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ORIGINAL ARTICLE
Parameters influencing pressure during pumping of self-compacting concrete
Dimitri Feys Geert De Schutter
Ronny Verhoeven
Received: 7 November 2011 / Accepted: 12 July 2012 / Published online: 27 July 2012
RILEM 2012
Abstract The main difference between conven-
tional vibrated concrete (CVC) and self-compacting
concrete (SCC) is observed in the fresh state, as SCC
has a significantly lower yield stress. On the other
hand, the placement of SCC by means of pumping is
done with the same equipment and following the same
practical guidelines developed for CVC. It can be
questioned whether the flow behaviour in pipes of
SCC is different and whether the developed practical
guidelines can still be applied. This paper describes
the results of full-scale pumping tests carried out on
several SCC mixtures. It shows primarily that the
slump or yield stress of the concrete is no longer a
dominating factor for SCC, as it is for CVC. Instead,
the pressure losses are well related to the viscosity and
the V-funnel flow time of SCC. Secondly, bends cause
an additional pressure loss for SCC, which is in
contrast to the observations of Kaplan and Chapdel-
aine and the estimation of the practical guidelines is
not always on the safe side. Finally, due to the specific
mix design of SCC, blocking is less likely to occur
during pumping operations, but the same rules as for
CVC must be applied during start-up.
Keywords Self-compacting concrete Rheology Viscosity Pressure loss Pumping
1 Introduction
1.1 Research significance
Since the development of self-compacting concrete
(SCC) in the late 1980s [1], the research on this
concrete type has focused on several aspects: from raw
materials, properties in fresh state up to mechanical
and structural properties and durability. When focus-
ing on the properties in fresh state, there is still a
research gap between the characterisation of the fresh
concrete properties when it leaves the mixer or the
concrete truck and the flow of concrete in the
formwork. In fact, SCC is mostly cast in the same
way as conventional vibrated concrete (CVC): by
means of large concrete buckets moved with a tower
crane or a rolling bridge (in case of a precast plant), or
by means of a concrete pump. As a result, although
there has been very little research on the pumping of
D. Feys (&)Concrete Division, Faculty of Engineering, Universite de
Sherbrooke, 2500, Boulevard de lUniversite, Sherbrooke,
QC J1K 2R1, Canada
e-mail: [email protected]
G. De Schutter
Magnel Laboratory for Concrete Research, Department
of Structural Engineering, Faculty of Engineering, Ghent
University, Technologiepark 904, 9052 Zwijnaarde,
Belgium
R. Verhoeven
Hydraulics Laboratory, Department of Civil Engineering,
Faculty of Engineering, Ghent University, Sint-
Pietersnieuwstraat 41, 9000 Ghent, Belgium
Materials and Structures (2013) 46:533555
DOI 10.1617/s11527-012-9912-4
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SCC, it is done in practice, with the same equipment
and following the same rules which have been
developed for CVC. The main difference between
CVC and SCC is observed in the fresh state, as SCC
has a significantly lower yield stress [2]. Therefore, it
can be questioned how the flow of this concrete type in
pipes is influenced by its fresh properties and are the
rules developed for CVC [3, 4, 5] still (partially) valid?
This paper discusses full-scale experiments inves-
tigating the pumping of SCC. The main subject is the
flow behaviour in straight pipes, while trying to give
an estimation for the velocity profile. A comparison is
made with the rules of thumb for CVC and the full-
scale experiments on CVC, performed by Kaplan [6]
and Chapdelaine [7]. In the final stage, the behaviour
in bends is briefly discussed and compared to the
existing literature.
1.2 Rheological properties of fresh concrete
It is generally accepted that fresh concrete is a
Bingham material, showing a yield stress and a plastic
viscosity [8, 9]. The yield stress is the resistance to the
initiation of flow, while the plastic viscosity is a
measure for the resistance to a further increment in
flow rate (Eq. 1). Due to thixotropy, structural break-
down and loss of workability caused by chemical
reactions, the yield stress and plastic viscosity are not
constant in time [2, 8, 10, 11]. Furthermore, the
rheological properties depend on the shear-history the
material has undergone.
s s0 lp _c 1s s0 K _cn 2s s0 l _c c _c2 3where s is the shear stress (Pa); s0 is yield stress (Pa);lp is plastic viscosity (Bingham) (Pa s); _c is shear rate(s-1); K is consistency factor (H.-B.) (Pa sn); n is
consistency index (H.-B.) (-); l is linear term (mod.Bingham) (Pa s); c is second order parameter (mod.
Bingham) (Pa s2).
In literature, it is stated that the rheological
behaviour of fresh SCC can deviate from the linear,
Bingham behaviour in some specific situations. In
these cases, shear-thickening has mostly been
observed, necessitating the application of a different
rheological model [12, 13, 14, 15]. Most authors apply
the Herschel-Bulkley equation on the results (Eq. 2),
but the modified Bingham model [14, 16] has also the
capacity to describe shear-thickening behaviour and is
preferred by the authors (Eq. 3). The modified Bing-
ham model is applied on the results in this paper which
show shear-thickening behaviour. Note that it is not in
the scope of this paper to describe the physical causes
of shear-thickening, as these are explained in [14, 17].
On the other hand, shear-thickening has a large
consequence on the pressure during pumping, as
shown in this paper.
2 Flow behaviour of conventional vibrated
concrete in pipes
In this section, an overview is given of the existing
knowledge on the flow behaviour of CVC in pipes and
it is indicated whether the described phenomena are
applicable on SCC.
2.1 Flow or friction
As concrete is a concentrated suspension of solid
particles, the type of stress transfer during the move-
ment of concrete in pipes can be different. If the stress
transfer is dominated by direct contact between the
(large) solid particles, namely the coarse aggregates,
the friction between these aggregates will be the
determining factor for the force necessary to move the
concrete in a pipe. This can occur if insufficient cement
paste or mortar is present to lubricate the coarse
aggregates, as can be seen in Fig. 1 (right) [18, 19, 20].
This situation is defined by Browne and Bamforth [18]
as unsaturated concrete, and the pressure during
pumping of unsaturated concrete evolves exponen-
tially with the length of the pipe, as shown in the right
part of Fig. 2 [18].
In the opposite case, when sufficient cement paste
or mortar is present (Fig. 1, left), direct contact
between the coarse particles is avoided and the
shearing takes place in the cement paste [18, 20]. As
a result, the concrete can be regarded as a suspension
and rheology can be applied to study the flow
behaviour. The stress transfer is of the hydrodynamic
type and Browne and Bamforth [18] defined such
concrete as saturated. In this case, the pressure
decreases (as it is the case for Newtonian liquids)
linearly with the length of the pipe (Fig. 2, left) and the
pressure loss is constant in a horizontal straight section
534 Materials and Structures (2013) 46:533555
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with a constant diameter. Browne and Bamforth [18]
have proven mathematically that the case of friction
requires significantly higher pressures to pump con-
crete. Friction needs thus to be avoided at all times.
The recommendation of some practical guidelines to
have a certain minimum paste or mortar content, or a
certain minimum slump, is based on the avoidance of
friction [35, 21, 22, 2325].
