Civil Engineering Reference
In-Depth Information
40
Relative humidity, percent
Concrete temperature,
°
C
100
To use these charts:
90
35
80
1. Enter with air temperature, move
up
to relative humidity.
70
30
60
2. Move
right
to concrete temperature.
50
25
3. Move
down
to wind velocity.
40
20
4. Move
left:
read approximate rate of
evaporation.
30
15
20
10
10
5
5 0 5 0 5 0 5
Air temperature,
°
C
Wind velocity, km/h
Metric
4
40
35
3
Relative humidity, percent
Concrete temperature,
°
F
30
100
100
25
20
2
80
15
90
10
5
1
60
80
0
0
40
70
60
One or more of the precautions listed
below can minimize the occurrence of
plastic shrinkage cracking. They should be
considered while planning for hot-weather
concrete construction or while dealing with
the problem after construction has started.
They are listed in the order in which they
should be done during construction.
1. Moisten concrete aggregates that are
dry and absorptive.
2. Keep the concrete temperature low by
cooling aggregates and mixing water.
3. Dampen the subgrade (Fig. 13-9) and
fog forms prior to placing concrete.
4. Erect temporary windbreaks to reduce
wind velocity over the concrete surface.
5. Erect temporary sunshades to reduce
concrete surface temperatures.
20
50
40
40
60
80
100
Air temperature,
°
F
Wind velocity, mph
Inch-Pound Units
0.8
0.6
25
20
0.4
15
10
0.2
5
2
0
0
Fig. 13-8. Effect of concrete and air temperatures, relative humidity, and wind velocity on rate of evaporation of surface
moisture from concrete. Wind speed is the average horizontal air or wind speed in km/h (mph) measured at 500 mm (20 in.)
above the evaporating surface. Air temperature and relative humidity should be measured at a level approximately 1.2 to
1.8 m (4 to 6 ft) above the evaporating surface and on the windward side shielded from the sun's rays (
Menzel 1954
).
