Estimation Method on Deterioration of Marine Concrete Structures Due to Chloride Attack
Koji TAKEWAKAAssociate Professor
Dept. of Ocean Civil Engineering Kagoshima University
Contents• Outline of deterioration process of marine
concrete structure
• Examination of durability for marine concrete structure in durability design
• Simulation model of corrosion of reinforcement in concrete
• Evaluation of structural performance of concrete structure deteriorated due to corrosion of reinforcement
Outlineof
Deterioration Process
Outlineof
Deterioration Process
Deterioration process on marine concrete structures
Concrete (pH-12.5)
Passive film Passive filmdestruction
Chloride ions H2O
O2
Rust (volumetric expansion)
Crack
DelaminationRebar
Chloride-induced deterioration process
ⅡPropagation
period
Ⅳ
Chloride-induced deterioration process
period
ⅢAcceleration
Deterioration
period
IV
Deg
radat
ion o
fst
ruct
ura
lper
form
ance Life of
Structure
Incubationperiod
Ⅰ
Deterioration process on marine concrete structures
Det
erio
ration
Deterioration process on marine concrete structures
Definition of stages in the deterioration process and primary factors characterizing each stage
StageNo. Definition of period
Primary factorscharacterizing the
deterioration
IPeriod of chloride penetration until the chlorideconcentration around rebars up to the thresholdvalue
・ Chloride diffusion rate・ Cover thickness
II Period of the corrosion progress on rebar untilconcrete cracks due to the corrosion appear
・ Rebar corrosion rate・ Resistivity against cracking of concrete
III Period of the corrosion progress on rebar afterappearance of concrete cracks
IV Period of degradation of structural performanceinduced by rebar corrosion and concrete cracks
・ Rebar corrosion rate・ Width of cracks due to rebar corrosion
Deterioration process on marine concrete structures
Marine environment
Chloride penetration into concrete
Passive film on reinforcement is lost
Reduction of Cross-section of reinforcement
Corrosion of reinforcement starts
Degradation of structural performance of the structure
Introduce of corrosion cracking and spalling of
concrete
Water Oxygen
Deterioration process on marine concrete structures
Penetration of chloride into concrete
Penetration of Cl- via pores to the interior of concrete
Cement hydrate binds some of Cl- chemically Fredel’s salt (C3A・CaCl2・nH2O)
Only the free chloride diffuses into concrete
When critical concentration of free Cl- accumulates on reinforcement surface, corrosion starts on it
In sea water, Splash zone, Marine atmospheric Zone
Example of chloride penetration profile into concrete
Chloride distribution profiles in concrete bridge beams in coastal zone after 17 years of service
14
12
10
8
6
4
2
0
16
0
2
4
6
8
10
12
14
16
Cl-
in c
oncr
ete
(kg/
m3 )
0 1 53 7 99 7 5 3 1 0Depth from concrete surface (cm)
Beam No. G1Beam No. G2Beam No. G3
Mountain side
Coastal side
Microstructure of Cement paste
Gel pores Capillary pores
Water In hydrationUnhydrated
cement
Original particle
boundary
Hydrate
Unhydratedcement
Inner productsC-S-H grains
Schematic representation of porosity classification in concrete
10-210-410-610-810-10
Por
osity
dis
tribu
tion
Radius of pore (m)
Gel pores
Capillary pores
Entrained air
Construction pores
Interlayer pores Micro pores Macro pores1A ~ 50nm 10nm ~ 50µm 50µm ~°
Binding of chloride ions into cement hydrate
Free Cl -
Physicallyabsorbed Cl-
Chemicallybound Cl-
Cement hydrate
Cement hydrate
Chemical binding equation
OHCaClOAlCaOOHCaClOHOAlCaO
2232
22232
103463
⋅⋅⋅→++⋅⋅
Fredell’s salt
Deterioration process on marine concrete structures
Penetration of chloride into concrete Diffusion equation
(Modified Fick’s second low)
CKzC
yC
xCD
tC
⋅−
∂∂
+∂∂
+∂∂
=∂∂