For SCC, friction is less likely to occur (in regular
conditions), as by definition, contacts between coarse
particles must be avoided to fulfil the filling and
passing ability criteria [26]. It can also be observed
that the amount of coarse aggregates is reduced in SCC
mix design, compared to regular CVC [26].
Kaplan discussed in his thesis different causes of
blocking [6, 27]. He states that blocking during start-
up is most common. It is caused by the loss of cement
paste at the pipe walls and by inertia, relative to the
viscous drag of the inserted cement paste, forcing the
coarse aggregates to move ahead of the bulk concrete
Fig. 1 Distinction between hydrodynamic interactions (paste suspends aggregates) (left) and friction (paste fills partly the voidsbetween the aggregates) (right) during the flow of concrete through pipes
Pressure
Length
Pressure
Length
Fig. 2 The pressure decreases linearly over the length of a straight, horizontal pipe in case of hydrodynamic interactions (left), whilefriction causes an exponential decrease of the pressure with the length of the pipe (right). Figure after Browne and Bamforth [18]
Materials and Structures (2013) 46:533555 535
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with each stroke of the pump [27]. As a result, the
concentration of coarse aggregates increases and can
transform a saturated concrete into an unsaturated
concrete. The stress transfer switches from hydrody-
namic to friction and if the pump cannot deliver the
pressure needed to move the concrete any further, the
pipe gets blocked.
Blocking during start-up has been observed in this
research project when inserting SCC into a 100 m long
horizontal circuit. Figure 3 shows the evolution of the
pressure in two measurement sections along the pipe.
The sudden shocks in the pressure (down to zero and
back up) are due to the working principle of the pump
(which is explained further). With time, the pressure
slightly increases as more concrete is inserted in the
pipes. Suddenly, the pressure rises up to 55 bar, as the
concrete blocks in the pipe. The pumping is conse-
quently stopped and a front of aggregates, similar to
the one depicted in Fig. 1 (right), must be removed
before continuing. Although a mixture of water and
cement was inserted in front of the concrete, blocking
did occur in case of SCC. As a result, the same
practical rules recommended for CVC must be applied
during the insertion of SCC.
2.2 Lubrication layer
For CVC, it is known that during pumping, the
concrete moves as a large plug in the pipe, surrounded
by a lubrication layer [6, 7]. This layer consists of
cement paste or mortar, as the coarse aggregates move
away from the zone with the largest shear rate, which
is at the wall. The entire velocity difference between
pipe wall and concrete is concentrated in this layer. In
literature, it is reported that the thickness of the
lubrication layer varies between a few mm up to 1 cm
[6]. As it is currently impossible to directly measure
the thickness, although efforts have been made [28,
29], it is unsure what the exact thickness is.
The lubrication layer facilitates the pumping of
concrete through pipes. If no lubrication layer could be
formed, the pumping pressure would be significantly
higher to pump the concrete at the same discharge rate.
Some authors take the effect of the lubrication layer
into account by introducing a slipping or sliding
velocity [18, 19, 24, 30, 31]. The principle of slippage
and lubrication layer is visualized in Fig. 4 [32]. The
total velocity at a certain distance r from the centre of
the pipe is then composed of the slipping velocity
(which is constant) and a shearing velocity (which can
vary). The shearing velocity depends on the applied
shear stress (which is related to the pressure loss per
unit of length and the pipe radius) and the yield stress
of the concrete. For CVC, the shearing velocity can be
zero across the pipe, reflecting the plug flow.
Kaplan [6] and Chapdelaine [7] related pumping
pressures to the properties of the lubrication layer. To
measure these properties, they both modified an
existing concrete rheometer in a so-called tribometer.
In concrete rheometry, the slip between the rheom-
eter walls and the concrete is avoided by installing
ribs. These ribs are removed in a tribometer and the
flow properties of the concrete near a smooth surface
are measured. Similar as in rheology, the yield stress
(Pa) and the viscous constant (Pa s/m) of the lubrica-
tion layer are determined by changing the rotational
velocity and measuring the resulting torque, which is
transformed into a shear stress (Eq. 4) [6, 7, 33]. Note
that the viscous constant has a different dimension
than the plastic viscosity. Namely, the calculation of
the shear rate in the lubrication layer is impossible, as
its thickness is unknown. Therefore, the thickness of
the lubrication layer is incorporated in the viscous
constant, for an assumed linear velocity distribution in
the lubrication layer.
s s0;i gi v 4where s is the shear stress (Pa); s0,i is yield stress of thelubrication layer (Pa); gi is viscous constant of the
-10
0
10
20
30
40
50
60
1140 1160 1180 1200 1220 1240
Section 1Section 3
Pres
sure
(bar
)
Time (s)
Fig. 3 The pressure at two different measurement sections inthe long pumping circuit increases slightly as concrete is being
inserted gradually in the pipes. Around 1,205 s, a transition
takes place from hydrodynamic interactions to friction, as
insufficient cement paste is available between the aggregates
and the concrete blocks at 1,210 s, corresponding to the pressure
peak
536 Materials and Structures (2013) 46:533555
-
lubrication layer (Pa s/m); v is velocity difference over
the lubrication layer (m/s).
3 Experimental work
3.1 Test-setup
The experimental part of this research was carried out
on full-scale pumping circuits. The total length of the
first circuit was 25 m, constructed with steel pipes
with an inner diameter of 106 mm. After the exit of the
pump, a 12 m straight, horizontal section was
installed, followed by a 180 bend (composed of two90 bends with a 1 m pipe in between). The secondpart of the circuit was inclined, in order to feed the
concrete back to the pump (Fig. 5). In this way, the
circuit is a loop circuit as the pumped concrete was
reutilised several times. This circuit was used to
determine the relationship between the rheological
properties and the pumping pressure of the concrete.
The main results discussed in this paper were obtained
in this small circuit.
A second and third circuit, with lengths of 100 m
(Fig. 6) and 80 m respectively, consisted of extending
the small 25 m circuit with four straight sections,
connected with 180 bends in between. The last bend,before starting the inclined part, was composed of two
90 bends with a 1 m pipe in between. Several testshave been performed on these longer circuits, but only
the results on blocking, discussed previously and the
results for the pressure losses in bends are included in
this paper.
The pump was a truck-mounted piston pump, capable
of delivering a pressure of 95 bar or a discharge rate of
150 m3/h (or 40 l/s). The discharge rate can be
controlled in 10 steps, varying between 4 to 5 l/s up to
approximately 40 l/s. For safety reasons, only the five
lowest discharge rates were applied, with a maximum of
20 l/s. The pump itself has two pistons, which alter-
nately push the concrete inside the pipes and pull
concrete from the pumping reservoir. When the pushing
piston is empty (and consequently the pulling piston is
full), a powerful valve inside the reservoir changes the
connection between the pistons and the circuit. This
provokes a sudden decrease and increase in pressure
during approximately one second. As shown in Fig. 7, it
can be clearly seen in the measured pressure evolution. It
can also be clearly heard on site.
