SOME ISSUES CONCERNING THE

AUTOMATIC MEASURING OF

CONCRETE WORKABILITY DURING

MIXING TIME

Bogdan CAZACLIU – IFSTTAR, Francebogdan.cazacliu@isttar.fr

Aggregates & Materials Processing Laboratory

Basic principles of in-mixer sensors

• Power curve stabilization level WATTMETERbefore stabilization MIXOMETER

• Drag force under mixing VISCOPROBE, MFMmixer stopped …

• Composition water content Moister metersair entrained …

• Other methods

Power curve (or torque)

Ordinary concrete SCC …

tf < th = ts

mixing time

mixing power

high w/p, low sp/c

th < tf

exp. decay → t *

low w/p, high sp/c

mixing power

mixing time

ts

overmixing

Cazacliu B., Mixing self compacting concrete: mixers, mixing methods, mixing time, RILEM Publications PRO90 2013

WATTMETER

Hatt 1921Tests of Concrete Mixer

Level ofstabilized power

WATTMETER

STRONG

• Maintenance- No sensor in the mixer

• Cheap• Well established

• OK for VIBRATED concrete

WEAK

• RheologyPViscosity 2 parameters 1 measure

P = PWall Slip 2 new parameters

PCrashing depends on wearing

• For SCC- No stabilization- Small sensitivity

• For DRY concrete

MIXOMETER

MIXOMETER – mixing mechanisms m

ixin

g p

ow

er

(kW

)

0

1

2

3

0 2 4 6 8 10

time (minutes)

8

dry granules

granular suspension

wet granules

dry powder

powder agglomerates

1st

mechanism2nd

mechanism3rd

mechanism

4th

mechanism

Cazacliu B., In-mixer measurements to describe the mixture kinetics during concrete mixing, Chemical Engineering Research and Development, Vol.86, 1423-1433, 2008

Wet powder Uniform Concrete

MIXOMETER – mixing mechanisms

Power measurement for batchesof a same mix-design

RMC Plant

0%

1%

2%

3%

4%

08/04 11/04 02/05 05/05 09/05 12/05 03/06 07/06

10/20

4/10

Aggregates moisture evolution

Measured by dryingRMC Plant

0 20 40 60 80 100 120 140

0

20

40

60

80 Puissance de malaxage

temps de l’opération (s)

∆ ≈ ± 10 l/m3

moisture mixing power

operation time

same concrete during 2 months

Ngoc-Dong Lê, Amélioration de la régularitédu béton en production, PhD 2007

Estimates:

- The time needed tofinish the mixing

- The deviation inwater content(or consistency)

PatentSkako / IFSTTAR

MIXING TIME (s)

1st batch/4:

Water deviation:

Next batch:

POWER (kW)

Mixing index

MIXOMETER

WATTMETER

STRONG

• Maintenance- No sensor in the mixer

• Cheap• Well established

• OK for VIBRATED concrete

WEAK

• RheologyPViscosity 2 parameters 1 measure

P = PWall Slip 2 new parameters

PCrashing depends on wearing

• For SCC- No stabilization- Small sensitivity

• For DRY concreteMIXOMETER

DRAG

FORC

E

Drag force

LICHTENBERG 1926 - method of and

apparatus for determining the consistency

of concrete

strain gauge

in concrete immerged sphere

VISCOPROBE

3

5

7

9

11

13

-15 0 15 30 45 60 75 90

Viscoprobe average signal

WATER

introduction

3

4

5

6

7

8

-15 0 15 30 45 60 75 90

wattmeter signal

WATER

introduction

Around

nomina

l

-10

-8

+0

+2

+4

+6.5

+9

+10

The viscoprobe average force curves follow the wattmeter curves,with a better differentiation

VISCOPROBE

Cazacliu B., Brunquet E., On-line mixing end-point detection by power measurement, Rilem Proceedings pro054, 2007

3

5

7

9

11

13

-15 0 15 30 45 60 75 90

Viscoprobe average signal

3

4

5

6

7

8

-15 0 15 30 45 60 75 90

wattmeter signal

Upper

+9

+10

+20

+24

Much better with upper water proportioning

Good repeatability – see curves +9 and + 10

VISCOPROBE

3

4

5

6

7

8

-15 0 15 30 45 60 75 90

wattmeter signal

3

5

7

9

11

13

-15 0 15 30 45 60 75 90

Viscoprobe average signal

For low water proportioning(-16l/m3 ie slump flow 49cm ) the viscoprobe average force show a minimum when wattmeter shows a second peak!

