CONTENTS INTRODUCTION Process of Corrosion Causes of Corrosion Effects of Corrosion CORROTION RESISTANT STEEL COATINGS TO REINFORCEMENT Encapsulation Cathodic Protection/Sacrificial Anode Cathodic Protection/ Impressed Current Alkaline Slurry Coating Reinforcement Protection CATHODIC PROTECTION Sacrificial Anode Impressed Current

1. I AM MOHANRAJA.G
ME- Structural Engineering
Thanthai Periyar Government
Institute of Technology,
Vellore.

2. CONTENTS
⬥ INTRODUCTION
⬦ Process of Corrosion
⬦ Causes of Corrosion
⬦ Effects of Corrosion
⬥ CORROTION RESISTANT STEEL
⬥ COATINGS TO REINFORCEMENT
⬦ Encapsulation
⬦ Cathodic Protection/Sacrificial Anode
⬦ Cathodic Protection/ Impressed Current
⬦ Alkaline Slurry Coating
⬦ Reinforcement Protection
⬥ CATHODIC PROTECTION
⬦ Sacrificial Anode
⬦ Impressed Current
2

3. STRUCTURAL HEALTH MONITORING
⬥ Objective of Structural Health Monitoring
⬥ Steps of Structural Health Monitoring
⬥ Need for Structural Health Monitoring
⬥ World wide SHM Projects
⬥ How to do SHM in Practice
⬥ Current Practice
⬦ Static Based
⬦ Vibration Based
⬥ SHM by Structural Sys Identification
⬥ Structural Health Monitoring Challenges
⬥ Monitoring Metric
⬥ Application
⬥ Technology Solution
3

4. 4
INTRODUCTION
Premature failure of steel-reinforced concrete
structures has been one of the major problems confronting
civil engineers. The reinforcement used to provide strength to
the concrete structure, in most cases, is found to be the main
culprit. This is primarily due to early corrosion of steel
reinforcement A number of methods and materials have been
developed or are being developed to prevent corrosion of
reinforcement steel. This Seminor reviews the work carried
out so far on reinforcement corrosion, its mechanism and
prevention.

5. 5
Process of Corrosion
⬥ Corrosion of metals is an electrochemical process, involves transfer of charge
from one species to another
⬥ For corrosion to occur, there must be two half cell reactions, one capable of
producing electrons (anodic reaction) and the other capable of consuming
them (cathodic reaction)
⬥ For corrosion of steel, the anodic reaction can be
⬥ And the cathodic reactions can be

6. Causes of Corrosion
⬥ Steel in concrete is usually in a no corroding, passive condition
⬥ However, steel is often used in severe environments where sea
water or deicing salts are present
⬥ When chlorides moves into the concrete it disrupts the passive
layer protecting the steel, causing it to rust and pit
⬥ Carbonation is another cause of steel corrosion, when concrete
carbonates to the level of the steel rebar, the normal alkaline
environment which protects the steel form corrosion is replaced
by a more neutral environment 6

7. 7
Effects of Corrosion
⬥ The formation of rust leads to a loss of bond
between the steel and concrete
⬥ Corrosion of steel produces a bulky reaction
product with volume 7-8 times that of steel
⬥ This puts pressure on the surrounding concrete
cover which first cracks and eventually spalls
⬥ Extensive corrosion of the steel can lead to
mechanical weakening of the reinforced
structure
⬥ The ultimate result can be collapse of the
structure
Image Space
Image Space

8. 8
CORROTION RESISTANT STEEL
What does corrosion resistant means?
Corrosion resistance can be defined as the ability to protect
the substrate from corrosion. In this case coating microstructure, in
particular the appearance of open porosity and cracks, can be more
important than the coating composition.
Corrosion resistant steel are defined as the class of steel that
are inherently resilient to degradation caused by corrosion. A steel
that is not naturally corrosion resistant can be made so by combining it
with small amounts of another metal in a process known as alloying

9. 9
Pure Steel
⬥ Usage of pure steel which is free of
impurities makes it resistive to
corrosion
⬥ An example of such structure using
pure steel is the Iron Pillar in New
Delhi which hasn’t corroded for
hundred of years
⬥ Pure steel, though resistant to
corrosion, will not be strong enough
to be used in structures as the
impurities added increase the
structural strength of steel
Image Space