3.2 Measurement systems
3.2.1 Pressure loss
In the horizontal straight section of the 25 m circuit,
two pressure sensors were installed at a distance of
10 m from each other. The pressure sensors are
equipped with a metallic seal, resistant to abrasion,
to avoid the insertion of cement or concrete in the
pressure chamber. The pressure chamber is filled with
oil and transfers the pressure applied on the seal to the
sensor. The sensors have a maximum capacity of
Fig. 4 Distinction between no-slip (left), slip (middle) andlubrication (right). In case of a lubrication layer, the velocity atthe wall is zero (no slip), but the velocity gradient near the wall
is larger, in this case over a distance h1 from the wall. This larger
velocity gradient is caused by the lower viscosity of the
lubrication layer (lm) compared to the viscosity of the concrete
(ls). When concrete is pumped, it could be that the yield stress ofthe concrete outside the lubrication layer is higher than the
applied shear stress. In that case, the velocity in the concrete
would be constant, while the velocity gradient is maintained in
the lubrication layer. Figure from Thrane [32]
Materials and Structures (2013) 46:533555 537
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35 bar, with a safety factor of 2 for accidental
overload. With these sensors, the pressure difference
between two points can be measured and the pressure
loss per unit of length can be calculated. The pressure
sensors were connected to a data-acquisition system,
registering the local pressures at a rate of 10 Hz.
Fig. 5 25 m pumping circuit. The straight, horizontal section on the left contains the pressure sensors
Fig. 6 Extension of the pumping circuit to 100 m
538 Materials and Structures (2013) 46:533555
-
In the vicinity of each pressure sensor, a set of three
strain gauges was attached to the outer wall of the pipe.
The strain gauges allowed to measure the expansion
and contraction of the pipe (which had a thickness of
3 mm), which is related to the locally applied pressure
[6]. The strain gauges served as a back-up system in
case something happened with one of the pressure
sensors. The output of the strain gauges was calibrated
with the measured pressures when the pressure sensor
was working correctly, while during failure of the
pressure sensor, the strain gauges served as full
measuring units.
For the longer circuits, the pressure sensors were
installed in the last horizontal straight section. Several
other pipes were also equipped with strain gauges in
order to follow the pressure evolution through the
circuit. In the 100 m circuit, such an equipped section
was installed 0.5 m before the last 180 bend, while inthe 80 m circuit, an equipped section was installed in
between the two 90 bends before the inclined part.In this way, the pressure loss over a bend can be
accounted for. The location of the measurement
sections for each circuit is shown in Fig. 8.
As can be seen in Fig. 7, the pressure evolution with
time shows large peaks due to the change of the valve
of the pump. Only the values of the pressure in
equilibrium (during pushing of a piston) were taken
into account for the analysis.
3.2.2 Discharge rate
The determination of the discharge rate was not
straightforward as no electromagnetic discharge meter
was at disposal. Instead, the time needed for a certain
number of strokes of the pump (the emptying of one
piston) was recorded, both by hand with a stopwatch,
and with the files delivering the pressure evolution
with time (similar as Fig. 7). As the volume of one
pumping piston is known (83.1 l), the discharge rate
can be calculated. But the pistons are normally not
completely full, inducing an error (over-estimation of
volume) in this procedure. The filling coefficient of the
pistons must be known to properly determine the
discharge rate [6, 7]. Therefore, a special calibration
procedure has been employed. It consisted of pumping
concrete in a closed reservoir, which was connected to
a load cell. Knowing the density of the concrete, the
discharge rate can be calculated based on the load
variation with time. As the load cell was connected to
the same data acquisition system, measuring at 10 Hz,
the discharge rate could be determined, for one stroke,
during the period that the pressure was in equilibrium.
As the total time measured by the stopwatch also
includes the time of the change of the valve (the so-
called dead time), a second error is induced in the
manual measurements (over-estimation of time). By
coincidence, both errors compensate each other and
Upstream pressure (bar)
Time (s)0
2
4
6
8
10
12
14
16
18
20
0 50 100 150 200 250
0
1
2
3
4
5
6
7
8
72 72.5 73 73.5 74 74.5 75
strain gauges
pressure sensor
Upstream pressure (bar)
Time (s)
High Q
Low Q
Fig. 7 Evolution of theupstream pressure (closest
to the pump) with time,
clearly showing the change
of the valve of the pump (see
inset). The discharge rate(Q) is decreased stepwise,
maintaining each step for
five full strokes of the pump
Materials and Structures (2013) 46:533555 539
-
the discharge rate measured by the stopwatch method
is the same discharge rate applied when the pressure is
in equilibrium, as demonstrated in Fig. 9. Note that in
Fig. 9, the maximum discharge rate applied was
25 l/s.
3.3 Concrete
In total, 19 concretes were tested in the described
pumping circuits, of which 18 were SCC, and one was
a pumpable CVC mixture. All concretes were
prepared in a ready-mix concrete plant and transported
to the laboratory. Usually, the production and trans-
port of the concrete took 45 min1 h.
Except for the mixtures developed by the concrete
plant, all mixtures contained ordinary portland cement
(CEM I) and limestone filler as powder materials. The
maximum aggregate size of the SCC was 14 mm. The
superplasticizer employed was a poly-carboxylate
with guaranteed workability retention of 100 min. In
Table 1, the mix designs for all concretes for which
results are used in this paper are shown.
3.4 Testing procedure
Shortly after the delivery of the concrete, a sample was
taken and the fresh properties were tested by means of
the standard tests on SCC (slump flow, V-funnel, etc.)
and by means of the Tattersall Mk-II rheometer
(Fig. 10) [8, 14]. During the initial characterization of
the SCC, the concrete was inserted in the pipes. The
first 250 l of pumped material, which was a mixture of
the preparatory cement paste, aggregates and concrete,
was removed from the site. In contrast to the 100 m
circuit, no blocking was observed during the insertion
of any of the concretes in the 25 m circuit. The
Fig. 8 Schematic presentation of the pumping circuits, showing the locations of the pressure sensors and strain gauges
540 Materials and Structures (2013) 46:533555
-
reservoir of the pump was filled and 250 l of concrete
was left aside before the concrete truck left the lab.
The total amount of concrete inside the pipes and the
reservoir of the pump was approximately 1 m3.
At a concrete age of 60 min (if possible), a first
pumping test was executed. This test consisted of
pumping the concrete through the pipes at the five
lowest discharge rates available on the pump. These
discharge rates corresponded to the steps of the pump,
step 1 being around 5 l/s, step 2: approx. 8 l/s, step 3:
1213 l/s, step 4: 1516 l/s and for step 5, a discharge
rate of 1820 l/s was obtained. For security reasons,
the discharge rate was not increased above 20 l/s,
except for some special cases. During the test, all steps
were maintained for five full strokes each, which
means that for each discharge rate, the contents of five
pistons was pushed through the pipes. The discharge
rate was decreased stepwise and the test had a total
duration of around 4 min (Fig. 7). This testing proce-
dure was repeated each 30 min, until it was decided to
discard the concrete and clean the circuit. In most
cases, three to four tests were executed for each
concrete. In between these tests, the concrete was at
rest or other types of tests were executed, such as the
discharge calibration tests. Even after a rest period of
approximately 25 min, the re-start, which could be
compromised by thixotropic build-up, did not deliver
any problems.