2
2
2
2
2
2
Cl-
conc
entra
tion(
C)
Depth from concrete surface (x)
t1
t2
t3
t1 < t2 < t3 : Age of structure
C: Concentration of Cl-at depth (x,y.z) after t
D: Diffusion coefficient
K: Cl- binding coefficient
Deterioration process on marine concrete structures
Critical chloride content [C
l- ]
pH11.5
6.0][
][≥−
−
OHCl
Non-corrosion
Corrosion
Effect of Chloride concentration and pH on initiation of corrosion
Deterioration process on marine concrete structures
Critical chloride content
In case of ordinary reinforcing bar in concrete
0.05% Cl- related to the weight of Concrete
=0.4% Cl- related to the cement weight
or
1.2 kg/m3 of Cl- per unit concrete volume
Deterioration process on marine concrete structures
Corrosion process on reinforcement
Cl-, H2O, O2Cl-, H2O, O2Cl-,
Cl-
Anode CathodeCathode
Fe2+ + 2(OH)- → Fe(OH)2
2Fe(OH)2 + 2(OH)- → 2Fe(OH)3
I
Corrosion current ∝ Corrosion rate
H2O+1/2O2+e- →2(OH)-
Fe→Fe2++ 2e- e-
Passive film)6020( Α−
Deterioration process on marine concrete structures
Corrosion process on reinforcement
Anode CathodeCathode
IcorrRc
Electric resistance of concrete
Rp
Polarization resistance
Icorr
Corrosion current ∝ Corrosion rate ∝ 1/Rp
Deterioration process on marine concrete structures
Corrosion process on reinforcement
Corrosion weight loss of reinforcement (W)
pcorr R
kI 1⋅=
Corrosion current: Icorr
Rp: Polarization resistance
k: Constant (25~50mV)
Corrosion Weight loss: W[ ] tI
FnFeW corr ⋅⋅⋅
=
[Fe]: Atomic weight (55.84 g)n: Atomic value (Fe: n=2)F: Faraday’s Constant (96,500 A/sec)
Deterioration process on marine concrete structures
Corrosion crack on concrete
Rust:this volume is two to fourtimes of the steel’s one
Tensile stress distributing around steel bar
Stress distributing on concrete surface
Tensile stress
Compressive stress
tp
φ
Corrosion crack
Corrosion crack
(a) Thin Cover1.5< (2tp+φ)/ φ ≤ 3.0
(b) Thick Cover (2tp+φ)/ φ >3.0
Deterioration process on marine concrete structures
Relationship between corrosion amount and corrosion crack on concrete
0.01
0.02
0.03
00. 1 0. 2 0. 3 0. 40
0.10
0.08
0.06
0.04
0.02
00 0. 1 0. 2 0. 3
Cor
rosi
on lo
ss (g
/cm
2 )
Cor
rosi
on lo
ss (g
/cm
2 )
Corrosion crack width (mm) Corrosion crack width (mm)
c/d=5.27
c/d=2.38c/d=2.13
c/d=1.42
c/d=3.35
c/d=2.63
c/d=2.13
Round Bar Deformed Bar
c/d: Cover thickness/diameter of rebar
0
0.05
0.1
0.15
0.2
0.25
0.3
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6Crack width (mm)
Cor
rosi
on lo
ss (g
/cm
2)HSC: c/d= 2.66 HSC: c/d= 2.00NSC: c/d= 2.13NSC: c/d= 2.63
High strength concrete have smaller crack width opening than High strength concrete have smaller crack width opening than normal strength concrete for same corrosion lossnormal strength concrete for same corrosion lossConcrete strength also influences on the crack width openingConcrete strength also influences on the crack width opening
Relationship between corrosion amount and corrosion crack on high strength concrete
Deterioration process on marine concrete structures
Conceptual figure of degradation process of performance on structure
Water-proofness
Safety forthird parties
Aesthetics
Load bearingcapacity
Elapsed time
Stage I Stage II Stage III Stage IV
Deg
rada
tion
ofea
ch p
erfo
rman
ce
Example of performance degradation on RC beam due to rebar corrosion
0
20
40
60
80
100
120
0 0.1 0.2 0.3 0.4Corrosion Loss (gm/cm2/cm)
Stre
ngth
ratio
(%)
NSC: Mangat et al.NSC: Almusallam et al. HSC: Takewaka et al
Singly reinforced concreteSingly reinforced concrete
Experiment result for loss in load-bearing capacity
Example of performance degradation on RC beam due to rebar corrosion
0
20
40
60
80
100
120
0 0.1 0.2 0.3 0.4
Corrosion Loss (gm/cm2/cm)
Stre
ngth
ratio
(%)
NSC: Umoto et al.HSC: Takewaka et al.