Minimum of force for the viscoprobe

Maximum of power !

Low

-16

-11

VISCOPROBE

Particle Image Velocimetry Nuclear Magnetic Resonance

What is the structure of the flow

Philippe Poullain, Étude comparative de l’écoulement d’un fluide viscoplastique dans une maquette de malaxeur pour bétons : PIV, IRM et simulation numérique, PhD 2003

Experimental

3 drag force probes

- Viscoprobe (planetary movement)- MFMi (circular movement)- MFMe (circular movement)

blades

wW

W

W

W

MFMi

MFMe

Viscoprobe

scraper

5 levels of mixing speed W:( with constant w/W )

100% (nominal), 75%, 50%, 25%, 10%

What is the structure of the flow

Ngoc-Dong Lê, Amélioration de la régularité du béton en production, Degree awarded May 2007

Rheometry on samplesfor each tested concrete

(9 SCC mixture tested)blades

wW

W

W

W

MFMi

MFMe

Viscoprobe

scraper

for a known rheology the drag force is a measure

of the concrete velocity around the probe

Drag force = F (rheology, velocity)

Experimental

What is the structure of the flow

code FloMix (IFSTTAR) :

- velocity field determined by

FME fictitious domain methods- 2D, non-slip boundary conditions- several Bi and Re numbers tested

Velocity intensity scaled 0 to 0.5 of scraper velocity

Bi = 0, 32, 64 and 100; Re = 1

Bi = τo / µΩ

Re = ρΩR² / µ

Numerical simulations

What is the structure of the flow

addition of two flows + mixing star flowinteraction flow

low Re / Bi high Re / Bi

Non-inertialreference frame !

structure of the flow

0

50

100

150

200

250

300

350

400

450

0 10 20 30 40 50 60 70 80

Force at v = 0 by Viscoprobe, Fo (N)

Yield stres

s by rheo

metry

, t o

(Pa)

BAP1

BAP2

BAP3

BAP4

BAP5

validity limit

wall slippingin-mixer lower density …

c* = F0/t0RVisco²

Concrete rheology - Drag force

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80 90 100

Viscoprobe slope, p (N.s/m)

Visco

sity by rheo

meter, µ

(Pa.s)

l* = p/µRVisco

wall slippingin-mixer lower density …

validity limit

Concrete rheology

0

20

40

60

80

100

120

140

160

180

200

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 1,9 2 2,1

Vitesse (m/s)

Force de trainée (N)Ftrainée

rhéomètre

100%75%50%

25%10%

Rheometer fluidity curve

In-mixer fluidity curve

velocity (m/s)

Drag force (N) Vibrated concrete

WATTMETER

STRONG

• Maintenance- No sensor in the mixer

• Cheap• Well established

• OK for VIBRATED concrete

WEAK

• RheologyPViscosity 2 parameters 1 measure

P = PWall Slip 2 new parameters

PCrashing depends on wearing

• For SCC- No stabilization- Small sensitivity

• For DRY concrete

MIXOMETER DR

AG FORC

E

COMPO

SITION

Moisture content

Cazacliu B., In-mixer measurements to describe the mixture kinetics during concrete mixing, Chemical Engineering Research and Development, Vol.86, 1423-1433, 2008

13

23

33

mixing power [kW]

70

74

78

0 30 60 90 120 150

time (s)

local moisture [%]

3

7

11

drag force [N]

wet paste fluiddry

W/P 0.309

13

23

33 mixing power [kW]

70

74

78

0 30 60 90 120

time (s)

local moisture [%]

3

7

11

drag force [N]

wet paste fluiddry

W/P 0.326

∆∆∆∆ ≈ 2.5 L/m3

Moisture content

Moisture content

Composition ≠ Workability

Microstructure + Temperature

Basic principles of in-mixer sensors

• Power curve stabilization level WATTMETERbefore stabilization MIXOMETER

• Drag force under mixing VISCOPROBE, MFMmixer stopped …

• Composition water content Moister metersair entrained …

• Other methods

Other methods

Clagett 1938 - Method of determining the

consistency of concrete mixtures

CONCLUSION

COSTS RHEO

WATTMETER

MIXOMETER

MOISTURE METER

VISCOPROBE

WATTMETER

MIXOMETER

MOISTURE METER

VISCOPROBE

CONCLUSION

Slump (cm): 0 … 10 … 20 …

MOISTURE METER

VISCOPROBE

WATTMETER

MIXOMETER

OUINON NON

OUINON

OUINON

OUI NON

THANK YOU !

Acknowledgement to SKAKO Concrete