The output of a mixer essentially depends upon the capacity of a mixer. In addition, it depends upon the duration of mixing, supply of materials to the mixer and the speed at which charging and discharging operations are carried out. Sometimes the speed of transporting concrete from mixer to the formwork limits the output of a mixer. The following example illustrates the calculation of output of a mixer per day.
Calculating output of a mixer of 200 litres capacity per day
Time required for one batch of concrete
Raising skip, discharging into drum and lowering = ½ min
Adding water and mixing in the drum (During this time the skip is reloaded) = 2 min
Discharging content of drum and completing loading of skip = ½ min
Then total time required for one batch of concrete = ½ + 2 + ½ = 3 min
In a day of 8 hours there will be effective mixing for 7 hours. One hour being occupied in clearing drum, chutes, etc and starting and oiling the engine.
No. of batches in one working hour = 60/3 = 20 (considering 3 minutes mixing cycle)
No. of batches in 7 hours = 20 x 7 = 140
Considering 90% efficiency, output per batch = 200 x (90/100) = 180 litres
Output per day = 180 x 140 = 25200 litres = 25.2 cu-m (say 25 m3)
Calculating Time Required to Complete a Job
Output also enables to calculate time required to complete a job. The following example illustrates this.
Find the working hour required to complete a concrete slab 30 m * 50 m 8 0.20 m size using 200 T mixer.
With three minute cycle time for one complete operation,
The output per hour = 20 * 180 = 3600 litres i.e. 3.6 cubic meters
So number of working hours = (30*50*0.2)/3.6 = 83.3 hours