6/23/2014

Chapter 10:

Pumpability of Concrete

Dr. Ahmad Mechaymech 1

Outline

1- Introduction
2- Types of concrete pumps
3- Choosing the best pumping system for the job
4- Tips for optimizing pump performance
5- Troubleshooting and General Safety
Considerations
6- Case study
Dr. Ahmad Mechaymech 2

1
 6/23/2014

1- Introduction
Pumping is a very efficient and reliable means of
placing concrete, w hich makes it a very economical
method as well.

A pump could be the only way of placing concrete in

a certain location. Such as a high rise building, or
large slabs where the chutes of the concrete truck
can’t reach where the concrete is needed.

The ease and speed of pumping concrete makes it

the most economical method of concrete placement.
Dr. Ahmad Mechaymech 3

2- Types of Concrete Pumps

1- Boom pump
2- Line pumps
3- Separate placing booms
4- MixerPump
Dr. Ahmad Mechaymech 4

2
 6/23/2014

1- Boom pumps
Boom trucks are self-contained units consisting of a truck and frame,
and the pump itself.
- Used for concrete pours for everything from slabs and medium high-
rise buildings, to large volume commercial and industrial projects. They
range from single-axle truck mounted pumps used for their high
maneuverability, suitability for confined areas, and cost/performance
value, to huge, six-axle rigs used for their powerful pumps and long
reach on high-rise and other large-scale projects.

Boom pumps

Booms for these trucks can come in configurations of three

and four sections, with a low unfolding height of about 490
cm. This low unfolding height is ideal for placing concrete
in confined areas.
Boom trucks often remain in the same place for an entire
pour. This allows ready mix trucks to discharge their loads
directly into the pumps hopper at one central location and
helps to create a more efficient jobsite traffic flow.
variety of options are given: from chassis and pump size, to
boom configurations, remote control, and outrigger options.

Dr. Ahmad Mechaymech 6

3
 6/23/2014

2- Line Pumps
Line pumps are versatile, portable units typically used
to pump not only structural concrete, but also grout,
wet screeds, mortar, shotcrete, foamed concrete, and
sludge.

Line Pumps

Line pumps typically employ ball-valve-type pumps.

While the smaller models are often called grout
pumps, many can be used for structural concrete and
shotcreting where low-volume output is suitable.
Also used for repairing underwater concrete, filling
fabric forms, placing concrete in heavily reinforced
sections, and building bond beams for masonry walls.

Dr. Ahmad Mechaymech 8

4
 6/23/2014

3- Separate concrete placing

Options for placing booms:

- Cross frame: Foundation mounting with bolted cross frame.

- Crane tower mount: Boom and mast mounted on crane tower.

- Side mount: Mast mounted to the side of a structure with

brackets.
- Wedge mount: Boom and mast inserted in floor slab with
wedges.

- Ballasted cross frame: Zero elevation ballasted cross frame.

- Anchored: Boom and mast are anchored to a supporting

surface. Dr. Ahmad Mechaymech 9

Separate concrete placing

- Separate concrete placing booms can be used when a boom
truck is unavailable, or in situations where the boom truck may
not be able to conveniently access the pour site.
- For instance, contractors use the truck-mounted pump with
placing boom in its conventional mode for part of a day on slab
pours or other ground level placements and quickly remove the
boom for remote placements later in the day. Typically, the boom
is remounted on a pedestal, which can be located few meters
from the pump and connected with a pipeline.

Dr. Ahmad Mechaymech 10

5
 6/23/2014

4- Mixerpump
For small jobs, the all-in-one MixerPump drives to the
jobsite, then mixes fresh concrete and pumps the concrete
wherever the contractor wants it to go.