10. 10
Cathodic Protection
⬥ The steel rebar are coupled with with
reactive metals such as Cu, Zn etc.
⬥ This creates negative charge on the
rebar
⬥ The OH- ions that are produced are
attracted towards the anode made of
Cu or Zn
⬥ Thus the reactive metal is corroded
and the steel is protected
⬥ This method provides non uniform
resistance to corrosion and the steel
further away from anode is corroded
Image Space

11. 11
Epoxy coated rebar
⬥ A fusion based epoxy coating is applied
to steel rebar through shot blasting
⬥ The epoxy coating acts as a protective
layer and prevents the corrosion of steel
⬥ But epoxy coating of rebar reduces the
bond strength between concrete and
steel
⬥ The epoxy coating can be easily
damaged during transportation and
handling, the exposed steel can corrode
under the coating
⬥ The epoxy coating of rebar is expensive
and increases the costs by approx. Rs.
8-10 thousand per ton
Image Space
Image Space

12. 12
Galvanized Rebar
⬥ Galvanized rebar have a protective layer of
zinc metal
⬥ The zinc coating serves as a barrier to
corrosive elements that the rebar is exposed
to when embedded in concrete
⬥ It also provides a level of cathodic protection
where the zinc will preferentially corrode
when in contact with bare steel
⬥ But galvanizing also reduces the bond
strength between rebar and concrete
⬥ The steel is exposed below zinc coating
during cutting and bending
⬥ Galvanizing of rebar is expensive and costs
around Rs. 4000 per ton
Image Space

13. 13
Stainless Steel Rebar
⬥ Stainless steel rebar have inherently good
corrosion resistance
⬥ They don’t have the any coatings which can
chip, crack or degrade and cause corrosion
⬥ Capable of withstanding shipping, handling and
bending
⬥ However, the mechanical properties of
stainless steel are not at par with construction
grade steel (strength ~216MPa)
⬥ Due to reduced strength, the quantity of steel
used is increased
⬥ The stainless steel rebar are prohibitively
expensive and hence are not widely used
Image Space

14. 14
Fiber Rebar
⬥ These rebar are made from fiber-reinforced
plastic
⬥ The material used for fabrication of rebar is
resistant to corrosion
⬥ But it has lower bonding strength with
concrete compared to that of steel as grip is
provided by epoxy coating
⬥ The strength of the material is also lower than
that of steel
⬥ Fiber rebar is are relatively new and therefore
are prohibitively expensive
Image Space

15. 15
Corrosion Resistant Steel (CRS) Rebar
⬥ CRS rebar are inherently resistant to corrosion
⬥ They are manufactured b y adding 0.5% of Copper,
Nickel or Chromium to increase the resistance
⬥ CRS rebar are only Rs. 2-2.5K expensive than normal
rebar and can double the life of structure under
harsh conditions
⬥ The rebar can withstand rough handling and
transportation; can be cut and bend without
lowering their resistance to corrosion
⬥ The mechanical properties of CRS rebar is at par with
normal rebar
⬥ Use of CRS Rebar can provide a cost saving of 4-5%
with welding
Image Space

16. 16
COATINGS TO REINFORCEMENT
⬥ Reinforcing steel is naturally protected from corrosion when
surrounded by an alkaline environment of newly cast , good
quality concrete.
⬥ In certain repair situation, additional protection for the encased
reinforcement is prudent.
⬥ Protection system fall into four categories
⬦ Encapsulation
⬦ Cathodic Protection/Sacrificial Anode
⬦ Cathodic Protection/ Impressed Current
⬦ Alkaline Slurry Coating
⬦ Reinforcement Protection

17. 17
Encapsulation
⬥ Insulating the bar from electrical currents in the surrounding concrete can be
accomplished by encapsulating the bar with epoxy
⬥ When new bars are used, fusion bonded epoxy is provides the best
protection.
⬥ Bard=s are Shot-blasted and heated and powdered epoxy is sprayed into
them under controlled environment.
⬥ In field application where encapsulation of existing bars is necessary, epoxy
resin is sprayed or more commonly, brushed into the bars,
⬥ With field application of epoxy it is very difficult to achieve 100% coverage of
the exposed bars
⬥ Intersections and black side of bar create almost impossible access.
⬥ Encapsulation works well when all bars in the affected member are protected
however, when bars are partially coated either within the repair zone or
adjacent to the repair, electrical currents can become concentrated in the
unprotected bars and accelerated corrosion may be a problem.