Doubly reinforced concrete Doubly reinforced concrete with shear with shear rebarsrebars
Experiment result for loss in load-bearing capacity
Flexural Failure
Shear Failure
Example of performance degradation on RC beam due to rebar corrosion
Experiment result for loss in ductility of RC beam
0.0
1.0
2.0
3.0
4.0
5.06.0
0.0 0.1 0.2 0.3 0.4Corrosion Loss (gm/cm )2
Duc
tility
Singly RC beam
Doubly RC beam
Example of performance degradation on RC beam due to rebar corrosion
Analytical result for loss in fatigue property
Corrosion crack width on concrete surface (mm)
Num
ber o
f cyc
lic lo
adin
g at
fatig
ue fa
ilure
1.E+04
1.E+05
1.E+06
1.E+07
0 0.5 1 1.5 2 2.5
Examination results
Analysis result in case that pitting corrosion depth is equal to (corrosion weight loss + 0.15)
Extra Costs for maintaining durability of structure during the service life
Stage I Stage IIStage III
Stage IV
Det
erio
ratio
n C
ost f
or
mai
ntai
ning
du
rabi
lity
1 5
25
125
“The law of fives”presented by De Sitter
Examination in
Durability Design
Examination Examination inin
Durability DesignDurability Design
Schematic of design for structure
Structural design
Durability design Landscape
design
Integrated design
Performance-based design
What is “ Durability of structure”
Qualitative performance
Resistance against deteriorating actions from surrounding environment
To keep the all of required performances on structure to their levels more than the required ones during the service life
Durability designDesign carried out to ensure that the structure can maintain its required performance (functions) during the
service life under environmental actionsdefined by Asian concrete model code
Evaluation of long-term-performance
Examination of durability
General principle
All required performances for structure, such as serviceability, restorability and safety under actions in normal use, wind action and seismic action, shall be examined respectively in regard of their long-term performances in the service life.
Examination of durabilityExamples of durability-limit-state
Durability-limit-state A: All performances maintain the initial conditions.
Durability-limit-state B: Though some material used in structure deteriorates, negligible decay in any performance of structure occurs.
Durability-limit-state C: Though some structural performance deteriorates, function of structure keep in the required condition and the damages are repairable.
Examination of durabilityDurability Limit state Class A
Class C
Deterioration can occur on both performance of structure and material within allowable range .
corrosion initiationtime
Some deterioration on material, No deterioration of structure performance.
( initial period +propagation period)
Corrosion crackGeneration time
No deterioration of both structure performance and
material.