11

Mixerpump
The pump easily disconnects from the mixer whenever it
isn't needed, then quickly re-attached when it is, providing a
simple "ON/OFF" solution.
A single power source drives both mixer and pump
packages.
It can pump pea-gravel mixes, ¾" blend mixes, 1" big rock
mixes, and even low-slump shotcrete mixes. The tapered
underside of the volumetric mixer allows for ample storage
of pipes and hoses.
Dr. Ahmad Mechaymech 12

6
 6/23/2014

3- Choosing the best pumping

system for the job

1- Proper sizing lines and equipments

2- Line diameter
3- Line length
4- Pipeline layout
5- Choosing the proper hose

Dr. Ahmad Mechaymech 13

1- Proper sizing of lines and

equipment
The major factors affecting pipeline pressure are:
• Pumping rate
• Line diameter
• Horizontal and vertical distances
• Configuration, including reducing sections
Other factors must be taken into account when
determining line pressure:
• The vertical rise
• The number and severity of bends
• The amount of flexible hose used in the line
14
Dr. Ahmad Mechaymech

7
 6/23/2014

2- Line diameter

In general, the larger the inside diameter of the

pipeline, the less pressure required to move the
concrete through the pipeline at a given rate.

There is a major drawback to large-diameter

pipelines however: the larger the line, the more
labor, blocking and bracing it will require.

Rule of thumb: the maximum size aggregate

should be no more than one-third the inside
diameter of the delivery system.
15
Dr. Ahmad Mechaymech

3- Line length
Friction between the pumped concrete and the internal pipeline
wall means that the line length directly affects the line pressure
requirement. The longer the pipeline length, the more steel pipe,
with its smooth interior surface, becomes desirable.

The convenience of easy access for truck mixers must be

weighed against the desirability of locating the pump closer to
the placement point.
Consider using two lines and two pumps when there is a large
distance between the pump and the furthest placement point.
The end of the first pump feeds into the hopper of the second
pump. This may operate more efficiently than a single system
operating at excessive line
16
Dr. Ahmad Mechaymech

8
 6/23/2014

4- Pipeline layout

For the least line resistance, the pipeline should contain a

minimum number of bends.
Reductions in pipe diameter within the same line also
increases resistance, so the same diameter line should be
used throughout whenever possible. If the diameter must be
reduced within the line, reducers should be used. The longer
the reducer the better: it takes far more energy to pump
concrete through a reducer four feet long than it does one
eight feet long.
Dr. Ahmad Mechaymech 17

5- Choosing the proper hose

Hoses are manufactured for specific applications, and
using the proper hose for the proper application is
paramount for safety on the concrete pumping site. Here
are a few pointers:

Hose designated as a discharge type should be used only

at point of placement for discharge. Rule of thumb: Never
use a discharge hose in less than a 24-inch radius.

For boom truck applications, a specially reinforced hose

is recommended. Rule of thumb: Never use a boom hose
in less than a 30-inch radius.

Dr. Ahmad Mechaymech 18

9
 6/23/2014

4- Tips for optimizing pump

performance
1. Specify a pumpable concrete mix
2. Proper pump truck positioning
 Placing the boom
 Power lines
 Excavations
 other obstructions
 Stabilizing the pump truck
3. Pumping tips for insulating concrete forms (ICFs)
 Pre-pour checklist
 The mix
 The equipment
 Curing
 Placement and pour pattern
 Blowout prevention 19

1. Specify a pumpable concrete mix

How Concrete Moves Through the Pump Line

When concrete is pumped through the pump line, it is separated

from the pump line walls by a lubricating layer of water, cement
and sand.

Naturally, the concrete mix must be suitable for its particular

application, but it must also contain enough water for the mix to
move easily through the reducers, bends and hoses found in
most basic pipeline setups.

It is important to have all concrete mixes specified as

"pumpable" prior to any concrete pours. There are mixes that do
not pump at all or cause the pump lines to clog- big problems if
you have 8 trucks arriving on the job ready to discharge
concrete. 20
Dr. Ahmad Mechaymech

10
 6/23/2014

2- Proper pump truck positioning

The primary concern when utilizing a pump truck during a
pumped concrete pour is safely positioning the truck where the
boom can reach the concrete placement site. The key word here
is "safely”.

