Civil Engineering Reference
In-Depth Information
Air
Air,
CO,
CO
2
,
Air
supply
Air
Fan
Flame
a) Direct-fired heater
Air,
CO,
CO
2
,
Enclosure
Stove pipe vent
Air
Clean
heated
air
only
Air
supply
Air
Fan
Flame
b) Indirect-fired heater
Fig. 14-21. With air temperatures down to -23°C (-10°F),
concrete was cast in this insulated column form made of
19-mm (
3
⁄
4
-in.) high-density plywood inside, 25-mm (1-in.)
rigid polystyrene in the middle, and 13-mm (
1
⁄
2
-in.) rough
plywood outside. R value: 1.0 m
2
Fig. 14-22. Two types of air heaters.
· °C/W (5.6
[
°F · hr · ft
2
]
/Btu). (43461)
14-20). Forms built for repeated use often can be econom-
ically insulated with commercial blanket or batt insula-
tion. The insulation should have a tough moisture-proof
covering to withstand handling abuse and exposure to
the weather. Rigid insulation can also be used (Fig. 14-21).
Insulating blankets for construction are made of fiber-
glass, sponge rubber, open-cell polyurethane foam, vinyl
foam, mineral wool, or cellulose fibers. The outer covers
are made of canvas, woven polyethylene, or other tough
fabrics that will withstand rough handling. The
R
value for
a typical insulating blanket is about 1.2 m
2
· °C/W for 50 to
70 mm thickness, 7(°F · hr · ft
2
)/Btu, but since
R
values are
not marked on the blankets, their effectiveness should be
checked with a thermometer. If necessary, they can be used
in two or three layers to attain the desired insulation.
HEATERS
Three types of heaters are used in cold-weather concrete
construction: direct fired, indirect fired, and hydronic
systems (Figs. 14-22 to 14-25). Indirect-fired heaters are
vented to remove the products of combustion. Where heat
is to be supplied to the top of fresh concrete— for example,
a floor slab—vented heaters are required. Carbon dioxide
Fig. 14-23. An indirect-fired heater. Notice vent pipe that
carries combustion gases outside the enclosure. (43459)
