Page 80 - Masonry and Concrete

Concrete Construction Techniques
79
CONCRETE CONSTRUCTION TECHNIQUES

pletely undone. There are, however, a number of recommendations
which can help avoid problems. The following protective measures
should be taken when temperatures are 90°F or above, especially when
accompanied by windy conditions or relative humidities below 25%.

■ To decrease the possibility of plastic shrinkage cracking, use the
largest size and amount of coarse aggregate compatible with the
job requirements and, if ordering from a ready-mix supplier,
specify a water-reducing admixture.

■ Locate control joints at slightly closer intervals than when con-
creting in milder temperatures, and plan the locations of con-
struction joints ahead of time with smaller working areas in
mind.
■ Use sunshades or windbreaks as appropriate, and avoid work-
ing during the hot afternoon.

■ Have enough workers on hand to keep the job running smoothly
and quickly.

■ If you are mixing concrete on site, sprinkle aggregate stockpiles
ahead of time for evaporative cooling and use ice as part of the
mixing water.

■ Reduce the time between mixing and placing as much as possi-
ble and avoid excessive mixing. Do not add water to ready-
mixed concrete at the job site.
■ Moisten the forms and reinforcement and moisten soil sub-
grades before placing the concrete.
■ Cure the concrete for at least three days, but preferably for one
week. When forms are removed, provide a wet cover for newly
exposed surfaces.

The primary concern of hot-weather concreting is the rapid loss of
mixing water to evaporation. All of the protective measures outlined
are aimed at preserving the moisture needed for cement hydration and
curing. If adequate moisture can be maintained in the concrete for at
least three and preferably seven days, there will be no decrease in the
quality of the concrete compared to that placed and cured in milder
weather.

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