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Influence of theInfluence of theRheological PropertiesRheological Properties

on theon theFresh Concrete PressureFresh Concrete Pressure

Carsten BohnemannWolfgang Brameshuber

Institute of Building Materials Research, RWTH Aachen University (ibac)

18th Colloquium “Rheological Measurements of Building Materials“Regensburg, March 11-12, 2009

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OutlineOutline

Influence of the rheological properties on the

fresh concrete pressure

Research methods for the fresh concrete pressure

Initial situation

Rheological equations of state

Summary

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Fresh Concrete Pressure According to DIN 18 218Fresh Concrete Pressure According to DIN 18 218

fresh concrete pressure depends on:– velocity of placing– consistency

nonexistence of self-compactingand vibrated (F5 / F6) concretes

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Influence Factors on the Fresh Concrete PressureInfluence Factors on the Fresh Concrete Pressure

– formwork geometry

– formwork roughness

– stiffness and density of the formwork

– formwork height

– ambient temperature– reinforcement

Procedural factors

Concrete factors

Further factors

Specific formwork factors

– consolidation of concrete

– velocity of placing

– pouring method

– fresh concrete density

– consistency / rheological properties

– fresh concrete temperature

– setting time

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Flow Behaviour of Fluids and Ductile MaterialsFlow Behaviour of Fluids and Ductile Materials

Newtonian flow behaviour

• Newton: = ·

= 0 + k · n

Ductile flow behaviour

• Bingham:

• Herschel-Bulkley:

 = 0 + pl · 

0

20

40

60

80

100

120

0 20 40 60 80 100 120

shear thickeningBingham

shear thinning

tana'=pl'

yield stress 0

shear stress

shear rate

tana=pl

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Determination of Momentum CurvesDetermination of Momentum Curves

Bingham: T = g + h · N

T: shear stress

N: rotational speed

g: relative yield stress

h: relative viscosity

Viskomat NT

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Display of Relevant Data of the Viskomat NTDisplay of Relevant Data of the Viskomat NT

0

40

80

120

160

0 5 10 15 20

0

10

20

30

40N in 1/min and T in Nmm

time in min

temperature in °C

rotational speed N

shear stress T

temperature

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Approximation of Momentum Curves with Herschel-BulkleyApproximation of Momentum Curves with Herschel-Bulkley

n > 1: shear thickening

n < 1: shear thinning

n = 1: Bingham

T: shear stress

N: rotational speed

F: relative yield stress

k: slope factor

n: curve form factor

Herschel-Bulkley: T = F + k · Nn

0

10

20

30

40

50

60

0 50 100 150

flow curve

Herschel-Bulkley

T in Nmm

N in 1/min

F= 2.33 NmmV= 0.28 Nmm·min

Herschel-Bulkley T=2.33+0.24·N1.04

V: relative average viscosity

(slope at N = 60 rpm)

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Description of ConcretesDescription of Concretes

Vibrated Concrete (VC)

VC-F5VC-F6

Self-Compacting Concrete (SCC)

SCC-PT-hvSCC-PT-lvSCC-VAT-hvSCC-VAT-lv

PT: powder typeVAT: viscosity agent typehv: high viscositylv: low viscosity

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Mix DesignMix Design

0.420.40.520.470.560.47-w/ceq

1.5% per volumeair content

1.0-1.0stabilizer

1.51.21.72.72.13.9% per mass

(binder)

superplasticizer

172317501689174215841664aggregate

180170200180190160water content

75100250fly ash

395340300

kg/m³

CEM II/A-LL 42.5 R

87654321

VC

F6

VC

F5

SCC

VAT-lv

SCC

VAT-hv

SCC

PT-lv

SCC

PT-hv

content/value

unitmaterial

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Description of MortarsDescription of Mortars

Mortar of the Vibrated concrete (VM)

VM-F5VM-F6

Self-Compacting Mortar (SCM)

SCM-PT-hvSCM-PT-lvSCM-VAT-hvSCM-VAT-lv

PT: powder typeVAT: viscosity agent typehv: high viscositylv: low viscosity

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Momentum Curves of MortarsMomentum Curves of Mortars

