Influence of Pumping on Fresh Concrete Properties for SCC - American Concrete · PDF file · 2017-08-05Institut für Keramik, Glas- und Baustofftechnik I Professur Baustofftechnik

Institut für Keramik, Glas- und Baustofftechnik I Professur BaustofftechnikACI Spring 2015 – Monday April 13th

Pumpability of Self Consolidating Concrete

Influence of Pumping on Fresh Concrete

Properties for SCC

Thomas A. BIER – Keisuke TAKAHASHI

Professorship for construction materials

Institute of Ceramic, Glass and Construction Materials

Faculty of Mechanical, Process and Energy Engineering



Outline

Earlier Experiences

Field Trials

Literature on Mixing

Materials and Testing

Macrolevel

Influence on rheological Properties and workability

Microlevel

Hydration, Chemistry and Microstructure

Concept and Summary

Conclusions



Abstract

During field trials, involving pumping of self compactingconcrete, changes in rheological properties have been observed. Inorder to predict possible changes, studies were undertaken on selfcompacting mortar (SCM) where various mixing as well aspumping intensities were applied. As a result not only changes inrheological properties but also changes in hydration kinetics wereobserved. It has been shown that mixing and shear stress duringpumping, respectively, do exhibit a pronounced influence onrheological properties of self-compacting mortars. The changes inrheological properties can be explained by the dispersion of theparticles as well as an accelerated formation of pre-hydratesduring early hydration.



Process Chain Underground Pumping



Process Chain Underground Pumping



Slump Flow Value

F1 F2 F3

650

660

670

680

690

700

710

720

730

740

750

760

770

780

Slu

mp

[m

m]

Truck No.

CEMIaboveground CEMIunderground CEMIIaboveground CEMIIunderground

Self Compacting Concrete Underground ; Dahlhaus, Bier et. al, Ibausil, 2006



Slump Flow Time

-- F1 F2 F3

2

4

6

8

10

12

14

16

18S

lum

p t

ime t 5

0 [

s]

Truck No.

CEMIaboveground CEMIunderground CEMIIaboveground CEMIIunderground

Self Compacting Concrete Underground ; Dahlhaus, Bier et. al, Ibausil, 2006



Mixing time and mixing speed

Lowke, D.; Schießl, P.: Effect of mixing energy on fresh proporties of SCC in: Proceedings of the 4th International

RILEM Symposium on Self-Compacting Concrete, Chicago, USA, 2005

Optimum mixing time: SCC. B is longer than SCC. AChemical additive contents: SCC. C is higher than SCC. B



Mixer

Pressurized vesselMortar

Pressure regulator

Pressure gauge

Nitrogen gasholder

Gas regulator

Pressurization apparatus

1100rpm

Handheld mixer

Mortar

Handheld mixer

All tests were conducted at 20 ˚C using the same mortar mixed for 2 min.

Measured pumping pressure was 2 MPa @ 50 m and 3 MPa @ 100 m.

Snake pump

Composition of Materials

Cement Sand PCE HMC Others* Water

Grout 389 583 0.68 0.003 27.3 155

Cement paste 565 0 0.99 0 0 225



Mixer

Pressurized vesselMortar

Pressure regulator

Pressure gauge

Nitrogen gasholder

Gas regulator

Factors Pumping Mixing Pressurization Sedimentation

Para-

meters

Pumping

distances

Additional mixing

periods

Pressure values Sedimentation

periods

0, 50 and 100 m 0, 3 and 5 min 0, 2 and 3 MPa 0, 3 and 5 min

Pressurization apparatus

1100rpm

Handheld mixer

Mortar

Handheld mixer

All tests were conducted at 20 ˚C using the same mortar mixed for 2 min.

Measured pumping pressure was 2 MPa @ 50 m and 3 MPa @ 100 m.

Snake pump

Testing methods



Flow Curves

Shear stress vs. shear rate

0

50

100

150

200

250

300

350

400

450

500

0 25 50 75 100

Shea

r st

ress

(Pa

)

Shear rate (sec-1)

Before pumping (0 m)

After pumping (50 m)

After pumping (100 m)

0

50

100

150

200

250

300

350

400

450

500

0 25 50 75 100

Shea

r st

ress

(P

a)

Shear rate (sec-1)

1 min of mixing

2 min of mixing

5 min of mixing

7 min of mixing

Pumping Mixing



Rheographs:

Effects of several factors on rheology

-1

1

3

5

7

9

11

0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4

Yie

ld s

tre

ss

Plastic viscosity

Pumping

mixing

Pressurization

SedimentationRef.

