Mixing equipment, drilling equipment, compressed
air equipment, and miscellaneous construction and
maintenance equipment are procured for the Naval
Construction Force (NCF) to support specific
construction and maintenance operations.
This chapter covers the characteristics and basic
principles of operations of mixing equipment, drilling
equipment, compressed air equipment, and mis-
cellaneous construction and maintenance equipment.
These types of equipment play a vital part in NCF
operations; therefore, as an equipment operator, you
should become familiar with the capabilities of the
equipment and how it can be used to serve the
purpose for which it was designed.
CONCRETE TRANSIT MIXER
A concrete transit mix truck, sometimes called a
TM, is a traveling concrete mixer (fig. 14-1). The truck
carries a mixer and a water tank from which the operator
can, at the proper time, introduce the required amount
of water into the mix. The operator picks up the dry
ingredients at the batch plant along with a chit that tells
how much water is to be introduced to the mix. The
mixer drum is kept revolving en route and at the jobsite,
so the dry ingredients do not segregate.
When a TM is used for mixing concrete, 70 to 100
revolutions of the drum at the rate of rotation,
designated by the manufacturer as mixing speed, are
usually required to produce the specified uniformity.
No more than 100 revolutions at mixing speed should
be used. All revolutions after 100 should be at the rate
of rotation designated by the manufacturer as
agitating speed. Agitating speed is usually about 2
to 6 revolutions per minute, and mixing speed is
generally about 6 to 18 revolutions per minute.
Mixing for long periods of time at high speeds, about
1 or more hours, can result in concrete strength loss,
temperature rise, excessive loss of entrained air, and
accelerated slump loss.
Concrete, mixed in a transit mixer, should be
delivered within 1 1/2 hours or before the drum has
revolved 300 times after the introduction of water to
cement and aggregates or the cement to the aggregates.
Mixers and agitators should always be operated within
the limits of the volume and speed of rotation designated
by the manufacturer.
The operator must have the proper chutes at the
delivery site or on the truck before delivering concrete.
Open-trough chutes should be of metal or metal-lined,
Figure 14-1.Concrete transit mixer.