How to concrete in hot weather

As we read in the earlier blog post, Hot Weather Concreting can affect the strength of a structure. It is therefore important to know what precautions we can take to avoid the ill-effects of concreting during hot and arid weather.

The first immediate solution for concreting in arid and hot weather /low humid regions is to pour concrete during early morning or late evening. This may mitigate the bad effects to a large extent. In case, if the concreting pour has to be done during the day, other precautionary measures could be undertaken for better results.

  • Lower the temperature of the concrete ingredients before they are used for concrete mixing.
  • High early strength cements to be avoided unless the initial high strength of concrete is required at the site
  • Aggregates may be protected from direct rays of the sun during concrete production by providing shades over the stockpiles.
  • Sprinkling the stockpiles of coarse aggregates with water and keeping them moist is another option to be considered.

The only precaution to be taken care is not to flood them so as to affect the moisture content considered during concrete mix design.

The mixing water has the greatest effect on the temperature of concrete since it has a specific heat of about 4 to 4.5 times that of cement or aggregate. Hence chilled water or ice is preferred during concreting at high temperatures. If at all ice is added to the mixing plant directly, it is added in the crushed state only and complete melting is to be ensured before mixing of concrete ingredients is complete.

Use of chemical admixtures like water reducers/retarders helps in delaying the setting of concrete. However, use of these chemical admixtures needs to be carefully done as per manufacturer’s specifications and expert engineer’s advice.

Also, need to plan adequate manpower and machinery to complete the concrete pour at the shortest time possible during hot weather.

Painting the mixer machine surface and transporting trucks with white or lighter color and covering them with wet burlaps minimizes the radiation effects. Also, reducing the time between water added during concrete mix and concrete pouring negate the workability loss.

Finishing, and curing of concrete

The next important precautions to be taken are in placement, finishing, and curing of concrete. The speed of placement and finishing helps to minimize problems in hot water concreting. Protection and curing have to be started immediately after the surface is hardened enough. This can be in the form of covering the concrete surface with wet burlap, curing compounds or sprinkling of water initially. Moist curing shall commence once the concrete surface has attained some degree of hardening sufficient to withstand surface damage. Continuous curing is important, because volume changes due to alternate wetting and drying promote the development of surface cracks.

Once concrete cubes are cast for testing of the concrete for compressive strengths, adequate protection to be made for cube specimens from being exposed to direct sunlight or else evaporation of water in the cube will lead to lower compressive strength reported when tested for 7 days and 28 days.

It is important to take adequate measures at every step involved in concreting from material storage to concrete mixing, transportation, placing, finishing, curing and concrete cube casting.

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