Self Consolidating Concrete - University Of Illinois 07... · CEAT Brown Bag Seminar, 4/07 Self Consolidating Concrete Leslie Struble Civil and Environmental Engineering University

CEAT Brown Bag Seminar, 4/07

Self Consolidating Concrete

Leslie StrubleCivil and Environmental

EngineeringUniversity of Illinois


Scope of talk

• What is SCC?• How is SCC made? • How is SCC tested? • SCC research at UIUC• The Good, the Bad, and the Ugly


What is SCC?• Definition

A high-performance concrete that flows under its own weight to fill completely the formwork without vibration or mechanical consolidation.

• Benefitsplace in highly congested formworkplace without vibrationself-leveling, less need to screedfaster construction

• Flowing into double T beam forms

ACI 237 ETS Report


How is SCC made?

• High-range water reducer (polycarboxylate)

• High paste content• Viscosity Modifying Admixture

(VMA)• Smaller aggregate and optimized

gradation


Typical SCC mixtures

SG UNIT OPC 1 SCC 1 SCC 2 SCC 3 SCC 4Cement (Type I) 3.15 lb/yd3 726 661 601 685 679Fly Ash (Class C) 2.65 lb/yd3 0 157 325 0 151Coarse Aggregate, 3/4" (20mm) 2.70 lb/yd3 1853 367 1365 1627 579Coarse Aggregate, 3/8" (10mm) 2.70 lb/yd3 0 1075 0 0 1018Fine Aggregate (FM = 2.57) 2.64 lb/yd3 1192 1403 1336 1389 1389Water 1.00 lb/yd3 290 311 301 278 267Superplasticizer (CAE) 1.06 fl oz/yd3 22 63 29 49 36Viscosity Modifying Admixture (VMA) 1.00 fl oz/yd3 22Slump flow (standard slump for OPC) in 5 30 28 26 27Paste content by Volume % 32 37 40 33 34FA/CA ratio -- 0.64 0.97 0.98 0.85 0.87w/cm 0.40 0.38 0.33 0.41 0.32

GradedAggregate

MineralFiller

VMA StrongWall

Precast Beam


Review of SCC mixes shows departure from normal concrete

0.0

0.5

1.0

1.5

2.0

2.5

50 55 60 65 70 75 80 85 90 95 100

AGGREGATE CONTENT (%)

FA/C

A R

ATI

O

SCC Database

Mixtures studied

SCC4OPC1

SCC3 SCC2 SCC1

Typical non-SCC materials, according to ACI mixture proportioning method

•Higher FA/CA ratio•Higher paste content


How do SCC strategies affect properties and performance?

• SCC Strategies– high paste content– VMA (thickeners)– smaller aggregate &

controlled gradation– HRWR (CAE)– mineral fillers & additives

• Properties– flowability– stability– shrinkage and

creep• Performance

– segregation– strength and stiffness– early age cracking– deformation– prestress Loss– long term durability


Fresh SCC properties

• Flowability: flows easily at suitable speed into formwork

• Passing ability: passes through reinforcements without blocking

• Segregation resistance: the distribution of aggregate particles remains homogeneous in both vertical and horizontal directions– Static segregation due to gravity, vertical direction– Dynamic segregation due to flow, horizontal direction


Flowability• Slump flow (C1611), also tests dynamic

segregation


Passing ability

• L-box test


Passing ability

• J-ring test (C1621)


Segregation• Column segregation test (C1610)

.

SI = 100(CAB - CAT) / [0.5 (CAB + CAT)]


SCC Research at UIUC

• Rheology• Segregation• Formwork pressure• Creep and shrinkage • SCC research group: Prof. D. Lange,

myself, Matt D’Ambrosia, Ben Birch, Fernando Tejeda, Lin Shen

• Funded by IDOT


Rheology

• Concrete rheometer measures yield stress and viscosity– Yield stress: <100 Pa for SCC, >500 for normal concrete– Plastic Viscosity: ~50 Pa.s for SCC, same as normal

concrete

y = 1.7941x + 0.3206

y = 1.8014x + 0.2719

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00

Rotational speed (rad/sec)

Tor

que

(N.m

)

test 1 test 2 Linear (test 2) Linear (test 1)

y = 1.7941x + 0.3206

y = 1.8014x + 0.2719

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00

Rotational speed (rad/sec)

Tor

que

(N.m

)

test 1 test 2 Linear (test 2) Linear (test 1)


Segregation

• Static segregation mainly controlled by gravity • Dynamic segregation depends on flow rate and

friction (formwork, floor, etc)• Segregation affects strength and stiffness, creep

and shrinkage

Static segregation Dynamic segregation


New ways to measure static segregation

• Visual examination of hardened concrete (visual index)

• Segregation probe (developed at UIUC)