18. 18
Cathodic Protection/Sacrificial Anode
⬥ Protecting bars from corrosion can be accomplished by coating them with a
sacrificial metal.
⬥ Zinc is the metal commonly used for this purpose
⬥ Zinc applied to the bars with a brush.
⬥ Recently , Molten zinc has been used(California DOT) as a sacrificial surface-applied
coating.
⬥ This method is used after all surface are repaired.
⬥ The surface-applied zinc is electrically connected to the reinforcing steel .
⬥ Since this method is sacrificial , the service life is dependent upon the degree of exposure
to a corrosive environment and anode activity
⬥ This method of protection is used only on an experimental basis

19. 19
Cathodic Protection/ Impressed Current
⬥ Protecting bars from corrosion can be accomplished by reversing the
electrical current flow which causes the corrosion process.
⬥ Anode are installed on or near the concrete surface and are electrically connected to the
reinforcing bars
⬥ Electrical current is pumped into the circuit protecting the bars
⬥ Impressed current must be balanced with the environment on a continual basis in order
to provide protection.
⬥ Constant monitoring and necessary adjustments are required.

20. 20
Alkaline Slurry Coating
⬥ Like un carbonated concrete , alkaline slurry coating protects the reinforcing
steel from corrosion(Alkaline) fillers.
⬥ Some questions exists concerning whether the epoxy insulates the alkaline fillers from
direct contact with the rebar and whether epoxy provides any benefits other than
electrical insulating the bars.
⬥ There are many unanswered questions regarding reinforcement protective systems and
their effects on surround reinforcement.
⬥ By protecting reinforcement steel in a repaired area we have created an island new
material.
⬥ In doing so, potentially more corrosion could occur than would have originally.
⬥ Only independent research, testing and monitoring will answer these question

21. 21
Reinforcement Protection
⬥ The reinforcement in new construction in can be protected using the
following
⬥ Cement-based coating
⬥ Galvanizing/Zinc-Based paints
⬥ Epoxy Coating
⬥ Bitumen-based paints
⬥ Phosphate coating
⬥ Coating for reinforcement bars must satisfy the following
⬥ Ensure uniform coating on the deformed surface configuration of the bars
⬥ Be flexible enough to allow post-coated bending bars
⬥ Be mechanically stable to sustain handling, transportation and fabrication of
reinforcement
⬥ Provide the facility to easy application
⬥ Resist Corrosion

34. Conclusion
3
4
 Cathodic protection is a method to control the corrosion of steel
in contaminated concrete that works by making the embedded
reinforcing steel cathodic. When the steel becomes cathodic,
hydroxyl ions are accumulated around it making it passive for a
longer time. The reinforcing steel is electrically connected to
another metal that becomes the anode with or without the
application of an external power supply. Cathodic protection is
used to protect almost any type of reinforced concrete
structure, including horizontal slabs, walls, towers, beams,
columns and foundations.

35. What is Structural Health Monitoring (SHM)
“The process of implementing a damage
detection and characterization strategy for
engineering structures”
SHM Involves:
Health monitoring
Operational Evaluation
Data Feature Extraction
Statistical Models Development 3
5

36. Objective of Structural Health Monitoring
3
6
 Performance enhancement of an existing structure
 Monitoring of structures affected by external factors
 Feedback loop to improve future design based on
experience
 Assessment of post-earthquake structural integrity
 Decline in construction and growth in maintenance needs
 The move towards performance-based design philosophy

37. Determination of damage existence
Determination of damage’s geometric location
Quantification of damage severity
Prediction of remaining life of the structure
Steps of Structural Health Monitoring
3
7

38. Need for Structural System Identification
Courtesy: Google Im
6age

39. Worldwide Monitoring Projects
7

40. How to Do SHM in practice?
• Visual Inspection
 Fully experience-based
 Subjective/Non-quantitative
• Non-Destructive Evaluation (NDE)
 Various technologies for different purposes
 Demands a high degree of expertise
 Time consuming and costly
 Works only in accessible regions of the structure
 Interruption and downtime
 Labour intensive and risky
8

41. Current Practice : Visual Inspection
9
vibration-based methods are gaining popularities in
structural health monitoring and damage detection

