Civil Engineering Reference
In-Depth Information
400
Cured normally
(never frozen)
300
Frozen dry
200
Frozen wet
100
Fig. 14-11. Example of a concrete floor that was saturated
with rain, snow, or water and then frozen, showing the need
for air entrainment. (69869)
0
0
10
20
30
40
50
60
floor surface. This could also result in greater deflection of
the floor and a surface that is less wear-resistant than it
might have been.
Number of cycles of freezing and thawing
Fig. 14-10. Effect of freezing and thawing on strength of
concrete that does not contain entrained air (cured 7 days
before first freeze) (
Powers 1956
).
TEMPERATURE OF CONCRETE
Air entrainment should always be used for construc-
tion during the freezing months. The exception is concrete
work done under roof where there is no chance that rain,
snow, or water from other sources can saturate the concrete
and where there is no chance of freezing.
The likelihood of water saturating a concrete floor
during construction is very real. Fig. 14-11 shows con-
ditions in the upper story of an apartment building during
winter construction. Snow fell on the top deck. When
heaters were used below to warm the deck, the snow
melted. Water ran through floor openings down to a level
that was not being heated. The water-saturated concrete
froze, which caused a strength loss, particularly at the
Temperature of Concrete as Mixed
The temperature of fresh concrete as
mixed
should not be
less than shown in Lines 1, 2, or 3 of Table 14-1 for the
respective thickness of section. Note that lower concrete
temperatures are recommended for more massive
concrete sections because heat generated during hydra-
tion is dissipated less rapidly in heavier sections. Also
note that at lower ambient air temperatures more heat is
lost from concrete during transporting and placing; hence,
the recommended concrete temperatures as mixed are
higher for colder weather.
Table 14-1. Recommended Concrete Temperature for Cold-Weather Construction—Air-Entrained Concrete*
Thickness of sections, mm (in.)
Less than
300 to 900
900 to 1800
Over
Line
Condition
300 (12)
(12 to 36)
(36 to 72)
1800 (72)
1
Minimum temperature
Above -1°C (30°F)
16°C (60°F)
13°C (55°F)
10°C (50°F)
7°C (45°F)
of fresh concrete as
2
mixed
for weather
-18°C to -1°C (0°F to 30°F)
18°C (65°F)
16°C (60°F)
13°C (55°F)
10°C (50°F)
indicated.
3
Below -18°C (0°F)
21°C (70°F)
18°C (65°F)
16°C (60°F)
13°C (55°F)
Minimum temperature of fresh concrete
as placed
and maintained.
**
4
13°C (55°F)
10°C (50°F)
7°C (45°F)
5°C (40°F)
* Adapted from Table 3.1 of
ACI 306R-88
.
** Placement temperatures listed are for normal-weight concrete. Lower temperatures can be used for lightweight concrete if justified by tests.
For recommended duration of temperatures in Line 4, see Table 14-3.
