Evaluation of Thixotropy of SCC and Inflence on … · and Inflence on Concrete Perfomance ... Positive Aspects of Structural Build-up Reduction in formwork ... constant shear rate

IBRACON, October 9, 2012

Kamal Henri Khayat

54th Congresso Brasilleiro do Concreto

Maceio – Oct. 9, 2012

Evaluation of Thixotropy of SCC

and Inflence on Concrete Perfomance


230-MPa RPC

foot bridge,

Sherbrooke

0

100

200

300

400

0 0.005 0.01 0.015

HPC

RPC + fibers

(pressed and

confined)

Str

ess

(MP

a)

Strain (mm/mm)

NSC

RPC + fibers

0.02

HPC: Concrete with improved mechanical properties & service life

Confederation Bridge, N.B. – PEI

100-year design life


HPC: Concrete with improved workability

Owners:

Material Suppliers:

Engineering Firms:

Testing Labs:

Industrial Research Chair on High-Performance

Flowable Concrete with Adapted Rheology (FCAR)

Inspecsol

Prefab:

IBRACON, October 9, 2012 5

Yie

ld s

tres

s

Plastic viscosity

HPC

SF-SCC

Flowable Mass Conc.

FR-SCC SCC

Underwater Conc.

Rheological parameters of FCAR


6


Recommendations

for Design & Testing

of FCAR

Theme I – Influence of Mixture Constituents, Mix

Design, & Temperature on Rheology of FCAR

Theme III - Rheological Properties and

Granular Flow Modeling

Theme II – Test Methods to Evaluate Flow

Properties of FCAR

IRC Research Program

Theme V - Field Validation and

Guidelines

Theme IV – Mix Design

and Engineering

Properties of FCAR


Conventional

concrete

high passing ability (low t0 + mod. visc.)

low resistance to flow (low t0)

Flow behavior of SCC is complex and must be

optimized to secure adequate performance

high stability (moderate visc.)


1.0 0.8 0.6 0.4 0.2 0

0

1

2

3

4

5

6

7

8

W/CM = 0.47

W/CM = 0.37

F = 650 mm

Speed ( Rev/s )

To

rqu

e (

N m

)

Reduce water content to enhance viscosity


Incorporate VEA to enhance viscosity

1.0 0.8 0.6 0.4 0.2 0

0

1

2

3

4

5

6

7

0

Low VEA

Moderate VEA

Speed (Rev/s)

To

rqu

e (

N m

)

W/CM = 0.47

F = 650 mm


Thixotropy – variation of viscosity with time at constant shear

rate (reversable)


Negative Aspects of Structural Build-up

Multi-layer casting

After 5 min of rest time,

the 2 layers can mix well

After 20 min of rest time, the

2 layers do not mix at all

Casting point


Negative aspect of structural build-up (thixotropy)


Positive Aspects of Structural Build-up

Reduction in

formwork pressure

after casting due

to structural build-

up at rest

Improved static

stability 50%


Factors Affecting Form Pressure of CVC

- Fluidity level

- Casting rate

- Coarse aggregate volume

- Binder content and type

- Presence of admixtures

- Temperature of fresh concrete

- Minimum dimension of formwork

- Degree of vibration

- Etc.

Rodin, 1952

Effect of Consistency Level

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100 150 200 250 300 350

Time after casting (min)

P(m

axim

um

) / P

(hyd

rosta

tic)

SF =

750 mm

SF = 650 mm

SF = 550 mm Slump = 220 mm

HRWRA

w/cm = 0.40

S/A = 0.46

Ternary cem. = 450 kg/m3

PC

R = 10 m/h

H = 2.8 m

D = 200 mm

Lift height = 3.5 m

W = 0.9 m (9 x 4 m)

R ~ 1 m/hr

Lift height = 2.8 - 3 m

W = 0.2 m R ~ 2 m/hr


Lift height > 3 m

W = 0.15 m

R ~ 8-10 m/hr


Normal concrete with slump < 175 mm at time of casting

Immersion of vibrator < 1.2 m in fresh concrete. Underneath concrete is not re-vibrated

