toshiharu kishi the university of tokyo institute of ...vinhbd/researchprojects/kishi in vietnam...
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Highly Reliable Concrete Highly Reliable Concrete as A Constitutive Material as A Constitutive Material
for Sustainable Development of Societyfor Sustainable Development of Society
��Research and Practical ActivitiesResearch and Practical Activities��
The University of TokyoInstitute of Industrial Science
Toshiharu KISHI
Bitter experiences from structure’s durability in Japan
In the late 1960’s – 70’s, the rapid economic growth era, the quantity and number of structures have higher priority rather than their quality in construction.
In 1990’s the economic growth was stagnated, thus durable structures are required for ever lasting society at this moment.However, it became apparent that those structure do not
have enough durability at all.This means Japan will surely face the serious heavy
maintenance loads for deteriorated structures in a decade.
We have to learn what are critical points to pay much attention from the past bitter experiences and must not repeat similar mistakes.
The pumping transport of fresh concrete has high efficiency in construction and thus it became standard method in the rapid economic growth era in Japan.
However, this technology might implicitly change the property of concrete from the past sticky but dense one to pumpable but porous one. For regret the higher pumpability has been pursued by increasing W/C, that is, the addition of mixing water for easy casting.Further, this kind of low quality concrete is vulnerable from
poor construction and human related errors in casting.
Consequently, the reliability of concrete and the durability of RC structures were drastically lost, nevertheless old RC structures constructed 80 years ago are still sound in service.
Not only structural performance but also durability of structures are greatly important since infrastructures must continuously sustain the social activities over the generations.
It must be noted that the quality of structure does not become apparent whether enough or poor in durability point of view in the first decade from construction though the long-term service life is expected to most of structures. There is a dormant and silent period of structure.However, the warrant by constructor is limited for only the
first several years. This mismatch is terrible and serious.
To cope with this problem and secure durability of RC structures several countermeasures are necessary.It must be noted that most substantial, effective and costless
means can be adopted at design and construction stages.
Practical and Innovative Countermeasures for Higher Durability
Durability verification designVerifications for structural performance and strength are not
sufficient to satisfy versatile requirements of structures.
Expansive ConcreteShrinkage is one of substantial drawbacks of concrete and
expansive additive is most effective to overcome.
Self Compacting ConcreteFresh concrete can be cast by gravity and free from poor
skill of casting.
Quality inspection system for newly cast concreteI wish to develop since it seems substantial to assure.
Introduction of durability verification design scheme
in JSCE standard specification for concrete structures
(firstly implemented in1999 & modified in 2002)
Durability design of concrete structureLoad and environmental conditions, Service time
Determination of material properties and structural details
Examination of durability of concrete structureCarbonation depth and chloride concentration, etc.
Design and selection of materialsConcrete���materials (cement, admixtures,aggregates)
Determination of mix proportion and production method
Examination of material propertiesDesign strength, Design carbonation speedDesign diffusion coefficient of chloride, etc.
6500
2500
2600
1050
0D25@100
90
120�
��
ƒRƒ“ƒNƒŠ[ƒg‚Ì‘Åž‚Ý‚‚³
3750
3750
3000
Durability checking for substructure of bridge
Design service life : 50 yearsEnv. conditions : 500m from sea shore, No freezing and thawing
Chloride ion, Carbonation, Cracking under constructionChloride ion, Carbonation, Cracking under construction
Assumption forStructural details
Example of Examination for Durability of Structures and Design of Mix Proportion
Lift
heig
ht fo
r cas
ting
There are two ways to conduct durability design of concrete structures.
Procedure 1It is checked whether design values are ok or not.
Procedure 2Minimum value that satisfies requirements is computed.
Procedure 1
Env.condition Service life Diffusion coeff. of Cl-
Clim Cd ( , C0, c, t, Dd)Corrosion initiation limit of chloride concentration Design concentration of Cl-
StructuralDetails
Check
Input�Design value�
OKNG
Cover thickness or design value should be revised
To design of mix proportion of concrete
Coeff. of the structure
It is checked whether design valuesare ok or not.
clγ
iγ
If, result NG (Requirements are not satisfied.)
Modification of design1. Same concrete quality is assumed,
but cover thickness is increased to 90mm 110mm2. Same structural details,
but quality of concrete is enhanced Dk 1.15 0.77����� There are many other options to adopt �����
It is dependent on the decision of designer.
