The Effect of Autogenous Shrinkage on FlexThe Effect of Autogenous Shrinkage on Flexural Cracking Behavior of ural Cracking Behavior of

Reinforced HSC Beams and Improvement by Reinforced HSC Beams and Improvement by Using Low-shrinkage HSCUsing Low-shrinkage HSC

Fourth International Seminar on Self-desiccation and Its Importance in Concrete Technology 20/June/05, Gaithersburg, Maryland, USA

Masahiro SUZUKIMasahiro SUZUKI P.S. Mitsubishi Construction Co., Ltd., JapanP.S. Mitsubishi Construction Co., Ltd., Japan

Makoto TANIMURAMakoto TANIMURA Taiheiyo Cement Corporation, JapanTaiheiyo Cement Corporation, Japan

Ryoichi SATORyoichi SATO Hiroshima University, JapanHiroshima University, Japan

1

Autogenous shrinkage (AS) properties of HSC using Autogenous shrinkage (AS) properties of HSC using various materialsvarious materials Comprehensive approach for reducing ASComprehensive approach for reducing AS----- well studied!! ----- well studied!!

Evaluation of AS effect on cracking performance of RC Evaluation of AS effect on cracking performance of RC flexural beams, effectiveness of low shrinkage-HSC on the flexural beams, effectiveness of low shrinkage-HSC on the improvement of cracking performanceimprovement of cracking performanceCalculation method for crack width of RC beam Calculation method for crack width of RC beam considering shrinkage/expansion effect before loadingconsidering shrinkage/expansion effect before loading

However, few investigations on the effect of AS on However, few investigations on the effect of AS on structural performance. Only a few reports on structural performance. Only a few reports on evaluation method for cracking behavior considering AS evaluation method for cracking behavior considering AS ObjectivesObjectives

BackgroundBackground 2

RC beam specimenRC beam specimen

40

125

210

40

120

40

100

2100

2700

Thermo couple

(Tension reinforcement ratio ; 1.36%)

Anchorage Area

Wire strain gauge

Tested zone

Contact gauge (20@40)

Load

Displacement transducer50 90 80 80

D19

800100

125

40

125

210

40

120

40

100

2100

2700

Thermo couple

(Tension reinforcement ratio ; 1.36%)

Anchorage Area

Wire strain gauge

Tested zone

Contact gauge (20@40)

Load

Displacement transducer50 90 80 80

D19

800100

125

(Unit; mm)

Dimension; 200x250x2700 mmTwo-point loading; span:2100mm, pure flexural zone:800mm

EvaluationsEvaluationsBefore loadingBefore loading Steel strainSteel strain 　　　　 Restrained stress on bottom fiberRestrained stress on bottom fiberUnder short-term loadingUnder short-term loading - Crack width; Contact-type strain gauge- Crack width; Contact-type strain gauge

3

Crack widthCrack width

Sealed curing period;30-50 days

Steel strainSteel strain

Mixture investigatedMixture investigated

W/(C+EX); 0.3W/(C+EX); 0.3 EX content; 40 kg/mEX content; 40 kg/m33

SRA content; 6 kg/mSRA content; 6 kg/m33

Targeted concrete strength; 70 N/mmTargeted concrete strength; 70 N/mm22 at 28 days at 28 days

ConCon NCNC NENE NSNS NESNES LCLC LELE LSLS LESLES

CemCem Ordinary PortlandOrdinary Portland Belite-rich low heat PoBelite-rich low heat Portlandrtland

EXEX --AdAdd.d. --

AddAdd..

--AdAdd.d. --

AdAdd.d.

SRASRA -- --AdAdd.d.

AddAdd..

-- --AdAdd.d.

AdAdd.d.