0

5

10

15

20

25

30

35

40

45

50

0 20 40 60 80 100 120

SCM-PT-hv SCM-PT-lv

SCM-VAT-hv SCM-VAT-lv

VM-F5 VM-F6

rotational speed in 1/min

torque in Nmm

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Herschel-Bulkley ApproximationHerschel-Bulkley Approximation

Herschel-Bulkley: T = F + k · Nn

SCM-PT-hv: T = 0.74 + 0.22 · N1.06

SCM-PT-lv: T = 0.02 + 0.13 · N0.98

SCM-VAT-hv: T = 0.34 + 0.19 · N0.93

SCM-VAT-lv: T = 0.00 + 0.24 · N0.78

VM-F5: T = 1.34 + 0.17 · N0.97

VM-F6: T = 3.07 + 0.30 · N0.82

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Experimental Set-Up for Pressure Measurements Experimental Set-Up for Pressure Measurements

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Measurement Method of Fresh Concrete PressureMeasurement Method of Fresh Concrete Pressure

detail load celllocation load cells

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Research Program for Pressure MeasurementsResearch Program for Pressure Measurements

SCC-PT-lv10 2.0 m/hpump

SCC-PT-hv9

SCC-VAT-lv11

SCC-PT-lv810.0 m/h

SCC-PT-hv7

VC-F66

VC-F55

SCC-VAT-lv4

SCC-VAT-hv3

SCC-PT-lv2

2.0 m/hconcrete

bucket

SCC-PT-hv1

4321

velocity of placing

pouring method

concretewall

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Pressure vs. Time – Wall 1Pressure vs. Time – Wall 1

0

10

20

30

40

50

60

70

0 0.5 1 1.5 2 2.5 3

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5load cell bottomload cell 2nd from bottomload cell 2nd from topload cell tophydrostatic pressurefilling level

pressure in kN/m²

time in h

interruptioninterruption

filling level in m

SCC-PT-hvconcrete bucket

vc= 2 m/h

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Pressure vs. Time – Wall 2Pressure vs. Time – Wall 2

0

10

20

30

40

50

60

70

0 0.5 1 1.5 2 2.5 3

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5load cell bottomload cell 2nd from bottomload cell 2nd from topload cell tophydrostatic pressurefilling level

pressure in kN/m²

time in h

interruptioninterruption

filling level in m

SCC-PT-lvconcrete bucket

vc= 2 m/h

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Pressure vs. Time – Wall 1 to 6Pressure vs. Time – Wall 1 to 6

0

10

20

30

40

50

60

70

0 0.5 1 1.5 2 2.5 3

SCC-PT-hvSCC-PT-lvSCC-VAT-hvSCC-VAT-lvVC-F5VC-F6hydrostatic pressure

pressure in kN/m²

time in h

load cell bottomconcrete bucket

vc= 2 m/hinterruption

interruption

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Pressure vs. Time – Wall 1, 2, 7 and 8Pressure vs. Time – Wall 1, 2, 7 and 8

0

10

20

30

40

50

60

70

0 0.5 1 1.5 2 2.5 3

SCC-PT-hv, 2 m/hSCC-PT-lv, 2 m/hSCC-PT-hv, 10 m/hSCC-PT-lv, 10 m/hhydrostatic pressure

pressure in kN/m²

time in h

load cell bottomconcrete bucket

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Pressure vs. Time – Wall 9, 10 and 11Pressure vs. Time – Wall 9, 10 and 11

0

10

20

30

40

50

60

70

0 0.5 1 1.5 2 2.5 3

SCC-PT-hv

SCC-PT-lv

SCC-VAT-lv

hydrostatic pressure

pressure in kN/m²

time in h

load cell bottompump

vc= 2 m/h

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SummarySummary

Low influence of SCC type on fresh concrete pressure

Increasing pressure by decreasing the viscosity

High influence on fresh concrete pressure by velocity of placing

Hydrostatic pressure for formwork dimensioning at pumping

Decrease of pressure at the bottom during interruption

Fresh concrete pressure of SCC compared to VC significantly lower (concrete bucket, 2 m/h)

Low influence of rheological properties at higher velocity of placing or at pumping