Improperly positioned, a pump truck can cause death or serious

injury, making a nightmare out of what may have appeared to be
a standard, "every day" pour. The pumping crew can only utilize
the pump truck and boom when the conditions are entirely safe.
Prior to extending the pump truck boom on a new job site:

 Power lines
 Excavations
 Other obstructions
 Stabilizing the pump truck 21

Proper pump truck positioning

 Power lines
The truck boom, chassis, remote-control cable, and steel-braided
end hose are great conductors of electricity. And with its high
water content, the concrete itself can become a deathly electric
conduit if any part of the pump machinery comes in contact with
power lines. This is why more concrete pump operators die from
electrocution than any other job-related cause. And even the
rubber boots or rubber-soled workboots worn by concrete
workers will not protect them from the 8,000 volts most residential
power lines carry if that worker is in contact with any part of the
equipment that touches a power line. 22

11
 6/23/2014

Proper pump truck positioning

 Power lines
Half of all accidents involving booms and power
lines happen when the machine is being folded,
unfolded or removed. Placing a full-time spotter in
position to keep an eye on the boom if its at all
possible to inadvertently hit an electric wire is
recommended.

The American Concrete Pumping Association requires that the boom tip and
23
any other section of the boom be at least 5 meters from power lines.

Proper pump truck positioning

Excavations
Remember the "one-to-one" rule when pumping concrete near
an excavation or land that falls off steeply from the pump: For
every foot of depth, position the pump at least one foot back
from the edge. Pumps can be placed closer to the edge of a
slope than to a vertical drop-off. For instance, on a one-to-one
slope, the pump often does not require much of a setback.
When pumping into an excavation, take into consideration the
fact that most boom pumps have a much higher upward reach
than downward. A boom pump that can reach 92 m high may
have only about half that reach downward. 24

12
 6/23/2014

Proper pump truck positioning

Other obstructions

Obstructions on the job site other than power lines

may cause problems, as well. Pay careful attention to
objects such as cranes, scaffolding or buildings.
Make sure the booms length and articulation is right
for the job. A boom too short for the job may be able
to place the concrete correctly, but may also be too
short to clear other obstructions.

Dr. Ahmad Mechaymech 25

Proper pump truck positioning

Stabilizing the pump truck
Wood and aluminum pads and layers of 10X10 or 10X15 cm
boards (called cribbing) are often used under the pump
trucks outriggers to spread out its load. This requires
determining the load bearing capacity not only of the soil, but
of the cribbing, as well.

Calculating Pressures on Ground Surfaces (physical)

Since operators often don't know the soils bearing capacity,
a physical test is often used.

Calculating Pressures on Ground Surfaces (mathematical)

Dr. Ahmad Mechaymech 26

13
 6/23/2014

3. Pumping tips for insulating

concrete forms (ICFs)
ICFs, one of the hottest trends in concrete construction today, are
hollow blocks or panels made of rigid polystyrene foam erected and
filled with concrete to produce insulated walls. Since concrete must
be placed into ICFs at a more controlled rate than on standard pours,
great care must be taken in selecting the proper materials, equipment,
and pour procedures.

Pre-pour checklist
The mix
The equipment
Curing
Placement and pour pattern
Blowout prevention 27

Pumping tips for insulating concrete forms

Pre-pour checklist
A pre-pour inspection should be conducted. Here are some
problem points to check for:
- Check all measurements, including footprint, wall openings,
lintels. Check for level, plumb and square walls and openings.
- Ensure that all reinforcing steel has been properly placed
and inspected by the local building department, if required by
local codes.
- Make sure that all sleeves, fasteners, braces for the formwork
and provisions for attaching floor decks are in place.
- Check form system for irregularities, including damaged
forms, gaps, weak spots and irregular joints.