Class B
Durability-limit-state for marine concrete structures
Examination of durability
Durability-limit-state A:• All performances maintain the initial condition
crd tt ≤td : Design service life of marine concrete structuretcr: Duration until reinforcement starts to corrode
tcr is seemed to be the duration until concentration of Cl-accumulating on reinforcement surface reaches a critical
value for starting corrosion
Examination of durabilityEvaluation method in durability-limit-state A
0.1lim
),( ≤⋅C
C Tdcγ
C(c, Td) : Chloride content at reinforcement position duringservice life of structure
Clim : Critical chloride content γ : Safety factor
This concept was Introduced in 1999 version of JSCE standard specification for design of
concrete structure as the verification method of durability of concrete structure
• In sea water or tidal zone
• In splash zone or atmospheric zone
),( TdcC
⋅−=
dTdc TD
cerfCC2
10),(
xCD
tC
2
2
∂∂
=∂∂
Simplified Fick’s second law
C0 : Chloride content on concrete surfaceD : Chloride diffusion coefficient of concreteTd : Design service lifec : Minimum cover thicknessW : Accumulated chloride amount on concrete surface during unit time
Theoretical analysis
⋅−−
⋅=
dd
dTdc TD
cerfD
cDTc
DTWC
21
24exp2
22
),( π
ηπ
η deserfs
∫ −=0
22)(here,
C: Concentration of Cl- at depth x after tD: Diffusion coefficient
logD = 4.5(W/C)2
+0.14(W/C) - 8.47
-8
-7
-6
0.3 0.5 0.7 0.9W/C
log(
D)
logD = 19.5(W/C)2
- 13.8(W/C) - 5.74
-9
-8
-7
-6
0.3 0.5 0.7W/C
log(
D)
(a) In case of OPC (b) In case of BFSC
Relationship between chloride diffusion coefficient and W/C of concrete
Durability-limit-state for marine concrete structures
Durability-limit-state B:• Though some material used in structure deteriorate,
negligible decay in any performance of structure occurs
ckcrd ttt +≤td : Design service life of marine concrete structuretcr: Duration until reinforcement start to corrode
tck: Period of corrosion progress on reinforcement from start of corrosion until occurrence of corrosion crack on concrete
ckcrd ttt +=
tcr: Duration until reinforcement start to corrode
tck: Period of corrosion progress on reinforce-ment from start of corrosion until corrosioncrack occurs on concrete
20
1
2
)]/1([4 CCerfDct
ddcr −⋅= −
th
CN
ck ECWcc
tβ
ααα φ
⋅
⋅
−⋅⋅⋅+
=1)/(
1)1(7.1 85.0
th
CN
ck ECWcc
tβ
ααα φ
⋅
⋅
−⋅⋅⋅+
=1)/(
1)1(7.1 85.0
c : Concrete coverW/C : Water to cement ratioα N : Factor for strength of concrete: = 0.5/(W/C)αφ : Factor for diameter of rebar(φ): = 2/φEh : Factor for environment: = 1.5 (in sea water)
2.5 (tidal zone)3.5 (splash zone, coast line)2.0 ( others)
β t : Factor for average temperature: = 0.7 (under 10°C) 1.0 (10 ~ 20°C)
1.3 (over 20°C)α C: Factor for type of cement: = 1.0 (OPC)
1.25 (BFSC)
Relationship between minimum cover thickness and maximum W/C required for durability
Design conditionOPC, Design service life: 50 years
Durability-Limit-state A Durability-Limit-state B
0
5
10
15
20
25
0.35 0.45 0.55 0.65 0.75
W/C
Cov
er
thic
kness
(c
m) Splash zone
0.1km
In sea water
0
20
40
60
80
0.35 0.45 0.55 0.65 0.75W/C
Splash zone
Coast line
0.25km
0.5km
0
20
40
60
80
0.35 0.45 0.55 0.65 0.75W/C
Cove
r t
hic
kness
(cm
) Splash zoneCoast line 0.25 km0.5 km1 km
Relationship between minimum cover thickness and maximum W/C required for durability
Design conditionBlast furnace slag: 50%, Design service life: 50 years
Durability-Limit-state A Durability-Limit-state B
0
5
10
15
20
25
0.35 0.45 0.55 0.65 0.75
W/C
Cove
r th
ickn
ess
(cm
)
Splash zone
0.1km
In sea water
0
20
40
60
80
0.35 0.45 0.55 0.65 0.75
W/C
Cove
r th
ickn
ess
(cm
)
Splash zone
Coast line
20
40
60
80
0.35 0.45 0.55 0.65 0.75
W/C
Splash zone Coast line
0.25 km0.250.5 km0.51 km1
Computer Simulation Model
Computer Simulation Computer Simulation ModelModel
Simulation model for deterioration of concrete structure in marine environment
To evaluate more directly the durability in actual condition by using deterioration simulating model
Simulation model• Concrete model considering scatter of quality• Penetration model of chloride and oxygen• Corrosion model of reinforcement
• Progress of corrosion of reinforcement• Period of corrosion crack generation
