LSUgoodbadugly

8/3/2019 LSUgoodbadugly

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1

Self Consolidating Concrete:

The Good, the Bad, and the Ugly

Sponsored by

David A. Lange

Department of Civil and Environmental Engineering

University of Illinois at Urbana-Champaign

ILLINOISUniversity of Illinois at Urbana-Champaign

Co-workers: Prof. L. Struble, Matt DAmbrosia, Ben Birch,Lin Shen, Fernando Tejeda


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SCC: The Good, the Bad, and the Ugly

1967


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Background

Developed in Japan in the late 1980s

Flows into formwork without vibration or mechanicalconsolidation

Flowable properties achieved with: Ultra high-range water reducer

(polycarboxylate)

Viscosity Modifying Admixture (VMA)

High cementitious materials or

powder content Small coarse aggregate and

higher sand fractionACI 237 ETS Report


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Potential benefits of SCC

Improved consolidation

Reduced labor cost

Accelerated construction

Reduced noise

Performance Requirements

Flowability into formwork and through reinforcement

Stability (resistance to segregation)

but what about hardened concrete properties?


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UIUC database of SCC proportionsshows a departure from normal OPC

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/CA

RATIO

SCC Database

Mixtures studied

SCC4

OPC1

SCC3SCC2

SCC1

Typical non-SCC

materials, according toACI mixture

proportioning method


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UIUC SCC Control Mixtures

SG UNIT OPC 1 SCC 1 SCC 2 SCC 3 SCC 4

Cement (Type I) 3.15 lb/yd3 726 661 601 685 679

Fly Ash (Class C) 2.65 lb/yd3 0 157 325 0 151

Coarse 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 1018

Fine Aggregate (FM = 2.57) 2.64 lb/yd3 1192 1403 1336 1389 1389

Water 1.00 lb/yd3 290 311 301 278 267

Superplasticizer (CAE) 1.06 fl oz/yd3 22 63 29 49 36

Viscosity Modifying Admixture (VMA) 1.00 fl oz/yd3 22

Slump flow (standard slump for OPC) in 5 30 28 26 27

Paste content by Volume % 32 37 40 33 34

FA/CA ratio -- 0.64 0.97 0.98 0.85 0.87

w/cm 0.40 0.38 0.33 0.41 0.32

Graded

Aggregate

Mineral

Filler

VMA Strong

Wall

Precast

Beam


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How do SCC strategies affectperformance?

SCC Strategies high paste content

VMA (thickeners)

smaller aggregate &

controlled gradation HRWR, SP (CAE)

Mineral fillers & additives

Properties

Stability

Shrinkage and creep

Strength and Stiffness

Performance

Segregation

Early age cracking

Deformation

Prestress Loss

Long Term Durability


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SCC Flow Characteristics: The Good!

Flowing into concrete pumpMDD-UIUC


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Standard tests have been developed

Slump flow test (ASTM C1611) L-box test


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J-ring test, also for passing ability(ASTM WK7552)

Test is performed using a standard slump cone

Height difference is measured on each side of ring


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Rheological parameters used to defineflow behavior

Concrete rheometer measures yield stress and viscosity

Yield stress: 86 Pa (< 100 for SCC, ~200-300 for normal concrete)

Plastic Viscosity : 517 Pa.s (about 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)

Torque(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)

Torque(N.m

)

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


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Segregation of SCC:The Bad

5

6"161

m =18g


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How do we evaluate segregation?

Hardened Visual Stability Index (VSI) Rating Criteria forConcrete Cylinder Specimens

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

in the size and areapercentage of coarse

aggregate throughdepth

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

size and areapercentage of coarse


2: UnstableSlight paste or mortar

layer visible (1), obvious difference

in the size and areapercentage of coarse


0 1 2 3


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HVSI and Image Analysis

Coarse aggregate % measured at different levels in SCC cylinder

051015202530354045

0-2 2-4 4-6 6-8

Depth

Coarseaggregate

%


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What about fresh SCC?

