Page 78 - Masonry and Concrete

Concrete Construction Techniques
77
CONCRETE CONSTRUCTION TECHNIQUES

■ If you are ordering from a ready-mix supplier, specify heated
concrete with a minimum temperature as recommended in Fig-
ure 3-37.

■ Remove ice and snow from inside forms and thaw frozen sub-
grade before concrete placement.
■ If you are mixing concrete on site, store ingredients in a heated
area if possible, and use heated water for mixing.
■ Reduce the time between mixing and placing as much as possi-
ble to reduce heat loss. Work with smaller batches if necessary.
■ Keep concrete temperatures above the minimum recommended
in Figure 3-37 for the number of days recommended in Figure 3-
38. Place insulation blankets on slabs immediately after concrete
has set sufficiently so that concrete surface is not marred. Pro-
vide double or triple thickness of insulation at corners and edges
of slabs where concrete is most vulnerable to freezing. Use wind-
screens to protect slabs and other flatwork from rapid cooling.
■ Delay form removal as long as possible to minimize evaporation
and to reduce damage to formed surfaces caused by premature
form stripping.

Sections Less Sections 12 to
Condition Than 12 in. Thick 36 in. Thick

Minimum temperature } above 30°F 60 55
of concrete as mixed } 0°F to 30°F 65 60
in weather indicated } below 0°F 70 65
Minimum temperature of concrete
during placement and curing 55 50
Maximum gradual temperature drop
allowed in first 24 hours after
protection is removed 50 40

FIGURE 3-37
Recommended temperatures for cold weather concrete, degrees F (Adapted from
American Concrete Institute Standard ACI 306R).

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