42. NDT
Visual Inspection Magnetic Particle Testing
Dye Penetration Test Radiography Test 10

43. Eddy Current Test Ultrasonic Test
NDT
Acoustic Emission Test
43
Thermal Infrared Test

44. Monitoring Metrics
⬥ Measure:
• Acceleration
• Strain
• Climatic Conditions
• Curvature
• Displacements
• Load
• Tilt/Slope
• Scour
⬥ Identify
 Corrosion
 Cracking
 Strength
 Tension
 Location of
rebar/delaminations
44

45. How to Do SHM in practice?
45
Static-Based SHM
• Based on the premise that damage will alter the static
properties of the structure.
– e.g. displacements, rotations
• Drawback
Considerable static deflection requires large amount of
static force

46. How to Do SHM in practice?
46
Vibration-Based SHM
• Based on the premise that damage will alter the dynamic
properties of the structure.
– e.g. structural response, frequencies, mode shapes, damping
or modal strain energy change
• By measuring the structural response by means of sensors
strategically placed on the structure, and intelligently
analyzing these measured responses, it is possible to
identify damage occurrence.
• It can be done either in modal domain or physical domain

47. Vibration Based SHM: Sensors
• Different forms of dynamic structural response:
– Displacement, Velocity,Acceleration,Strain.
– Which ones to measure depends on monitoring conditionsand objectives.
• Sensing technology: an ever emerging field of study
• Based on what to measure, different sensors available:
– Laser Displacement Sensors (LDS)
– Velocity Transducers
– Seismometers
– PiezoelectricAccelerometers
– Strain Gauges
• Most of these sensors can be wirelessly connected 14

48. Accelerometer (Acceleration)
Load Cell (Force)
LVDT (Displacement)
StrainGauge (Strain)
Collection of Sensory Information
48

49. Vibration Based SHM: Sensors
49
Pros and cons of various types of sensors:
– Bandwidth:
• displacement sensors capture low frequency modes
• acceleration sensors capture high frequency modes
– Global vs. Local:
• strain gauges capture local dynamics better
• accelerometers/displacement sensors measure global
dynamics

50. Vibration Based SHM:Model-Based Techniques
50
*Based on a model (e.g. F.E.) of the monitored structure.
*Optimization based methods:
• An initial model is updated using measured structural response. Also called
FE model updating
• Optimization algorithms are run by iteratively changing the values of
some structural properties (e.g. Young’s modulus), so that the FEM parameters
match measured parameters.
• Measured parameters: Measured responses or some parameters obtained
from measured responses (e.g. modalproperties).
• Usually require repeatedly solving the forward problem.

51. Vibration Based SHM:Model-Based
Techniques
51
Alternatively, inverse problem solution approach:
• Identify modal parameters using some system
identification method.
• Use identified modal parameters to obtain physical
parameter (mass, damping, stiffness) matrices.
• Does not require repeatedly solving the forward
problem, but is more complicated.

52. Vibration Based SHM Model-Based Techniques
52
• PROS:
• Allow damage detection, as well as damage location and extent estimation. May
even be used to assess the damage type and to estimate the structure’s remaining
life, though research is still at its onset in this regard
• CONS:
• Require high user expertise
• Affected by modelling assumptions (e.g. boundary conditions,
number of DOFs, material properties, etc.)
• Often too many unknowns
• Usually computationally expensive

53. Vibration Based SHM:Data-Based
Techniques
53
Data-Based techniques are based on statistical, rather
than physical models of the structure. These methods
are called from the operations itself,and
⬥data-basedbecause the features extracted structural
response are obtained bysimple performed
on the response time histories do not
require any physical model
assumptions. These approaches are often said to “let the
data speak by themselves”.

54. Vibration Based SHM: Data-Based Techniques
54
PROS
• Do not require high user expertise.
• Often coined using machine learning knowledge: highly
computationally efficient and ideal to be automated.
• Takeinto account uncertainties inherently present in SHM.
• Free from modeling assumption induced errors.
CONS
• Without a physical model, can at most reach the second level of the damage
detection hierarchy (damage location).
• Being based on a statistical model of the features, they require
sufficient data to be available.