Estimation
Simulation model for deterioration of concrete structure in marine environment
Framework of Corrosion Simulation model
Oxygen DiffusionConcrete Quality
Progress of Corrosion
Initiationof Corrosion
CO
R R O S I O N
OM
DE
L
Cracks in ConcreteChloride Diffusion
Outline of the concrete modelcircular-pore
2 dimensional reinforced concrete model
Concrete
Sound part Steel
Pore distributionin concrete
Circular-pore distribution• Randomly located • Considering W/C and RH
Aggregate distributionin concrete
Circular-Aggregate distribution• Randomly located • Considering ITZ
Modified pore distribution
0
0.1
0.2
0.3
0.4
0.5
Pore diameter (cm)
Den
sity
of p
ore
volu
me W/C70%
W/C60%W/C50%W/C40%
10-8 10-6 10-4 10-2 1
Capillary pores
Macro pores
(by Shimomura et al)V’(r) = V’(∞)・B・C・rC-1・exp (-Brc)
V’(r) : Density of pore volumeB,C: Parameters depending on W/C
Modified relative humidity
Water-filled pore
Air-filled pore
Steel
Concrete
Water-filled pore volumeTotal pore volume
Relative humidity =
Model of aggregateInterfacial transition zone ( ITZ )
Coarse Aggregate
Steel
Wet-ITZ
Dry-ITZ
Concrete
The zone with several micrometers thickness lying between aggregates and hardened cement paste matrix, which has higher porosity than the bulk cement paste
Steel
Wet-aggregate
Dry-aggregate
Water- filled pore
Air- filled pore
Specification of a route on which chlorides reach rebar in minimum diffusion time
Minimum diffusion route
For each section (1cm)
Many diffusion route
Minimum diffusion time
One specific route
Chloride Penetration Model
Circumference
Diffusion route
Wet-ITZsurrounding aggregateInstantly
Dry-ITZsurrounding aggregateCircumference
Water-filled poreInstantlyAir-filled pore
Cl-
Cf : free chloride concentration
K : combined coefficientf
ff KCxC
Dt
C−
∂
∂=
∂
∂2
2
Diffusion of Free chloride described by Modified Fick’s 2nd law
Oxygen Penetration Model
Instantly
Instantly
Diffusion coefficient
(1.0E-6 cm2/s)Diffusion coefficient
(1.0E-6 cm2/s)
Diffusion route
Wet-ITZ Surrounding aggregateDry-ITZ Surrounding aggregateWater-filled poreAir-filled pore
O2
Diffusion of oxygen described by stationary state condition
( Fick’s first low )Distribution of concentration
x
C1
C2
Diffusion
qdxdCDq =
q : Flow rate of substanceC: concentration of substanceD: Diffusion coefficient
Cracked concrete Model
Cracks may exist by externalloading, drying shrinkage etc..
Bilinear route
Crack position
Definition of effective crack length
Treat as sound concrete
Effective crack length
Cra
ck le
ngth
Steel
Relationship between effective crack and diffusion coefficient
infinity
1( = in water)
1/101/100 5 cm
3.75cm
2.5cm1.25cm
Effective crack length
0 cm
Diffusioncoefficient
Corrosion model- based on macrocell corrosion theory-
Specification of Anode and Cathode area
Steel section
ACCCCC C C C
Anode
Cl- Concentration at rebar > tolerance
Corrosion reactions start
A A
Estimation of corrosion rateCorrosion model
Cathodic control Anodic controlO2+2H2O+4e- → 4OH- Fe2- → Fe2++2e-
4Fe2-+8OH-+O2+H2O→ 4Fe(OH)3
iAiC
The lower rate between iA and i C is selected as the corrosion rate at anode portion
Oxygen diffusion amount to each
section
Calculate corrosion amount
Change of anode area
SIMULATION RESULTSSIMULATION RESULTS
SIMULATION RESULTSSIMULATION RESULTS
Corrosion initiation time
W/C (%)
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
40 50 60 70Cor
rosi
on in
itiat
ion
time
(yea
rs)
RH 40%RH 60%
RH 80%
W/C (%)
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
40 50 60 70Cor
rosi
on in
itiat
ion
time
(yea
rs)
RH 40%RH 60%
RH 80%
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
40 50 60 70Cor
rosi
on in
itiat
ion
time
(yea
rs)
RH 40%RH 60%
RH 80%
RH 40%RH 60%
RH 80%
SIMULATION RESULTSSIMULATION RESULTS
Corrosion initiation time
0102030405060708090
5 7.5 10 12.5Cover thickness (cm)
Cor
rosi
on in
itiat
ion
time
(yea
rs) W/C 40 %
W/C 50 %
W/C 60 %
W/C 70 %
RH 80%
0102030405060708090
5 7.5 10 12.5Cover thickness (cm)
Cor
rosi
on in
itiat
ion
time
(yea
rs) W/C 40 %
W/C 50 %
W/C 60 %
W/C 70 %
RH 60%
the larger the cover thickness, lifetime increases clearly.Relative humidity is also influential parameter.
