1-CONCRETE CASTING IN NORMAL WEATHER CONDITIONS
The point where concrete will be poured must be the place where it will be placed. Pouring the concrete in one point and then drawing or transferring it to the place where it will be placed must be avoided. Concrete can be spread up to maximum 3 meters from the point it is poured.
Concrete to be placed is piled up on one point especially on flooring and road constructions and then it is tried to be spread. This application should be avoided.
Concrete should be poured in horizontal layers. The thickness of each layer should be 15 to 30 cm. The layer thickness should be equal and homogeneous at each part. Layer thickness in elements such as columns and concrete shear walls should be 30-45 cm. Thickness may increase in other mass concretes such as dams.
Concrete should always be poured in the middle of the form. Concrete crashing form side decomposes.
Take down the pump hose as possible as to the form base. This prevents decomposition of concrete. Fresh concrete is not dropped freely from a high distance. Drop the fresh concrete from a height of up to 80 cm.
Concrete should always be poured into the form in vertical direction and perpendicularly.
Placing concrete should be started from corners of the form.
Drizzle is suitable for concrete casting. Avoid from concrete casting under heavy rain.
Concrete casting should be seamless and continuous. It should not be cold joint.
2- CONCRETE CASTING IN HOT WEATHER CONDITIONS
Points you should pay attention during concrete casting in hot weather conditions;
Since extremely hot weather and low humidity causes the water on the concrete surface quickly evaporate, they adversely affect production, placement, curing and structure of the concrete.
A result of evaporation of water in the fresh concrete, temperature of concrete increases and this causes a much faster hydration.
According to TS 1248 Standard, during concrete casting temperature of 5-30 °C is considered as normal temperature and temperature higher than 30 °C is considered as the abnormal temperature.
The effect of hot weather to concrete
- Amount of mixture water for desired concrete viscosity will increase.
- Increase in concrete temperature (hydration) causes concrete setting in less time.
- An increase occurs in contraction (plastic shrinkage) cracks.
- While durability in hardened concrete rapidly increases in early days, 28-day durability decreases which leads to an increase in cracking tendency and a faster drying and shrinkage.
Temperature of the concrete to be placed in +5 °C of weather temperature must be between 10-30 °C, while the most suitable mixture temperature for concrete is 15-16 °C.
Necessary measures to be taken can be listed as follows;
- You must use cement with low heat of hydration.
- You must cool the materials forming the concrete.
- You must take measures to prevent water loss by evaporation, for example; Curing Methods.
- If the concrete will be poured onto floor, you must compress, smooth and moisten the surface in advance in order to prevent the concrete water to be absorbed by the surface.
- If possible, you should prefer concrete casting at night.
- Concrete casting process should be carried out by numerous staff within the shortest time and must do vibration process.
- You must place the concrete not later than 30 minutes after preparation, if this time is extended we can prolong using additive material.
- You must smooth the surface of concrete after it is placed. You must implement water cure wherever possible when concrete surface becomes enough strong so as not to be damaged.
- Concrete surface must be kept wet for 24 hours after concrete surface hardened enough.
3- CONCRETE CASTING IN COLD WEATHER CONDITIONS
Extremely cold, dry and windy weathers are the leading unfavourable weather conditions for concrete casting and you need to take some precautions before you start concrete casting in such cases.
The effect of cold weather to concrete;
- Cold weather increases retention time of concrete and slows down gaining durability.
- Water inside the concrete freezes and increases the volume (approximately 9-10%) and causes high pressure to the form.
- Cold weather causes formation of cracks, as a result of melting ice, causes the formation gaps in the concrete.
- If freezing occurs in concrete, this causes very high rate of durability loss (45-55%).
- Forms can not be removed in time and this increases working time and this is not economical.
Issues that we need to pay attention to during concrete casting in cold weather.
- You should prefer low viscosity and use minimum water content required fort his viscosity.
- You should use the cement with heat of hydration and providing high early strength.
- You must apply insulation to the form before pouring, so you will have less heat loss in concrete.
- You should heat the form in critical weather conditions.
- In cold weather, both fresh concrete and hardening concrete rapidly loses heat and moisture. Therefore, you need to take some precautions.
- In the first instance we should avoid temperature of the concrete falling down from a certain value.
- TS considers that concrete will not be damaged due to frost after compressive strength will reach to 50 kgf/cm2. This time is 3 days at +10°C temperature for a high-quality concrete.
- According to the technical specifications, minimum concrete temperature must be between + 5°C and + 10°C.
- In fresh concrete, freezing during hardening is very dangerous. Turkish Standards has put some temperature restrictions on this topic. For example: fresh concrete mixture temperature between -1°C ~ +5°C of a concrete which has 31,5 mm largest aggregate particle should be minimum 15°C and placing temperature should be 13°C.
- You should protect the concrete from sudden temperature changes.
- You should always apply water cure to the concrete even in cold weather and you should not allow the hardened concrete to dry suddenly.