Before the start of a selected number of tests, concrete
was pumped in the closed reservoir to take samples for
the tests on fresh concrete. Initially, when taking the 12 l
sample in the rheometer bucket directly at the outlet of
the circuit, it was sometimes not fully representative for
the concrete inside the pipes. Taking a sample when the
valve of the pump changes delivers more aggregates, as
they move forward due to inertia, while the paste in the
concrete has stopped. Taking a sample as the pumping
cylinder just starts pushing delivers more paste, as the
paste moves almost instantly, while the aggregates,
which have slowed down, need to be accelerated. As a
result, the sample for the rheometer sometimes contained
very few aggregates (as it was almost mortar), or too
many aggregates to be considered as SCC. As a result,
some rheological tests were conducted on a sample that
was not representative for the concrete inside the pipes,
and these results were not used in the analysis. The
decision was made based on visual observations. In a
later stage during the research, this problem was omitted
by taking the sample for the rheometer from the 100 l
sample taken from the pump for the tests on fresh SCC.
The latter concrete was not visibly affected by the
changes of the valve, as the concrete sample was
sufficiently large to be considered as homogeneous. As a
result, it is advised to take a sufficiently large volume of
concrete on the jobsite (wheelbarrow instead of a bucket)
when analysing or sampling concrete after pumping.
0
5
10
15
20
25
30
0 5 10 15 20 25 30
Stopwatch
Output File
Discharge rate from stopwatch or output file (l/s)
Disc
harg
e ra
te fr
om
lo
ad c
ell (
l/s)
Fig. 9 Calibration of thedischarge rate shows that
both methods with the
stopwatch, as with the
output file (similar as Fig. 7)
represent the real discharge
rate (measured with the load
cell)
Materials and Structures (2013) 46:533555 541
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Table 1 Mix designs for pumped concretes (units in kg/m3)
SCC 1 SCC 2 SCC 3 SCC 4 SCC 5 SCC 6
Gravel 8/16 434 434 434 459 434 434
Gravel 3/8 263 263 263 278 263 263
Sand 0/5 853 853 853 901 853 853
CEM I 52.5 N 360 360 360 300 360 360
Limestone filler 239 239 239 200 239 239
Water 165 165 165 165 165 165
SP (l/m3) 11 11 15.22 12.16 20.95 13.33
Powder content (kg/m3) 599 599 599 500 599 599
W/C-ratio () 0.458 0.458 0.458 0.550 0.458 0.458
W/P-ratio () 0.275 0.275 0.275 0.330 0.275 0.275
Slump flow at plant (mm) 690 710 710 720
Remarks
SCC 7 SCC 8 CVC 1 SCC 9 SCC 10 SCC 12
Gravel 8/16 434 434 410 434 434
Gravel 3/8 263 263 248 263 263
Sand 0/5 853 853 805 853 853
CEM I 52.5 N 360 360 400 360 360
Limestone filler 239 239 300 239 239
Water 165 165 165 165 165
SP (l/m3) 12.69 14.44 18.15 11 ?
Powder content (kg/m3) 599 599 328 700 599 599
W/C-ratio () 0.458 0.458 0.538 0.413 0.458 0.458
W/P-ratio () 0.275 0.275 0.521 0.236 0.275 0.275
Slump flow at plant (mm) 650 680 700 650 675
Remarks Plant-Mix Target SF
Contains FA
SCC 13 SCC 14 SCC 15 SCC 16 SCC 17
Gravel 8/16 434 434 434
Gravel 3/8 263 263 263
Sand 0/5 853 853 853
CEM I 52.5 N 360 360 360
Limestone filler 239 239 239
Water 165 160 165
SP (l/m3) ? 21.9 ?
Powder content (kg/m3) 599 599 581 599 581
W/C-ratio () 0.458 0.444 0.452 0.458 0.452
W/P-ratio () 0.275 0.267 0.324 0.275 0.324
Slump flow at plant (mm) 700 640 650 700 700
Remarks Target SF Plant-Mix Target SF Plant-Mix
Target SF
542 Materials and Structures (2013) 46:533555
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The rheological properties were measured with the
Tattersall Mk-II rheometer. As the rheological prop-
erties need to be expressed in fundamental units when
applying them on the pumping data, the torque-
rotational velocity data were transformed into shear
stress and shear rate according to the procedure
described in the PhD work of Feys [34]. Although
the transformation procedure is not perfect, it is shown
in literature that the Tattersall Mk-II rheometer
delivers similar results as the ConTec rheometer
[35]. Note furthermore that the same study concluded
that the Tattersall Mk-II rheometer is not capable of
correctly measuring the rheological properties of very
fluid concretes.
As the concrete is pumped in a loop circuit, it is re-
used several times and it underwent changes in the
rheological properties. As the rheological properties of
the concrete are measured each time when executing a
pumping test, the further derived relationship between
the rheological parameters and the pumping pressure
is independent of the changes occurring in the
concrete. Each combination rheologypumping pres-
sure is used as an independent data point.
4 Results for straight pipes
The main results reported in this paper are valid for
straight, horizontal sections and are based on the
results obtained with the 25 m circuit. Due to a
change in rheological properties of the concrete
during pumping, the pressure loss for the test at 120
and 150 min of age (tests 3 and 4) was lower than
the pressure loss for test 1 at 60 min and even test 2
at 90 min of age (Fig. 11) [34]. As a result, there is
a discrepancy between the test results of the first
pumping test (at 60 min of age) and the measured
rheological properties of the corresponding concrete.
As the concrete sample was taken before the test, it
did not undergo the same shear history as the
concrete in the pipes. Furthermore, during the first
test (60 min) and potentially during the second test
(90 min), the concrete was not in equilibrium
conditions. This implies that these results cannot
be employed in the analysis of a potential rheology-
pumping relation. The discussion on the changes in
properties due to pumping is beyond the scope of
this paper.
Fig. 10 Tattersall Mk-II rheometer used to measure the rheological properties of the pumped concretes
Materials and Structures (2013) 46:533555 543
-
4.1 Velocity profile and existence of a lubrication
layer for SCC
4.1.1 Existence of lubrication layer
The existence of a lubrication layer during pumping of
SCC has not been measured directly, but can be
indirectly proven with the following mathematical
procedure: The equilibrium of forces in a straight,
horizontal pipe expresses the relationship between the
pressure loss per unit of length (in Pa/m) and the shear
stress at the inner wall of the pipe (in Pa), by means of
Eq. 5.
sw DptotL
R2
5
where sw is the shear stress at the pipe wall (Pa); Dptotis total pressure loss over the length L (Pa), L is length
of the considered section (m); R is radius of the pipe
(m).
It is further known from rheology that in a circular
pipe, the shear stress decreases linearly from its
maximum value at the wall to zero in the centre,
regardless of the rheological properties of the material
[36] (Fig. 12). The shear stress distribution is thus only
influenced by the pressure loss per unit of length and
the pipe radius. Knowing the rheological properties of
the concrete (which are measured with the Tattersall
Mk-II rheometer), the shear rate distribution across the
pipe can be calculated. Integrating the shear rate over
the pipe radius delivers the velocity profile. In this case,
it is assumed that the velocity at the wall is zero. By
integration of the velocity profile over the cross section
of the pipe, the discharge rate corresponding to the
pressure loss and rheological properties is obtained.
In this procedure, two assumptions have been
made: the velocity at the wall is zero (there is no
slippage) and the material is homogeneous (the
rheological properties are constant in the entire cross
section of the pipethere is no lubrication layer).