R ≤ 4.5 m/h

ACI 347-04 [Hurd, 2002]

Pmax

Cas

ting

dept

h (H

)

Lateral pressure

Pumping from bottom:

Pmax = γc H + 25% pump surge pressure

max

785(kPa) 7.2

17.8

w c

Rp C C

T

Columns (R and H not specified) or walls with R < 2.1 m/h, H ≤ 4.2 m

Cw : Unit weight coefficient Cc : Chemistry coefficient

w max w c

max

30 C (kPa) P 150C C (kPa)

P cH

max

1156 244(kPa) 7.2

17.8 17.8

w c

Rp C C

T T

Walls (R < 2.1 m/h, H > 4.2 m) or walls 2.1 < R < 4.5 m/h, H not specified


Modified ACI 347-04 [Hurd, 2002]

Density (kg/m3) Cw : Unit weight coefficient

< 2240 Cw = 0.5 [1 + w/2320] ≥ 0.80

2240 -2400 Cw = 1.0

> 2400 Cw = w/2320 kg/m3

Cc: Chemistry coefficient Cc

Cem

ent

typ

e o

r b

len

d

Type I, II, III without retarders 1.0

Type I, II, III with retarders 1.2

Other types or blends containing < 70% slag or 40% FA without retarder

Other types or blends containing < 70% slag or 40% FA with retarder 1.4

Blends containing > 70% slag or 40% FA

Retarders (set retarder, retarder water reducer, retarding midrange WRA, or HRWRA) that delay setting


Various models to evaluate lateral

pressure R T H Form

width Time ρ Thixotropy Slump

Set

time

Waiting

period

1- ACI 347-04 x x x x

2- U.K. (CIRIA Report 108) x x x x

3- Japan - Standard

Specifications for Concrete

Structures (2002)

x x x x

4- Sweden (Design of Vertical

Concrete Formwork) x x x

R = Rate of casting

T = Temperature

H = Casting depth


Various models to evaluate lateral

pressure R T H Form

width Time ρ Thixotropy Slump

Set

time

Waiting

period

1- ACI 347-04 x x x x

2- U.K. (CIRIA Report 108) x x x x

3- Japan - Standard

Specifications for Concrete

Structures (2002)

x x x x

4- Sweden (Design of Vertical

Concrete Formwork) x x x

5- Khayat & Assaad [2005] x x x x

6- Roussel and Ovarlez [2005] x x x x x

7- Lange et al., [2005] x x x x

8- Khayat & Omran [2009] x x x x x x x

9- DIN 18 218 :2010-01 (2010) x x x x

10- Gardner et al., 2011 x x x S-

flow loss

R = Rate of casting

T = Temperature

H = Casting depth


Outline

• Thixotropy determination: structural breakdown

and structural build-up at rest

• Thixotropy vs. form pressure exerted by SCC

• Structural build-up vs. drop in interlayer bond


0

40

80

120

160

0 200 400 600 800 1000 1200

Time (s)

= fixed

= 0.03 s-1

sample at rest

Sh

ea

r s

tre

ss

(P

a)

Structural build-up

(flocculation, coagulation)

Thixotropy – variation of viscosity (or shear stress) with time under

constant shear rate - structural build-up when left at rest (reversible)

Modified MK-III

rheometer


4 minutes resting time

Importance of Restructuring !!

0

300

600

900

0 5 10 15 20 25

Time (sec)

Vis

co

sit

y o

f c

on

cre

te (

Pa

.s)

2 minutes resting time

N = 0.9 rps

Formwork pressure = f (restructuring of the concrete)

Slump = 200 mm

450 kg/m³ of binder

w/cm = 0.42

VMA


0

200

400

600

800

1000

1200

1400

0 15 30 45 60

∆η

ap

p @

N=

0.7

rp

s (P

a.s

)

Rest time (min)

1. Structural breakdown: drop in app. viscosity (∆ηapp

)

Typical SCC mixtures

Shear rate (1/s)

Sh

ea

r s

tre

ss

(P

a)

t i

t e . h app, e

h app, i

Time (s)

Sh

ear

stre

ss (

Pa

)

t e

t i

i eapp

t th

0.7 rps .


