durability presentation

7/29/2019 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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Internal Cracking and Spalling


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External Cracking and Spalling


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Deterioration of Bridge Structure


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Transport Mechanisms

Concrete contaminated during construction

Capillary Action

Permeation

Diffusion

Osmosis (coatings)


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MOISTURE ONLY

EVAPORATION OF

DIFFUSION

GF SLAB

CAPILLARYGW L

MOVEMENTMOISTURE

DIFFUSION

COLUMN

DIFFUSION

EVAPORATION OF

MOISTURE ONLY

FOOTING

BLINDINGCONCRETE


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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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