section-14 DURABILITY R1

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NEW UNIFIED CONCRETE CODE Limit State Version (IRC:112-2011)

SECTION 14 : DURABILITY PROVISIONS

ALOK BHOWMICKMANAGING DIRECTOR,

B & S ENGINEERING CONSULTANTS PVT. LTD.315-316, VISHAL CHAMBERS, SECTOR 18, NOIDA U.P

BSECIRC:112-2011


CONTENT OF PRESENTATION

1. Historical Perspective, Definitions

2 D t i ti M h i2. Deterioration Mechanism

3. Design for Durability

4. Good Detailing practice from Durability Considerations

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• Untill about 30 years ago, durability was not seen as a serious issue for concrete.

• Durability became an issue only when

IRC:112-2011 SECTION 14 : DURABILITY PROVISIONS

HISTORICAL PERSPECTIVE

Durability became an issue only when following problems were noted all over the world :

1. Very serious deterioration of bridge decks in USA, UK and all other countries due to corrosion of reinforcement, due to use of de-icing salt in bridge decks in winter.

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2. Major deterioration in problems in the Middle East due to chloride induced corrosion in a particularly aggressive environment.



3. Severe cracking in structures in many countries resulting from alkali-silica reaction

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Deterioration in Bridges

from durability reasons

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Durability of concrete is its ability toresist weathering action, chemical

WHAT IS DURABILITY ?

attack, abrasion or any process ofdeterioration. The cause may resideinside the concrete itself, or bepresent in the service environmentto which the concrete structure isexposed’.

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Durability Requirements :

‘Fulfilment of the requirements of t t l f t d i bilitstructural safety and serviceability, within the planned use and the

foreseeable actions, without unforeseen expenditure on maintenance and repair’.

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WHY DURABILITY CONSIDERATIONS ARE IMPORTANT FOR CONCRETE ?

• Concrete property changes with time.

• It is no longer sufficient for the structure to have only “Strength”. The structure shall last also.

• So far the practice had been to provide a few deemed to satisfy clauses in the code to ensure durability (e,g. On minimum cover, crack width control, maximum spacing of rebars, minimum concrete grade, minimum cement content, maximum w/c ratio …etc.)

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HISTORICAL PERSPECTIVE1. DEEMED TO SATISFY CLAUSE SUFFERS FROM

FOLLOWING :

• Fails to acknowledge that structures deteriorate progressively. p g y

• Takes limited account of impact of conceptual & detailed design, construction quality and methods.

• Has limited flexibility.

2. The new code has defined the end of service life, which demands that structure must be designed for durability.

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HISTORICAL PERSPECTIVE• The LS code has given more importance to durability, in

line with the present international practices. The structure has to be designed for durability. Durability is covered exclusively in a separate chapter now (section 14).

• Classification of Service Environment – Four classes defined now as against Two earlier.

• Design Service life has been accounted for in the provisions of durability.

• Additional provisions for specific mechanism of deterioration added.

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Factors affecting Durability• Service Environment• Detailing (Cover Shape & Size)



• Detailing (Cover, Shape & Size)• Construction Method (Workmanship)• Type & Quality of Materials used• Cement Content & W/C ratio• Repair & Maintenance

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DETERIORATION MECHANISM

Concrete Deterioration Mechanism

Mechanical & Reinforcement /Chemical /

Most serious form of degradation of Concrete

Mechanical & Physical

Deterioration

Reinforcement / Prestressing Steel

Corrosion

Abrasion

Sulphate

Attack

Alkali - Aggregate

Reaction Carbonation Chlorides

Depassivation

Chemical / Biological

Deterioration

Acid

Attack

Frost Attack

Plastic Shrinkage

Thermal Effects

ImpactErosion

Chloride CO2

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1. Since the maximum damage caused in RCC structures worldwide is primarily due to corrosion of reinforcement, the environmental classification in IRC codeenvironmental classification in IRC code is based on specific mechanism of duration (i,e. corrosion only).

2. However, relative importance of the various mechanism of deterioration will vary from region to region.

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3. Most of the reactions in concrete, which causes deterioration are expansion -producing and presence of water or moisture is requiredmoisture is required.

4. For ensuring durability, It is therefore important that ingress of moisture in concrete is restricted to the extent possible.

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The deterioration process can be divided into two phases :

• During the initiation phase no weakening



During the initiation phase no weakeningof the concrete or of the function of thestructure occurs.