Time intervals for assessing thixotropy

1

Time (min)

Ro

tati

on

al s

pe

ed

(rp

s)

0.3 rps

0.5 rps

0.7 rps

0.9 rps

Rest of 5 min

Testing & rehomogizing = 2.5 min

T = 0 - 30 min


1

Sh

ea

r s

tre

ss

(P

a)

0

200

400

600

800

0 5 10 15 20 25

Time (sec)

0

200

400

600

800

0.2 0.4 0.6 0.8

Rotational speed (rps)

Ab1 (J/m³.s)

N = 0.3 rps

N = 0.9 rps N = 0.5 rps

N = 0.7 rps

1. Structural breakdown: structural breakdown area (Ab1)

τ τ

0.9

3

1 i e

0.3

Lapasin et al. [1983] Ab = (N)- (N)dN J/m .s


0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 10 20 30 40 50

Lateral pressure (kPa)

Heig

ht

of

co

ncre

te (

m)

rgh

at casting

~ 50% after 4 hr

R = 10 m/hr

Lateral pressure envelope of SCC

Slump flow = 650 mm

60 70

H = 2.8 m

D = 200 mm


Thixotropy vs. Lateral Pressure

0

20

40

60

80

100

50 200 350 500 650 800

Breakdown area (J/m³.s)

P(m

ax

imu

m)

/ P

(hyd

ros

tati

c)

(%)

Ab1 vs. Pressure at 0 min;

R² = 0.89 Ab2 vs. Pressure at 100 min;

R² = 0.85 Ab3 vs. Pressure at 200 min;

R² = 0.84

70 SCC

mixtures


R ~ 6-10 m/hr


Typical Formwork Pressure Diagram

0

1

2

3

4

5

6

0 20 40 60 80 100 120

Pressure developed on formwork (kPa)

He

ad

of

co

nc

rete

(m

)

Hydrostatic pressure

Slump flow = 720 mm

S/A = 0.50

Ternary cement = 475 kg/m³

w/cm = 0.40

R = 6.5 m/h

right after casting

1 h 3 h

P(max)



P(m

ax

imu

m)

/ P

(hyd

ros

tati

c)

0.0

0.2

0.4

0.6

0 200 400 600 800 1000 1200

Pressure Variations with Thixotropy

BIN-0.50-Nap (Ab1 = 260 J/m³.s)

TER-0.50-Nap

(310 J/m³.s)

TER-0.44-Nap

(405 J/m³.s)

S / A

PNS

R = 6 m/h

R = 6.5 m/h

R = 7.5 m/h


0

40

80

120

160

0 200 400 600 800 1000 1200 Time (s)

= fixed

= 0.03 s-1

sample at rest

Sh

ear

stre

ss (

Pa)

Structural build-up

(flocculation, coagulation)

Structural build-up: increase in shear stress (or viscosity)

when the material is left at rest

2. Structural build-up at rest: Re-structuring


0

500

1000

1500

2000

2500

0 15 30 45 60

Rh

eom

eter

-τ0

rest

(Pa)

Rest time (min)

Static shear stress at rest (τ0rest)

R(t) (Pa/min)

Ri (Pa)


w/p 0.37-0.47

Slump flow 600-720 mm N = 0.03 rps

0.00

0.05

0.10

0.15

0.20

0 5 10 15 20

To

rqu

e (N

.m)

T max

Time (sec)

RixR(t), (Pa2/min)


Portable vane (PV) test


w/p 0.37-0.47

Slump flow 600-720 mm

0

2000

4000

6000

8000

10000

0 15 30 45 60 75 P

V τ

0res

t (P

a)

Rest time (min)