Following this procedure, the Poiseuille equation is
obtained for Newtonian liquids [37, 38] and the
BuckinghamReiner equation (Eq. 6) is concluded for
Bingham liquids [8, 36, 39]:
Concrete age (min)
Pres
sure
lo
ss (k
P a/m
)
0
5
10
15
20
25
30
35
40
45
50
60 80 100 120 140 160 180 200
19-20 l/s15-16 l/s12-13 l/s8-9 l/s5-6 l/s
Fig. 11 The evolution of the pressure loss at each discharge rate decreases during the first three tests, remains constant and increasesafterwards. Test results from SCC 8
Q p 3 R4 Dptot 416 s40 L4 8 s0 L R3 Dptot 3
24 Dptot 3L lp6
544 Materials and Structures (2013) 46:533555
-
For modified Bingham materials, a more extended
equation has been derived in [40] (Eq. 7):
Q p D3
6720 c4 s3w
hl7 W l6 140 l c3 s30 s3w
:
2 W l4 c sw 6 s0 14 l5 c s0 70 s20 c2 l3 8 W c3 sw s0 3 sw 4 s0 2 W l2 c2 3 s2w 24 s20 8 sw s0
120 W c3 s3w 64 W c3 s30i
7with W
l2 4 c sw 4 c s0
p:
If no lubrication layer were formed, these theoretical
equations should match the experimentally obtained data.
In the last three columns of Table 2, the discharge rate,
experimental and predicted pressure loss respectively, are
shown for different tests. The predicted pressure loss is
based on the BuckinghamReiner equation (Eq. 6) if the
concrete shows Bingham behaviour (c/l = 0). In case ofc/l[0, Eq. 7 is used. From Table 2, it can be seen thatthe theoretical equations provide a significantly higher
estimation of the pressure loss at a certain discharge rate
compared to the experiments [34], which is similar as
concluded for CVC by Kaplan [6]. This difference can
sometimes attain one order of magnitude. Furthermore,
the predictions based on Eq. 7 provide a higher over-
estimation than the predictions based on Eq. 6. This can
be attributed to the extrapolation of the rheological data
outside the shear rate range used in the rheometer, which
is explained in Sect. 4.2.1.
As a result, the most probable explanation is that a
lubrication layer must be formed, also in case of SCC,
to facilitate the pumping. These results are in line with
the observations of Jacobsen et al. [41].
4.1.2 Velocity profile for SCC
On the one hand, the lubrication layer is formed in the
vicinity of the pipe wall, but in the centre of the pipe,
the concrete (especially SCC) is assumed to have the
same rheological properties as measured in the
rheometer. As the shear stress distribution in the pipe
is known, the plug radius, which defines the boundary
between sheared and unsheared concrete, can be
calculated as rplug R s0=sw (if s0 B sw). For CVC,the plug radius is in most cases almost equal to the
radius of the pipe, as the concrete yield stress is higher
CVC
SCC
dp/dx fixed
velocity
shear stress fixed
shear stress
shear rate
CC
SCC
lubrication layer
lubrication layer
velocity
Yield stress
Yield stress
CVC: Shear stress < Yield stress Plug flow + lubrication layer
SCC: Shear stress > Yield stress Plug flow + lubrication layer + shearing flow
Fig. 12 Theoretical velocity profiles for CVC and SCC. As amain difference, the plug in SCC is much smaller and a part of
the concrete itself is sheared in the pipes. This is caused by the
yield stress of the concrete. For CVC, the shear stress is in most
cases lower than the yield stress. The flow is only made possible
by the lubrication layer. For SCC, the yield stress is sufficiently
low to cause shearing in the concrete, but a lubrication layer is
proven to be present
Materials and Structures (2013) 46:533555 545
-
Table 2 Fresh properties and rheological properties of theconcrete during different pumping tests, reported in Figs. 13,
14 and 15. The last three columns indicate the discharge rate,
experimental and theoretical pressure loss. The theoretical
pressure loss is based on the BuckinghamReiner equation if c/
l = 0, or it is based on the extended version for the modifiedBingham model if shear-thickening is observed
Q (l/s) Dp (kPa/m)experimental
Dp (kPa/m)theoretical
SCC 1 Slump flow (mm) 710 Yield stress (Pa) 49.0 18.7 53.9 373
Age (min) V-Funnel (s) 5.3 l (Pa s) 24.7 15.2 41.0 270
130 c/l (s) 0.012 11.8 28.5 185
App visc at 10 s-1 (Pa s) 35.5 7.4 15.7 97
4.6 9.2 53
SCC 2 Slump flow (mm) 660 Yield stress (Pa) 114.4 19.2 63.5 251
Age (min) V-Funnel (s) 4.5 l (Pa s) 39.5 16.0 50.2 210
125 c/l (s) 0 12.2 35.9 161
App visc at 10 s-1 (Pa s) 50.9 8.0 21.7 108
4.5 11.8 63
SCC 2 Slump flow (mm) 523 Yield stress (Pa) 162.5 18.9 62.4 216
Age (min) V-Funnel (s) 4.9 l (Pa s) 34.1 15.4 48.1 178
180 c/l (s) 0 11.7 33.9 137
App visc at 10 s-1 (Pa s) 50.3 7.9 22.7 95
4.5 13.3 58
SCC 3 Slump flow (mm) 470 Yield stress (Pa) 270.1 18.5 86.6 287
Age (min) V-Funnel (s) 5.3 l (Pa s) 45.8 14.7 65.7 231
170 c/l (s) 0 11.4 48.4 182
App visc at 10 s-1 (Pa s) 72.8 7.6 31.5 126
4.3 18.9 77
SCC 3 Yield stress (Pa) 410.1 18.6 91.5 312
Age (min) l (Pa s) 48.6 15.4 73.2 262
195 c/l (s) 0 12.1 55.3 210
App visc at 10 s-1 (Pa s) 89.6 7.7 36.2 141
4.3 22.4 88
SCC 4 Yield stress (Pa) 83.0 19.1 53.9 221
Age (min) l (Pa s) 35.2 15.5 41.7 180
90 c/l (s) 0 12.1 27.7 142
App visc at 10 s-1 (Pa s) 43.5 8.3 18.3 99
4.8 10.1 59
SCC 4 Slump flow (mm) 700 18.5 53.7
Age (min) V-Funnel (s) 3.2 15.0 39.5
115 12.4 29.9
8.4 19.0
4.7 10.6
SCC 4 Slump flow (mm) 645 Yield stress (Pa) 140.6 19.8 52.3 209