• During the propagation phase activedeteriorations proceeds rapidly and inmany cases with acceleration.

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1. A durable concrete structure has a long initiation phase and a slow propagation



t of a

ccep

tabl

e da

mag

e

DESIGN SERVICE LIFE

p p gphase.

2. The ideal situation by design of new structure is if the initiation phase goes upto say 50 years !

Lim

it

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WHAT IS DESIGN SERVICE LIFE OF A STRUCTURE ?

The assumed period for which a structure is to be used for its intended purposes with anticipatory maintenance, but

without major repair being necessary.

What is the end of Service Life ?(Not defined properly in IRC:112-2011)

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There is need to precisely define the condition which can be treated as “end of service life”.

This can be either in the form of % depassivation or surface cracking or spalling of concrete cover.

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Mechanical & Reinforcement /ChemicalMechanical & Physical

Deterioration


Corrosion

Abrasion

Sulphate

Attack

Alkali - Aggregate


Depassivation

Chemical

Deterioration

Acid

Attack

Frost Attack

Plastic Shrinkage

Thermal Effects

ImpactErosion

Chloride CO2

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Effects of Physical Deterioration :

ABRASION / EROSION / CAVITATION :


DETERIORATION MECHANISM BSEC

ABRASION / EROSION / CAVITATION :



• RESISTANCE TO ABRASION CAN BE OBTAINED BY :• USING HIGH STRENGTH CONCRETE

• USING ABRASION RESISTANT AGGREGATES

• GOOD CURING

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• GALVANISATION / EPOXY COATINGS INREBARS SHALL BE ABRASION RESISTANTSO THAT THERE ARE NO DAMAGE CAUSEDDURING HANDLING / PLACEMENT.



• COATINGS IN PRESTRESSING STEEL SHALLALSO BE ABRASION RESISTANT.

• ABRASION RESISTANCE IS ALSO AREQUIREMENT FOR THE SHEATHING DUCTSBEING USED.

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Abrasion Damage in Concrete

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Effects of Physical Deterioration :

FROST ATTACK :

1. Capillary pore water in concrete expands by 9%



p y p p yafter freezing, and produces strong pressure whichcauses failure, rupture and scaling.

2. Saturation of water is formulated due to repeatedfreezing and thawing. When it reaches the criticalsaturation, concrete will be destroyed by freezing.

3. The effective way to prevent freezing and thawingdestruction is to add chemical air-entraining agent.

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FROST ATTACK ….contd.4. With the addition of an air

entrainment admixture, concrete is highly resistant to freezing and thawing.

5. During freezing, the water displaced by ice formation in the paste is accommodated so that it is not disruptive; the microscopic air bubbles in the paste provide chambers for the water to enter and thus relieve the hydraullic pressure generated.

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FROST ATTACK ….contd.

6. Concrete with a low water-cement ratio (0.40 or lower) is more durable than concrete with a high water-cement ratioconcrete with a high water-cement ratio (0.50 or higher).

7. Air-entrained concrete with a low water-cement ratio and an air content of 5 to 8% will withstand a great number of cycles of freezing and thawing without distress.

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Freeze & Thaw Effect

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Deterioration


Corrosion

Abrasion

Sulphate

Attack

Alkali - Aggregate


Depassivation

Chemical

Deterioration

Acid

Attack

Frost Attack

Plastic Shrinkage

Thermal Effects

ImpactErosion

Chloride CO2

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Effects of Chemical Deterioration :ALKALI AGGREGATE REACTION (AAR) :

CERTAIN CONSTITUENTS IN AGGREGATES CANREACT HARMFULLY WITH ALKALI HYDROXIDES IN



CONCRETE CAUSING SIGNIFICANT EXPANSIONS.THERE ARE THREE FORMS OF THIS REACTION:

1. ALKALI SILICA REACTION (ASR)

2. ALKALI CARBONATE REACTION (ACR)

3. DELAYED ENTRINGITE FORMATION (DEF)

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Effects of Chemical Deterioration : AARALKALI SILICA REACTION (ASR):

• ASR is chemical reaction between alkali in cement

and silica in aggregates



and silica in aggregates.

• Alkali is sodium or potassium

• A gel is formed and expansion takes place in

presence of moisture, which comes from rain water.

• Concrete forms surface cracks called map cracking

• Deterioration is caused by spalling.