τ0rest = Tmax /G


Motion takes place in the form of

planer fluid layers gliding over each

others in the direction of the slope

r = density of sample

g = gravitation constant

h = mean central height of slumped sample

a = critical angle of plane at flow start

sins ght r a

Step 1

60 mm

120 mm

Step 2

a

Step 3

Inclined plane (IP) test


Inclined plane (IP) test

r = density of sample

g = gravitation constant

h = mean central height of slumped sample

a = critical angle of plane at flow start

0 sinrestIP ght r a0

200

400

600

800

1000

0 10 20 30 40 50

Rest time (min)

IP t

0res

t (P

a)


w/p 0.37-0.47

Slump flow 600-720 mm


y = 0.95 x R² = 0.82

0

300

600

900

1200

0 300 600 900 1200 1500

IP τ

0res

t (P

a)

Rheometer τ0rest (Pa)

Yield stress at rest: PV and IP tests vs. rheometer

y = 1.00 x R² = 0.82

0

500

1000

1500

2000

2500

0 1000 2000 3000

PV

τ0

rest

(P

a)

Rheometer τ0rest (Pa)

Good relationships between static yield

stress from PV and IP vs. rheometer

Data at 15 min rest time


• ρ: unit weight of SCC

• H: casting depth in the form

• R: casting rate

• T: concrete temperature

• Dmin: formwork width

• TI: thixotropy index:TI@fixed temperature (22ºC) or TI@various temperature (ti).

Thixotropy as input to evaluate formwork

pressure for SCC

P

Pmax = ρgH [a1H + a2R + a3T + a4Dmin + a5TI@fixed Temp.]

Pmax = ρgH [a1H + a2R + a3T + a4Dmin + a5TI@various Temp.]

RMC Research & Education Foundation

Strategic Development Council of ACI

SDC Members (2007 – 2009)


Pressure device to determine

lateral pressure

Digital

manometer to

control overhead

air pressure

(up to 13 m high)

190 mm

63 mm

577 m

m

700 mm

63 mm

Fresh

concrete

500 mm

19 mm

19 mm Pressure

sensor

Pressure

sensor

Honeywell pressure

sensor

(1400-kPa capacity)


Pressure variations

0

40

80

120

160

200

240

280

320

0 20 40 60 80 100 120 140

Pre

ss

ure

(k

Pa

)

Time (min)

Hydrostatic pressure

H = 0.5 m

H = 0.35 m

SCC4

Ф= 560 mm

R = 10 m/hr

VMA = 2.8 L/m3

Sudden

increase in

pressure

reflects "blow-

up" of

overhead

pressure at

sensor location decrease in pressure

reflects material

restructuring

Reach to hydrostatic

0

40

80

120

160

200

240

280

320

0 20 40 60 80 100 120 140

Lat

eral

pre

ssu

re (

kPa)

Time (min)

= 560 mm

R = 10 m/hr

Eq. hydrostatic pressure

H = 13 m @ 72 min


2

4

6

8

10

12

14

0 50 100 150 200 250

Lateral pressure (kPa) C

asti

ng

dep

th (

m)

560 mm 660 mm

Slump flow

0 50 100 150 200 250 300

400 l/m3

370 l/m3

340 l/m3

Paste volume

Use of pressure device to validate mix design

R = 10 m/hr

Hydrostatic

pressure


NCSS, 2007 software

800 data points to

derive models

H = 1 - 13 m

R = 2 - 30 m/h

T = 10 - 32 ºC

γc = unit weight (e.g. 23.5 kN/m3)

d = min. formwork dimension

(0.2 – 1.0 m)

Dmin = Equivalent to d

For 0.2 < d < 0.5 m, Dmin = d

For 0.5 < d < 1.0 m, Dmin = 0.5 m

t

t

cmax min MSA WT0

cmax min MSA WT

cmax

rest@15 min

0rest

HP = 112.5 - 3.8 H + 0.6 R - 0.6 T + 10 D f × f

100

HP = 109.5 - 3.9 H + 0.7 R - 0.6 T + 3 D f × f

1

- 0.021 PV

- 0.29 P00

HP = 106 - 4 H + 0.6 R -

100

V (t)

t t0rest@15min 0rmin MSA Wes Tt 0.63 -T + 10 D 0.00015 PV × PV (t f × f)