Column Segregation TestASTM Work Item WK3224

26 h x 8 vertical column

Fresh concrete placed in tube, then split

into four sections after 15 min rest Coarse aggregate washed and weighed for

each section

Segregation Index (SI) defined as weight% top vs. bottom

Not an adequate field test!

M1M42

1M1-M4SI


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The Segregation Probe

Applicability:

Rapid surface segregation measurement

Sensitive to small changes in stability of SCC

Suitable for field measurement

Procedure:

Cast fresh concrete into 6 x 12 cylinder

Wait for 15 min, avoid excessive disturbance Put ring on surface gently

Wait for at least 1 min until ring stops settling

Take reading

5

6"161

m =18g


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Segregation Probe relates to HVSIrating of cylinder

SegregationProberesults

1/8 2 2 2

HVSI 0 1 3 3 3


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Robustness of SCC

Robustness can be evaluated with respect to flow or stability

Why examine robustness of SCC:

Due to its high flowability, SCC is much more susceptible to

stability problem than normal concrete Small changes in moisture content of aggregates or dosage of

admixtures may affect the fresh properties significantly

Procedure

Mix raw material or sample from truck

Set segregation probe gently on surface Wait 1 min for ring to settle

Take reading

Add incremental dose of water or superplasticizer

Repeat step 1~5


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Slump Flow vs. RobustnessIncreasing slump flow significantly reduced the robustness


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Paste Content Affects RobustnessHigher paste content enhanced robustness


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Dynamic Segregationof SCC

Flowing SCC may have a tendency to segregate duringplacement

How far can SCC travel without segregation?

Test: Measure coarse aggregate fraction as function ofdistance.


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Dynamicsegregation

occurredabruptly after45 of flow

0%

20%

40%

60%

80%

0 10 20 30 40 50 60

Distance Traveled (ft)

AggregateContent

A

0

E

44

F

53

G

56

D

366

B

20

C

29 Static segregation

tests do not predictdynamic segregation


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Segregation Acceptance Criteria

How does segregation effect hardened properties?

Differential stress development

Model used layered approach

Properties of paste, mortar, and concrete


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Segregation Shrinkage Test

Cast vertically to produce asegregated cross section

Laid flat to measuredeflection caused byautogenous shrinkage ofsegregated layer


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Model validation typical results

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0 2 4 6 8 10 12 14 16

Measured Deflection

FEM Calculated Deflection

Deflection

(in)

Concrete Age (d)


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Model confirms HVSI judgment

0

50

100

150

200

250

300

350

400

450

0 1 2 3

SCC1 SCC2

SCC3 SCC4

Stress(psi)

HVSI Rating


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Early Age Cracking: The Ugly!

0.016 (0.4 mm)


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Early age tensile stress was greater inSCC than most previous test results

UIUCRestrainedStressDatabase

0

50

100

150

200

250

300

350

400

0 1 2 3 4 5 6 7 8

Age (days)

Shrin

kage

Stress

(psi

)

SCC-wall


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Restrained Stress Test Machine (RSTM)

LVDT Extensometer

Load cell

Actuator

3 in (76 mm)

3 in (76 mm)

Feedback Control

Sealed for 24h, then dried at 50% RH, 23oC

Companion specimen for free shrinkage measurement


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Typical Restrained Test Data

-300

-250

-200

-150

-100

-50

0

50

100

150

200

0 1 2 3 4 5 6 7

Time (days)

Strain(me)

0

1

2

3

4

5

6

7

8

9

10

Applied

Load

(kN)

Restrained Specimen

Free Specimen

Load (kN)

Creep

Cumulative Shrinkage +Creep

-c tot sh

e e e

ec

cttJ )',(

1

n

tot el i

i

e e

( )c

el

E t

e


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Stress development in SCC indicatespotentially poor cracking performance

Autogenous shrinkage in low w/c materials generatessignificant stress at early age