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Mechanism :

• The reaction can be visualized as a two-step process:process:– Alkali hydroxide + reactive silica gel →

alkali-silica gel– Alkali-silica gel + moisture → expansion

The reaction has great affinity for moisture

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Effects of Chemical Deterioration : AAR

CONTROL OF ASR:• USE OF LOW ALKALI PORTLAND CEMENT (LESS

THAN 0.6% EQUIVALENT Na2O) WHEN ALKALI SILICA



THAN 0.6% EQUIVALENT Na2O) WHEN ALKALI SILICA REACTIVE CONSTITUENTS ARE SUSPECTED TO BE PRESENT IN THE AGGREGATE.

• IF LOW ALKALI CEMENT IS NOT AVAILABLE, THE TOTAL ALKALI CONTENT CAN BE REDUCED BY REPLACING A PART OF HIGH ALKALI CEMENT WITH SUPPLEMENTARY CEMENTITIOUS MATERIALS SUCH AS FLY ASH, GROUND BLAST FURNACE SLAG AND SILICA FUME, OR USE BLENDED CEMENT.

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Alkali Silica ReactionAlkali Silica Reaction

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Photographs showing repair of Bridges affected by AlkaliPhotographs showing repair of Bridges affected by Alkali--Silica ReactionsSilica Reactions

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• Utilization of silica fume, fly ash, and blast furnace slag as partial replacement of cementreplacement of cement will reduce the expansion.

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Effects of Chemical Deterioration : AAR

ALKALI CARBONATE REACTION (ACR):

• THE AGGREGATES [DOLOMITE - CALCIUM



MAGNE-SIUM CARBONATE] HAVE SPECIFIC

COMPOSITION THAT IS NOT VERY COMMON.

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Effects of Chemical Deterioration : AARALKALI CARBONATE REACTION (ACR):

• ACR IS A CHEMICAL REACTION BETWEEN



HYDROXYL IONS ASSOCIATED WITH THE ALKALIS,

SODIUM AND POTASSIUM IN THE CEMENT AND

CERTAIN DOLOMITIC TEXTURES IN THE

AGGREGATE RESULTING IN EXPANSION AND

EVENTUALLY CRACKING OF THE HARDENED

CONCRETE. (ACR is not as widespread as ASR)

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Effects of Chemical Deterioration :

ACID ATTACK



Concrete is susceptible to acid attack because of p

its alkaline nature. The components of the cement

paste breaks down during contact with acids.

Sulphuric acid is very damaging to concrete as it

combines an acid attack and a sulfate attack.

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Effects of Chemical Deterioration : Sulphate Attack



Sulfate attack can be ‘external’ or ‘internal’.

External: due to penetration of sulfates in solution, in groundwater for example, into the concrete from outside.

Internal: due to a soluble source being incorporated into the concrete at the time of mixing, (e,g. gypsum in the aggregate, for example).

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Effects of Chemical Deterioration :DELAYED ENTRINGITE FORMATION

• SPECIAL TYPE OF INTERNAL SULPHATE ATTACK



IS CALLED DELAYED ENTRINGITE FORMATION.

• THE RELATED EXPANSION PRODUCES CRACKING,

SPALLING & STRENGTH LOSS, SINCE IT OCCURS

IN HARDENED CONCRETE.

• ITS DAMAGING EFFECT IS RELATED TO INTERNAL

SULPHATE SOURCE

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• External Sulfate attack is possibly the most common and widespread form of chemical attack on concrete. In case soluble sulphates is >0.1% in soil, it will have detrimental affect on concrete More than 0 5% is verydetrimental affect on concrete. More than 0.5% is very dangerous.

• Damage caused by sulfate attack normally occurs as cracking, crumbling and scaling of the concrete. In addition to physical deterioration, sulfate attack may also destroy the binding capability of the cement, thus affecting the mechanical properties of the concrete (strength, elastic modulus).

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• Sulfate attack occurs as a chemical reaction of sulfate ions (aggressive substance) with the aluminate component of the hardened concrete


(reactive substance).

• Sulfate attack may also occur as a physical attack on concrete due to the crystallization of sulfate salts within the cement matrix. Regions of concrete structures experiencing sulfate attack normally display a characteristic whitish appearance.

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• Damage is usually initiated in areas most susceptible to the ingress of contaminants, such as corners and edges of concrete elements. As


gthe attack progresses, extensive cracking and spalling of the concrete may occur.