Empirical models for K0 = f (H, R, T, D

min, PV

thixo index)


Empirical models for K0 = f (H, R, T, D

min, IP

thixo index)

K0 = [112 - 3.83 H + 0.6R - 0.6T + 0.01Dmin - 0.023 IPτ0rest@15min] x fMSA x fWT

0

20

40

60

80

100

0 400 800 1200 1600 2000

K0 (

%)

IPτ0 rest@15min (Pa)

K0@H=1m K0@H=2m

K0@H=4m

K0@H=6m

K0@H=8m

K0@H=10m

K0@H=12m

R = 2 m/hr

T = 22 oC

Dmin = 200 mm

MSA = 14 mm

Waiting Time = 0

Static yield stress after 15 min of rest [Ri] (Pa)


Effect of casting rate on lateral pressure characteristics

0

20

40

60

80

100

0 10 20 30

K0

(%)

Casting rate (m/hr)

SCC40

SCC51

SCC52

SCC53

SCC54

SCC46

SCC55

SCC56

H = 3 m

(

(High

thixotropy)

Pressure can be reduced by:

lowering casting speed, or

increasing thixotropy


PVτ0rest@15min = 1200 Pa

R (m/hr)

1 2 5 10 15 20 25 30

H (

m)

0 0 0 0 0 0 0 0 0

1 17 17 17 18 19 19 20 21

2 32 32 33 34 35 37 38 40

3 45 45 46 49 51 53 55 57

4 56 57 58 61 64 67 70 72

5 66 67 69 72 76 79 82 86

6 74 75 77 81 85 90 94 98

7 80 81 84 89 94 98 103 108

8 84 86 89 94 100 105 111 117

9 87 88 92 98 105 111 117 123

10 88 89 94 100 107 114 121 128

11 87 89 93 101 108 116 124 131

12 85 86 93 100 108 116 124 133

13 80 82 91 96 105 114 123 132

< 50 kPa

50- 80 kPa

80 - 110 kPa

110 - 140 kPa

140 - 170 kPa

>170 kPa

PVτ0rest@15min = 200 Pa

R (m/hr)

1 2 5 10 15 20 25 30

H (

m)

0 0 0 0 0 0 0 0 0

1 22 22 22 23 23 24 25 26

2 41 42 42 44 45 47 48 49

3 59 60 61 63 65 67 69 71

4 76 76 78 81 83 86 89 92

5 90 91 93 96 100 103 107 110

6 103 104 106 110 114 119 123 127

7 114 115 118 123 127 132 137 142

8 123 124 128 133 139 144 150 155

9 131 132 136 142 148 154 161 167

10 136 138 142 149 156 163 170 177

11 140 142 147 154 162 169 177 185

12 143 144 151 158 166 174 183 191

13 143 145 154 159 168 177 186 195

Charts for relative lateral pressure K0


Integrated research laboratory on materials valorization and

innovative and durable structures - 2007-2009


Snap

form ties Tie clamps

16 mm bars

@ 30 x 40 cm

Formwork

Wall

# 7

Wall

# 8 Wall

# 6

2 walls/day

Sheathing

& form ties Wall

studs &

Wales


Level 1000, H = 3.7 m

(effect of casting rate)

Level 2000, H = 4.4 m

(effect of thixo.)

Wall #1 VCC

Wall #2 SCC1

Wall #3

SCC1

Wall #4

SCC1

Wall #5

VCC

Wall #6

SCC1

Wall #7

SCC2

Wall #8 SCC3

Slump/ slump flow (mm)

120 ± 30

650 ± 25 120 ±

30 650 ± 25

HRWRA type --- PCP --- PCP PNS

Vp (L/m3) --- Low, 330 --- Low 330

High 370

Low 330

R (m/hr) 7.5 5 10 15 7.5 10

W/CM 0.40 0.35 0.40 0.37 0.35 0.42+VMA

Air content < 3.5%, concrete temp. = 22 – 25 oC

Investigated parameters


Full characterization

10 persons to carry out > 17 tests

H2

H1

h2 = 150 - H2

h1 = 600 - H1

H2

H1

h2 = 150 - H2

h1 = 600 - H1

Strength

Shrinkage


Lateral pressure [wall # 6, SCC1, R = 10 m/h]