The concrete committee provide the computer software that can assist calculation of examination.
It can be downloaded from the Web.(Japanese version)
Here, two options are introduced.
Procedure 1Designer sets first assumption of concrete properties
Diffusion coeff. of Cl: 1.15cm2/year Carbonation speed : 9mm/√t Examination
))1.0(1(20 tD
cerfCCd
cld�E
�E�E −= γ
cCWbCWD p ++= )/()/(log 2a
Diffusion coeff. is evaluated based on W/C.a, b, c: material constants
Formula for quantitative verification
Cd: Concentration of chloride ion in vicinity of steel.C0: at the surface of concrete.D: Diffusion coefficient for chloride ion.c: Concrete cover.t: Service life time in years.erf(*): Error function.
Designed material properties, such asDiffusion coeff. of chloride
Carbonation speedCompressive strength, etc.
are examined to satisfy requirements.
Designed material properties, such asDiffusion coeff. of chloride
Carbonation speedCompressive strength, etc.
are examined to satisfy requirements.
Material selections and design of mix proportion are done,
so that the above properties are fulfilled.
Material selections and design of mix proportion are done,
so that the above properties are fulfilled.
Procedure 1
Clim Cd (γcl, C0, c, t, Dd)
Minimum value is computed Structural details
are not changedStructural details are not changed
Procedure 2Env.condition Service lifeStructural details
Input�Design value�
Minimum value that satisfies requirements is computed.
Corrosion initiation limit of chloride concentration Design concentration of Cl-
Coeff. of the structure
To mix proportion design of concrete
Check
iγ
Dd
6500
2500
2600
1050
0D25@100
90
120
��
�ƒRƒ“ƒNƒŠ[ƒg‚Ì‘Åž‚Ý‚‚³
3750
3750
3000
Minimum values of material properties that
satisfy requirementsare obtained byreverse analysis.
Diffusion coeff. 0.823Carbonation speed 3.84
Minimum values of material properties that
satisfy requirementsare obtained byreverse analysis.
Diffusion coeff. 0.823Carbonation speed 3.84
Structural details are fixed.Structural details are fixed.Then, mix proportion is
designed to satisfythe above.
Then, mix proportion is designed to satisfy
the above.
Software Software applicationapplication
If mix design cannot satisfy requirements including cost,structural details will be modified.
If mix design cannot satisfy requirements including cost,structural details will be modified.
Lift
heig
ht fo
r cas
ting
Procedure 2
Material / Mix proportionMaterial / Mix proportion
0.1≤′′
γcp
ckp f
fRequirement for strength
20.1
100645.11
1=
−=γ
Vp
Strength of samples
Freq
uenc
y
f’cpf’ck’
γp: safety factor consideringthe variation in production
( ) 0.15.246.14
242.1 ≤⋅+−
⋅WC
W/C<0.56 isrequired.
W/C<0.56 isrequired.
From requirement of strength ���� W/C<0.56
From requirement for chloride penetration����W/C<0.51
From requirement for carbonation����W/C<0.66(considering situation with chloride supply)
Similar calculations are done for other requirements
W/C=51% is selected as minimum valueW/C=51% is selected as minimum value
Mix proportion of concrete will be determined with other conditions for construction such as slump, etc.Mix proportion of concrete will be determined with other conditions for construction such as slump, etc.
CPRC
• Better Flexural Behavior
• Higher Shear Capacity
• Improved Tension Stiffening
• The chemical prestressed reinforced concrete (CPRC) is the RC which is prestressed by expansive agent.
Background
Concrete under Compression
Steel Under Tension In addition, CPRC also shows the potential to resist the cracking
Chemical Prestressed Reinforced Concrete (CPRC)
Load- Average crack width0
2
4
6
8
10
12
0 0.1 0.2 0.3 0.4
Load
(kN
)
Load- Crackwidth D10
0
5
10
15
20
25
0 0.05 0.1 0.15 0.2
Crack width (mm)
Load
(kN
)
Reinforcement Ratio: 0.84% Reinforcement Ratio: 1.91%
Crack Width (mm) Crack Width (mm)
RC
Dry CPRC
Wet CPRC
RC
Dry CPRC
Wet CPRC
CRACK WIDTH is effectively REDUCED in CPRC with practical reinforcement ratio.
