Page 79 - Masonry and Concrete

Concrete Construction Techniques
78 CHAPTER THREE

To Protect
from Damage For Safe
by Freezing Form Removal
Construction Type I or Type III Type I or Type III
and Service Conditions II Cement Cement II Cement Cement
Not loaded during
construction, not exposed
to freezing in service 2 1 2 1
Not loaded during
construction, exposed to
freezing in service 3 2 3 2
Partially loaded during
construction, exposed to
freezing in service 3 2 6 4

FIGURE 3-38

Days of protection required for cold weather concrete. (Adapted from American Concrete
Institute Standard ACI 306R.)

■ Wrap protruding reinforcing bars with insulation to prevent
heat drain.

Whenever you can schedule concrete pours during milder weather,
it is best to do so, but in some climates this is impractical. When cold
weather concreting cannot be avoided, quality does not have to be sac-
rificed if proper precaution is exercised.

3.8.2 Hot Weather Concreting

Hot weather can also be damaging to concrete. The fresh mix will
require more water than usual to achieve the required slump and work-
ability, will set faster and have reduced working time, will more likely
experience plastic shrinkage cracking on the surface, and will suffer
variations in air content. The hardened concrete will have lower
strength, more drying shrinkage and tendency to crack, less durability
in freeze-thaw exposures, and less uniform surface appearance. The
adverse effects of hot weather increase as temperatures rise, relative
humidity falls, and wind increases, and the damage can never be com-

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