A minimum w/c ratio can reduce early age cracking in

restrained concrete

0

50

100

150

200

250

300

350

400

450

0 2 4 6 8 10

Age (days)

Shrin

kage

Stress

(ps

i)

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


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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 10

Age (d)

Stress-S

trengthRatio

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 in one or two days

High stress-strength ratio induces microcracking damage

Lack of creep relaxation intensifies stress rapidly

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 2 4 6 8 10

Age (days)

Spec

ificCre

ep

(x10-6

m/m/ps

i)

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


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0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 2 4 6 8 10Age (days)

Spec

ificCreep(x10-6/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

OPC-MB3SCC1-MB3

SCC2-MB3

SCC3-MB3

SCC5-MB3

Models of SCC Creep Compliance atEarly Age depends on w/c and paste%

0.39, 37%

0.34, 34%


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Early age shrinkage of SCC varies withpaste content and w/b ratio

0.39, 37%

0.34, 34%

0.41, 33%

0.40, 32%

0.33, 40%

w/b, paste%

-1000

-900

-800

-700

-600

-500

-400

-300

-200

-100

0

0 5 10 15 20 25 30

Age (days)

F

ree

Shrin

kage

(x10-6

)

OPC1, w/c = 0.40

SCC1, w/c = 0.39

SCC2, w/c = 0.33

SCC3, w/c = 0.41

SCC5, w/c = 0.34

Typical ConcreteSafe Zone ?


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-180

-160

-140

-120

-100

-80

-60

-40

-20

0

20

0 5 10 15 20 25 30

Age (d)

Auto

genous

Shrin

kage

(1

0-6

m/m)

OPC1, w/c = 0.40

SCC1, w/c = 0.39

SCC2, w/c = 0.33

SCC3, w/c = 0.41

SCC4, w/c = 0.32

Low w/c drives autogenous shrinkage

Typical ConcreteSafe Zone ?

0.39, 37%

0.34, 34%

0.41, 33%

0.40, 32%

0.33, 40%

w/b, paste%


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Can we design SCC mixtureproportions for low shrinkage?

Tazawa et al found that 0.30was an acceptable threshold

In our study, 0.34 keeps totalshrinkage at reasonable levels

0.42 eliminates autogenous

shrinkage Application specific limits

High Restraint: 0.42

Med Restraint: 0.34

Low Restraint: w/c based onstrength or cost

0

100

200

300

400

500

600

700

800

900

0.30 0.32 0.34 0.36 0.38 0.40 0.42

w/cm

A

utogenousShrinkageStrain(x10-6)

Autogenous Shrinkage (28d)

Total Shrinkage (28d)


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0

100

200

300

400

500

600

700

800

900

30% 32% 34% 36% 38% 40% 42%

Paste Content by Volume

AutogenousShrinkageStrain(x10-6)

Autogenous Shrinkage (28d)

Total Shrinkage (28d)

Limit Paste Content too

Below 32%, SCC has questionablefresh properties

Is 34% a reasonable compromise?

Application specific limits

High Restraint: 25-30%

Med Restraint: 30-35%

Low Restraint: Based on cost

TABLE 4.3 From Draft of ACI 237 ETS

Summary of Self-Consolidating Concrete ProportioningTrial Mix Parameters

Coarse aggregate by volume 28% - 32%

Paste Content by volume 34% - 40%

Mortar Fraction by volume 68%-72%

Typical w/cm 0.320.45

Typical powder content 650*800 pounds


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SCC Rapid Placement: The Good

UIUC Strong Wall (80L x 5W x 30H)

Pumped in one continuous pour, tight reinforcing prohibited vibration

Interstate 74 retaining walls in Peoria, IL


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SCC Formwork Pressure-- The Bad

ACI 347-01 Guide toFormwork for Concreteguidance does not addressSCC directly

Pressure equations apply

to normal concrete When in doubt, designfor full hydrostaticpressure

Result: expensive formwork or shorter pourheights

Little field data availableconcerning actual pressurereadings from cast in placeoperations.