Problem from Drying Condition is MORE SEVERE in the case of HIGHER reinforcement
Crack width is reducedCrack width is reducedDrying
effectDrying effect
Cracking load and Load-Crack width
Crack Pattern
Normal RC under bending CPRC under bending
The normal RC and CPRC loaded under tension
Number of cracks is reduced in the case of flexural loading but no clear effect in the case of direct tension test
no cracks between main cracks
smaller crack spacing
crack spacing is almost same
Crack Pattern (Bottom Side)
Constant Moment
Constant Moment
443WET CPRC
444DRY CPRC
665RC
D13D10D6
No. of crack in No. of crack in constant moment spanconstant moment span
RC
DRY CPRC
WET CPRC
RC
DRY CPRC
WET CPRC
D6
D10
LESS CRACK in CPRC !!!
SMALLER CRACK WIDTH and FEWER
CRACKS could be obtained at the same
time by CPRC !!!
Higher Crack Resistance of Pre-deformed CPRC
The CPRC with higher chemical prestrain (lower The CPRC with higher chemical prestrain (lower reinforcement) shows the better performance!!!reinforcement) shows the better performance!!!
0
0.05
0.1
0.15
0.2
0.25
0.3
0 0.2 0.4 0.6 0.8 1P/Py
Avg
Cra
ck W
idth
N6D13CPRC 6D13N6D16CPRC6 D16
Crack Width- Load to Yielding Load Ratio
Load normalized by Yielding Load (P/Py)
Ave
rage
Cra
ck W
idth Normal D16
Normal D13
CPRC D16
CPRC D13
0 0.2 0.4 0.6 0.8 1 Raktipong, 2002
Nonlinear Behavior of CPRC before Cracking
Length: 1m-1
0
1
2
3
4
5
6
0 100 200 300 400
Strain of Mortar (ƒ Ê)
Stress of Mortar CP
NM
0
10
20
30
40
50
60
70
80
0 100 200 300 400
Strain of Mortar (ƒÊ )
Load (KN)
CP
NM
3 days
Load - Strain
Stress - Strain
Hosoda & Shibata, 2000
Mortar (computed)
Specimen
Uni-axial Tension Test (Expansive Mortar restrained by Steel, 3 days)
-1
0
1
2
3
4
5
6
0 100 200 300 400
Strain of Mortar (ƒ Ê)
Stress of Mortar CP
NM
0
10
20
30
40
50
60
70
80
0 100 200 300 400
Strain of Mortar (ƒÊ )
Load (KN)
CP
NM
3 days
Chemical prestress �Calculated chemical prestress
Load - Strain
Stress - Strain
due to chemical prestress
due to utilization of re-barderived from
nonlinear behavior of mortar
Crack resistance of RC member was improved
c
sss A
AECP ε=
Deformability due to nonliniarity
Behavior after Cracking �Tension Stiffening�
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 500 1000 1500 2000
Tensile Strain (µ)
Tens
ile S
tress
(MP
a)
C = 0.4C = 0.2
Shawky model(C = 0.7)
Release of tensile stress is moderate.
Normal Concrete
Reinforcement: 2.8%
�Tamai�1987�
Chemical prestressed concrete shows high stiffness even after cracking in comparison with normal concrete.
Unique !!
Ishimura &Hosoda, 2001
Cross Area 100×100 mm2
Length: 2100 mm
P: D19 (2.865 %)
Uni-Axial Tensile Testing for Chemical Prestressed RC
Ribbed BarExpansive
ConcreteERM�2
Ribbed BarExpansive
ConcreteERM�1
Screwed BarExpansive
ConcreteESM�2
Screwed BarExpansive
ConcreteESM�1
Screwed BarExpansive
ConcreteESN�2
Screwed BarExpansive
ConcreteESN�1
Ribbed BarNormalNR�2
Ribbed BarNormalNR�1
Screwed BarNormalNS�2
Screwed BarNormalNS�1
Type of Steel
Type of Concrete
Code Name
W/C = 50%Expansive agent = 60kg/m3
Wet curing Loading at 28 days
Tension Stiffening Tensile stress carried by concrete after cracking
Normal RCLoadLoad
Ave. StrainAve. Strain
Bare steel barRC member
Tension Stiffening
Cracking
Ave. StressAve. Stress
Ave. StrainAve. Strain
Tensile Strength
CPSCPS
Tensile Strength
The origin is shifted.
