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.