Civil Engineering Reference
In-Depth Information
Wall or slab thickness, in.
0
12
24
0
12
24
0
12
24
10
50
5
40
0
30
-5
20
-10
10
-15
0
-20
-10
-25
-20
-30
-30
-35
-40
-40
Cement content
237 kg/m
3
(400 lb/yd
3
)
Cement content
296 kg/m
3
(500 lb/yd
3
)
Cement content
356 kg/m
3
(600 lb/yd
3
)
-45
-50
-50
-60
0
100
200
300
400
500
600
0
100
200
300
400
500
600
0
100
200
300
400
500
600
Wall or slab thickness, mm
Fig. 14-16. Thermal resistance (R) of insulation required to maintain the concrete surface temperature of walls and slabs
aboveground at 10°C (50°F) or above for 7 days. Concrete temperature as placed: 10°C (50°F). Maximum wind velocity:
24 km/h (15 mph). Note that in order to maintain a certain minimum temperature for a longer period of time, more insulation
or a higher R value is required (adapted from
ACI 306
).
a temperature of 2°C (35°F). Insulation can be selected
based on
R
values provided by insulation manufacturers
or by using the information in Table 14-4.
When concrete strength development is not deter-
mined, a conservative estimate can be made if adequate
protection at the recommended temperature is provided
for the duration of time found in Table 14-3. However, the
actual amount of insulation and length of the protection
period should be determined from the monitored in-place
concrete temperature and the desired strength. A correla-
tion between curing temperature, curing time, and com-
pressive strength can be determined from laboratory
testing of the particular concrete mix used in the field (see
“
Maturity Concept
” discussed later in this chapter).
ACI
306
states that with a compressive strength of 3.5 MPa (500
psi), concrete will normally have sufficient strength to
resist early frost damage. If the concrete will be in a satu-
rated condition when frozen, the concrete should be prop-
erly air entrained and must have developed a compressive
strength of 28 MPa (4000 psi).
Corners and edges are particularly vulnerable during
cold weather. As a result, the thickness of insulation for
these areas, especially on columns, should be about three
times the thickness that is required to maintain the same
for walls or slabs. On the other hand, if the ambient
temperature rises much above the temperature assumed
in selecting insulation values, the temperature of the
concrete may become excessive. This increases the proba-
bility of thermal shock and cracking when forms are
removed. Temperature readings of insulated concrete
should therefore be taken at regular intervals and should
not vary from ambient air temperatures by more than the
values given in
ACI 306
. In addition, insulated concrete
temperatures should not be allowed to rise much above
27°C (80°F). In case of a sudden increase in concrete tem-
perature, up to say 35°C (95°F), it may be necessary to
remove some of the insulation or loosen the formwork.
The maximum temperature differential between the con-
crete interior and the concrete surface should be about
20°C (35°F) to minimize cracking. The weather forecast