0

10

20

30

40

50

60

70

0 200 400 600 800 1000 1200

Time (min)

Pmax (kPa)

1.2 m PVC

column

@ 1.82 m @ 2.33 m

@ 3.85 m from top

@ 3.34 m

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

0 20 40 60 80 100

Fo

rmw

ork

hei

gh

t (m

)

Pmax (kPa)

Hydrostatic

pressure

@2 hr

@6 hr Pmax

formwork base

@4 hr


8 full-scale R/C columns

Mixture Relative

thixotropy

Casting rate (m/h)

2 5 5 +

20’ WP 10 13 15 22

SCC-L Low -- -- -- -- Col.#1 -- Col.#2

SCC-M Medium -- Col.#7 Col.#8 --

SCC-H High Col.#5 Col.#3 -- Col.#4 -- Col.#6 --


ACI 347-04 vs. field measurements

Casting rate limited to 4.5 m/h (ACI 347-04)

Walls and columns cast of ≤ 5 m/h are considered

max W C

785P = C C 7.19 +

17.78

R

T

y = 1.16x R² = 0.62

0

20

40

60

80

100

0 20 40 60 80 100

Pre

dic

ted

Pm

ax (

kPa)

Measured Pmax in field (kPa)

Wall element #2

3 columns (# 3, 5, 7)

Cc : Chemistry coefficient = 1.2

Limited data


Khayat & Omran [2009] vs. field measurements

y = 1.01 x R² = 0.97

0

20

40

60

80

100

0 20 40 60 80 100

Mea

sure

d P

max

in f

ield

(kP

a)

Predicted Pmax (kPa)

C… C…

8 column elements

6 wall elements cast

with SCC


Round-Robin Tests for prediction of form pressure (May 2012)

:.

Member Special property to be measured

T. Proske, Germany Setting time

M. Beitzel, Germany Structural build up / BT2

N. Roussel, France Structural build up / Plate test

K. Khayat, USA Structural build up / Inclined plane,

Portable Vane

A. Omran, Canada Pressure column

D. Lange, USA Pressure decay

J. Gardner, Canada Slump loss

Y. Vanhove, France Friction stress / Tribometer


Outline






Structural build-up can lead to aesthetic problems in terms of

casting folds in multi-layer placements

New layer

(U de Sherbrooke, 1997)

Top layer

Bottom layer

Lift line


Interlayer bond strength (slanted shear strength)

Casting

30º

Small notch

1

2

100 mm

20

0 m

m

1

2

2 1

1

2


Variation of residual bond strength with thixotropy and

delay time between successive lifts

0

20

40

60

80

100

0 10000 20000 30000 40000 50000 60000 70000 80000 90000 100000

Re

sid

ual

bo

nd

str

en

gth

, %

Thixotropy index from PV, Pa.Pa/min

Delay time = 0 min

15 min

30 min

45 min

60 min

P

P


Statistical model

RBS = Residual bond strength

DT = Delay time between 2 layers

30

40

50

60

70

80

90

100

010

2030

4050

60

10000

20000

30000

40000

50000

60000

70000

80000

90000

Re

sid

ua

l B

on

d s

tre

ng

th,

(%)

Delay time, (m

in)ts(15) R

SBU , (Pa.Pa/min)

R2 = 0.99

90%

80%

70%

60%

0.1608 1.0922 % Ln 100 Eq. E.10SSh PVthix2RB DT A DT


Residual bond strength

1

2

Casting point

100 mm

200 mm

200 mm

100 mm

Flexural stress

150 mm

25 mm

100 mm

25 mm

50 50 50 mm

1 2

Casting point

1

2

Direct shear stress

P

P/2 P/2


Variation in residual bond with thixotropy and test methods

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80 90 100

A thix , Pa.Pa/min × 1000

tc , m

in

Critical delay time to reach 90% residual bond strength


• Thixotropy of SCC can be assessed by structural breakdown


• Breakdown area (Ab) or drop in apparent viscosity to assess

thixotropy are determined using concrete rheometer

• Structural build-up at rest can be determined as:

Variation of drop in apparent viscosity with time using

concrete rheometer

Variation of static yield stress at rest using concrete

rheometer

Variation of static yield stress at rest using empirical tests

(inclined plane and portable vane tests)

Conclusions


Conclusions

• Increase of thioxotropy leads to reduction in form pressure

exerted by SCC

• Residual interlayer bond of SCC increases with decrease

thixotropy (structural build-up at rest)

• Long delayed time between casting two successive SCC

layers leads to reduction in interlayer bond

• Residual inter-layer bond strength is more critical in shear

than in flexural or compression failure modes


NRMC Research & Education Foundation, ACI Foundation

NSERC IRC HP-Flowable Concrete with Adapted Rheology

J. Assaad, A. Omran, W. Magdi

S. Naji, P. Billberg, A. Yahia,

O. Bonneau, N. Petrov

R. Morin, M. D’Ambrosia

Acknowledgment


Outline





• Mixture parameters affecting thixotropy (form

pressure) of SCC

Effect of Consistency Level

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100 150 200 250 300 350


P(m

ax

imu

m)

/ P

(hyd

ros

tati

c)

SF =

750 mm

SF = 650 mm

SF = 550 mm Slump = 220 mm

HRWRA

Slump flow = 650 mm

w/cm = 0.40

S/A = 0.46

Ternary cement = 450 kg/m3

PC HRWRA

R = 10 m/h

Effect of Set-Modifiers (Cohesion)

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100 150 200 250 300 350


P(m

ax

imu

m)

/ P

(hyd

ros

tati

c)

Set-retarding

agent

Set-accelerating

agent

Without set-

modifying agent

Slump flow = 650 mm

w/cm = 0.42

Sand-to-total agg. = 0.44

Ternary binder = 450 kg/m3

Effect of HRWRA Type

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100 150 200 250 300 350


P(m

ax

imu

m)

/ P

(hyd

ros

tati

c)

Melamine

HRWRA

Naphthalene

HRWRA

Polycarboxylate

HRWRA

Slump flow = 650 mm

w/cm = 0.36

Sand-to-total aggregate ratio = 0.46


Effect of powder polysaccharide-based VEA

content with variable SP dosages

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100 150 200 250 300 350 400


P(m

axim

um

) /

P(h

yd

rosta

tic)

N-no VEA

(reference SCC )

high VEA dosage

low VEA dosage

Slump flow = 650 mm

w/cm = 0.40

Sand-to-aggregate ratio = 0.46


Naphthalene

HRWRA

Incorporation of low thickener VEA in SCC with 0.40

w/cm can lead to lower lateral pressure than in SCC

with 0.36 w/cm and no VEA

Medium or high content of polysaccharide-based

VEA + PNS-based HRWRA resulted in higher

residual pressure and lower rate of pressure drop

after casting compared to SCC with low dosage of

VEA (attributed to increased HRWRA demand)

Similar results with cellulose VEA + polycarboxylate-

based HRWRA

Effect of Stabilizers

Effect of Thickner Type (low concentration)

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100 150 200 250 300


P(m

ax

imu

m)

/ P

(hyd

ros

tati

c)

C-Cell-L

N-Poly-L

N-Pow-L M-PC-L

Slump flow = 650 mm

w/cm = 0.40



Mixtures incorporating TEA exhibited the lowest

initial pressure and the fastest rate of pressure drop

Unlike conventional VEA, increase in TEA lead to

further reduction in initial pressure and increased

rate of drop in pressure

Effect of Stabilizers

Effect of Binder Type

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100 150 200 250 300 350


P(m

ax

imu

m)

/ P

(hyd

ros

tati

c)