Dr. Ahmad Mechaymech 28

14
 6/23/2014

Pumping tips for insulating concrete forms

 The Mix

Rule of thumb: Use concrete with a 4- to 6-inch

slump, made with 3/8-inch maximum-size course
aggregate.
This size aggregate requires a higher sand
content, a greater amount of water, and therefore
an increased cement content in order to achieve a
6-inch slump with the necessary strength, so
order the mix accordingly. 29

Pumping tips for insulating concrete forms

 The equipment
Polystyrene foam forms are less tolerant to concrete pressures
than wood or aluminum forms, which means a 2-inch diameter
hose is the ideal size for placement. This lets the line pump run
at full speed without danger of a form blowout.

In addition, the smaller diameter slows the flow of concrete,

giving the hose operator better control of the placement.
Reducers may be used on a boom pump to bring the diameter
down to 2 or 3 inches, and 90-degree elbow fittings attached at
the end of the hose assembly creates an "S" in the line, breaking
30
the long fall of the concrete.

15
 6/23/2014

Pumping tips for insulating concrete forms

 Curing
ICFs insulate fresh concrete, which means the material
cures properly even in extreme weather conditions.
However, if the temperature at the job site is going to fall
below freezing within a couple of days after the pour,
blankets should be put along the exposed top of the wall
for insulation.
If the weather is very hot and dry, use plastic sheeting over
the exposed top in order to prevent excessively rapid
drying of the concrete.
Do not proceed with an ICF pour during a heavy rain. If
there is standing water in the form cavities, drain the
cavities prior to placing the concrete.
31
Dr. Ahmad Mechaymech

Pumping tips for insulating concrete forms

 Placement and pour pattern
Most ICF manufacturers provide the proper pour pattern to
use with their products. Here are some rules of thumb:
- Start the pour placement under windowsills up to 3 feet, or
the bottom of the sill. Then, starting at a corner, place the
concrete around the wall perimeter in 3-foot lifts between the
windows.
Using hammers to tap 2X4 blocks placed flat against the wall,
agitate the formwork on the ground, or the floor beneath the
pour. While some ICF manufacturers recommend the use of
immersion vibrators, others prohibit them because they can
damage the forms. Always check with the manufacturer prior
to any use of these devices.
Dr. Ahmad Mechaymech 32

16
 6/23/2014

Pumping tips for insulating concrete forms

 Blowout prevention
Blowouts in ICFs are rare, but here are some tips on
reducing the risk of such an occurrence:

- Have a worker continuously tap the formwork during

concrete placement to check for any voids. If a hollow
sound in an otherwise solid wall is detected, dislodge the
clog and fill the void by slipping a long piece of strapping
or rebar into the concrete from above, and slide it up and
down above the void.
Dr. Ahmad Mechaymech 33

Pumping tips for insulating concrete forms

 Blowout prevention

- A bulge in the formwork is a warning sign of a possible

blowout. In this case, the placing crew should be signaled to
move the pour away from the problem area. The bulge can
then be braced with a 2X2-foot square of plywood wedged to
the wall with a wooden kicker.
- In case of a blowout, the torn foam must be cut away, and
the concrete scooped out to a level below the blowout. Then,
replace the foam and set a square of plywood against the
wall, front and back, to cover the damaged area.
34
Dr. Ahmad Mechaymech

17
 6/23/2014

5- Troubleshooting and General Safety

Considerations

A- Removing blockages:
 Location a blockage
 Clearing the blockage
 Causes of blockages

B- Safety considerations:
 Checking for wear
 Securing the system
 Clearing the system
 Safety “don’t” for pump operators
Dr. Ahmad Mechaymech 35

A- Removing blockages
 Location a blockage
Variations in the mix, whether too rocky, wet or dry, foreign
matter in the mix (such as old concrete that has broken away
from mixer fins, or unmixed clumps of concrete), and other mix
anomalies are tip-offs that problems may have occurred, or may
be about to occur.

