Curing the Concrete
"It is necessary to protect the concrete against various negative factors until it reaches sufficient strength and durability. The methods that are implemented to create the humidity and temperature conditions required to maintain the concrete are called curing methods. There are 4 different types of curing;
1. Curing by sprinkling water
It is a type of curing applied on the columns, shear walls, claddings, beams, vertical and horizontal surfaces by spraying water to prevent getting dry and to provide continuous wetness.
The cure should be applied for not less than 7 days (Water spraying should initially be done at pressures that will not damage the concrete).
2. Curing by covering with wet sacks
It is the most effective and safe method of curing.
The covering is wetted right after the concrete casting and continuously throughout the curing process not to let the concrete to get dry.
The curing time must be long enough allowing the concrete to attain the compressive strength equivalent to the compressive strength of concrete of 7 days.
3. Curing by covering with an impermeable membrane
Particularly the small size constructional components are protected by covering them with impermeable plastic covers.
The spray membrane can be applied 3 to 7 hours after compacting.
4. Curing with Construction Chemicals
It is a curing method, where construction chemicals are applied or sprayed on the concrete surfaces.
The concrete must be protected against some physical and chemical factors until it attains sufficient strength and durability. These factors are;
- Vibrations and shocks,
- Impacts, heavy loads, vehicular traffic,
- Flowing waters,
- Heavy rains,
- Strong winds,
- Extremely cold weather conditions, frosts,
- Extreme rises in temperature,
- Harmful chemical effects that may originate from the ground, water and air,
- Other mechanical effects.
Concrete Casting in Hot Weather Conditions
The conditions, in which the average air temperature remains above +30 °C for three consecutive days during concrete casting, are considered as hot weather conditions in respect of concrete casting.
Appropriate measures should be taken against the adverse effects of these conditions as high air temperature causes accelerated hydratation, increased loss of consistency, increased need for mixing water, decreased strength and durability, increased evaporation and large volume changes.
Measures that can be taken in concrete casting during hot weather conditions;
Fresh concrete should be placed, compacted and its surface should be finished as soon as possible.
If possible, the casting should be performed at night, that is during the cooler hours of the day.
Before casting, the area around the mold and casting should be thoroughly wetted leading to lower temperatures and humidity.
After the first surface finishing is carried out immediately after placing the concrete, the second surface finishing should be performed at the stage when stepping on the concrete surface leaves a mark with a depth of 1-2 mm.
Water curing should be started immediately after the second surface finishing and all the concrete surfaces should be watered with plenty of water for at least 3 days so that they remain wet.
Water curing should be continued for at least 14 days after casting so that the surfaces remain moist and are not allowed to get dry. The temperature of the curing water should not be too low compared to the concrete temperature, and should be as close as possible to the concrete temperature, especially during and after setting.
Formed surfaces should not be forgotten, and kept moist, while water curing is applied to form-free surfaces.
Surfaces should be covered with impermeable covers, plastic covers or wet sacks against evaporation and water loss, and the concrete should be protected from the direct effects of sun and wind. In particular, the sacks should be continously watered so that they remain wet.
Wind protectors should be installed against the wind, and in this way the concrete should be protected from the wind.
Concrete Casting in Cold Weather Conditions
The conditions, in which the average air temperature remains below +5 °C for three consecutive days during concrete casting, are considered as cold weather conditions in respect of concrete casting.
Hydratation of cement slows down in cold weather conditions. Decelerated hydratation also reduces the rate, which the concrete gains its strength.
Formwork striking times are prolonged.
Freezing of fresh concrete, especially during setting, can cause very serious damages. For this reason, The Turkish Standards Institution has introduced some temperature limitations (for example, for a concrete with a largest aggregate grain size of 31.5 mm, and at -1 °C ~ 5 °C air temperature, the temperature of the fresh concrete mixture should be at least 15 °C and the placing temperature should be at least 13 °C).
Measures that can be taken in concrete casting during cold weather conditions;
The formwork can be insulated before casting. The exposed surfaces of the concrete can be covered with insulating covers immediately after casting to preserve the hydratation heat.
At critical temperatures (below -5 ° C) the formwork should be heated. The parts, where concrete was poured, should be enclosed in an impermeable cover and a heating system should be established in order to maintain the temperature of the air at +5 °C at the very least.
In case of frequent freeze-thaw events and sudden temperature changes, this protection should be extended for 7 to 14 days.
It will be advantageous to carry out the concrete casting during the daytime hours, that is the warmer hours of the day.
Formwork striking times should be prolonged. The concrete strength should be determined on the basis the samples taken from concrete casting cured under the same conditions as the concrete within the structure, and formwork striking should be allowed as per the concrete strength measured."