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SCC formwork pressure tests

SCC approaches full hydrostatic pressure during rapidplacement

PVC column tests to study the effect of

Consistency of concrete Set-modifying admixtures

Temperature of concrete

Mixture design approach

on SCC formwork pressure


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How is SCC different from OPC?

After one hour, SCC pressure decreased 10%vs. 40% for regular concrete

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4 5 6 7

Time [Hr]

Measuredp

ressure/Hydrostaticpressure

2.5" slump

31" slump flow

28" slumpflow

20" slumpflow


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Temperature significantly affectsformwork pressure


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Mechanism of pressure decay

Pressure decrease is a combination of physical (internalfriction) and chemi-physical (gelation) phenomena

Internal friction is a function of the aggregate content and the

workability of concrete All this happens well BEFORE SET


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Modeling approach is semi-empirical

Step 1: Characterize the characteristic pressure decay of thematerial

Step 2: Impose variable pressure head on the material that is

undergoing gelation, stiffening


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Step 1: Mathematical Fit for Pressure DecaySignature

Measured and Model Values

0.0

0.2

0.4

0.6

0.8

1.0

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5Time [min]

HydrostaticPressure

20 C

10 C

40 C

Model 40 C

Model 20 C

Model 10 C

C(t) C0

(at2 1)

Where:

C0 = Initial value

(Approx. 0.90 1.00)

a, alpha = Define

the initial and final

slope of curve

Difficult to find one family of curves to model the different

behavior


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Relate Horiz Pressure to Vert Pressure

RttCtPh

)()(

Where:

Pv=Vertical pressure

Ph=Horizontal pressure

= Unit weight of theconcrete

R= Rate of pouring

t = time

C(t) is experimentallyobtained from the lab

column result

The maximum pressure willbe the equilibrium between

the increase in head and the

value of K(t)

Pvh

>weight

PhCPv

Ph

C(h)

since hRt


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0

5

10

15

20

25

30

0 2 4 6 8

Time [hr]

Pressure[p

si]

0.0

0.2

0.4

0.6

0.8

1.0

C(t)

Head 1

Lat. Press. 1

Model 20 C


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Note:

Maximum

lateral

pressure is

reached long

before end

of of pour.

0

5

10

15

20

25

30

0 2 4 6 8

Time [hr]

Pressure[p

si]

0.0

0.2

0.4

0.6

0.8

1.0

C(t)

Head 1

Lat. Press. 1

Model 20 C


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Modeling Variation in Pour Rate

0

5

10

15

20

25

0 1 2 3 4 5 6

Time [hr]

Pressure

[ps

i]

0.0

0.2

0.4

0.6

0.8

1.0

Function

C(t

)

Head 16 ft/hr

Horiz. Press. 16 ft/hrHead 8ft/hr

Horiz. Press. 8ft/hr

Head 4 ft/hr

Horiz. Press. 4 ft/hr

Funct. press. decrease

16 ft/hr

8ft/hr

4 ft/hr

Note how the

maximum pressure

is very different for

two different

pouring rates usingthe same concrete.


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Lab Test to ValidateModel

Fill first 3 column

Fill second 3 column

Creates a 6 column

Measure pressure in formwork asconcrete hardens

0

1

2

3

4

5

6

0 2 4 6

Time [hr]

Pressure

[psi]

Head


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Observed Pressure

0

1

2

3

4

5

6

0 2 4 6

Time [hr]

Pressure[

psi]

MEASURED

Head

Second PourTime 1 hr

First PourTime 0


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C(t)

0.000

0.250

0.500

0.750

1.000

0 2 4 6 8

Time [hr]

C(t)

C(t) for 20 C


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0

1

2

3

4

5

6

0 1 2 3 4 5 6

Time [hr]

Pressure[psi]

0.0

0.2

0.4

0.6

0.8

1.0

Valuefor

C(t)

