durability presentation
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Maintenance Management And Rehabilitation
ofReinforced Concrete Structures
Technical Presentation
By
Tony Carpenter
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All Elements and Materials Deteriorate
For structures it is important to define at the outset
the required useful life expectancy.
We term life expectancy
Service Life
Introduction
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Physical Deterioration
Fire Damage
Over Loading by tenants/occupier
Thermal Expansion and Contraction
Impact Damage and Abuse
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Chemical Deterioration
Sulphate Attack
Alkali-Aggregate Reactions
Chemical Spillage
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Electro-Chemical Deterioration
Corrosion or rusting of steel reinforcement,
having been depassivated either by
Carbonation or Chloride contamination ofsurrounding concrete, or a combination of
the two.
Chloride Induced Electro-chemical
deterioration is generally the most common
form of reinforced concrete deterioration
experienced in the Gulf.
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Electro-Chemical Deterioration
Internal Cracking and Spalling
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Electro-Chemical Deterioration
External Cracking and Spalling
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Electro-Chemical Deterioration
Deterioration of Bridge Structure
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Transport Mechanisms
Concrete contaminated during construction
Capillary Action
Permeation
Diffusion
Osmosis (coatings)
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Transport Mechanisms
MOISTURE ONLY
EVAPORATION OF
DIFFUSION
GF SLAB
CAPILLARYGW L
MOVEMENTMOISTURE
DIFFUSION
COLUMN
DIFFUSION
EVAPORATION OF
MOISTURE ONLY
FOOTING
BLINDINGCONCRETE
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Transport Mechanisms
S E E P A G E
D I F F U S I O N
G W L
G L
B L I N D I N G
C O N C R E T E
E V A P O R A T I O N O F
M O I S T U R E O N L Y
M O I S T U R E O N L Y
E V A P O R A T IO N O F
C A P I L L A R Y /
M O V E M E N T
M O I S T U R E
B A S E M E N T W A L L
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Service Life
Technical Service life
Age of Structure
Acceptable Limit
Initiation Phase Propagation Phase
Damage
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Achieving Service Life
Design
Materials
Workmanship
Preventive Maintenance
Repairs/Rehabilitation
Substantial Reconstruction
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Technical Service life
Age of Structure
Acceptable Limit
Damage
The Law of Fives (de Sitter)
A B C D
Service Life Curve
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Existing Structures
Age of many concrete structure means
owners becoming faced with rapidly
increasing maintenance/rehabilitation
costs as deterioration move to phase D.
Why?
Lack of trained civil maintenance staff
Low priority given to civil works
No real appreciation of condition and
consequences of not taking action
No medium term planning
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Actions to be Taken
Adopt same attitude to civil works as
applied to plant!
Develop maintenance programme for
reinforced concrete structures
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Advantages/Benefits
Budgets planned well in advance
Human resources efficiently managed
Operations planned to minimise disruption of users
Extends service life of structure
Maintains capital investment
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Maintenance Management
Start with Investigation of Structures
Archive search
Site investigation
- Visual inspection
- Sampling and testing
Assessment and RecommendationsPrioritise rehabilitation activities
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Time For Intervention
CRITICALITY CODE DAMAGE CODE DETERMINING FACTOR
1 2 3 4
1 A B C* D* Life/Welfare, Capital loss
2 A/B B/C C* D* Interruption of operation
3 B/C C* D* D* Maintenance inconvenience
4 E* E* E* E* Cost effectiveness
A Immediate Action D < 6 years
B < 1 year E at failure
C < 3 years
* Based on regular inspection and monitoring
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Corrosion
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Attack of gasses Attack of non-electrolytes
e.g. oils
Chemical corrosion
Atmospherically
exposed steel
structures
(Moist and water)
Anodic and Cathodic
areas wich cannot
be separated
Micro-electrolytic
corrosion
Submerged og
cast in items
in water, soil or
concrete
Separate
Anodic and Cathodic
areas
Macro-electrolytic
corrosion
Electrochemical corrosion
Corrosion
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Micro-electrolyticcorrosion
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Macro-electrolyticcorrosion
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CO2
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-CO2CO2
CO2CO2
CO2CO2
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CO2
Cl-
Cl-Cl-
Cl-
Cl-
Cl-
Cl-CO2CO2
CO2CO2
CO2CO2
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CO2
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Cl-CO2CO2
CO2CO2
CO2CO2
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Fe++
2e-
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2Fe 2Fe++ + 4e-
Anode Cathode
4e- + O2 + 2H2O 4(OH)-
2Fe + O2 + 2H2O 2Fe++ + 4(OH)-
O2 O2O2
H2O H2O
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0 1 2 3 4 5 6 7
Fe
FeO
Fe3O4
Fe2O3
Fe(OH)2
Fe(OH)3
Fe(OH)3, 3H2O
Volume
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Local Repair
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Fresh
corrosion
Local Repair
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Fresh
corrosion
Local Repair
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Anode
Cathode
Rectifier+ -
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Cl- Cl-
Cl-
Cl-
Cl-
Cl-
Cl-
Rectifier+ -
Anode
OH-OH-OH-
OH-OH-
OH-
OH-
OH-
OH-
OH- OH-
OH-
OH-
OH-
OH-
OH-OH-OH-
Cathode
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Advantages Only method to prevent/stop chloride initiated
corrosion of black steel
Chloride content in the concrete is not essential
Extends service life considerably on patch-repairedstructures
Condition of structures can be monitored instantly
Disadvantages Require specialised contractor
Extensive supervision is needed during installation
Regular Performance Verification is indispensable
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Thank You for YourAttention
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