The Effect of Autogenous Shrinkage on The Effect of Autogenous Shrinkage on Flexural Cracking Behavior of Flexural Cracking Behavior of Reinforced HSC Beams and Improvemen Reinforced HSC Beams and Improvemen t by Using Low-shrinkage HSC t by Using Low-shrinkage HSC rth International Seminar on Self-desiccation and Its Importance in Concrete Technol 20/June/05, Gaithersburg, Maryland, USA Masahiro SUZUKI Masahiro SUZUKI P.S. Mitsubishi Construction Co., Ltd., Japan P.S. Mitsubishi Construction Co., Ltd., Japan Makoto TANIMURA Makoto TANIMURA Taiheiyo Cement Corporation, Japan Taiheiyo Cement Corporation, Japan Ryoichi SATO Ryoichi SATO Hiroshima University, Japan Hiroshima University, Japan 1
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The Effect of Autogenous Shrinkage on Flexural Cracking Behavior of Reinforced HSC Beams and Improvement by Using Low-shrinkage HSC Fourth International.
RC beam specimen (Unit; mm) Dimension; 200x250x2700 mm Two-point loading; span:2100mm, pure flexural zone:800mm Evaluations Evaluations Before loading Steel strain Restrained stress on bottom fiber Steel strain Restrained stress on bottom fiber Under short-term loading - Crack width; Contact-type strain gauge - Crack width; Contact-type strain gauge 3 Crack width Sealed curing period;30-50 days Steel strain
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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., JapanMakoto TANIMURAMakoto TANIMURA Taiheiyo Cement Corporation, JapanTaiheiyo Cement Corporation, JapanRyoichi 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
40120
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
40120
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
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 fle
xura
l cra
ckin
g m
omen
t (N
C=1
.0)
Mixture
6.6kNm11kNm
Flexural cracking momentFlexural cracking moment 7
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
ShrinkageRestrained 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
mom
ent
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
ShrinkageRestrained 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
mom
ent
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
imum
cra
ck w
idth
(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
imum
cra
ck w
idth
(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)
Measured valueCalculated value considering restrained stressCalculated value neglecting restrained stress
Max
imum
cra
ck w
idth
(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