Facts About Concrete Curing | Concrete Curing Time, Methods and Factors
Concrete curing time
Exposed surface of the concrete should be kept with contact
of water either through ponding or by covering with a layer of jute sac, canvas
or similar material continually for at least seven days. This period must be
extended to 10 days in case the concrete has been applied in hot and dry
weather conditions. If mineral admixtures or blended cements are used, then the
seven-day time period must be extended to 10 days and 10 days must be extended
to 14 days.
The curing time of concrete depends on following factors:
- Mixture Proportions
- Specified Strength
- Size and shape of concrete member
- Temperature of the surrounding
- Exposure conditions in the future
PPC concrete curing time
Generally, OPC cement is used to cast concrete. But for
economy purpose, PPC cement is used. Curing time of concrete increases when you
use PPC cement because admixtures like fly ash is used in PPC cement.
Therefore, for ambience temperature of 45 degree Fahrenheit, the curing time
extends to 10 days and at temperature of 40 degrees Celsius, the curing time
extends to 14 days. But for slabs with larger span, the table in the succeeding
section gives the exact curing time.
Curing meaning in construction
The meaning of curing is to maintain a supply of water to
the concrete at ambient temperature so that the concrete gains adequate
strength. Curing just means supply of water to the concrete surface. There are
two importance of adding water to the concrete- one is to decrease the
temperature of concrete and minimizing cracks by absorbing the heat of
hydration and second purpose is to help cement in doing chemical reaction so
that a strong bond forms between cement and aggregates.
Concrete curing start time
Typically, the starting of curing time is 24 hours. However,
there is a rule of thumb to the concrete curing start time. If the concrete
doesn’t form any mark when you press on the concrete surface with your thumb,
then it is time to start the curing of concrete.
Concrete Curing time in Winter
Minimum curing time of concrete
The minimum curing time of concrete is 7 days. Concrete
should not be cured for less than 7 days. Both the Indian standard IS: 456 and
American concrete institute has agreed on the fact that the concrete should be
cured for at least 7 days at an ambient temperature of 40 Degree Fahrenheit. American
concrete institute has stated that the minimum time through which concrete should
be cured must be the time when the concrete gains 70% of the strength.
- ASTM C 150 Type I cement seven days
- ASTM C 150 Type II cement 10 days
- ASTM C 150 Type III cement 3 days
- ASTM C 150 Type IV or V cement 14 days
- ASTM C 595, C 845, C 1157 cements variable
Concrete Drying time before rain
A bit of rain during casting of concrete won’t be a big problem. But a higher volume of rain during concrete can immediately result in creeping due to excess water. The creeping occurs through the crevices in the formwork. Honeycomb can form due to the rain. The concrete has a time period of 24 hours when you can put your steps in the concrete. And it is not advisable to expose concrete to rain within 24 hours. After 24 hours, some amount of rain is ok because you don’t have to add water in order to do ponding in the slab.
Concrete Curing methods
The purpose of curing is to maintain the supply of water.
Both the cold water and hot water are used for the process of curing. Hot water
gives high initial strength but 28 days’ compressive strength might be
compromised. The following are the methods used in concrete curing.
Ponding
Ponding refers to the accumulation of water above the slab surface. Small strips are created in between so that each section of slab can be checked for curing. The time period at which striking in slab is done is mentioned in the table below.
| Type of formwork | Minimum formwork before striking formwork |
| Vertical formwork to columns, walls, beams | 16-24 hours |
| Soffit formworks to slab | 3 days |
| Soffit formworks to beams | 7 days |
| Props to slabs | |
| Spanning up to 4.5m | 7 days |
| Spanning more than 4.5m | 14 days |
| Props to beams and arches | |
| Spanning up to 6m | 14 days |
| Spanning more than 6m | 21 Days |
Wetting of Surface
This method is used for curing the column and footings. This
method is also used in all other places where ponding is not possible. The
materials used are moisture retaining fabrics like jute, cotton rags and
burlap. You have to make sure that you apply water to the fabrics periodically
to not let them dry.