MEASURED

Head

ModelPrediction

C(t) for 20 C

Second Pour

Time 1 hr

First PourTime 0


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Field Data Collection

Sensors mounted in forms

Pressure readings takencontinuously during placement

Fill rate data also recorded


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Typical Results

Use depth measurements fromstart and stop of individualtrucks

To generate filling height curve forduration of placement of concrete

0

5

10

15

20

25

0 20 40 60 80 100 120

time(min)

FillingHeight(ft)


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Typical Results

0

5

10

15

20

25

0 20 40 60 80 100 120

time(min)

Pressure(psi)andFilling

Heig

ht(ft)

Filling Height

Pressure

Max pressure = 5.2 psi @ 21 minutes with 7.05 ft of concrete20.14 ft/hr Total height = 15.88 ft, filled in 91 minutes 10.47 ft/hr


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Fraction of Hydrostatic Pressure

Calculated pressure as a function of height of concrete

1 ft of concrete fully liquid 1 psi of pressure

0

5

10

15

20

25

0 20 40 60 80 100 120

time(min)

Pressure(p

si)andFilling

Height(ft)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Fractiono

fHydrostatic

Pre

ssure

Filling Height

Pressure

Fraction of Hydrostatic Pressure


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Case Study: Application of modelingapproach to I-74 project at Peoria


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Example: Column from Field Measurement

Measured from 2.5 column of concrete

Calculated C(t) from column data

Generate curve to match measured data tocreate model curve

0

0.5

1

1.5

2

2.5

3

0 60 120 180 240 300 360 420time (min)

Pressure

(ps

i)

0

0.2

0.4

0.6

0.8

1

1.2

0 60 120 180 240 300 360 420time(min)

C(t)

column

model


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Example: Filling Rate Curve and MeasuredPressure from Field

0

5

10

15

20

25

0 60 120 180 240 300 360 420

Time (min)

P

ressure

(ps

i)orH

eighto

f

Concre

te(ft)

Height of Concrete OverSensor

Measured Pressure


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Example: Overlay C(t) Model Curve

0

5

10

15

20

25

0 60 120 180 240 300 360 420

Time (min)

Pre

ssure(psi)orHeight

ofConcrete

(ft)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

C(t)

Height of Concrete OverSensorMeasured Pressure

C(T) model curve


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Example: Model vs. Actual Pressure

0

5

10

15

20

25

0 60 120 180 240 300 360 420

Time (min)

0.00.2

0.4

0.6

0.8

1.0

1.2

C(t)

Height of ConcreteOver SensorMeasured Pressure

Predicted Pressure

C(T)


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Advantages of model

Provides a better approximation than assuming full liquid head

Uses a simple, repeatable test for generating model curve

Model seems to be conservative


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Effect of Energy in Placement

Laboratory Work

Look at pressure when column is vibrated after placement

Field Work

Look at behavior of wall pours when placed using truck dump, pumper

placement, and bucket dump


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Lab Column with vibration every 10min

Concrete placed in Column Vibrated every 10 minutes with pencil vibrator for 30 seconds SCC will maintain hydrostatic pressure if agitated Effect of agitation will be minimized with increasing cover height and time

0

1

2

3

4

5

6

0 60 120 180 240 300 360 420Time (min)

Pressu

re(ps

i)

5.5 feet deep4 feet deep2.5 feet deep1 foot deep


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SCC doesnt have to be ugly!

Todays problems

Segregation

Sensitivity to slight changes in water

Cracking tendencies

Higher formwork pressure

are becoming addressed through research & experience


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SummarySCC: The Good, the Bad, and the Ugly

The Good,

Improved consolidation for tight forms or bar spacing

Labor cost savings

Aesthetic finish

Rapid placement

the Bad,

Avoid segregation problems with proper testing in the lab and field

Formwork Pressure models will assist formwork design

and the Ugly

Limit w/b and paste content to avoid cracking

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