Civil Engineering Reference
In-Depth Information
primarily dependent upon the aggregate temperature,
cooling the mixing water can be effective.
The approximate temperature of concrete can be cal-
culated from the temperatures of its ingredients by using
the following equation (NRMCA 1962):
Of all the materials in concrete, water is the easiest to
cool. Even though it is used in smaller quantities than the
other ingredients, cold water will produce a moderate
reduction in the concrete temperature. Mixing water from
a cool source should be used. It should be stored in tanks
that are not exposed to the direct rays of the sun. Tanks
and pipelines carrying mixing water should be buried,
insulated, shaded, or painted white to keep water as cool
as practical. Water can be cooled by refrigeration, liquid
nitrogen, or ice. Cooling the mix water temperature 2.0°C
to 2.2°C (3.5°F to 4°F) will usually lower the concrete tem-
perature about 0.5°C (1°F). However, because mix water is
such a small percentage of the total mixture, it is difficult
to lower concrete temperatures more than about 4.5°C
(8°F) by cooling the water alone.
Ice can be used as part of the mixing water provided
it is completely melted by the time mixing is completed.
0.22 (
T
a
M
a
+
T
c
M
c
) +
T
w
M
w
+
T
wa
M
wa
T
=
where
0.22 (
M
a
+
M
c
) +
M
w
+
M
wa
T
= temperature of the freshly mixed concrete, °C (°F)
T
a
,
T
c
,
T
w
, and
T
wa
= temperature in °C (°F) of aggre-
gates, cement, added mixing water, and free water on
aggregates, respectively
M
a
,
M
c
,
M
w
, and
M
wa
= mass, kg (lb), of aggregates,
cementing materials, added mixing water, and free water
on aggregates, respectively
Example calculations for initial concrete temperature
are shown in Table 13-1A.
Table 13-1A (Metric). Effect of Temperature of Materials on Initial Concrete Temperatures
Initial
Specific heat
Joules to vary
temperature of
Total joules
Material
Mass,
M
, kg
kJ/kg • K
temperature, 1°C
material,
T
, °C
in material
(1)
(2)
(3)
(4)
(5)
Col.1 x Col. 2
Col. 3 x Col. 4
Cement
335 (
M
c
)
0.92
308
66 (
T
c
)
20,328
Water
123 (
M
w
)
4.184
515
27 (
T
w
)
13,905
Total aggregate
1839 (
M
a
)
0.92
1692
27 (
T
a
)
45,684
2515
79,917
Initial concrete temperature =
79,917
2515
= 31.8°C
To achieve 1°C reduction in initial concrete temperature:
Cement temperature must be lowered =
2515
308
= 8.2°C
Or water temperature dropped =
2515
515
= 4.9°C
Or aggregate temperature cooled =
2515
1692
= 1.5°C
Table 13-1A (Inch-Pound Units). Effect of Temperature of Materials on Initial Concrete Temperatures
Initial
Btu to vary
temperature of
Total Btu's
Material
Mass,
M,
lb
Specific heat
temperature, 1°F
material,
T
, °F
in material
(1)
(2)
(3)
(4)
(5)
Col.1 x Col. 2
Col. 3 x Col. 4
Cement
564 (
M
c
)
0.22
124
150 (
T
c
)
18,600
Water
282 (
M
w
)
1.00
282
80 (
T
w
)
22,560
Total aggregate
3100 (
M
a
)
0.22
682
80 (
T
a
)
54,560
1088
95,720
Initial concrete temperature =
95,720
1088
= 88.0°F.
To achieve 1°F reduction in initial concrete temperature:
Cement temperature must be lowered =
1088
124
= 8.8°F
Or water temperature dropped =
1088
282
= 3.9°F
Or aggregate temperature cooled =
1088
682
= 1.6°F
