Test Methods to Evaluate Structural Various Models to ... · 0 200 400 600 800 1000 1200 Time (s) ... PV test IP test Correlations using CEM Mixtures. ACI Spring Convention – Minneapolis

ACI WEB SESSIONS

Field Measurements of Form Pressure Exerted by Self-Consolidating Concrete

ACI Spring 2013 ConventionApril 14 - 16, Minneapolis, MN

ACI WEB SESSIONS

Kamal H. Khayat, Ph. D., received his B.S., M.Eng., and M.S. in civil engineering with emphasis in structural engineering, construction engineering and management and a Ph.D. in civil engineering with emphasis in civil engineering

materials, all from the University of California at Berkeley. This was followed by a post-doctoral fellowship at the same institute.

Dr. Khayat is active on several technical and code committees, including Chair of ACI (American Concrete Institute) 237 SCC and RILEM (International Union of Testing and Research Laboratories for Materials and Structures) Technical Committee 228 Mechanical Properties of SCC. He served as member of the Canadian Standards Association Committee A23.1/A23.2 Concrete Materials and Methods of Concrete Construction/Methods of Test for Concrete A23.1 and a number of TRB Committees.

ACI Spring Convention – Minneapolis April 14, 20133 3

Test Methods to Evaluate Structural Build-up of SCC and Influence on

Form Pressure

Kamal Khayat, Missouri University of Science & Technology

Ahmed Omran, Université de Sherbrooke, Canada

ACI Spring Convention

Minneapolis - April 14, 2013

RMC Research & Education Foundation

Strategic Development Council of ACI

SDC Members (2007 – 2009)ACI Spring Convention – Minneapolis April 14, 2013

Various Models to Evaluate Lateral Pressure

R T HForm 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 xS‐

flow loss

R = Rate of castingT = TemperatureH = Casting depth

ACI Spring Convention – Minneapolis April 14, 2013

Positive Aspects of Thixotropy

Reduction in formwork pressure after casting due to structural build-up at rest

Improved static stability

50%


Factors Affecting Thixotropy of Concrete

Rodin, 1952

• w/cm• Coarse agg. characteristics• S/A• Vp (paste volume)• Binder type and content• SCMs and fillers• Admixtures

Mix design

Consistency level

Thixotropyor

Structural build-up at rest

Temperature


Outline

• Thixotropy determination:

• structural breakdown

• structural build-up at rest

• Thixotropy vs. form pressure exerted by SCC


0

40

80

120

160

0 200 400 600 800 1000 1200

Time (s)

= fixed

= 0.03 s-1sample at rest

Sh

ear

stre

ss (

Pa)

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 5 10 15 20 25

Time (sec)

Vis

cosi

tyo

f co

ncr

ete

(Pa.

s)

2 minutes resting time

N = 0.9 rps

Formwork pressure = f (restructuring of the concrete)

Slump = 200 mm450 kg/m³ of binderw/cm = 0.42 VMA


R ~ 6-10 m/hr


Typical Formwork Pressure Envelops

0

1

2

3

4

5

6

0 20 40 60 80 100 120

Pressure developed on formwork (kPa)

Hea

d o

f co

ncr

ete

(m)

Hydrostatic pressure

Slump flow = 720 mm S/A = 0.50Ternary cement = 475 kg/m³ w/cm = 0.40

R = 6.5 m/h

right after casting

1 h3 h

P(max)


Time after casting (min)

P(m

axim

um

) / P

(hyd

rost

atic

)

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-0.44-Nap(405 J/m³.s)

S / A

PNS

R = 6 m/h

R = 6.5 m/h


Time Intervals for Assessing Thixotropy

1

Time (min)

Ro

tati

on

alsp

eed

(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

ear

stre

ss (

Pa

)

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 rpsN = 0.5 rps

N = 0.7 rps

1. Structural breakdown: structural breakdown area (Ab1)

τ τ0.9

31 i e

0.3

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


0

40

80

120

160

0 200 400 600 800 1000 1200Time (s)

= fixed

= 0.03 s-1

sample at rest

Shea

r str

ess

(Pa)

Structural build-up

(flocculation, coagulation)

Structural build-up: increase in shear stress (or viscosity) when the material is left at rest

Structural build-up at rest: Re-structuring


0

500

1000

1500

2000

2500

0 15 30 45 60

Rhe

omet

er-τ

0 re

st (P

a)

Rest time (min)

Static Shear Stress at Rest (τ0rest)

R(t) (Pa/min)

Ri (Pa)

Typical SCC mixturesw/p 0.37-0.47

Slump flow 600-720 mmN = 0.03 rps

0.00

0.05

0.10

0.15

0.20

0 5 10 15 20

Torq

ue (N

.m)

