throughout the depth. The strokes will eliminate any
voids when the concrete is placed in the cone.
If the cone is overfilled, the excess concrete is made
flush with the top of the cone with a straightedge. The
cone is raised from the concrete by raising the cone
carefully in a vertical direction. The slump is determined
by measuring the difference between the height of the
cone and the height of the concrete specimen (fig. 7-3).
The slump is recorded in inches on the quality control
report.
After the slump measurement is completed, the side
of the mix is tapped gently with the tamping rod. The
behavior of the concrete under this test is a valuable
indication of the cohesiveness, workability, and
placability of the concrete mix. If the mix is
well-proportioned, tapping will only cause it to slump
lower and retain its original identity, and a poor mix will
crumble, segregate, and fall apart. Normally, the EAs
perform three slump tests per truck load of concrete.
Another test performed by the EAs on a concrete mix is
a concrete strength test. This test is performed to control
the quality of concrete manufactured in the field, to
evaluate the performance of available materials used in
a concrete mix, and to establish mix proportions that
give concrete the required strength.
PLANT SAFETY
1.
2.
3.
All personnel working in the batch plant area
should wear hard hats at all times.
When hoppers are being charged with a
clamshell or loader, personnel should stay away
from the area of falling aggregate.
Housekeeping of the charging area is important.
Keep the area clean and free of spoiled material
and overflow.
4.
5.
6.
Respirators must be worn by all personnel when
handling bag or bulk cement.
Particular attention should be given to any rash
or other irregularities of the skin as it might
indicate “cement poisoning.”
Vapor type of goggles should be worn by
personnel in batch plant operations.
TRANSIT MIXER SAFETY
The use of transit mixers on construction projects
impose traffic problems that must be considered.
Caution must be used during backing of the transit
mixer. Backing should be controlled by a signalman,
positioned so the operator can clearly observe the
directions given. Extrement caution must be used when
traveling on a construction site. The stability of the
mixer is greatly reduced with the extra weight of the
concrete. Also, the weight of the mixer can crush newly
placed underground utilities, sink in the mud, crack
sidewalks, and so forth. In such cases, a slow speed is
recommended.
Some additional safety precautions that must be
enforced are as follows:
1.
2.
3.
4.
Reduce speed before making a turn or applying
the truck brakes.
Secure the discharge chute properly, using the
lock provided.
Check to make certain other personnel are in the
clear before starting the mixer charging or
discharging.
Make sure the mixer is stopped before making
any adjustments.
7-8