Age (min) V-Funnel (s) 4.1 l (Pa s) 31.6 16.0 38.3 170
145 c/l (s) 0 11.9 26.3 128
App visc at 10 s-1 (Pa s) 45.7 8.1 17.2 90
4.8 10.1 56
546 Materials and Structures (2013) 46:533555
-
Table 2 continued
Q (l/s) Dp (kPa/m)experimental
Dp (kPa/m)theoretical
SCC 5 Slump flow (mm) 660 Yield stress (Pa) 73.4 18.7 53.9 174
Age (min) V-Funnel (s) 4.3 l (Pa s) 28.2 14.5 35.5 136
105 c/l (s) 0 12.2 26.5 115
App visc at 10 s-1 (Pa s) 35.5 8.3 16.1 79
4.7 9.6 47
SCC 6 Slump flow (mm) 688 18.9 49.7
Age (min) V-Funnel (s) 3.4 15.4 38.9
135 12.3 29.2
7.8 18.6
5.4 12.2
SCC 7 Slump flow (mm) 695 Yield stress (Pa) 31.2 20.2 40.8 388
Age (min) V-Funnel (s) 3.0 l (Pa s) 16.4 16.9 30.5 320
120 c/l (s) 0.023 12.4 20.6 191
App visc at 10 s-1 (Pa s) 27.1 8.0 11.7 96
5.5 7.5 55
SCC 7 Slump flow (mm) 710 Yield stress (Pa) 29.4 20.2 40.0 365
Age (min) V-Funnel (s) 3.5 l (Pa s) 14.7 15.8 29.7 241
150 c/l (s) 0.021 12.3 21.1 160
App visc at 10 s-1 (Pa s) 23.8 8.5 13.8 90
5.4 8.7 47
SCC 8 Yield stress (Pa) 21.8 19.4 31.8 397
Age (min) l (Pa s) 3.5 16.5 24.8 290
150 c/l (s) 0.134 12.8 17.1 178
App visc at 10 s-1 (Pa s) 15.1 8.3 10.6 79
5.9 7.6 42
SCC 8 Slump flow (mm) 693 Yield stress (Pa) 21.4 20.1 33.9 328
Age (min) V-Funnel (s) 3.1 l (Pa s) 9.4 16.3 24.4 226
180 c/l (s) 0.033 12.5 16.5 142
App visc at 10 s-1 (Pa s) 17.7 9.2 11.6 85
5.5 7.6 33
SCC 8 Slump flow (mm) 570 Yield stress (Pa) 50.0 20.6 37.1 110
Age (min) V-Funnel (s) 3.5 l (Pa s) 16.2 16.5 27.4 89
210 c/l (s) 0 12.6 18.3 68
App visc at 10 s-1 (Pa s) 21.2 8.9 11.1 49
5.2 6.7 30
SCC 9 Yield stress (Pa) 11.9 19.3 25.6 233
Age (min) l (Pa s) 0.6 15.6 18.7 153
105 c/l (s) 0.484 12.0 14.6 91
App visc at 10 s-1 (Pa s) 7.6 8.8 9.5 50
8.6 7.7 48
SCC 10 Slump flow (mm) 685 19.6 20.9
Age (min) V-Funnel (s) 2.5 15.8 14.6
240 12.6 7.7
7.9 2.3
6.1 2.7
Materials and Structures (2013) 46:533555 547
-
than the shear stress at the pipe wall. As a conse-
quence, CVC flows at uniform velocity, surrounded by
the lubrication layer [] (Fig. 12). The calculations for
SCC have shown that in all cases, even at the lowest
discharge rates, a part of the SCC is sheared (Fig. 12),
as the largest plug radius calculated for the entire set of
experiments is 3.7 cm (SCC 3195 min). This is
attributed to the low yield stress of this type of
concrete, compared to the shear stress at the pipe wall.
As a result, the velocity profile of SCC is assumed to
be composed of a small plug in the centre of the pipe, a
lubrication layer near the wall and sheared concrete in
between (Fig. 12). Note that this type of behaviour
was predicted by Kaplan in [6].
When considering the concrete as a homogeneous
material in the pipe, the shear rate can be calculated
based on the pressure loss per unit of length (exper-
imentally obtained) and the rheological properties of
Table 2 continued
Q (l/s) Dp (kPa/m)experimental
Dp (kPa/m)theoretical
SCC 13 Slump flow (mm) 750 Yield stress (Pa) 6.7 19.5 13.3 183
Age (min) V-Funnel (s) 2.0 l (Pa s) 2.3 15.7 9.3 121
120 c/l (s) 0.091 12.9 6.5 84
App visc at 10 s-1 (Pa s) 7.2 10.1 3.9 53
SCC 12 Slump flow (mm) 645 Yield stress (Pa) 11.6 19.1 25.7 40
Age (min) V-Funnel (s) 2.1 l (Pa s) 6.4 15.3 18.8 32
150 c/l (s) 0 11.6 13.3 25
App visc at 10 s-1 (Pa s) 7.6 8.0 8.0 17
6.9 6.8 15
SCC 15 Slump flow (mm) 570 Yield stress (Pa) 40.6
Age (min) V-Funnel (s) 3.4 l (Pa s) 9.8 13.2 22.9 44
120 c/l (s) 0 10.0 16.4 34
App visc at 10 s-1 (Pa s) 13.9 6.2 9.3 22
4.0 6.3 15
SCC 15 Slump flow (mm) 445 Yield stress (Pa) 88.8 17.0 30.7 43
Age (min) V-Funnel (s) 3.7 l (Pa s) 7.0 12.8 23.4 33
210 c/l (s) 0 8.9 16.6 25
App visc at 10 s-1 (Pa s) 15.9 5.1 10.7 16
3.6 8.6 13
SCC 16 Slump flow (mm) 535 Yield stress (Pa) 34.4
Age (min) V-Funnel (s) 3.9 l (Pa s) 9.8 13.9 27.1 46
210 c/l (s) 0 10.4 19.2 35
App visc at 10 s-1 (Pa s) 13.2 6.6 12.4 23
3.9 8.4 14
SCC 17 Slump flow (mm) 750 18.6 23.5
Age (min) V-Funnel (s) 2.2 14.7 16.8
120 11.0 11.7
7.7 7.9
4.2 4.1
CVC 1 Slump (mm) 240 Yield stress (Pa) 122.7 20.2 28.4 105
Age (min) l (Pa s) 15.2 15.6 21.8 83
210 c/l (s) 0 11.8 15.6 64
App visc at 10 s-1 (Pa s) 27.5 7.6 9.2 44
4.7 4.7 29
548 Materials and Structures (2013) 46:533555
-
the concrete, according to the procedure explained in
Sect. 4.1.1. The test results at the highest discharge
rate indicate a maximum shear rate between 30 and
60 s-1 for homogeneous concrete. Increasing pipe
diameter would lower these values, but increasing
discharge rate increases these shear rates. In case a
lubrication layer is considered, these shear rates would
be significantly higher. Assume that the lubrication
layer has rheological properties that are 10 times lower
than these of concrete, the shear rates would be
approximately 10 times higher. (This is just to give an
example as there is no proof for this statement.)
No tribological measurements to characterize the
lubrication layer properties were performed in this
research project. In any case, performing tribological
measurements on SCC would not be straightforward,
as the basic assumption for concrete tribology is that
the concrete itself is not allowed to be sheared [6, 7,
33]. Due to the low yield stress of SCC, this assumption
is unlikely to be fulfilled, complicating significantly
the testing and data transformation procedure.