SIMULATION RESULTSSIMULATION RESULTS
Corrosion crack generation time
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40 50 60 70W/C
Cor
rosi
on c
rack
gen
erat
ion
time
(yea
rs)
Max.value Avg.value Min.value
RH 60 %
Maximum
Average
Minimum0
SIMULATION RESULTSSIMULATION RESULTS
Corrosion crack generation time
50
100
150
200
250
300
5 7.5 10 12.5Cover thickness (cm)
Cor
rosi
on c
rack
gene
ratio
n tim
e (y
ears
) W/C 40 %
W/C 50 %
W/C 60 %
RH 80%
0
W/C 70 %
Initial crack modelSIMULATION RESULTSSIMULATION RESULTS
Corrosion initiation time
W/C 40%
0
2
4
6
8
10
0 5 10 15 20
Section number
Cor
rosi
on in
itiat
ion
time
(yea
rs)
0 cm 1.25 cm 2.5 cm3.75 cm 5 cm
Effective crack length
5 cm of cover thickness
Initial crack modelSIMULATION RESULTSSIMULATION RESULTS
Corrosion crack generation time
0
5
10
15
20
25
30
0 1.25 2.5 3.75 5Effective crack length (cm)
Cor
rosi
on c
rack
ge
nera
tion
time
(yea
rs)
W/C 40%W/C 50%W/C 60%W/C 70%
5 cm cover thickness
Example for evaluation of structural performance of deteriorated RC structure
Example for evaluation of Example for evaluation of structural performance of structural performance of deteriorated RC structure deteriorated RC structure
DYNAMIC BEHAVIOR OF REINFORCED DYNAMIC BEHAVIOR OF REINFORCED CONCTERE STRUCTURES DETERIORATED BY CONCTERE STRUCTURES DETERIORATED BY
CORROSION OF REINFORCEMENTCORROSION OF REINFORCEMENT
IntroductionIntroduction
some structures in the severe environmental condition may be in a deteriorated condition due to the corrosion of reinforcement
piers are relatively vulnerable to earthquake because it is suffered with a very large inertial force
IntroductionIntroductionLarge
EarthquakeCorrosion of
Reinforcement
Some pier with corrosion of reinforcement may not have the structural capacities it was designed for
Rehabilitation and Repairing is being
popular
Evaluation of the dynamic behavior of the piers deteriorated by corrosion becomes necessary
IntroductionIntroduction
Objective
Evaluate the dynamic properties such as,stiffnessstiffness, ductilityductility and energy absorptionenergy absorption ofthe piers deteriorated by the corrosion of reinforcement
Behavior of the corroded piers against the cyclic loading which are designed by
Ordinary design, using JSCE code.Seismic design part of JSCE along with the verification of ductility according to JRA’s specification
MethodologyMethodology
Specimen Type
S. No.
Designation Design Principle Axial Load
Corrosion Lossgm/cm2/cm
1 POA-1 0.002 POA-2 0.193 POA-3 0.384 POA-4 0.565 PON-1 0.006 PON-2 0.197 PON-3 0.388 PON-4 0.56
Using JSCE code for ordinary reinforced
concrete design
200 kN
0
MethodologyMethodology
Specimen Type (Contd..)