A rising in line resistance, as shown on the pump pressure

gauge, indicates line blockage. The first suspect spot for
blockage is the reducer, which connects the concrete pump to
the pipeline system. A quick build-up in pressure prior to the jam
indicates the blockage is most likely in the pump area. Slow
pressure build-up is indicative of a jam further down the line,
nearer the delivery end.
Dr. Ahmad Mechaymech 36

18
 6/23/2014

A- Removing blockages
 Location a blockage

The operator needs to examine the system, especially at the

elbows or discharge hose. This can be done by tapping the
hammer along the pipeline. Where concrete is jammed, the
hammer will produce a dull thud, as opposed to a more
ringing sound where the line is clear.

All pipe joints should also be inspected for grout leakage,

as well, as this can be indicative of grout loss and
subsequent blockage.

By carefully walking over or stepping on the discharge

hose to depress it, a blockage may be located where the
soft hose becomes firm, indicating jammed aggregate.
37

A- Removing blockages
 Clearing the blockage
A break loose a minor rock jam, should not be tried more than a
couple of times. As it can jam the pipeline even tighter, the
reversal method doesn't work, the operator must locate the
blockage, then break back the line and clear it out.
Be sure: the line is no longer under pressure prior to clearing a
blockage, stand to one side of the line and remove the coupling
nearest the jam, let all the free-flowing concrete run out of the
open end of the line by lifting the line, then bend the hose or tap
on the pipeline in the area of the jam and shake out loose
particles. Dr. Ahmad Mechaymech 38

19
 6/23/2014

A- Removing blockages
 Clearing the blockage

Important safety tip: when trying to clear a line blockage,

NEVER use compressed air. If a greatly increased pump
pressure wont move the blockage, compressed air wont be
able to either. While using compressed air utilizing proper
safety precautions is OK for cleaning out unblocked
sections of pipe, using it on blockages can cause all kinds
of problems, including the need to relieve the built-up air
pressure, residual air pockets, and additional blockages
due to segregation.
Dr. Ahmad Mechaymech 39

A- Removing blockages
 Causes of blockages
There are basically three main causes of pump line blockages: a
deficiency in the mix design; problems with the pipeline itself; and the
human factor or operator error.

The Wrong Mix

The most common mix problem is concrete that does not retain its
mixing water. Concrete can bleed due to poorly graded sand that allows
water to bleed through the small channels formed due to voids in the
sand, or if the concrete is too wet.
Insufficient mixing can cause segregation in the mix. For successful
pumping, aggregate must have a full coating of cement grout to lubricate
the mix as it is being pumped.
A delay in placing the concrete due to traffic or job site problems, as well
as hot weather conditions, may cause the concrete to begin to set
prematurely. This creates a mix that may be too stiff to pump, because it
wont fill the pumping cylinders, causing excessive pumping pressures. 40

20
 6/23/2014

A- Removing blockages
 Causes of blockages
Problems with the Pipeline

The entire pumping system must be evaluated for the job it is to

perform. Considerations include a properly sized system including
pump capacity and motor horsepower to move the concrete
through the full length of the pipeline.
Pipes that have been improperly cleaned may cause blockages
where old concrete has set, and may cause bleeding and
segregation. Defective couplings, gaskets, or weld collars also can
result in the loss of grout.
Another thing to look for are bends that are too short, too sharp, or
too numerous, all of which increase concrete pumping pressure.
Variations of pipeline diameter, such as when a larger diameter
hose is coupled with a smaller one, may cause blockages or rock
jams because the concrete cant flow as quickly through the smaller
diameter pipeline. Dr. Ahmad Mechaymech
41

A- Removing blockages
 Causes of blockages
Operator Error

The most common error from inexperienced operators is setting

up the pumping system improperly. Operators must know to set
up each job so that pipe or hose only needs to be removed, not
added on. This is because if the placing crew has to add hose
once the pour is in progress, the dry conditions inside the added
hose is likely to cause a blockage.
Careless handling of flexible rubber discharge hoses can also be
a problem, since kinking can occur. A rock jam is likely to be the
end result of a kinked hose, as the inside hose diameter is
reduced, which restrains the aggregate in the line while the
lubricating grout is allowed to pass. Premature localized wear of
the hose, and eventual rupture of the hose, may also occur at the
point where the hose is kinked. 42