Visual examination• Hardened Visual Stability Index (VSI) rating

criteria for concrete cylinder specimens

0: StableNo paste or mortar layer visible at top of cylinder, no apparent difference

in the size and area percentage of coarse

aggregate through depth

1: StableNo paste or mortar layer visible at top of cylinder, slight difference in the

size and area percentage of coarse

aggregate through depth

2: UnstableSlight paste or mortar

layer visible (<1”), slight difference in coarse aggregate through

depth

3: UnstableSignificant paste or mortar layer visible

(>1”), obvious difference in the size and area

percentage of coarse aggregate through

depth

0 1 2 3


Segregation probe

• Quick and easy• Set on top of concrete and

measure settlement• Correlates well with HVSI

33310HVSI

2”2¼”2½”¼”1/8”Segregation Probe results


• Robust mix resists segregation due to small changes in w/cm

• Segregation probe allows us to characterize robustness

• Robustness measured as margin in w/cm between target and maximum allowable penetration

Robustness


Dynamic segregation

• Flowing SCC may segregate during placement

• May be sufficient to impact hardened concrete performance - shrinkage, elastic modulus, creep


UIUC strong wall

•Cast 2004•Used SCC to achieve consolidation with congested formwork


Dynamic segregation in strong wall

• In strong wall, segregation occurred abruptly at 45’ of flow

• Static segregation tests did not predict dynamic segregation

A0’

B20’

C29’E

44’F53’

G56’

D36’6”

Pump locationA0’

E44’

F53’

G56’

D36’6

”

B20’

C29’

33.7%

63.6%

0%

20%

40%

60%

80%

0 10 20 30 40 50 60Distance Traveled (ft)

Aggr

egat

e C

onte

nt

Coarse Aggregate

Total Aggregate - estimate


Measuring dynamic segregation

• Visual inspection of slump flow • Loss of aggregate during flow in trough

(developed at UIUC)


Modeling dynamic segregation• Dynamic segregation

depends on flow velocity and aggregate properties

• Model using forces on aggregate: drag from paste (depends on paste velocity, rheology), friction from formwork (depends on aggregate size, density)


Evaluating creep and shrinkage

LVDT ExtensometerLoad cell

Actuator

3 in (76 mm)

3 in (76 mm)

Feedback Control

• Restrained stress test machine• Sealed for 24 h, then dried at 50% RH, 23oC• Companion specimen tested for free shrinkage


Creep and shrinkage results

•Early age tensile stress was greater in SCC than in most previous concretes tested •If aggregate content low, creep and shrinkage high 0

50

100

150

200

250

300

350

400

0 1 2 3 4 5 6 7 8Age (days)

Shr

inka

ge S

tress

(psi

)

SCC, w/cm = 0.34, 36% paste

•Low w/cm also produces autogeneous shrinkage•High paste and low w/c a dangerous combination


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 2 4 6 8 10Age (d)

Stre

ss-S

treng

th R

atio

OPC1, w/c = 0.40

SCC1, w/c = 0.39

SCC2, w/c = 0.33

SCC3, w/c = 0.41

SCC4, w/c = 0.34

Microcracking

• Occurs one or two days after drying • Induced by high stress-strength ratio • Intensified by lack of creep relaxation

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 2 4 6 8 10Age (days)

Spec

ific

Cre

ep (x

10-6

m/m

/psi

)

OPC1, w/c = 0.40

SCC1, w/c = 0.39

SCC2, w/c = 0.33

SCC3, w/c = 0.41

SCC4, w/c = 0.34


Cracking

0.016” (0.4 mm)

• Surface cracks in UIUC strong wall due to early age shrinkage, probably caused by segregation


Evaluating formwork pressure

• Using pressure transducers to study formwork pressure


Formwork pressure results

• Pressure decreases as cement flocculates and hydrates

• Concrete stays at full hydrostatic pressure only during rapid placement or with continuous shearing

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 20 40 60 80 100 120time (min)

FW p

ress

ure/

HS

pre

ssur

e

bucket

truck

pumper


The Good, the Bad, and the Ugly

• The Good: high flowability• The Bad: segregation, high

formwork pressure• The Ugly: shrinkage cracking

Presentation by D. Lange


Summary• SCC is an exciting new concrete technology• Recommendations for SCC mix proportioning:

– Design to prevent static segregation– Set limits on flow length to prevent dynamic segregation– Set limits on paste contents to avoid shrinkage– Avoid low w/cm ratios to reduce shrinkage– Set limits on placement to reduce formwork pressure

• Challenges remain: – New tests to measure properties– New models to predict performance– New strategies to control segregation, cracking, formwork

pressure

Documents

Self Consolidating Concrete - University Of Illinois 07... · CEAT Brown Bag Seminar, 4/07 Self Consolidating Concrete Leslie Struble Civil and Environmental Engineering University