S. No.
Designation Design Principle Axial Load
9 PEA-1 0.0010 PEA-2 0.1911 PEA-3 0.3812 PEA-4 0.5613 PEN-1 0.0014 PEN-2 0.1915 PEN-3 0.3816 PEN-4 0.56
Using seismic resistant part of JSCE code in
conjunction with JRA’s specification
200 kN
0
Corrosion Lossgm/cm2/cm
MethodologyMethodology
Specimen Size220 mm
500 mm
1200 mm 320 mm
1000
mm
1200
mm
220 mm
Ducts for post-tensioning
Duct for anchor bolt
Reinforcement Arrangement
4 – D 20φ 9 @200 mm
φ 9 @200 mm6 – D 20
12.7 mm PC Tendons
Ordinary Design
4 – D20φ 9 @80 mm
φ 9 @200 mm6 – D 20
12.7 mm PC Tendons
Seismic Design
Accelerated Corrosion Test
`
Test specimen
3.5% NaCl solution
Longitudinal rebar (anode)
Titanium net (cathode)
Tank
+-
Current supplier
Hydraulic Actuatorwith Force Sensor
Reaction Frame
Anchor Bolt
Test Specimen
Dial Gauge
12.7 mm Tendon
Hydraulic Actuatorwith Force Sensor
Reaction Frame
Anchor Bolt
Test Specimen
Dial Gauge
12.7 mm Tendon
Hydraulic Actuatorwith Force Sensor
Reaction Frame
Anchor Bolt
Test Specimen
Dial Gauge
12.7 mm Tendon
Loading Test
Condition
Loading Cycles
Lateral Load History
-150
-100
-50
0
50
100
150
0 4 8 12 16
Cycle Number
Dis
plac
emen
t (m
m) Load Control
Displacement Control
MethodologyMethodology
Comparison of Various Corrosion Loss
0.13 gm/cm2 0.45 gm/cm20.04 gm/cm20.0 gm/cm2
10 c
m
Results and DiscussionResults and Discussion
Load Displacement Curve
-80
-60
-40
-20
0
20
40
60
80
-120 -80 -40 0 40 80 120Displacement (mm)
Load (
kN
)
4 5 6 7 8 9 10 11 131214
15
Seismic DesignNo Axial LoadNo Corrosion
Results and DiscussionResults and Discussion
Load Displacement Curve
-80
-60
-40
-20
0
20
40
60
80
-120 -80 -40 0 40 80 120Displacement (mm)
Load (
kN
)
4 5 6 7 8 9 10 11 1213
14
Seismic DesignNo Axial Load0.17 gm/cm2
Corrosion loss
Results and DiscussionResults and Discussion
Load Displacement Curve
-80
-60
-40
-20
0
20
40
60
80
-120 -80 -40 0 40 80 120Displacement (mm)
Load (
kN)
4 5 6 7 8 9 10 1112
Seismic DesignNo Axial Load0.22 gm/cm2
Corrosion loss
Results and DiscussionResults and Discussion
Load Displacement Curve
-80
-60
-40
-20
0
20
40
60
80
-120 -80 -40 0 40 80 120Displacement (mm)
Load (
kN
)3 4
56
7
Seismic DesignNo Axial Load0.44 gm/cm2
Corrosion loss
Results and DiscussionResults and Discussion
Strength Degradation
0
40
80
0 0.2 0.4 0.6Corrosion loss (gm/cm2)
Str
engt
h
(kN
) PONPOAPENPEA
Results and DiscussionResults and Discussion
Strength Degradation ( Contd…)
0
40
80
120
0 0.2 0.4 0.6Corrosion loss (gm/cm2)
Stre
ngth
Rat
io (%
)
PON POA PEN PEA
Best fit curve from experimental results
result of theoretical calculation of strength reduction due to loss of area of steel only
Pc=(1-0.6745∆w2-0.2969∆w)Pu
R2=0.8323
Results and DiscussionResults and Discussion
Ductility Degradation
Displacement (mm)
Loa
d (
kN)
Pu
Py
0.8 Pu
δy δu
µ=δu/δy
Results and DiscussionResults and Discussion
Ductility Degradation (Contd…)
02468
10
0 0.2 0.4 0.6Corrosion loss (gm/cm2)
Duc
tility
PONPOAPENPEA
Results and DiscussionResults and Discussion
Ductility Degradation (Contd…)
0
40
80
120
0 0.2 0.4 0.6Corrosion loss (gm/cm2)
Duc
