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pneumatic wheels instead of steel wheels.
Alternatively, wooden plank way is made over
which barrows are moved to check vibrations in
barrow and thus result in reduced segregation.
These are most useful for small jobs, small hauls,
and over muddy ground. The average capacity
of a wheel barrow is 35 litres (80 kg).
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X Chutes are used to transport concrete
below the ground levels. These are made with
metal sheets with a slope more than IV: 2.5H to
ensure that unloaded concrete slides easily without segregation. This method of transporting
concrete should be avoided until unevitable such as lack of space or congested reinforcement.
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X Dumpers, lorries or, trucks are used economically for hauls up to 5 km. Dumpers are
usually of capacity 2 to 3 cu m whereas trucks are of 4 cu m capacity. For long hauls agitators
are used to prevent segregation. The concrete should be covered with tarpaulins to prevent
evaporation of water from concrete. A truck mixer is shown in Fig. 10.7(a).
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2 2
X These are used when concreting is to be done in a valley or for
construction work of piers, dams etc. The bucket is brought close to the mix site, filled and
moved over ropeway to the site of deposition. The bucket may be of tilting type or with a gate
at bottom for discharging concrete. Concrete should be discharged from the smallest height.
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2
X The use of belt conveyors for transporting concrete is very little. The two main
objections are segregation and drying, and stiffening of concrete. Concrete segregates due to
steep slopes, changes of directions, and the points where belt passes over rollers. The drawback
is that the concrete will have to be remixed at the place of deposition which is not recommended.
" 2 2 r X This is the most useful and advantageous method of transporting concrete for
multistorey buildings. The mixer feeds the skip which moves up over rails up to the level of
deposition. If height of travel is too much, the concrete may require a turning over before
deposition in to the place.
X Pumping of concrete is done for multistorey buildings, tunnels, and bridges. The
concrete is fed from the hopper into the pump cylinder largely by gravity, assisted by the
vacuum created on the suction stroke of the piston and forced into the pipe line on the pressure
stroke. The pipes are made of steel, aluminium, or plastic of sizes ranging from 80 to 200 mm
diameter. The aluminium pipes have a draw back of formation of hydrogen gas and are not
recommended. The pumps of capacity 15 to 150 m^3 /hr are available. These can pump concrete
400 m horizontally and up to 80 m vertically. The pumpable concrete should be cohesive and
fatty. It should have a slump of 50 to 100 mm or even more and a compacting factor of 0.9 to
0.95. Pumping compacts the concrete partially and reduces the slump by about 25 per cent at
the delivery end. Sometimes, admixtures are added to offer additional lubrication, reduced
bleeding, and segregation. Generally, air entraining admixtures are used giving an air content
of 3 to 5 per cent.
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