4

Low-shrinakge HSCsLow-shrinakge HSCsReference HSCReference HSC

Equation for calculating restrained stress on Equation for calculating restrained stress on extreme bottom fiber extreme bottom fiber

　　　 　

cc

gg

c

scssss A/I

)Ch)(Cd(1

A

P,AEP

sP: axial force in reinforcement, sE: Young’s modulus of reinforcement

s: measured strain in reinforcement, sA: cross-sectional area of reinforcement

c: stress on the extreme bottom fiber, cI: moment of inertia of gross concrete section

cA: cross-sectional area of concrete, d: effective depth, h: height of beam

gC: distance from the extreme upper fiber to the centroid of the gross concrete section

Equilibrium of the force between concrete and rebarEquilibrium of the force between concrete and rebar Navier’s assumptionNavier’s assumption

5

-2

-1

0

1

2

0.1 1 10 100

NCNENSNES

LCLELSLES

Res

trai

ned

str

ess

at e

xtre

me

bot

tom

fib

er

(

N/m

m2 )

Temperature adjusted concrete age (days)

(Compression)

(Tension)

Restrained-shrinkage/expansion stressRestrained-shrinkage/expansion stress 6

Tension

Compression

1.5 N/mm2

－ 1.5 N/mm2

Low-shrinkage HSCs are obviously effective in reducing Low-shrinkage HSCs are obviously effective in reducing AS-restrained stress.AS-restrained stress.

0

0.5

1

1.5

2

2.5

3

NC NE NS NES LC LE LS LES

Measured valueCalculated value neglecting restrained stress

Rat

io o

f fl

exu

ral c

rack

ing

mom

ent

(NC

=1.

0)

Mixture

6.6kNm

11kNm

Flexural cracking momentFlexural cracking moment 7

AS-restrained stress affects cracking load significantly.AS-restrained stress affects cracking load significantly. LS-HSC markedly improve cracking load.LS-HSC markedly improve cracking load.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

NC NE NS NES LC LE LS LES

Maximum crack widthMaximum crack spacing

Rat

io o

f m

axim

um

cra

ck w

idth

or

crac

k s

pac

ing

(NC

=1.

0)

Mixture

Reinforcement stress=200N/mm2

0.16mm

165mm

Maximum crack width/crack spacingMaximum crack width/crack spacing 8

LS-HSCs improve cracking performance significantly.LS-HSCs improve cracking performance significantly. --Decrease in crack width, while increase in crack spacing!!--Decrease in crack width, while increase in crack spacing!!

● ：Stress in concrete at the depth of tension reinforcement is zero○ ：Strain in tension reinforcement just before loading

Restrained stress intension

Expansion

No length change

Shrinkage

Restrained stressin compresssion

Cracked section

M

ex,crM

non,crM

sh,crM

sh,sεnon,sε

ex,sεsh,0sε

ex,0sεsh,siε

ex,siε

Full section

ex,0M

sh,0M

Steel strain

Ben

ding

mo

men

t M

sε

● ：Stress in concrete at the depth of tension reinforcement is zero○ ：Strain in tension reinforcement just before loading

Restrained stress intension

Expansion

No length change

Shrinkage

Restrained stressin compresssion

Cracked section

M

ex,crM

non,crM

sh,crM

sh,sεnon,sε

ex,sεsh,0sε

ex,0sεsh,siε

ex,siε

Full section

ex,0M

sh,0M

Steel strain

Ben

ding

mo

men

t M

sε

General evaluation method for crack width considering General evaluation method for crack width considering shrinkage/expansion effect before loadingshrinkage/expansion effect before loading

This concept incorporated into JSCE CODE-2002This concept incorporated into JSCE CODE-2002

9

Diferrenec in elastic strain component between steel and concrete; affect crack width

JSCE Code Equation for maximum crack widthJSCE Code Equation for maximum crack width

csd

s

ses321 '

Ec7.0c4kkk1.1maxW

se: stress change in tension reinforcement from the zero stress in concrete

at the depth of the tension reinforcement (N/mm2)

1k: coefficient depending on geometric details of surface of reinforcement

2k: coefficient which considers the influence of concrete quality on bond characteristics given by:

7.0)20'f(15k c2 , c'f : compressive strength of concrete (N/mm2)

3k: coefficient which considers the influence of multi-layers arrangement of reinforcement

c: cover (mm), sc: center-to-center distance of reinforcement (mm)

: diameter of reinforcement (mm)

csd' : strain which considers the influence of creep and shrinkage on increased crack width with time

10

0

0.05

0.1

0.15

0.2

0.25

0.3

0 100 200 300 400

NCNENSNES

LCLELSLES

Max

imu

m c

rack

wid

th (

mm

)

Reinforcement stress (N/mm2)

Verification of proposed concept for evaluating Verification of proposed concept for evaluating maximum crack width (1)maximum crack width (1)