tility
Rat
io (
%) PON
POAPENPEA
µc=(1-0.6208∆w2-1.0318∆w)µu
R2=0.93
µc=(1-3.2232∆w2-0.2765∆w)µu
R2=0.97
Pier with ordinary design
Pier with seismic design
Results and DiscussionResults and Discussion
Stiffness Degradation
-80
-60
-40
-20
0
20
40
60
80
-120 -80 -40 0 40 80 120Displacement (mm)
Load
(kN
) nth cycle
D
F
K = F/D
Results and DiscussionResults and Discussion
Stiffness Degradation (Contd)
02468
1012
0 5 10 15 20Corrosion loss (gm/cm2)
Stif
fnes
s (k
N/m
m) PEN-1
PEN-2PEN-3PEN-4
Number of loading cycle
Results and DiscussionResults and Discussion
Stiffness Degradation (Contd…)
K = 11.917e-0.6475N
R2 = 0.9839
0
2
4
6
8
0 5 10 15Cycle number
Stif
fnes
s (k
N/m
m)
PON-4bNaeK −=
Results and DiscussionResults and Discussion
Stiffness Degradation (Contd….)
05
1015202530
0 0.2 0.4 0.6Corrosion loss (gm/cm2)
'a' (
kN/m
m)
PONPOAPENPEA
Results and DiscussionResults and Discussion
Stiffness Degradation (Contd….)
0
0.2
0.4
0.6
0.8
0 0.2 0.4 0.6Corrosion loss (gm/cm2)
'b'
PONPOAPENPEA
Results and DiscussionResults and Discussion
Energy Absorption Degradation
Displacement (mm)
Loa
d (
kN)
Εn
Ε=ΣΕn
Results and DiscussionResults and Discussion
Energy Absorption Degradation
0
20000
40000
60000
0 0.2 0.4 0.6Corrosion loss (gm/cm2)
Tot
al E
nerg
y A
bsor
ptio
n (k
N-m
m)
PONPOAPENPEA
Results and DiscussionResults and Discussion
Energy Absorption Degradation (Contd…)
0
40
80
120
0 0.2 0.4 0.6Corrosion loss (gm/cm2)
Tot
al E
nerg
y A
bsor
ptio
n R
atio
(%)
PONPOAPENPEA
Ec = (1-2.1114*∆w)Eu
R2 = 0.90
Ec = (1-1.7952*∆w)Eu
R2 = 0.82
Pier with ordinary design
Pier with seismic design
Results and DiscussionResults and Discussion
Comparison of Strength and Ductility
0
20
40
60
80
100
0 20 40 60 80 100Strength Reduction (%)
Duc
tility
Red
uctio
n (%
) PONPOAPENPEA
Results and DiscussionResults and Discussion
Comparison of Strength and Energy Absorption
-10
10
30
50
70
90
0 20 40 60 80 100Strength Reduction (%)
Ene
rgy
Abs
orpt
ion
Red
uctio
n (%
)
PONPOAPENPEA
ConclusionsConclusions
Seismic performances of reinforced concrete structures are seriously affected by corrosion of reinforcement.
Strength of the pier is slightly reduced with the small increase in corrosion loss and with further increase degradation rate of strength is larger.
ConclusionsConclusionsSmall corrosion amount in reinforcement increases stiffness significantly. However, within few cycles it degrades quickly
With the increase in the corrosion loss of reinforcing bars, reduction rate of ductility and energy absorption of the pier is much higher than that of strength
Final RemarksFinal Remarks
Final remarksProblems awaiting solutions in near future
• To complete modeling performance degradation of structure with reinforcement corrosion process
• To evaluate environmental condition more correctly
• To evaluate construction works, including compaction, curing , etc.
• To establish life cycle cost evaluation method
• To systematize maintenance
• To establish total monitoring system including predictions of both chloride penetration and corrosion of reinforcement