Chemical Prestressed RCLoadLoad
Ave. StrainAve. StrainCPNCPN
CPSCPS
Cracking
Tension Stiffening
Evaluation of Tension Stiffening of CPRC
Tension Stiffening Modelc
t
tutt f ⎟⎟
⎠
⎞⎜⎜⎝
⎛εε
=σ
where; σt : average stress of concreteft : tensile strength of concreteεtu : strain corresponding
to the tensile strength of concreteεt : average strain of concretec : coefficient
(0.4 for reinforced concrete)
Avg. StressAvg. Stress
Average StrainAverage Strain
fftt
Model
Tension Stiffening of RCTension Stiffening of RC
0
0.5
1
1.5
2
2.5
0 500 1000 1500 2000
Average Strain
Con
cret
e St
ress
(Mpa
)
NR1
Model
0
0.5
1
1.5
2
2.5
0 500 1000 1500 2000
Average Strain
Con
cret
e S
tress
(Mpa
)
NR2Model
0
0.5
1
1.5
2
2.5
0 500 1000 1500 2000
Average Strain
Con
cret
e S
tress
(Mpa
) NS1
Model
0
0.5
1
1.5
2
2.5
0 500 1000 1500 2000
Average Strain
Con
cret
e St
ress
(Mpa
)
NS2
Model
Adjusted Tension Stiffening of CPCAdjusted Tension Stiffening of CPC
0
0.5
1
1.5
2
2.5
0 500 1000 1500 2000
Average Strain
Con
cret
e St
ress
(Mpa
) ESN1Model
0
0.5
1
1.5
2
2.5
0 500 1000 1500 2000
Average Strain
Con
cret
e St
ress
(Mpa
)
ESN1
Model
0
0.5
1
1.5
2
2.5
0 500 1000 1500 2000
Average Strain
Conc
rete
Stre
ss (M
pa)
ESM1
Model
0
0.5
1
1.5
2
2.5
0 500 1000 1500 2000
Average Strain
Con
cret
e St
ress
(Mpa
)
ESM2Model
0
0.5
1
1.5
2
2.5
0 500 1000 1500 2000
Average Strain
Conc
rete
Str
ess
(Mpa
)
ERM1
Model
0
0.5
1
1.5
2
2.5
0 500 1000 1500 2000Average Strain
Con
cret
e St
ress
(Mpa
) ERM2
Model
ESN2
0
0.5
1
1.5
2
2.5
0 400 800 1200 1600
Average Strain
Con
cret
e St
ress NR2
NS1
No Difference from Shape of Steel�RC
0
0.5
1
1.5
2
2.5
0 400 800 1200 1600
Average Strain
Con
cret
e St
ress NR1
NS2
0
0.5
1
1.5
2
0 400 800 1200
Average Strain
Con
cret
e St
ress
ERM2
ESM2
0
0.5
1
1.5
2
0 400 800 1200
Average Strain
Con
cret
e St
ress
ERM2
ESM1
�CPRC
Crack Patterns at 100 Crack Patterns at 100 kNkNNS2
NSN1
NR1
NM2
Crack Pattern after LoadingCrack Pattern after Loading
NS1
ESN2
Crack SpacingCrack Spacing
0
5
10
15
20
25
30
NS1 NR2 ESN2 ESM1 ERM1
Yielded Specimen
13.10 13.30
17.97
12.9817.58
0
5
10
15
20
25
30
NS2 NR1 ESN1 ESM2 ERM2
Loaded until 100 kN
18.17
13.69
20.98
26.6128.57
In general, the crack spacing of CPC is larger then RC. In the other words, there is
less number of cracks in CPC
Unit : cmUnit : cm
Bond characteristic of CPRC must not be judged by this experiment.
Strain distribution of embedded steel should be directly examined.
BondTension StiffeningCrack scattering =
Bond �Tension StiffeningCrack scattering �
From this experiment,
Features of CPRC- Tension Stiffening is remarkable.- Number of cracks is small and crack spacing is large.
--- Normal RC
--- CPRC
Discussion of Bond Characteristic of CPRC
ƒÐ t
cracking strain
ƒÃ t0
ƒÐ t
cracking strain
ƒÃ t0
RC zone
εt
σt
?Localization starts
Cracking
softening
0
Expansive Concrete
Cracking
Normal Concrete
Stress-Strain Relationship of Expansive Concrete
average stress-strain relationship
Recovery of Crack Resistance under Drying ?