4.2 Influence of rheological behaviour
4.2.1 Influence of viscosity
In Fig. 13, based on the results in Table 2 (except the
CVC), the pressure loss per unit of length is plotted as
a function of the apparent viscosity at a shear rate of
10 s-1. This apparent viscosity represents the incli-
nation of a straight line connecting the origin and the
rheological curve at a shear rate of 10 s-1 [36]. A
shear rate of 10 s-1 to calculate the apparent viscosity
is chosen, as it represents approximately 2/33/4 of the
maximum shear rate applied in the Tattersall Mk-II
rheometer (which is between 12 and 14 s-1). Calcu-
lating the apparent viscosity at or beyond the maxi-
mum shear rate in the rheometer would make the
results very sensitive to small errors due to the
fluctuations of the torque during the measurement.
Therefore, it appeared more appropriate to calculate
the apparent viscosity at 10 s-1. As stated above, the
shear rate in the sheared part of the concrete during
pumping can reach up to 60 s-1 (or even higher if a
higher discharge rate is applied), resulting in a
discrepancy in the range of shear rate between the
rheometer and the flow in the pipes. On the other hand,
the maximum shear rate obtained in the Tattersall Mk-
II rheometer is already a very high value for a concrete
rheometer. Increasing it further would significantly
increase the risk of (dynamic) segregation during
testing. As a result, it was decided not to increase the
maximum shear rate in the rheometer to maintain
sufficient quality of the rheometer results and to keep
the discrepancy between the rheometer and the pipe
flow.
y = 0.85x + 19.60R = 0.96
y = 0.67x + 14.01R = 0.96
y = 0.50x + 9.24R = 0.95
y = 0.33x + 5.40R = 0.95
y = 0.18x + 4.48R = 0.88
0
20
40
60
80
100
120
0 10 20 30 40 50 60 70 80 90 100
Pres
sure
lo
ss (k
Pa/m
)
Apparent Viscosity at 10 s-1 (Pa s)
Q = 18 - 20 l/sQ = 15 - 16 l/sQ = 12 - 13 l/sQ = 8 l/sQ = 5 l/s
Fig. 13 For each dischargerate, the pressure loss per
unit of length is correlated to
the apparent viscosity of
SCC, taken at a shear rate of
10 s-1
Materials and Structures (2013) 46:533555 549
-
Figure 13 shows that for each range of discharge
rates, a good correlation can be found between the
pressure loss per unit of length and the concrete
apparent viscosity. This good agreement is the conse-
quence of the shearing of the concrete. On the other
hand, the relationships are empirical, as they are only
valid for the range of discharge rates and for the pipe
diameter used. It is not in the authors intention to
provide prediction tools for the pressure, but only to
show that in case of SCC, the concrete viscosity is a
dominating factor.
The practical guidelines for pumping CVC
predict the total pressure based on the discharge
rate, diameter of the pipe, the equivalent length of
the pipeline and the spread value of the concrete [4,
25]. The latter value is a kind of measure, similar to
the slump test, related to the capability of the
concrete to form and maintain the lubrication layer.
For SCC however, the spread value would be very
high and if the guidelines are followed, very low
pressures would be needed. The practical experience
however indicates that in many cases, the pump
has to work more in case of SCC. This means that
the operators observe in general larger pressures
needed to pump SCC. As a result, the practical
guidelines to predict the pumping pressure cannot
be applied on SCC. Therefore, it would be better to
modify the practical guidelines for pumping of
SCC, in which the pressure loss is related to the
viscosity of SCC.
In the experimental work of Jodeh and Nassar [42],
two different SCC were pumped in a 250 m circuit.
Although both SCC had the same initial slump flow of
750 mm, a significant difference in total pressure was
monitored: 250 bar of SCC 1 compared to 92 bar for
SCC 2. The V-funnel flow times for SCC 1 and SCC 2
were 20 and 10 s respectively, showing the impor-
tance of viscosity on the total pressure. Figure 14
shows a good agreement between the pressure loss and
the V-funnel flow time of the tested concretes in this
experimental work.
In the work of Kaplan [6] and Chapdelaine [7] on
CVC, the pumping pressure is well related to the
viscous constant of the lubrication layer. They already
showed the importance of a viscosity term in this
casting process. The authors are convinced that the
characteristics of the lubrication layer (mainly the
viscous constant), together with the concrete viscosity,
should be able to give a good prediction of the pressure
needed to pump SCC. Only the difficulties in
performing tribological measurements, as stated in
the previous section, must be solved.
y = 15.38x - 11.21R = 0.77
y = 11.82x - 10.55R = 0.73
y = 8.71x - 8.70R = 0.69
y = 5.60x - 6.04R = 0.65
y = 2.92x - 1.65R = 0.61
0
10
20
30
40
50
60
70
80
90
100
1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
Pres
sure
lo
ss (k
Pa/m
)
V-Funnel flow time (s)
Q = 18 - 20 l/sQ = 15 - 16 l/sQ = 12 - 13 l/sQ = 8 l/sQ = 5 l/s
Fig. 14 The pressure loss per unit of length can be related to the V-Funnel flow time of SCC
550 Materials and Structures (2013) 46:533555
-
4.2.2 Shear-thickening
The SCC tested in this research project showed in
many cases shear-thickening behaviour. This can be
seen in Table 2 where the rheological properties of the
concrete, measured at each test used in the analysis,
are shown. The parameter c/l expresses the intensityof shear-thickening when applying the modified
Bingham model. The larger c/l, the more severe theshear-thickening, while c/l equal to zero reflectsBingham behaviour.
The shear-thickening behaviour of the concrete is
reflected in the pressure lossdischarge rate curve.
For each pumping test, the pressure loss at each
discharge rate is shown in Table 2 and an example is
shown in Fig. 15. This figure compares the pressure
lossdischarge rate curves of SCC 7 and the only
CVC which has been pumped. The SCC showed
shear-thickening, while the CVC was a Bingham
material, which is also observed in the pressure loss
discharge rate curve. As a result, shear-thickening is a
disadvantageous phenomenon, increasing pumping
pressures, and should certainly be accounted for.
Figure 15 also confirms the conclusion that the
viscosity is a dominating factor for the pumping
pressure, as the pressure loss is higher for the SCC
compared to the CVC. Note that SCC 7 and CVC have
a similar apparent viscosity at a shear rate of 10 s-1.
Extrapolating the rheological curve to the shear rate
range during pumping would deliver a larger apparent
viscosity for SCC 7, due to the shear-thickening
behaviour.
5 Results for bends
The practical guidelines take the influence of bends
and reducers into account by identifying an equivalent
length. For example, the Schwing-guide [25] and
Guptil et al. [4] state that a bend of 90 causes apressure loss which is equivalent to 3 m of straight
pipes. As a result, for each 90 bend, 3 m must beadded to the total circuit length to calculate the
pressure needed. In the research of Kaplan [6] and
Chapdelaine [7], it is concluded, somewhat surpris-
ingly, that the bends and reducers investigated in the
respective researches do not cause an additional
pressure loss. The bends and reducers can thus be
considered as a straight section.
In this project, the influence of a 90 and a 180bend have been investigated in the 80 and 100 m
circuits. A pressure measurement section was installed
just before and just behind the bend. The pressure loss
in a section containing a bend was compared with the
pressure loss in a straight section. By determining the
pressure loss per unit of length (of straight pipes) from
the latter section, the influence of the bend was
isolated in the former section. The bends have a centre
line radius (CLR) of 17 cm, which implicates a rather
short bend. The equivalent length for the bends is
calculated as the pressure loss over the bend divided
by the pressure loss per meter in a straight pipe. The
equivalent length of a bend is thus the length of a
straight pipe causing an equal pressure loss.
