During the summer season, rising ambient temperatures can impair the behavior of fresh concrete and the quality of the hardened material. Heat accelerates setting times and can cause harmful phenomena such as cracking due to plastic shrinkage, segregation, difficulty in compaction and failure to develop the final resistance. For this reason, it is essential to follow good practices in the design, production, transport, installation and curing of concrete in hot climates.
Negative effects of high temperatures on concrete
| PHENOMENON | CONSEQUENCE |
| Temperature rise of fresh concrete (>30°C) | Reduced setting time, difficult to machine |
| Fast evaporation of water | Plastic shrinkage and cracking |
| Increased risk of segregation | Inhomogeneous concrete, loss of strength |
| Formation of thermal shrinkage cracks | Impairment of durability |
Technical standards (e.g. UNI EN 206 and UNI 11104) recommend avoiding concrete castings at a temperature > of 35°C, unless corrective measures are taken.
How to use concrete correctly in summer
1. Fresh concrete temperature control
- Objective: to maintain the temperature of the concrete between 15°C and 30°C.
- Use:
- Cooled mixing water (up to 5–10°C).
- Shaded or wet gravel.
- Cement stored in cool environments.
- Concrete batching plants equipped with cooling systems (e.g. crushed ice, liquid CO₂).
2. Adjusting the mixture
- Addition of retardant superplasticizers: increase machinability and delay setting.
- Controlled water/cement ratio (W/C ≤ 0.50): avoids excessive evaporation and loss of strength.
- Reduction of transport and installation time: use concrete mixers protected from the sun.
3. Casting practices in summer conditions
- Avoid jets in the middle of the day (better in the early morning or late afternoon).
- Protect formwork and reinforcement from overheating (shading or wetting).
- Speed up installation and compaction: concrete tends to lose workability quickly.
4. Care and seasoning
Seasoning is essential in summer to avoid premature evaporation of water:
- Apply curing compounds (anti-evaporation products) immediately after finishing.
- Cover the jet with wet sheets or plastic films.
- In the case of large surfaces (e.g. flooring), start curing within 30 minutes of casting.
5. Quality Controls
- Measurement of the temperature of fresh concrete at the time of pouring.
- Verification of workability (slump test) on site.
- Storage of specimens (cubes) under thermally controlled conditions.
- In critical cases, use temperature and humidity sensors to monitor ripening on site.
Conclusion: Essential good practices
To avoid premature degradation or failure to achieve the required performance, it is essential:
- Check the temperature of the fresh concrete (<30°C).
- Use retardant additives and cooled water.
- Avoid jets during the hottest hours.
- Protect and cure the jet properly.
- Perform constant checks on the material and process.
