PORTLAND CEMENT CONCRETE - Materials for Civil and Construction Engineers - page 263

Main air valve
Pump

Pressure gauge

Petcock B

Air bleeder valve

Petcock A

Air chamber

Clamping device

Extension tubing for
calibration checks

Bowl

FIGURE 7.12 Pressure method apparatus for determining air
voids in fresh concrete - Type B Meter (ASTM C231). (Copyright
ASTM. Reprinted with permission.)

The water level in the container falls as the air rises to the top of the con-
tainer. Thus, the volume of air in the cement paste is directly measured. The
accuracy of the method depends on agitating the sample enough to remove
all the air from it.
The gravimetric method (ASTM C138) compares the unit weight of
freshly mixed concrete with the theoretical maximum unit weight of the
mix. The theoretical unit weight is computed from the mix proportions and

Watertight screw cap

0

1
2

3
4
5
6
7
8
9

Graduated neck
lined with glass or
transparant plastic

To p
section

Flanges with
gasket and clamps

FIGURE 7.13 Volumetric method (Roll-
A-Meter) apparatus for determining air voids in
fresh concrete (ASTM C173). (Copyright ASTM.
Reprinted with permission.)

Measuring
bowl