0.85

0.90

0.95

1.00

0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 F

low

va

lue

J14 efflux funnel time

Pressurization

Sedimentation

Pumping

mixing

Ref.

Reference point: after 2 min of mixing or before pumpingMixing: 1→2→5→7 min, Pumping distances: before→after 50m→after 100mPressurization: 0→2→3MPa, Sedimentation: 0→3→5 min



-1

1

3

5

7

9

11

0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4

Yie

ld s

tre

ss

Plastic viscosity

Pumping

mixing

Pressurization

SedimentationRef.

0.85

0.90

0.95

1.00

0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 F

low

va

lue

J14 efflux funnel time

Pressurization

Sedimentation

Pumping

mixing

Ref.

Shearing action during mixing and pumping process as well does exhibit the most pronounced effect

Pressurization and sedimentation induce only little changes Efflux time and flow value correspond to viscosity and yield stress, respectively

Rheographs:

Effects of several factors on rheology



αβ γ εδ

Elapsed time (h)

Hea

t re

leas

e ra

te (

mW

/g)

0 12 24

Hydration is

exothermal reaction

dissolution–precipitation process

12/34

The early hydration process

Calorimetry curve for OPC paste



αβ γ εδ


Elapsed time (h)

Hea

t re

leas

e ra

te (

mW

/g)

0 12 24

Pre-induction (α) and induction (β) periods

Initial dissolution and precipitationthat provide a coating of hydrates(metastable layer, Stein, J. appl. Chem. 1964)

Set up of concentration gradient due to

the increase of Ca2+ at the interface

(electrical layer, Juilland, CCR, 2010)

C3S, C3A +H2OCSH(m), Ettringite

The layers slow down the reaction rate




αβ γ εδ

Elapsed time (h)

Hea

t re

leas

e ra

te (

mW

/g)

0 12 24

Accelerated period (hardening process)

Metastable layer continuously dissolves

+H2OC3S, CSH(m) CSH(s) + Ca(OH)2

Set and increase in strength

Ca2+ & OH- increase slowly and approachthe critical supersaturation of Ca(OH)2

Ca(OH)2 and CSH grow at an exponential rate (massive hydration, 2nd peak)





0

1

2

3

4 8 12 16 200 24

2 min

1 min

7 min

Elapsed time (h)

Heat

rele

ase r

ate

(m

W/g

)

With increasing mixing time,

Initial dissolution rate at a given

time became more pronounced

(accelerated)

Start of massive hydration was

advanced (accelerated)

Second peak of the calorimetric

curves increased

Close Up

Hydration and Calorimetry



1 2 3 4 5 6 70.20

0.24

0.28

0.32

0.36

Am

ou

nt o

f P

CE

ad

so

rptio

n p

er

un

it S

BE

T (

mg

/m2)

SB

ET (

m2/g

)

Am

oun

t o

f P

CE

co

nsu

mp

tio

n (

mg

/g)

Mixing/settling time (min)

1

2

3

4

5

6

0.04

0.08

0.12

0.16

0.20

As mixing time became longer, Amount of PCEconsumption in thesolution phaseincreased▲ SBET increasedsignificantly PCE adsorption perunit SBET decreased

Sedimentation has little change

Adsorption behavior of PCE

in fresh cement paste

Extended surface area by mixing increases PCE consumption and

subsequently causes degrading changes in fluidity

Solid: mixing Dashed: sedimentation



Mechanism for changes in fluidity

Active PCE adsorb onto hydrates and disperse cement particles

Cement particle

Active PCE

Immediately after

adding water

After repetition, active

PCE decreases

Hydrates

Scraped

off

Inactive PCE

Adsorption of PCE Abrasion by shearing

action

Shearing action (dominanting factor) = Further hydrates formation

Loss in fluidity



Observation

Mechanisms

Graphical Summary and Concept

Micro-Level

Macro-Level

Technological

Properties



Conclusions

With extended mixing or pumping distance• Yield stress and flow value decrease

• Viscosity and efflux time increase

Analysis results using rheographs indicate• Shear stress during mixing and/or pumping is a major factor

influencing mortar rheology

On a microstructural level • the consumption of active PCE in solution,

• the increase in specific surface area of the cement

• and a subsequent decrease for PCE per unit SBET

can explain a change in state of dispersion and the

observed changes in rheological properties



Thank you for your attention!

Documents

Influence of Pumping on Fresh Concrete Properties for SCC - American Concrete · PDF file · 2017-08-05Institut für Keramik, Glas- und Baustofftechnik I Professur Baustofftechnik