Technical recommendations for concreting in hot weather

Concreting during the summer months requires special attention due to the impact that high temperatures can have on the properties of concrete, both in its fresh and hardened state.

To preserve the workability, strength, and durability of the material, we share the main recommendations outlined in the Structural Code (sections 52.3.2 and 52.5) and in standards UNE 83151-2 and UNE 83151-3:

1. Accelerated setting

High temperatures lead to a faster setting of the concrete, reducing the available time for placement and compaction. It is important to adjust on-site processes to maintain proper workability.

2. Evaporation of mixing water

Heat and wind increase the risk of water evaporation, which can compromise cement hydration. It is recommended to minimize the time between mixing, transport, and placement on site.

3. Proper curing

Applying adequate curing methods to retain moisture during the setting and hardening stages is essential to prevent surface drying and cracking.

4. Temperature control of test specimens

During the first 24 hours, test specimens must be kept on site at controlled temperatures:

• 20 °C ± 5 °C under normal conditions
• 25 °C ± 5 °C in hot weather

5. Limit conditions

If ambient temperatures exceed 40 °C or there are strong winds, concreting operations should be suspended to avoid premature material degradation.

These measures are intended to prevent negative effects such as loss of workability, cracking, reduced strength, or early drying.