Tmax

Time (sec)

RixR(t), (Pa2/min)


Field-Oriented Tests to Evaluate Thixotropy of Flowable Mortar and SCC

Inclined plane

Cone penetration

K-Slump Undisturbed slump spread

Portable vane

Falling ballACI Spring Convention – Minneapolis April 14, 2013

Mortar

Concrete

0 sinrestIP gh

Inclined Plane (IP) Test Free Surface Flow of Thixotropic Fluid

0

200

400

600

800

1000

0 10 20 30 40 50Rest time (min)

IP 0

rest

(Pa)

RixR(t), (Pa2/min)

Typical SCC mixturesw/p 0.37-0.47Slump flow 600-720 mm

R(t) (Pa/min)

Ri (Pa)

60 mm

120 mm

a


Portable Vane (PV) Test

Ri (Pa) R(t), (Pa/min) RixR(t), (Pa2/min)


0

2000

4000

6000

8000

10000

0 15 30 45 60 75

PV τ

0res

t(P

a)

Rest time (min)

τ0rest = Tmax /G


Portable Vane (PV) TestTypical SCC mixturesw/p 0.37-0.47Slump flow 600-720 mm

0

2000

4000

6000

8000

10000

0 15 30 45 60 75

PV τ

0res

t(P

a)

Rest time (min)

τ0rest = Tmax /G


Portable Vane (PV) Test


Undisturbed Slump Spread (USS) Test

USS = (D1+D2)/2

D1

D2

0

100

200

300

400

0 20 40 60 80Rest time (min)

Und

istu

rbed

slum

psp

read

(mm

) Spread below 100 mm is neglected


R(t): (mm/min)


Relative Errors (%) of Tests using SCC Mixtures

Rest time (min) PV test

Thixotropic SCC

15 19

30 12

45 9

Rest time (min) IP test

15 8

20 8

25 8

30 5


y = 4.59x + 95.79R² = 0.90

y = 1.05x + 34.99R² = 0.77

0

300

600

900

1200

1500

0 50 100 150 200 250

τ 0re

st(P

a)

∆SS (mm)

PV test

IP test

Correlations using CEM Mixtures


y = 0.95 xR² = 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 xR² = 0.82

0

500

1000

1500

2000

2500

0 1000 2000 3000

PVτ 0

res

t(P

a)

Rheometer τ0rest (Pa)

Good relationships between static yield stress from PV and IP vs. rheometer

Data at 15 min rest timeSCC


Good relationship between evolution of PV and IP static yield stress with time and the evolution of static yield stress from concrete rheometer

y = 2.52 xR² = 0.96

0

20

40

60

80

100

120

140

0 20 40 60

PVτ 0

rest

(t) (P

a/m

in)

Rheometerτ0rest (t) (Pa/min)

y = 0.60xR² = 0.93

0

5

10

15

20

25

30

35

0 20 40 60

IPτ 0

rest

(t) (P

a/m

in)

Rheometerτ0rest(t) (Pa/min)

Validation using SCC Mixtures

0 15 30 45 60

τ 0re

st(P

a)

minute


• 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 FormworkPressure

P

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

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


Pressure Device to Determine Lateral Pressure

Digital manometer to control overhead air pressure (up to 13 m high)

190 mm

63 mm

577 mm

700 mm

63 mm

Fresh concrete

500 mm

19 mm

19 mmPressure 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

ssu

re (

kPa)

Time (min)


H = 0.5 m

H = 0.35 m

SCC4Ф= 560 mmR = 10 m/hrVMA = 2.8 L/m3

Sudden increase in pressure reflects "blow-up" of overhead pressure at sensor locationdecrease 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

Late

ral p

ress

ure

(kPa

)

Time (min)

= 560 mmR = 10 m/hr

Eq. hydrostatic pressure H = 13 m @ 72 min


Validation: Pressure Response vs. 3-m Standing Column

0

10

20

30

40

50

60

70

20 40 60 80 100

Late

ral p

ress

ure

(kPa

)

Time (min)

SCC2 = 660 mmR = 10 m/hr

Pressure column

3-m PVC column



Repeatability of Pressure Responses

4 repetitions

0

40

80

120

160

200

0 20 40 60 80 100 120 140 160

Time (min)

Late

ral p

ress

ure

(kPa

)

R = 10 m/h = 660 mm 0

2

4

6

8

10

12

0 50 100 150 200 250 300

Lateral pressure (kPa)

Cas

ting

dept

h (m

) Hydrostatic pressure

H (m) RE (%)

1 ± 0.7

4 ± 2.4

8 ± 2.3

12 ± 4.0


2

4

6

8

10

12

14

0 50 100 150 200 250

Lateral pressure (kPa)

