OF CURING METHODS IN CONCRETE CONSTRUCTION:
There are various methods of curing concrete or Types of Curing, which are used on the site depending upon the size and nature of the work. There are three major methods of curing concrete by which concrete can be kept moist and humid or kept at a favorable temperature. Here we have given brief information on some of these methods.
Methods of Concrete Curing:
Following are the most important techniques which are prominently used for concrete curing all over the world.
This method of floor slab construction involves the use of concrete that has been allowed to harden for 14 days. The concrete is divided into small ponds, and these ponds are filled with water continuously until the surface is completely covered.
2. Wet Coverings:
This type of method is used for columns, footings and the bottom surface of slabs where ponding cannot occur. Impermeable coverings like gunny bags or hessian are required to cover the concrete; these membranes sprayed with water to keep moisture in.
3. Membrane Curing of Concrete:
Ponds are not suitable in high-temperature areas. Water evaporates when the air outside is too hot. To prevent this, membranes are used to keep the concrete dry and retain its moisture.
The membrane curing process seals off by forming an impermeable layer on the concrete surface, preventing evaporation.
This procedure is generally performed by spraying or brushing a curing compound onto the concrete.
There are numerous curing agents available to achieve membrane curing; nevertheless, the following four techniques are crucial and frequently employed.
Synthetic resin curing compound:
When applied to a concrete surface, synthetic resin hardens into an impermeable membrane that prevents water from evaporating from the concrete.
The synthetic resin membrane can be simply removed before continuing with the plastering process by sprinkling hot water over the concrete surface.
Therefore, it is appropriate for locations where concrete will receive further treatment.
Acrylic curing compound:
Acrylic-based curing compound is a polymer-based curing compound obtained from the polymers of acrylic acid.
The best part of this compound is that it does not need to be removed for plastering; it helps achieve excellent adhesion to plastering.
Wax Curing compound:
Wax curing compound has similar properties to synthetic resin. However, it is not recommended for use on surfaces to be painted or tiled because it will hamper the adhesion between surface and plastering or tiling.
Chlorinated rubber curing compound:
When chlorinated rubber is used to seal the concrete, it forms a thick membrane that seals the pores of the concrete effectively without leaving any minute holes.
However, chlorinated rubber is very expensive and it tends to deteriorate over time.
4. Steam Curing of the Concrete:
The process of spraying steam on precast concrete has been adopted at a precast concrete plant where the concrete members are mass-produced. Steam has heat moisture in it and is sprayed on the surface of the concrete to keep its moisture content high and also increase its temperature.
This helps speed up the curing process, which eventually results in more durable concrete.
5. Curing of Concrete by infrared radiation:
In areas with a chilly climate, this approach is used. In this process, the concrete is exposed to infrared radiation, raising its starting temperature and enhancing its strength. As boosting the beginning temperature of concrete does not reduce the final strength of concrete, this approach is more successful than steam curing.
This method is used for hollow concrete members, where heaters are installed in concrete members to emit 90 degree.
6. Curing of the Concrete Surface by an Electric Current:
In this method, alternating current is applied to concrete. Two electrodes—one at the top and another at the bottom of the cured concrete surface—function as electrodes, and then an alternating voltage is generated between them. By maintaining a 30V or 60V potential difference between these electrodes, curing by this method can be achieved in three days; however, curing at 28 days requires only three days.
7 days | For most concrete structures, the curing period at temperatures above 5º C (40º F) should be at least 7 days and not less than 3 days if high early strength concrete is used and the temperature is above 10º C (50º F).
A minimum of 28 days is required for concrete to attain maximum strength.
Curing serves to maintain the moisture in concrete by retaining it so that the concrete gains strength. It also prevents drying shrinkage until the concrete is strong enough to resist cracking. Curing improves strength, durability and water tightness—and can even increase wear resistance.
The chemical reaction between cement and water that binds sand and gravel together to make concrete takes nearly 28 days to complete, during which time you want to keep moisture in the concrete.
If concrete is not cured properly, its durability, strength and abrasive resistance can be compromised. Thermal cracks develop along with a considerable loss in the surface layer’s strength.
When it comes to concrete, the general rule of thumb is that it takes about 28 days for each inch of slab thickness to dry.
As soon as chemical reactions begin in concrete, the curing process begins.
Adding calcium chloride to the concrete mix before pouring would quicken the curing process by accelerating the rate of hardening. Steam-curing is one of several methods used to cure concrete quickly.
Concrete can achieve 65-70% of its designed compressive strength after seven days.