JSCE CODE-1996JSCE CODE-1996

0

0.05

0.1

0.15

0.2

0.25

0.3

0 100 200 300 400

NCNENSNES

LCLELSLES

Max

imu

m c

rack

wid

th (

mm

)

Reinforcement stress (N/mm2)

Improved accuracy

JSCE CODE-2002JSCE CODE-2002

11

Significant effect of AS on crack width; Reference HSC has 250x10-6 of steel stress at zero stress state; this means the influence of 25% for the steel stress of 200MPa(=1000x10-6)

Reinforcement stress (N/mm2) Reinforcement stress change(N/mm2)

Verification of proposed concept for evaluating Verification of proposed concept for evaluating maximum crack width (2)maximum crack width (2)

12

0

0.5

1

1.5

2

NC NE NS NES LC LE LS LES

Considering restrained stressNeglecting restrained stress

Rat

io o

f ca

lcu

late

d W

max

to

mae

sure

d W

max

Mixture

Reinforcement stress=200N/mm2

0

0.05

0.1

0.15

0.2

0.25

0.3

-300 -200 -100 0 100 200 300

Measured valueCalculated value considering restrained stressCalculated value neglecting restrained stress

Max

imu

m c

rack

wid

th (

mm

)

Reinforcement strain at zero stress state (x10-6)

Reinforcement stress=200N/mm2

(Shrinkage) (Expansion)

Conventional RC theory cannot evaluate the tendency of Conventional RC theory cannot evaluate the tendency of crack width of RC beams with AS and expansion.crack width of RC beams with AS and expansion. Proposed concept has acceptable accuracy for evaluating Proposed concept has acceptable accuracy for evaluating crack width.crack width.

Proposedconcept

Measured

Conventional theory

Range of conventional theory

Range of Proposedconcept

AS decreases significantly the cracking performances oAS decreases significantly the cracking performances of Reinforced HSC flexural beams.f Reinforced HSC flexural beams.

LS-HSCs markedly improve the flexural cracking perfoLS-HSCs markedly improve the flexural cracking performances; the combined use of Belite-rich low heat Portlanrmances; the combined use of Belite-rich low heat Portland cement and expansive additive is particularly effective.d cement and expansive additive is particularly effective.

It is verified that a new concept can evaluate crack widtIt is verified that a new concept can evaluate crack widths of the RC beams with wider range of early age deformahs of the RC beams with wider range of early age deformation with acceptable accuracy. This concept was adopted ition with acceptable accuracy. This concept was adopted into JSCE Code equation.nto JSCE Code equation.

ConclusionsConclusions 13

Time-dependent structural performance of LS-HSC beams will be presented by TANIMURA, at 7th HS/HPC symposium.

Thank you !!Thank you !!

Specimen for autogenous shrinkage measurementSpecimen for autogenous shrinkage measurement

250

125

100 100

200

125

250 250

500

Embedded gauge Thermo couple

250

125

100 100

200

125

250 250

500

Embedded gauge Thermo couple

Unit; mm

-600

-400

-200

0

200

400

600

0.1 1 10 100 1000

NCNENSNES

LCLELSLES

Au

toge

nou

s sh

rin

kag

e/ex

pan

sion

str

ain

(x1

0-6)

Temperature adjusted concrete age (days)

(Shrinkage)

(Expansion)

Autogenous shrinkage/expansion strainAutogenous shrinkage/expansion strain

High-mechanical performance and high-durability

Necessity of low-shrinkage HSCNecessity of low-shrinkage HSC

Significant autogenous shrinkage

Tensile restrained-stress before loading

Deterioration of serviceability performance of RC members

Low-shrinkage HSC-High cracking -High cracking resistanceresistance-Durable RC structure-Durable RC structure

High-strength

Low shrinkage

High-flowability

Assignment

Additional performance

generalization

Approach for low-shrinkage HSCApproach for low-shrinkage HSC

Belite-rich Portland cement

Low-heat Portland cement

Special admixturesLow-shrinkage cement

Expansive additive

Shrinkage reducing agent

Au

toge

nou

s st

rain

LPCLPC

Conventional HSCConventional HSC

EX+SRAEX+SRA

EXEX

SRASRA

Combination

Expansion rather than shrinkage

Au

toge

nou

s st

rain

Age

Control of autogenous shrinkage