21
 6/23/2014

Troubleshooting and General Safety

Considerations

A- Removing blockages:
 Location a blockage
 Clearing the blockage
 Causes of blockages

B- Safety considerations:
 Checking for wear
 Securing the system
 Clearing the system
 Safety “don’t” for pump operators
Dr. Ahmad Mechaymech 43

B- Safety considerations
 Checking for wear
Pumping performance as well as safe operation of
the pumping system may be affected by worn
couplings or gaskets, which may let air into the
line or allow grout to escape.
Couplings typically wear on the surface that
comes into contact with the pipe; and gaskets
need to be cleaned if they have concrete
remaining in the cavity. The gasket should be
replaced if the center lip is worn out. Valves
should be routinely inspected for wear and proper
settings.
Dr. Ahmad Mechaymech 44

22
 6/23/2014

B- Safety considerations
 Checking for wear

The most accurate way to inspect for worn pipeline

is with a gauge specifically designed to measure
the thickness of steel pipe. In addition, the pipe
ends must be inspected for wear, cleanliness and
to make sure they are compatible with other pipe
and couplings to be used on the job.
American-sized and European-sized raised ends
are not compatible. Compatibility must also be
ensured if pipe from different manufacturers are
used together, since pipe joints can pose a serious
hazard if the ends and coupling do not match.
Dr. Ahmad Mechaymech 45

B- Safety considerations
 Securing the system

Improper tie-down is one of the most common

causes of accidents when pumping concrete.
Support brackets, designed to hold pipeline in either
a horizontal or vertical position, should be spaced
every 10 to 15 feet in order to take weight off of the
coupling joint, and to transfer the pumping torque to
a building column or beam.

Dr. Ahmad Mechaymech 46

23
 6/23/2014

B- Safety considerations
 Clearing the system
If done improperly, cleaning the system after the daily
pumping job can be very hazardous. Water should be used
for cleaning whenever possible and practical.
If cleaning with compressed air, remember that the pressure
builds up, and may remain in the line even after the supply is
shut off, so a bleed-off valve should always be installed on
the system when using compressed air.

Remember that this pressure can be of sufficient force to

propel a clean-out ball through the open end with enough
force to penetrate a concrete block wall. Therefore, whether
using water or air pressure, install an end cap and a catcher
to prevent injury to workers or damage to property.
Dr. Ahmad Mechaymech 47

B- Safety considerations
 Safety “don’t” for pump operators

Carelessness in the field can cause accidents, no matter

how many safety measures are built in to the equipment
and procedures. Keep these safety "don'ts" in mind:

 DON‘T open a coupling that is under pressure

 Face an open discharge end of the pipeline

 Pick up a clogged hose that is under pressure

 Climb on a hydraulic system to clean a clogged line

Dr. Ahmad Mechaymech 48

24
 6/23/2014

Case study

In the following slides, a pumping test: setup

and procedures, selected from the experimental
program of thesis of Dimitri Feys, “Interactions
between Rheological Properties and Pumping of
Self-Compacting Concrete” (2009)

Dr. Ahmad Mechaymech 49

1- Concrete Pump
The concrete pump used is a truck-mounted piston pump.
The pump can achieve a maximal pressure (on the concrete) of 95 bar,
or a maximal discharge of 150 m³/h, which corresponds to 41.5 l/s.
Both the maximal concrete pressure and the maximal discharge
cannot be achieved simultaneously.

50

25
 6/23/2014

Concrete Pump

The pump contains 2 hydraulic cylinders having 230 mm in

diameter and 2000 mm of stroke length.

The pumping system is automatically generated by the

pump itself. Alternately, one cylinder pulls concrete from
the reservoir of the pump, while the other cylinder pushes
the concrete inside the pipes. When the cylinders are full
and empty respectively, a special valve switches the
connection between the pipe system and the cylinders.
51
Dr. Ahmad Mechaymech

Concrete Pump
The valve which makes the connection between the pipe
system and the cylinders of the pump is the “Schwing rock
valve”. This powerful valve changes very suddenly and
must turn inside the concrete reservoir, crushing
aggregates if necessary.

