Irc 112 Section-14

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

SECTION 14 : DURABILITY PROVISIONS

ALOK BHOWMICKMANAGING DIRECTOR,

B& S ENGINEERING CONSULTANTSPVT. LTD.

315-316, VISHALC HAMBERS, SECTOR 18, NOIDA U.P

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IRC:112-2011


CONTENT OF PRESENTATION

1. Historical Perspective, Definitions

. e er ora on ec an sm

3. Design for Durability

4. Good Detailing practice from Durability

Considerations

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IRC:112-2011







Considerations

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Untill about 30 years ago, durability was

not seen as a serious issue for concrete.

IRC:112-2011SECTION 14 : DURABILITY PROVISIONS

HISTORICAL PERSPECTIVE

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 inbridge 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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Durab il ity o f concrete is i ts ab il ity to

res is t weather ing action, chemical

WHAT IS DURABILITY ?

attack, abrasion or any process of

deterioration. The cause may reside

inside the concrete itself, or be

present in the service envi ronment

to which the concrete structure is

exposed.

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Durability Requirements :

Fulfilment of the requirements of

s ruc ura sa e y an serv cea y,

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 cementcontent, maximum w/c ratio etc.)

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1. DEEMED TO SATISFY CLAUSE SUFFERS FROM

FOLLOWING :

Fails to acknowledge that structures deteriorate

progressively.

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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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



,

Construction Method (Workmanship)

Type & Quality of Materials used

Cement Content & W/C ratio

Repair & Maintenance

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IRC:112-2011







Considerations

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DETERIORATION MECHANISM

Concrete Deterioration

Mechanism

f

Most serious form of

degradation of Concrete

Physical

Deterioration

e n orcemen

Prestressing Steel

Corrosion

Abrasion

Sulphate

Attack

Alkali - Aggregate

Reaction Carbonation Chlorides

Depassivation

emca

Biological

Deterioration

Acid

Attack

Frost

Attack

Plastic

ShrinkageThermal

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

is based on specific mechanism of

duration (i,e. corrosion only).

2. However, relative importance of the

various mechanism of deterioration willvary 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

.

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 :

Durin the ini tiat ion hase no weakenin



of the concrete or of the function of the

structure occurs.

During the propagation phase active

deter io rat ions proceeds rapidly and in

many cases with acceleration.

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1. A durable

concrete

structure has along initiation

phase and a slow

ro a ation



tofacceptable

damage

DESIGN SERVICE LIFE

phase.

2. The ideal

situation by

design of new

structure is if the

initiation phase

goes upto say 50

years !

Limi

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WHAT IS DESIGN SERVICE LIFE OF A STRUCTURE ?

The assumed period for which a stru cture is to be used forits int ended purposes wit h 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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Mechanism

f

Physical

Deterioration

e n orcemen

Prestressing Steel

Corrosion

Abrasion

Sulphate

Attack

Alkali - Aggregate


Depassivation

emca

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 :

USINGHIGHSTRENGTHCONCRETE

USINGABRASIONRESISTANT AGGREGATES

GOODCURING

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GALVANISATION / EPOXY COATINGS IN

REBARS SHALL BE ABRASION RESISTANTSO THAT THERE ARE NO DAMAGE CAUSED

DURING HANDLING / PLACEMENT.



COATINGS IN PRESTRESSING STEEL SHALL

ALSO BE ABRASION RESISTANT.

ABRASION RESISTANCE IS ALSO A

REQUIREMENT FOR THE SHEATHING DUCTS

BEING 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%



after 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

-(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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Mechanism

f

Physical

Deterioration

Prestressing Steel

Corrosion

Abrasion

Sulphate

Attack

Alkali - Aggregate


Depassivation

Deterioration

Acid

Attack

Frost

Attack

Plastic

ShrinkageThermal

Effects

ImpactErosion

Chloride CO2

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

CERTAIN CONSTITUENTS IN AGGREGATES CAN

REACT 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 : AAR

ALKALI SILICA REACTION (ASR):

ASR is chemical reaction between alkali in cement



.

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

rocess:

Alkali hydroxide + reactive silica gel

alkali-silica gel

Alkali-silica gel + moisture expansion

The reaction has great affinity for moisture

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CONTROL OF ASR:

USE OF LOW ALKALI PORTLAND CEMENT (LESS

THAN 0.6% E UIVALENT Na O 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 BYREPLACING 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 blastfurnace slag as partial

will reduce the

expansion.

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ALKALI CARBONATE REACTION (ACR):

THE AGGREGATES [DOLOMITE - CALCIUM



MAGNE-SIUM CARBONATE] HAVE SPECIFIC

COMPOSITION THAT IS NOT VERY COMMON.

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ALKALI 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 susce tible to acid attack because of

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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Effects of Chemical Deterioration : Sulphate Attack



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

. .

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 theconcrete (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 whitishappearance.

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Damage is usually initiated in areas most

susceptible to the ingress of contaminants, such

as corners and ed es of concrete elements. As


the attack progresses, extensive cracking and

spalling of the concrete may occur.

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Mechanism

f

Physical

Deterioration

Prestressing Steel

Corrosion

Abrasion

Sulphate

Attack

Alkali - Aggregate


Depassivation

Deterioration

Acid

Attack

Frost

Attack

Plastic

ShrinkageThermal

Effects

ImpactErosion

Chloride CO2

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Corrosion

occurs due tode-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 oxygenpresent 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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Chlorine 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



pas e; s s ca e car ona on.

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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IRC:112-2011


. e er ora on ec an sm an ac ors

influencing Durability



Considerations

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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 betaken 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,

Ver Severe and



Extreme;

This is in increasing order of likelihood of

chloride-induced corrosion and

carbonation - induced corrosion, dependingon the chances of carbonation and ingress of

chloride ions from outside.

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Moderate cate or is for situations where the

Not Sea Water !!



chances 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



wa ers con a n ng c or e w e nc u e n s

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 lessbecause 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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. ,

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/ round 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)



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

with the cements or binders available in

India.

2. So, the minimum strength grade specified

is an indirect control on the durabilityparameters.

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Adjustment for other Aggregate size

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DESIGN FOR DURABILITY BSEC

UNIFIED CONCRETE CODE

PART 4 : DURABILITY PROVISIONS



. e er ora on ec an sm an ac ors

influencing Durability



Considerations

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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


GOOD DETAILING PRACTICE BSEC

Drainage : Most Important for Durability



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Drainage :

Avoid Horizontal Surface in Substructure Detail topromote 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 isessentially 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 resistanceto 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 rotect itfrom chemical and h sical 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

coatin s 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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COATING ON REBAR :COST COMPARISON ON REBAR COATING

Rebar without Coating 1.0

Rebar with FBEC 1.3

Rebar with Hot-dipGalvanized Coating

1.5

Solid Stainless SteelRebar(316)

5.0

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As per MORTH

Guideline issued in

Jan-2000, for regions

within 15 Km radius of

CorrossivityMap 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

Irc 112 Section-14

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