TRUCK MIXERS
Special concrete transport trucks (in-transit mixers) are made to
mix concrete and transport it to the construction site. They can
be loaded from a "central mix" plant; with this process the
material has already been mixed prior to loading. The concrete
mixing transport truck maintains the material's liquid state
through agitation, or turning of the drum, until delivery. The
interior of the drum on a concrete mixing truck is fitted with a
spiral blade. In one rotational direction, the concrete is pushed
deeper into the drum. This is the direction the drum is rotated
while the concrete is being transported to the building site.
This is known as "charging" the mixer. When the drum rotates in
the other direction, the Archimedes' screw-type arrangement
"discharges", or forces the concrete out of the drum. From there
it may go onto chutes to guide the viscous concrete directly to
the job site. If the truck cannot get close enough to the site to
use the chutes, the concrete may be discharged into a concrete
pump, connected to a flexible hose, or onto a conveyor belt which
can be extended some distance (typically ten or more
metres).
Buckets suspended from cranes are also used to place the
concrete. The drum is traditionally made of steel but on some
newer trucks, fibreglass has been used as a weight reduction
measure.
A pump provides the means to move the material to precise locations, multi-floor buildings, and other distance-prohibitive locations.
Concrete mixers generally do not travel far from their plant, as the concrete begins to set as soon as it is in the truck. require that the concrete be in place within 90 minutes after loading. If the truck breaks down or for some other reason the concrete hardens in the truck, workers may need to enter the barrel with jackhammers