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