0.2
0.3
0.4
0.5
0.6
0.7
0 5 10
� � � � �
��
��
��
��
��
��
��
(tfm)
0.2
0.3
0.4
0.5
0.6
0.7
0 5 10
� � � � �
��
��
��
��
��
��
��
(tfm)
Normal RC
0 1 3 12
CPRC(Lime)
CPRC(Ettringite)
0
50
100
150
200
0 0.5 1 1.5(mm)
��(kN)
0
50
100
150
200
0 0.1 0.2 0.3 0.4 0.5(mm)
��(kN)
0
50
100
150
200
0 0.1 0.2 0.3 0.4 0.5(mm)
��(kN)
0
50
100
150
200
0 0.1 0.2 0.3 0.4 0.5(mm)
��(kN)
3M Drying Before Drying
Change of Crack Resistance of Normal RC under Drying(D16)
Max. Crack Width
Ave. Disp. Ave. Crack Width
Total Crack Width
0
50
100
150
200
0 0.5 1 1.5(mm)
��(kN)
0
50
100
150
200
0 0.1 0.2 0.3 0.4 0.5(mm)
��(kN)
0
50
100
150
200
0 0.1 0.2 0.3 0.4 0.5(mm)
��(kN)
0
50
100
150
200
0 0.1 0.2 0.3 0.4 0.5(mm)
��(kN)
1M Drying
3M Drying Before Drying
Change of Crack Resistance of CPRC under Drying(D16)
Max. Crack Width
Ave. Disp. Ave. Crack Width
Total Crack Width
Evaluation of early age development of materials and structures
10-1
100
101
102
104
103 Time
�Days)
Birth DeathEarly age development
Moisturetransport
Strength development
Thermal cracks
Shrinkage cracks
Hydration processMulti-component hydration heat model(by Kishi)
Micro-pore structure development
Pore structure development model (by Chaube)
Modeling based on micro mechanisms
Moisture isotherm Moisture transport�by Chaube & Ishida)
Multi-Component Model for Cement Hydration
HC S2
C A3
C S3
C AF4
Mono
C A3 + Gypsum
ETTRINGITE MONO-SULPHATE
Each component hydrationprogress dependent on
Hydration heat rate of each component at Ti OH
MonoSulphateC3S
C2S
C4AF
C3A
Typical componentcomposition of cement
T TRH H
Ei i T
i
OO
= −
, exp 1 1
Tota
l hea
t gen
erat
ion
rate
Temperature Moisture contentDegree of hydration
0 40 80 120 160 2000
1
2
3
4
5
6
Accumulated Heat (kcal/kg)
0 20 40 60 80 100 1200
1
2
3
Accumulated Heat (kcal/kg)
QC AF4 ,∞
0 50 100 150 200 250 300 350 4000
2
4
6
8
10
Accumulated Heat (kcal/kg)0 40 80 120 160 200 240
-10,000
-7,500
-5,000
-2,500
0
Accumulated Heat (kcal/kg)
Ther
mal
Act
ivity
(K)
100%3% 20%
stage1 stage2 stage3
(30%)
Slag
Fly Ash
Slag
Fly Ash
Hi,T
o(k
cal/k
g/hr
)H
i,To
(kca
l/kg/
hr)
Hi,T
o(k
cal/k
g/hr
)
H i,To : Referential heat generation rate
C A3C S3C AF4C S2
QC S2 ,∞ QC S3 ,∞ QC A3 ,∞QFA,∞ QSG,∞
QC AET3 ,∞QC AFET4 ,∞C A3
C S3
C S2
C AF4
C AFET4
C AET3
Reference Heat Rate & Thermal Activity
Hyd
ratio
n H
eat R
ate
Time
Retarding Effect
Tem
pera
ture
Time
Mineral composition
Time
Tem
pera
ture
Shortage of water
Hyd
ratio
n H
eat R
ate
Time
Ettringite formation
Interdependency of mineral reactions
C3S
C2S
C3AC4AF
SG
FA
ω freeFree Water
Ordinary cement
Super low heat cement
For Future Development – Functions of Concrete-
Numerical Analysis Experiment
Technology Development
Recycling
Maintenance
Expansive Concrete
New Structural System
Low W/C mixtureMany possibilities
CreepUnified theory
Intelligent material
MechanismElucidations
For most efficient and rational technology
development
MechanismElucidations