Cas

ting

dept

h (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

Validation: Effect of Slump Flow & Paste Volume

Effect of different slump flow values and paste volumes on lateral pressure envelopes

R = 10 m/h



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 kPa50- 80 kPa

80 - 110 kPa110 - 140 kPa140 - 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 #1VCC

Wall #2SCC1

Wall #3

SCC1

Wall #4

SCC1

Wall #5VCC

Wall #6

SCC1

Wall #7

SCC2

Wall #8SCC3

Slump/slump flow (mm)

120 ±30

650 ± 25120 ±30

650 ± 25

HRWRA type ‐‐‐ PCP ‐‐‐ PCP PNS

Vp (L/m3) ‐‐‐ Low, 330 ‐‐‐Low330

High 370

Low330

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 Material 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

Form

wor

k he

ight

(m)

Pmax (kPa)


@2 hr

@6 hr Pmax

formwork base

@4 hr


8 Full-Scale R/C Columns

MixtureRelative

thixotropy

Casting rate (m/h)

2 55 +

20’ WP10 13 15 22

SCC-L Low -- -- -- -- Col.#1 -- Col.#2SCC-M Medium -- Col.#7 Col.#8 --SCC-H High Col.#5 Col.#3 -- Col.#4 -- Col.#6 --


Predicted vs. Field Measurements

y = 1.01 xR² = 0.97

0

20

40

60

80

100

0 20 40 60 80 100

Mea

sure

d P m

axin

fiel

d (k

Pa)

Predicted Pmax (kPa)

C…C…

8 column elements6 wall elements cast with SCC


Conclusions

• Thixotropy can be assessed by structural breakdown and structural build-up at rest

• Structural breakdown area is determined using rheometer

• Structural build-up at rest can be determined using the structural growth approach - variations of static yield stress at rest - using:

• rheometer

• empirical tests: inclined plane / portable vane test methods

Static yield stress of inclined plane / portable vane tests correlatewell to that of concrete rheometer

Increase of thixotropy leads to reduction in lateral formworkpressure exerted by SCC

Field validation results are encouraging


Thank you !

1. Khayat KH, Omran AF, Naji S, Billberg P, Yahia A (2012) Field-Oriented Tests to Evaluate Structural Build-up atRest of Mortar and Flowable Concrete. J. of Mat. and Struc., 45(10):1547-1564.

2. Omran AF, Khayat KH (2011) Choice of Thixotropic Index to Evaluate Formwork Pressure Characteristics of Self-Consolidating Concrete. Submitted to J. of Cem. and Con. Res.: 34.

3. Omran AF, Naji S, Khayat KH (2011) Portable Vane Test to Assess Structural Build-Up at Rest of Self-Consolidating Concrete. ACI Mat. J., 108(6):628-637.

4. Khayat KH, Omran AF, Pavate T (2010) Inclined Plane Test Method to Determine Structural Build-Up at Rest ofSelf-Consolidating Concrete. ACI Mat. J. 107(5):515-522.

5. Khayat KH, Omran AF (June 2011) Field Validation of SCC Formwork Pressure Prediction Models. J. of Con.Inter., 33(Issue 6):33-39.

6. Khayat KH, Omran AF, D'Ambrosia M (Sept. 2010) Prediction of SCC Formwork Pressure in Full-ScaleElements. Proceedings of 6th International RILEM Symposium on SCC, and 4th North American Conference onDesign and Use of SCC (SCC2010), Montreal, Canada, RILEM State of the Art Reports, Vol.1(Part 6):231-242.

7. Khayat KH, Omran AF (July/August, 2009) Evaluation of SCC formwork pressure. Concrete Infocus Magazine, aPublication of the National Ready Mixed Concrete Association – SCC: Developing Guidelines to Lower LateralPressure:16-19.

8. Khayat KH, Omran AF (June 2009) Evaluation of SCC Formwork Pressure. Proceedings of 2nd Inter. Sym. onDesign, Performance and Use of SCC (SCC2009), Eds. C Shi, Z Yu, KH Khayat, P Yan, RILEM Publications sarl,Beijing, China:43-55.

9. Khayat KH, Omran AF, Naji S, Billberg P, Yahia A (Nov. 2008) Test Methods to Evaluate Form Pressure of SCC.Proceedings of 3rd North American Conference on Design and Use of SCC (SCC 2008), Eds. Shah SP,Chicago:308-314.

Documents

Test Methods to Evaluate Structural Various Models to ... · 0 200 400 600 800 1000 1200 Time (s) ... PV test IP test Correlations using CEM Mixtures. ACI Spring Convention – Minneapolis