Principle of the Schwing

rock valve

52

26
 6/23/2014

Concrete Pump
The operator of the pump, has a remote control, with which he can
move the placing boom, start and stop the pump, and control the
discharge. The discharge of the pump can be changed in 10 steps
from the minimal value, which is around 4-5 l/s, to the maximal
output of around 40 l/s.

53

2- Pipes and circuits

The pipes used for the pumping tests are steel pipes, with
an inner diameter of 106 mm, a wall thickness of 3 mm and
a length of 1 or 3 m. The pipe at the exit of the pump has a
larger diameter and as a result, a reduction to the 106 mm
inner diameter has been applied immediately after the exit
of the pump. The connections between the pipes have
been equipped with a rubber seals and Clamps.

Dr. Ahmad Mechaymech 54

27
 6/23/2014

Pipes and circuits

Top: flexible hose. Bottom left: Straight pipes of 1 and 3 m. Bottom

55
right: Combination of 2 curves, making a 180 ° turn.

Pipes and circuits

Short circuit Long circuit

A short loop circuit of 25 m of length has been built. After the exit of
the pump and the reduction pipe, a 90° curve has been installed,
followed by a straight horizontal section of 12 m. After, the concrete is
returned to the pump by a 180° turn, made by two curves and a 1 m
pipe in between. The circuit continues with an inclined straight part of
9 m, followed by the 4 m flexible hose. At the end of this hose, a 90°
curve is attached, in order to point the concrete flow down, inside the
sampling reservoir.

56

28
 6/23/2014

Pipes and circuits

57

Pipes and circuits

Long circuit

The circuit has been extended up to a maximal length of

105 m.

Dr. Ahmad Mechaymech 58

29
 6/23/2014

Pipes and circuits

Long circuit (105 m), seen

Long circuit (105 m), seen from the front side
from the rear side
of the
of the laboratory. Note that the pump and the
sampling reservoir are not yet installed. laboratory. 59

3- Measurement systems

1- Pressure losses
2- Rheological properties
3- Thixotropy
4- Temperature
5- Discharge

60

30
 6/23/2014

4- Problematic
3 different causes of blocking:
- Blocking during pumping operations, in most cases due to an error in
pipe configuration or concrete composition.
- Blocking during restart, the type of blocking is caused by segregation,
although this could also be caused by thixotropy.
- A third type of blocking can occur during cleaning with water.
The main part of the blockings occurs during start-up: the amount of
fine materials in the concrete decreases with increasing pumping
distance and as a result, a group of coarse aggregates moves ahead of
the bulk concrete. In this way, the maximum volume fraction decreases,
while the effective volume fraction increases. This leads to a significant
increase in viscosity, and combined with an increased importance of
friction caused by the coarse aggregates, the flow is finally stopped.
Dr. Ahmad Mechaymech 61

5- Conclusion

The decrease in fine materials during start-up is

caused by two phenomena: attachment to the wall,
in order to eliminate the roughness of the pipes,
and filling of the interior of the rubber seals.
Furthermore, due to inertia, the coarse aggregates
move ahead of the bulk concrete at the end of a
stroke.
This decrease in fine materials can be prevented by
pumping a water-cement mixture in front of the
concrete before start-up.
Dr. Ahmad Mechaymech 62

31
 6/23/2014

Conclusion

Pumping in an inclined upward pipe is the most

advantageous. For horizontal pipes, the cement
water mixture spreads in the whole circuit, only
covering the lower part of the pipes. Opening the
pipes in order to remove a blocking results in the
loss of a main part of this mixture. An inclined,
downward pipe is the worst case for start-up. Due
to gravity, the coarse aggregates fall down and
collect at the end of the downward section.

Dr. Ahmad Mechaymech 63

32