Machineries and equipments used for large concrete works:
Batching and mixing equipments
Batch mixing plant
Mixers
Concrete transporting equipments
Hoist, Chutes, Tower crane, Belt conveyors, Pumps, Cableways
Compacting equipments
3. Machineries and equipments used for large
concrete works:
1) Batching and mixing equipments
– Batch mixing plant
– Mixers
2) Concrete transporting equipments
– Hoist, Chutes, Tower crane, Belt conveyors,
Pumps, Cableways
3) Compacting equipments
Prof. Ashish Makwana 3
4. Fig. Flow chart of concreting
operations in large projectProf. Ashish Makwana 4
5. Batch Mixing Plant:
• In large project, the concrete is batched in a
central mixing plant and transported to the job
site in transit mix trucks or ready mix concrete
trucks.
• Main components of batch mixing plant are:
– Storage bins for sand, aggregate and cement,
raw water tank
– Belt conveyor for transporting sand, aggregate
and cement to the mixer.
– Refrigeration plant to supply chilled water.
– Mixers – 2 nos. each 3 cum. Capacity.
– Transit mixer for transporting concrete to the site
of work. Prof. Ashish Makwana 5
7. Transit mixer (Truck mixer):
• In the transit mixed or truck mixed concrete, the
materials are batched at a central batching plant
but are mixed in a mixer truck either in transit to
the site or immediately prior to the concrete
being discharged.
• Transit mixing permits a longer haul and is less
vulnerable in case of delay.
• Transit mix trucks are available in several sizes
up to 15 cum. The common sizes are in the
range of 6 to 8 cum.
• Concrete is mixed in a truck mixer with 70 to 100
revolution. ASTM C 94 allows a maximum of 1.5
hours or 300 revolutions whichever comes first.Prof. Ashish Makwana 7
8. Concrete mixers:
• According to the operating conditions:
– Batch mixers
– Continuous mixers
• According to the principle of mixing:
– Gravity type
– Type with forced mixing
• According to the condition of use:
– Stationary concrete mixers
– Portable concrete mixers
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9. (A) Batch Mixers:
• In this case, the mixers are charged with
materials in batches.
• Each new batch will be charged in to the drum of
the mixer only when the preceding batch has
been discharged.
• Batch mixers are used for normal concrete
works.
• They produce concrete batch by batch with time
interval.
Batch mixers classification:
• Tilting type, Non-tilting type, Reserving type
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10. • As per IS: 1971-1985, concrete mixers are
designated by a number representing its
nominal mixed batch capacity in liters.
(i) Tilting type: 85 T, 100 T, 140 T, 200 T
(ii) Non-tilting type: 200 NT, 280 NT, 375 NT, 500
NT, 1000 NT
(iii) Reversing type: 200 R, 280 R, 375 R, 500 R,
1000 R
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11. (B) Non-tilting type Mixers:
• In case of non-tilting type mixer, the mixing drum
of the mixer is cylindrical in shape and it
revolves about 2 horizontal axis.
• It has opening on both the sides.
• The various ingredients are charged into the
drum from one opening.
• For discharging concrete, a chute is introduced
in to the other opening of the drum by operating
a lever.
• It is seen that a little more of segregation takes
place, when a non-tilting mixer is used.
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13. (C) Tilting type mixer:
• This type of mixer consists of a conical drum
which rotates on an inclinable axis.
• The material for concrete is fed into the drum
either directly or through a loading skip.
• The mixed concrete is discharged by tilting the
drum. It has only one opening.
• The drum is tilted and reversed manually.
• About half the quantity of coarse aggregate is
placed in the skip over which about half the
quantity of sand is poured.
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14. • On that, the full quantity of cement i.e. one bag
is poured over which the remaining quantities of
coarse aggregate and sand is placed in
sequence.
• This prevents spilling of cement and blowing
away of cement in windy weather.
• Before charging the drum, about 25 percent of
the total quantity of water required for mixing is
fed into the drum to wet the drum and to prevent
sticking of cement at the bottom of the blades.
• After discharging the loaded skip into the drum,
the remaining 75 per cent of water is added to
the drum.
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15. • If plasticizer or super plasticizer is mixed with
that one liter of water and the same is added to
the mixer drum.
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16. (D) Mixing time:
• Mixing time is the time required to produce the
uniform concrete.
• It is reckoned from the time when all the
materials have been put into the drum.
• Concrete mixers are generally designed to run
at a speed of 15 to 20 revolutions per minute.
• For proper mixing about 25 to 30 revolutions are
required.
• The mixing time is related to the capacity of the
mixer.
• The mixing time varies between 1 to 2 minutes.
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17. (D) Mixing time: (continued..)
• Bigger the capacity of the drum more is the
mixing time. However, modern high speed pan
mixer used in RMC, mixes the concrete in about
15 to 30 seconds.
• If the concrete is mixed for a shorter time than
required, the quality of concrete will be poor.
• If the concrete is mixed for a comparatively
longer time, it is uneconomical from the point of
view of the rate of production of concrete and
fuel consumption.
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18. (E) Continuous mixers:
• Continuous mixers produce concrete
continuously without stoppage till such time the
plant is working.
• In such mixers, materials are fed continuously by
screw feeders and the materials are
continuously mixed and continuously
discharged.
• This type of mixers are used in large projects
like dams.
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