Figure 16 shows an example of the pressure
evolution with time, when applying a stepwise
decrease in discharge rate. Figure 16a shows the
pressure measured upstream (section A) and down-
stream (section B) of a straight section. The grey line
represents the pressure measured after a 90 bend,downstream of the straight section (section C).
Similarly, Fig. 16b shows the pressure measured in
the same straight section (black linessection AB),
and the pressure before a 180 bend, upstream of thestraight section (section C). The pressure difference
between the grey line and the closest black line
includes the corresponding bend and one meter of
straight pipes (as the pressure was measured in the
middle of a 1 m straight section).
0
5
10
15
20
25
30
35
40
45
0 5 10 15 20 25
Pres
sure
loss
(kPa
/m)
Discharge rate (l/s)
CVC
SCC
Fig. 15 The pressure lossdischarge rate curve reflects therheological behaviour of the concrete. While the CVC showed
perfectly Bingham behaviour, the SCC (SCC 7) displayed shear-
thickening in the rheometer
Materials and Structures (2013) 46:533555 551
-
Figure 17 shows the raw data for SCC 14, 15, 16
and 17. Each point corresponds to one full stroke of the
pump at a certain discharge rate. Figure 17a shows the
influence of a 90 bend and is based on the results ofSCC 16 and 17, while Fig. 17b shows the influence of
a 180 bend, based on SCC 14 and 15. From Fig. 17a
and b, it can be seen that for SCC, the equivalent
length shows a very large scatter, but it is in most cases
significantly higher than the length of the bend, which
is indicated by the grey dashed line in Fig. 17. The
statement in the practical guidelines that a 90 bend isequivalent to 3 m of straight section (full black line) is
-1
0
1
2
3
4
5
6
7
8
9
0 50 100 150 200 250 300 350 400
Pressure
(a)
(bar)
Time (s)
Section C
Section ASection B
Section A-B: 10.16 m straight
Section B-C: 1.01 m straight+ 90 bend
Section B
-2
0
2
4
6
8
10
12
14
0 50 100 150 200 250 300 350 400 450
Pressure(bar)
Time (s)
Section CSection A
Section B
Section C-A: 1.01 m straight+ 180 bend
Section A-B: 16.16 m straight
Section BSection C
Section ASection C
Section A(b)
Fig. 16 Example of thepressure evolution with time
when pumping concrete at a
stepwise decreasing
discharge rate. The blacklines represent the pressurein the two measurement
locations in the straight
section (sections A and B).
In Fig. 16a, the grey linerepresents the pressure
measured downstream of a
90 bend, downstream of thestraight section (section C).
In Fig. 16b, the grey line isthe pressure is measured
upstream of a 180 bend,upstream of the straight
section (section C). Note
that the pressure difference
between the grey line andthe corresponding upstream
or downstream black linealso includes 1 m of straight
pipes
552 Materials and Structures (2013) 46:533555
-
slightly above the average measured. On the other
hand, it is not a safe statement as some measurement
points indicate significantly larger pressure losses.
As a preliminary conclusion, it can be stated that the
equivalent length decreases with increasing discharge
rate and that for more viscous SCC, lower equivalent
lengths are obtained, as SCC 14 is more viscous than
SCC 15 and SCC 16 is more viscous than SCC 17.
Generally, it can be concluded that bends cause an
additional pressure loss in case of SCC, but more
research is needed to determine the exact magnitude
and the most important parameters.
6 Conclusions
Based on full-scale pumping tests, the similarities and
differences between pumping, CVC and SCC have
been investigated. Furthermore, the applicability of
the practical guidelines developed for CVC has been
verified for SCC.
In the practical guidelines, minimum values for the
amount of fines, slump, etc. are defined to avoid the
occurrence of friction in the concrete during pumping,
as friction would lead to excessive pumping pressures
and potentially blocking. Due to the adapted mix
Discharge rate (l/s)
Equi
vale
nt le
ngth
(m)
Equi
vale
nt le
ngth
(m)
90 Bend
0
1
2
3
4
5
6
7(a)
2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00
SCC 16SCC 17
Discharge rate (l/s)
0
2
4
6
8
10
12
14
2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00
SCC 14
SCC 15
180 Bend(b)
Fig. 17 Pressure loss over abend, expressed as the
equivalent length. The blackfull line represents thestatements in the practical
guidelines, while the dashedgrey line is the real length ofthe bend and corresponds to
the results of Kaplan and
Chapdelaine. For SCC,
bends cause an additional
pressure loss compared to a
straight section. The
additional pressure loss
appears to decrease with
increasing discharge rate
and increasing concrete
viscosity. In some cases, the
rule of thumb of the
practical guidelines is not
sufficient to quantify the
pressure loss over a bend
Materials and Structures (2013) 46:533555 553
-
design of SCC to fulfil the criteria on filling and
passing ability, blocking is less probable to occur
during pumping. On the other hand, several blockings
were observed during the insertion of SCC in the long
pumping circuits due to a lack of cement paste at the
concrete front. The preparation of a water-cement
mixture to be inserted before the concrete remains
necessary when SCC is employed.
Due to the significantly lower yield stress of SCC,
the velocity profile in a pipe is different. The velocity
profile of SCC is assumed to consist of a small plug in
the centre of the pipe, a lubrication layer at the wall
and a part of sheared concrete in between. In many
cases during pumping CVC is not sheared.
The practical guidelines for pumping concrete
relate the pressure loss to the spread or slump of the
concrete. This would imply that SCC should show
very low pressure losses during pumping. On the other
hand, as SCC itself is sheared (in addition to the
shearing of the lubrication layer), the viscosity
becomes a determining factor influencing pumping
pressures. Good correlations have been established
between the pressure loss and the apparent viscosity of
the concrete and between the pressure loss and the
V-funnel flow time.
Kaplan and Chapdelaine have found that a bend
does not increase the pressure loss during pumping of
CVC, while the practical guidelines state that a 90bend is equivalent to 3 m of straight pipes. The
preliminary results shown in this paper indicate that
during pumping of SCC, an additional pressure loss
occurs in the bends and that the pressure loss can even
be larger than the rules of thumb. It also appears that
the equivalent length of a bend is reduced with
increasing discharge rate and increasing viscosity, but
further research is needed to confirm these statements.
Acknowledgments The authors would like to acknowledgethe Research Foundation in Flanders, Belgium (FWO) for the
financial support of the project and the technical staff of both the
Magnel and Hydraulics laboratory for the preparation and
execution of the full-scale pumping tests.
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Materials and Structures (2013) 46:533555 555
Parameters influencing pressure during pumping of self-compacting concreteAbstractIntroductionResearch significanceRheological properties of fresh concrete
Flow behaviour of conventional vibrated concrete in pipesFlow or frictionLubrication layer
Experimental workTest-setupMeasurement systemsPressure lossDischarge rate
ConcreteTesting procedure
Results for straight pipesVelocity profile and existence of a lubrication layer for SCCExistence of lubrication layerVelocity profile for SCC
Influence of rheological behaviourInfluence of viscosityShear-thickening
Results for bendsConclusionsAcknowledgmentsReferences