Concrete Mixer Truck
Equipment used for transportation of concrete, from mixer
to placing site, depends upon the distances involved and the volume of concrete
to be placed. Wheelbarrows, with limited capacity say 0.04 m3, and
small motorized dumpers, with capacity up to 1.0 m3 are sued for
transporting and placing small quantities of concrete.
Concrete transit mixers are employed for transporting
large quantities of concrete over long distances. These mixers have a rotating
drum mixer mounted on a truck. These transit mixers transport wet concrete from
the mixer to the placing site, and their rotating drums carrying capacity
varies from 3 m3 to 9 m3 concrete. Concrete specifications
restrict the time from loading to discharge of the concrete mixer as one hour
without retarders, provided the drum is kept rotating to agitate the wet mix. For
long distances, say exceeding two hour’s travel time, the dry mix can be
transported in specially designed truck-mixers, and the concrete is
manufactured at the placing site by mixing these materials with water.
The number of truck-mixers required for transporting
concrete can be worked out by evaluating the cycle-time. Consider a typical mixer
cycle time data of 6 m3 truck-mixer, given below:
Loading time for 6 m3 truck-mixer = 14
minutes
Travel time of loaded truck-mixer to site = 7.5
minutes
Average waiting time at site = 7.5 minutes
Discharge time at site using concrete pump = 15
minutes
Travel time for return trip = 5 minutes
Total cycle time = 49 minutes
Therefore truck-mixers required for continuous supply
= (cycle time / discharge time) + 1 (spare)
= (49/15) + 1
= 5 nos.
Notes
· Cycle time
should be divided by discharge time (as illustrated above) or loading time,
whichever is higher.
· Concrete
placing rate at delivery site (m3/h) should be kept marginally less
than the loading (or production) rate due to the following reasons:
1. Concrete
placing should proceed continuously as waiting in between can result in
improper jointing, specially if the time interval between the initial-set
period.
2. Concrete
loading at the batching plant can be suitably controlled as and when the queue
of loaded truck-mixers starts building-up at the placing site.