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Deterioration


Corrosion

Abrasion

Sulphate

Attack

Alkali - Aggregate


Depassivation

Chemical

Deterioration

Acid

Attack

Frost Attack

Plastic Shrinkage

Thermal Effects

ImpactErosion

Chloride CO2

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Corrosion occurs due to de-passivationof iron-oxide

Corrosion – Most serious form of deterioration in Concrete

layer – alkaline environment surrounding the reinforcement.

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1. Passivity can be destroyed by chlorides and carbonation.

2. Once the passivity of steel has been eroded, corrosion will continue if there is sufficient moisture and oxygen ygpresent at the reinforcement.

3. Corrosion requires both water and oxygen. When concrete is wet, oxygen penetration is inhibited In very dry conditions, where oxygen levels are sufficient, moisture levels are low.

4. The greatest risk of corrosion is therefore in members subjected to cyclic wetting and drying.

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DETERIORATION MECHANISMChlorine ions penetrate to the surface of reinforcing bars from the protective layer,destroy passive film, and change bars from passive state into active state.

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• Cracking• De-lamination• Spalling of cover

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Carbonation :1. Atmospheric CO2 is converted to carbonic acid (H2CO3) in

the presence of moisture, which attacks hydrated cement t thi i ll d b ti



paste; this is called carbonation.

2. Carbonation lowers the pH value of concrete and reduces the protection to steel by the alkalinity of the surrounding medium.

3. Rate of Carbonation depends upon the concrete grade, relative humidity & integration of concrete in cover zone

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Graph showing variation of Carbonation Depth

with Time

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CORROSION PROTECTION MECHANISM & METHODS

Prevent entry at concrete surface.

If penetrates concrete surface, prevent reaching the reinforcement

If reaches reinft., control corrosion Best is to avoid reactive substance itself !

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2 D t i ti M h i d F t


2. Deterioration Mechanism and Factors influencing Durability



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IRC:112-2011SECTION 14 : DURABILITY PROVISIONS

DESIGN FOR DURABILITY

1. The first step is to establish the aggressiveness of the service environment (exposure conditions).

In deciding the appropriate class of service environment, the following factors are to be taken into account (fib, 2009):

a. The general environmental conditions of the area in which the structure is situated,

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b. The specific location and orientation of the concrete surface being considered and its exposure to prevailing winds, rainfall etc.,



c. Localised conditions such as surface ponding, exposure to surface runoff and spray, aggressive agents, regular wetting, condensation etc.

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2. To select the type of structure suitable for the chosen service environment.

3. To select the appropriate materials, mix proportions, workmanship, design and detailing, including minimum cover to steel

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4. There are four categories :

• Moderate, • Severe, • Very Severe and



y• Extreme;

This is in increasing order of likelihood of chloride-induced corrosion and carbonation - induced corrosion, depending on the chances of carbonation and ingress of chloride ions from outside.

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‘Moderate’ category is for situations where the Not Sea Water !!



g ychances of carbonation are insignificant because the pores of concrete are either saturated or dry. No ingress of chloride from external sources is anticipated. Inadequate workmanship can lead to corrosion of steel. Provision is also made against attack by other deleterious chemical agents, which are facilitated by the presence of moisture.

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1. ‘Severe’ category is for situations, where presence of moisture (wet, rarely dry) and some carbonation



under humid conditions can lead to corrosion of steel.

2. Wet, rarely dry includes concrete surfaces subject to long term water contact and many foundations. Concrete exposed to coastal environment can have access to chloride ions increasing the risk of chloride-induced corrosion.

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3. Concrete components exposed to industrial t t i i hl id ill b i l d d i thi



waters containing chloride will be included in this category.

4. In spite of presence of significant amount of chloride ions in sea water, risk of corrosion in concrete completely submerged in sea water below mid-tide level is comparatively less because of paucity of oxygen.

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1. When the relative humidity is between 50 to 70 percent, the chances of carbonation are very high. Exposure to



air-borne chloride ions in marine environment add significantly to the risk of chloride-induced corrosion.

2. Such exposure conditions are termed ‘very severe’. Saturated concrete subjected to cyclic freezing and thawing is prone to effects of expansion due to formation of ice, leading to spalling. Such conditions are anticipated in few areas in the colder regions of the country.

