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Guidance Notes - Concrete Mix
Concrete which can be pushed thro a pipeline
is called a pump able concrete
A normal concrete with increased fines content
Does not require any additional Cement
Control of workability of prime importance;
Slump range- 90 to 120 mm; individual slumpmeasurements may vary by 25 mm
Desired slump achieved by choosing proper
quality / dosage of super-plasticizer
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Concrete Mix Quality of Sand
Control of quality of sand very vital; sand
conforming to zone 1,2,3 or 4 may be used
There should be no silt content; wash the sand
thoroughly to remove all the silt
Depending upon the coarseness or fineness of
the sand, the sand content should be adjusted
based on trial mixes. Course aggregate shaped
should be cubical or spherical; river gravel
(shingle) gives the best result for pumping
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Sand Content
Pumpable concrete must slide along the wall of
the pipeline and be able to move thro the
bends
Cement and finer particles of sand acts as a
lubricant when the concrete passes thro the
pipeline. The contents of fines( Cement + Fine
Sand) should be 450 Kg/ cum Concrete with 20mm aggregates, or 400 Kg/cum with 40 mm
aggregates
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Influence of size, shape of Aggregates
Flaky, Longitudinal shapes have more surface
area than rounded; for flaky / crushed stones,
sand content increased by 10%; stone dust or
fillers are suitable to increase the sand content
The surface of aggregates may be very smooth
(as in the case of river gravel) or rough or sharp
edged ( Crushed material ); for flaky or sharpedged or crushed aggregates; the quantity of
fines should be increased by about 10%
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Priming of Dry Pipelines
Before starting pumping, the dry pipeline is
primed ( buttered ) using cement- water mix
Follow manufacturers recommendation as to
amount of cement to be used
Lubricating mix is charged in to the hopper with
pump switched off and pushed in to the pipeline
before the first regular concrete mix is pumped.This is done first before starting concrete
pumping; repeated if pumping is interrupted
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Priming of Dry Pipelines
Minimum quantity of lubricating mix :
- 50Kg of cement and water adequate for truck
mounted concrete pumps with placing booms
up to vertical reached of 25 m- 100 Kg of cement in water for larger reaches
For pipelines more than 50 m long, lubricating
mix is made of 2 parts of cement and 1 partsand and water
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Quantities of lubricating mixes-125mm dia
Length (m) Lubricating
Mix- Liter
Cement
(Kg)
Sand (Kg)
50 200 200 100
100 300 300 150
200 500 500 250
300 750 750 350
400 1000 1000 500
600 1500 1500 750
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Use of Fly ash/ Slag
For effective pumping minimum quantity of finematerials (cement, fly ash or slag+ fine fractionof sand passing thro 300) is required, usually
450 Kg/cum of concrete- about 450 KgFly ash or slag is necessary to get continuousgrading of fine materials including cement in theconcrete mix; for example:
cement: 250 Kg
fly ash: 80 Kg
fine sand: 120 Kg, total 450 Kg is ok
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Minimum cement content
Minimum cement content for pumped concreteis same as for normal concrete
Cement content includes cement + mineral
admixtures such as fly ash/ slagMinimum cement content is specified fordifferent environmental conditions:
Mild, Moderate- 300 Kg/ cum
Severe- 320 Kg/cumVery Severe- 340 Kg/cum
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Pipeline
3 dia are in normal use 100mm 125m 150mm
125mm most widely used
Choice of pipeline diameter depends on maxsize of coarse aggregate
- 125mm ID pipeline ok for 40mm aggregates
- 100mm used for 20mm aggregates
- 150mm used for larger size aggregate
100mm pipeline can be used for concrete with
20mm aggregates provided there is no oversize
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Pipeline Layout , Cleaning
Lay in one straight line, avoid / minimize bends
Lay vertically or horizontally; avoid inclined line
On completion of pumping activity the pipelinesare cleaned using a rubber ball and water under
pressure; the ball may also be pushed by
compressed air
A properly cleaned pipeline is necessary for
trouble free pumping; concrete and mortar
residues in the pipeline may clog concrete flow
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Distribution of Concrete
When using concrete pumps cost effective
distribution of concrete should be considered
Truck mounted concrete pumps achieve high
outputs because they place concrete exactly
where it is needed
Concrete is produced in a batching plant,
transported by truck mixers and fed to the pump
Pump can also be placed directly below the
batching plant, avoiding truck mixers
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Distribution of Concrete
Concrete can also distributed in an economical
manner by placing the concrete with stationary
concrete pumps in combination with secrete
placing booms
Horiz reach of separate placing booms range
from 20m to 50m; installed in the building to
enable coverage within the whole workingrange
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Separate Placing Booms
The placing booms are easily repositioned by
Tower cranes to cover large areas
Tubular columns for mounting the placing
booms equipped with quick connections; a
climbing device for climbing inside the building
Placer booms of more than 30m reach are
mounted on Tower crane masts
For larger buildings, many placer booms used,
each fed by a concrete pump
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Concrete distribution with end hose
A 3m long flexible end hose used for
distribution of concrete
2 additional men are required
The use of a chute, a circular distributor or a
combination of both instead of an end hose
should be preferred
For vertical placing, there must be a starting
distance between the concrete pump and the
vertical pipeline, atleast 10% of vertical distance
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Pumping Heights
Pumping height depends on the maximum
placing pressure of the concrete pump;
pumping heights of 700m have been achieved
for the construction of Burj Dubai Building
Horizontal placing distance of > 1200m has
been achieved in some Hydel Projects in India
With descending pipelines, ensure conc does
not break and segregate in the descending line;
install shut off wall after the descending line
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Blockages
Generally attributed to human failure
Blockages indicated by a rapid rise in pressure
Prevent foreign matter in the pipeline by using agrill in the charging hopper
Bleeding concrete; increase the fines
Inadequate mixing timeUnpumpable concrete, too thin consistencies,
long pumping interruptions, changes in conc
consistencies