6% SF +

22% FA

8% SF

Type I cement

Type III cement

Binder content =

450 kg/m³

Slump flow = 650 mm

w/cm = 0.40

S/A = 0.46

500 kg/m³

450 kg/m³

550 kg/m³

Effect of Binder Content

0.4

0

0.5

0.6

0.7

0.8

0.9

1.0

50 100 150 200 250 300 350


P(m

ax

imu

m)

/ P

(hyd

ros

tati

c)

400 kg/m³

Slump flow = 650 mm

w/cm = 0.40

Sand-to-total agg. = 0.46

Ternary cement

Effect of w/cm

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100 150 200 250 300 350


P(m

ax

imu

m)

/ P

(hyd

ros

tati

c)

w/cm = 0.36

Slump flow = 650 mm


Polycarboxylate-based HRWRA


w/cm = 0.46

w/cm = 0.40 Higher

HRWRA dosage

Effect of S/A (Internal Friction)

0.5

0.6

0.7

0.8

0.9

1.0

0 100 200 300 400


P(m

ax

imu

m)

/ P

(hyd

ros

tati

c)

Slump flow = 650 mm; w/cm = 0.40


R = 1.0

R = 0.75

R = 0.50

R = 0.40

R = 0.36 R = 0.30

R : sand-to-total

agg. ratio

Statistical models to predict: K0@Hi, ∆K(t), tc U

nit

s Predicting model in CODED values

(, Vca, S/A ) = -1 to +1 R2

Relative

error 95%

conf. limit

(%)

K0 at

var

iou

s H

% K0@H=4 m = 82 - 3.175 Vca - 3.015 + 1.6875 S/A + 0.9 . Vca 0.94 2.4

% K0@H=8 m = 67.2 - 4.7275 Vca + 4.0675 + 1.96 S/A + 1.1775 . Vca 0.94 2.3

% K0@H=12 m = 53.5 - 6.2775 Vca + 5.1175 + 2.2325 S/A 0.91 4

∆K

(t) %/min ΔK(t)(0-60min) = 0.1683 + 0.0325 Vca - 0.0175 S/A - 0.0075 S/A. Vca 0.98 1.4

%/min ΔK(t)(0-tc) = 0.16 - 0.00625 + 0.0044 S/A + 0.0006 Vca 0.88 4.6

t c

min tc = 587.7 - 48.56 Vca + 38.06 + 24.19 S/A + 9.9375 .S/A 0.98 5.5

Contour diagrams

= 720 mm

S/A, by volume

Vc

a, b

y v

olu

me

K0@H=4m (%)


Conclusions

• Thixotropy of SCC can be assessed by structural breakdown


• Breakdown area (Ab) or drop in apparent viscosity to assess

thixotropy are determined using concrete rheometer

• Structural build-up at rest can be determined as:

Variation of drop in apparent viscosity with time using

concrete rheometer

Variation of static yield stress at rest using concrete

rheometer

Variation of static yield stress at rest using empirical tests

(inclined plane and portable vane tests)


Conclusions

• Increase of structural breakdown or structural build-up at

rest leads to reduction in form pressure exerted by SCC

• Residual interlayer bond of SCC increases with decrease in

structural build-up at rest

• Long delayed time between casting two successive SCC

layers leads to reduction in interlayer bond

• Residual inter-layer bond strength is more critical in shear

than in flexural or compression failure modes

• Key parameters affecting thixotropy are similar for form

pressure and interlayer bonds characteristics

Conclusions 1/2

SCC of high thixotropy can exhibit:

lower initial lateral pressure

faster drop in pressure with time

Field studies validate importance of thixotropy

on form pressure characteristics

Conclusions 2/2

Formwork pressure of SCC = f (shear strength properties)

1) Internal friction Maximum initial pressure

(higher aggregate volume, lower binder content

and w/cm, use of SCM, lower consistency level, ...)

2) Cohesion Rate of pressure drop with time

(higher binder content, use of SCM and set-

accelerator, lower HRWRA, higher temperature,

lower consistency level, ...)





Documents

Evaluation of Thixotropy of SCC and Inflence on … · and Inflence on Concrete Perfomance ... Positive Aspects of Structural Build-up Reduction in formwork ... constant shear rate