Things to Consider about Hot Weather Concreting

When the temperature of freshly mixed concrete approaches approximately 25°C (77°F) adverse site conditions can adversely impact the quality of concrete. Ambient temperatures above 32°C (90°F) and the lack of a protected environment for concrete placement and finishing (enclosed building) can contribute to difficulty in producing quality concrete.

The use of liquid nitrogen is one option to reduce concrete's temperature during hot-weather concreting.

The precautions required to ensure a quality end product will vary depending on the actual conditions during concrete placement and the specific application for which the concrete will be used. In general, if the temperature at the time of concrete placement will exceed 25°C (77°F) a plan should be developed to negate the effects of high temperatures.

The precautions may include some or all of the following:

1. Moisten subgrade, steel reinforcement, and form work prior to concrete placement.
2. Erect temporary wind breaks to limit wind velocities and sunshades to reduce concrete surface temperatures.
3. Cool aggregates and mixing water added to the concrete mixture to reduce its initial temperature. The effect of hot cement on concrete temperature is only minimal.
4. Use a concrete consistency that allows rapid placement and consolidation.
5. Protect the concrete surface during placement with plastic sheeting or evaporation retarders to maintain the initial moisture in the concrete mixture.
6. Provide sufficient labor to minimize the time required to place and finish the concrete, as hot weather conditions substantially shorted the times to initial and final set.
7. Consider fogging the area above the concrete placement to raise the relative humidity and satisfy moisture demand of the ambient air.
8. Provide appropriate curing methods as soon as possible after the concrete finishing processes have been completed.
9. In extreme conditions consider adjusting the time of concrete placement to take advantage of cooler temperatures, such as early morning or night time placement.

With proper planning and execution concrete can be successfully placed and finished to produce high quality durable concrete at temperatures of 35°C (95°F) or more.

Additional information is available in the following references:

Hot Weather Concreting, IS014.05, reprinted from Chapter 13 of Design and Control of Concrete Mixtures, EB001.14, Portland Cement Association, 2002, 12 pages.

Hot and Cold Weather Concreting, CD057, Portland Cement Association, 2005

Hot Cement and Hot Weather Concrete Tests, IS015, Portland Cement Association, 12 pages, 1954