scc pumping

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

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

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

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


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]


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


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


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


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)


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


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


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


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


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



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



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



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


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



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


Table 2 continued





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



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



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


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



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



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


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


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





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



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


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



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


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


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


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


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


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


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


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


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


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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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

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