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1 Extreme’ category is for conditions where the risk



1. Extreme category is for conditions, where the risk of corrosion of steel and sulphate attack are the highest in concrete exposed to tidal, splash and spray zones in sea, because of accumulation of salts in the pores and accompanied by damage due to wave action.

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2. Concrete in direct contact with aggressive sub-soil/ground water can lead to severe attack to



soil/ground water can lead to severe attack to concrete in foundations, without being accessible to periodic inspection and maintenance.

3. If harmful effluents from nearby chemical industries are discharged into the water body, where the bridge is situated, it poses serious threat to the durability of concrete. Cyclic wet and dry conditions allow accumulation and build up of deleterious agencies.

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Example of a structure

in “Extreme”

climatic condition

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Clear cover to any reinft.



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Cover can be reduced by opting for HPC (M30 to M90)

In case of



In case of blended cement.

Reinft. has secondary role in PCC

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1. The values of minimum strength grade in Table 14.2 are those which can be generally expected with the corresponding water cement ratio andcorresponding water cement ratio and with the cements or binders available in India.

2. So, the minimum strength grade specified is an indirect control on the durability parameters.

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Adjustment for other Aggregate size

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DESIGN FOR DURABILITY BSECUNIFIED CONCRETE CODEPART 4 : DURABILITY PROVISIONS



2 D t i ti M h i d F t2. Deterioration Mechanism and Factors influencing Durability



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UNIFIED CONCRETE CODEPART 4 : DURABILITY PROVISIONS

GOOD DETAILING PRACTICE

Detailing to improve Durability :

1. Structural Scheme

2. Geometry, Size & Shape of Structure (to promote good drainage)

3. Drainage, Detailing for better Drainage

4. Reinforcement Detailing

5. Use of Controlled Permeability Formwork (CPF)

6. Protective Coatings in Concrete

7. Choice of Rebar Coating

8. Corrosion protection of Prestressing Steel

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Structural Scheme :

Example: Avoid Permanent Joints and Bearings, e.g. Integral Bridges

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Geometry, Size & Shape effects Durability :

Pier with lesser surface area / volume ratio is preferred


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Drainage : Most Important for Durability



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Drainage : Avoid Horizontal Surface in Substructure Detail to

promote quick run-off(e,g top of pier cap to be sloped outside)





Poor Drainage :Severe distress due to

corrosion induced by defective expansion joint detail

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Reinforcement Detailing :

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Controlled Permeability Formwork :1. The properties of ‘surface skin’ (the cover),

which is the “first line of defence” to



protect reinforcement, remain poorer.

2. Conventional steel or timber formwork is essentially impermeable and traps the entrapped air and water that migrate towards the formwork during compaction.

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Controlled Permeability Formwork :3. The resultant water/cement ratio in the

cover zone is higher than in the bulk, and



forms a weak link; having lower resistance to the ingress of air, water and CO2 etc. from the service environment.

4. Use of CPF helps to improve durability.

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Concrete Formwork: With Zemdrain® Vs Conventional



Reduced W/C of 0.20 - 0.25 from Bulk W/C of 0.35,

In another case, reduced w/c to- 0.40 / 0.35 from 0.50 bulk.

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Coatings in Concrete :

1. Coatings are sometimes given :

• To protect it from chemical and physical attack.



To protect it from chemical and physical attack.

• To protect products stored or processed indirect contact with the concrete from contamination caused by dust from the substrate.

• To improve its appearance, case of maintenance.

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Coatings in Concrete :

2. With the advancement in the polymer technology, materials are available which can be used as protective coatings in concrete.



coatings in concrete.

3. Some of the polymers available are Epoxy resin, Polyurethane resin, Acrylic resin, Polyester resin, silicone resin, silane / siloxane acrylic blend primer with a pigmented acrylic top coat..

4. Suitability of the coating system and cost are important factors in deciding about coatings.

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Material Cost Ratio



COATING ON REBAR :COST COMPARISON ON REBAR COATING

Material Cost Ratio

Rebar without Coating 1.0

Rebar with FBEC 1.3

Rebar with Hot-dip Galvanized Coating

1.5

Solid Stainless Steel Rebar(316)

5.0

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As per MORTH Guideline issued in Jan-2000, for regions within 15 Km radius of

Corrossivity Map of India

the coast, FBEC bars shall be used for Bridges.

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Protection Levels for pt-tendons based on aggressivity / exposure vs. structural protection layers



Source: fib bulletin 33

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THANK YOU

section-14 DURABILITY R1

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