55. Vibration Based SHM: Uncertainties
55
Many sources of uncertainty in the different stages of SHM: During data
acquisition:
• Measurement noise,
• Environmental effects (different temperature, humidity levels),
• Unknown and nonstationary inputs (traffic, wind, earthquake; may excite
different frequency regions),
• Missing data (not every point on the structure observed).
During feature extraction/modeling/identification:
• Modeling assumptions,
• Errors associated with any numerical method,
• Non-unique identification (many models may fit the measured data
equally well).

56. Courtesy of Prof. E. Chatzi, ETH
SHM by Structural System Identification
56

57. Infrastructure is expected to provide:
reliable service for long periods of time,
Undergoing major technology changes,
spanning several generations and experiencing dramatic
evolutions
Develop Wireless Sensor Networks
Reliable
Energy aware
Smart
Structural Monitoring Challenges
57

58. Some Barriers in SHM up today
 Conventional cables
 High installation costs
 Vulnerable to ambient signal noise corruption
 Vulnerable to earthquake conditions
Size and complexity of large structures require
a large number of sensing points to be installed.
58

59. Smart Sensor concept
Earthquake Event
Events Recorded
and stored in BS
Sensors Wake-up
(unique IDs)
Sensors go back
to sleep 59

60. Future of SHM
60

61. Study-1: G+8 storey RCC BSNL building in Guwahati (Borsaikia, Dutta,
Deb 2011)
• 1st Earthquake (11th Feb,2006) –Depth 33 Km in
Arunachal Pradesh-Tibet Border.
• 2nd Earthquake (12th Aug,2006) –Depth 66 Km in India-
Bangladesh Border. 29

62. Study-1: G+8 storey RCC BSNL building in Guwahati
(Borsaikia, Dutta, Deb 2011)
• Damage has been localized using Parametric State Space Modeling.
• Stiffness of Each storeys has been computed.
2 triaxial force balance in
ground and top floor, 4
uniaxial accelerometers in 1st,
3rd, 7th and top in shorter
direction and 3 uniaxial
accelerometers in 1st, 5th and
top of longer direction.
30

63. Study-2: Milikan Library, CalTech (Clinton et al
2006)
The current (2006) forced vibration
fundamental frequency of east–west is 22%
and of north-south is 12% lower than that
originally measured in 1968
• forced vibrations using varying forces.
• minor earthquake shaking.
• weather conditions (rain and wind
events, extremes in temperature)
Plan dimension is 21m × 22.9m and height
from basement is 48.9m
Sensors are densely mounted on the
building and these are continuously 31

64. Study-3: Long Beach Public Safety Building (LBPSB),
California (Chassiakos et al 2006)
• Six storey rectangular steel building built in 1950s,
having plan dimension of 82.3m × 21.3m.
• Due to 1994 Northridge earthquake this facility
need significant seismic mitigation measures.
• So health of this structure was monitored and it
was retrofitted.
• The ambient vibration data collected before,
during, and after the structural retrofit.
Mode Freq before Retrofit Freq after Retrofit % change
1 0.94 Hz 2.09 Hz 122.34 %
2 1.20 Hz 2.52 Hz 110.00%
3 1.47 Hz 2.87 Hz 95.24%
4 3.00 Hz 5.21 Hz 73.67%
5 4.25 Hz 7.60 Hz 78.82%
32

65. Study-3: Long Beach Public Safety Building (LBPSB),
California (Chassiakos et al 2006)
Finite element
model of pre-
retrofit Long Beach
Public Safety
Building
65
Finite element model of
post-retrofit Long Beach
Public Safety Building.

66. Application of SHM in ‘Housing for All’
Project
66
 North-East India is prone to earthquake hazards
 So monitoring is important to reduce seismic hazard
 Proposed Idea: One house will be properly instrumented among a
colony of houses
 Sensor data will be taken once in a year and the health of that
colony can be estimated
 Visual inspection and NDTs will be done in a regular basis
 This will also be used for post-earthquake health assessment and
validate retrofitting operations

67. Fibre Optics Laser Vibrometer
Ultrasonic Sensor
Sensor Technology
67

68. Technological Solutions
– Wireless Sensors
• Accelerometers/Inclinometers etc
– Laser Scanning
– RFIDs (Radio Frequency Identification)
– Acoustic Emissions
– MEMS (Micro-Electro-Mechanical Systems)
– Increase of Computation capabilities
– Fiber technologies
68