Durability Modified

8/8/2019 Durability Modified

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DURABILITY OF

STRUCTURES


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Concrete Is it trouble free?

MANDOVI BRIDGE IN GOA WAS OPENED TOTRAFFIC IN 1972 AND FAILED IN JULY 1989.

THANE CREEK ROAD BRIDGE OPENED FORTRAFFIC IN 1975 WAS CLOSED IN 1991.


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RLY BRIDGE OVER RIVER GANGES NEARALLAHABAD WAS BUILT IN 1990sDEVELOPED SERIOUSS PROBLEMS INBEARINGS, CRACKS IN BOX GIRDERS ANDA SPEED RESTRICTION OF 20 KMPH WASIMPOSED.

RLY BRIDGE OVER RIVER GANGES NEARROORKEE BUILT IN 1998 DEVELOPEDSERIOUS PROBLEMS IN BEARINGS,CRACKS IN BOX GIRDERS

Concrete Is it trouble free?


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Concrete

Essential Requirements

1.Strength Carry the designed loads

2.Durability Keep carrying withoutproblems


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Durability.

It does not mean indefinite Life

Concrete requires routine maintenance

It was earlier believed that strong concrete is also durableconcrete

Strength and durability have to be considered during the designstage


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What is Durability?

Ability of a structure to withstand

the deterioration, which is causedunder the influence of environment

throughout its desired life, without

the need for undue maintenance.


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Durability of Concrete

Resistance to Physical and Chemical

deterioration of concrete resulting from

1.Interaction with the environment

including weathering and abrasion

2.Interaction between the constituents of

which it is made and protection of

embedded steel from corrosion process


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Cracking in Concrete

Non-structural cracks in concrete

Plastic cracking

Thermal contraction and cracking

Long term drying shrinkage

Structural cracks in concrete

Under tensile structural loadsCan be controlled by detailing


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Environmental attack

Exposure to

Salts

Oxygen

Moisture

Carbon dioxide

Concrete cover is the prime defense andunfortunately it is of relatively poor quality


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PERMEABILITY

Factors effectingSTRENGTH Factors effecting PERMEABILITY

DEPENDS

ON

D

EPENDS

ON

STRENGTHVS

1.CE

MENTITIO

US

M

ATE

RIAL

Its contentW/C ratioHeat of

hydration

C3A content

2.CO

HESI V

E

CO

NC

RETE

CohesiveWorkable

3.COMAC

TION

Minm

Voids

4.CU

RING

Gel

formation

5.CO

VER

ExtentIntegrity

6.CR

ACK

WI

DT

H

1.Air

Voids

1.W/C

ratio

1.Cemen

t

Qualit

y


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Beneficial factors/actions against

this Increase in depth of cover

Low W/C ratio to minimize capillaries

High cement content providing high level

of alkalinity

Efficient curing of adequate duration

Coatings forming barrier to surface


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Effect of w/c ratio on permeability

Concrete produced with low water to cement ratio displays lowcoefficient of permeability of concrete as compared to concreteproduced with high water cement ratio

The coefficient of permeability of concrete made using samematerials but with different W/C ratios.

Coefficient of Permeability for different W/C ratio

Sr. No. Water Cement Ratio Coefficient of Permeability (Valenta)

1 0.35 1x 10-3

2 0.50 10 x 10-3

3 0.65 1000 x 10. 3


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Effect of Curing

Permeability (m2 x 10-17 ) Porosity (%)

Curing(days)

1 3 7 28 90 1 3 7 28 90

W/C

0.32 5.60 0.30 0.12 0.00 0.00 20.8 19.7 14.4 9.8 5.9

0.40 18.70 0.59 0.07 0.07 0.00 33.3 28.6 20.9 16.8 11.1

0.50 214.0 14.70 2.35 0.19 0.00 43.5 37.8 32.2 20.8 14.5


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LIFE OF BRIDGES-

CBC Cl. 16.1.3 IN SEA 50 YEARS

IN COASTAL AREAS 80 YEARS

REST OF INDIA 100 YEARS


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PROPOSED CODAL LIFE OF

MAJOR BRIDGESRLY BDS L.NO. 2002/CE-II/ASSETS/1 DT.1-7-2004STRUCTURE CODAL LIFE (YRS)

BRIDGE WORK-STEEL 60

BRIDGE MASONARY 100

STRUCTURES-STEEL 60

STRUC.-MASON&CONCRETE

65

RCC BRIDGE WORK 60

PSC BRIDGE WORK 40


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HOW TO BUILD DURABLE

STRUCTURES

DURABLE STRUCTURES ARE TO BE

- CONCEPTUALISED

- DESIGNED AND DETAILED

- SPECIFIED- CONTRACTED

- SUPERVISED

- CONSTRUCTED ( TO BE RUTHLESSLY

DEMOLISHED IF NOT CONSTRUCTEDAS SPECIFIED)

- MAINTAINED


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DURABILITY

FUNCTION OF

1. SELECTION OF PROPER FORM

2. PROPER DESIGN

3. CHOICE OF PROPER MATERIALS

4.GOOD QUALITY CONTROL

5. MAINTAINABILITY


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FORM

ALL COMPRESSION MEMBERS HAVEPROVED THEIR DURABILITY OVER

LONG TIME SIMPLE DETAILS AND FORMS

FORMS HAVING MINM. EXPOSURE TOCORRODING ENVIRONMENT

AVOID UNDUE EMPHASIS ONECONOMY BY ADOPTING THINNERSECTIONS


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DESIGN

ASSESSMENT OF LOADS

- FUTURE EXPECTED LOADS

-DERAILMENT CONDITION

- ERECTION LOADS

-TEMP. ACROSS X SECTION

-OCCASIONAL LOADS

PROPER DUCTILE DETAILING OFREINF.

CRACK WIDTH CONTROL


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CONTINUED- 1

LAPS IN REINF. AT CRITICALLOCATIONS AVOIDED. THE MECH. JT.

DEVICES BE LOCATED AT LOCATIONOF 50% OF MOMENT OF RESISTANCE

PSC STRANDS SOULD BE AVOIDED TOHAVE CURVATURE IN PLAN. INELEVATION THE CURVE BE ASGENTLE AS POSSIBLE


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CONTINUED-2

MINIMUM RESIDUALCOMPRESSION(5%) BE ALLOWED

IN EXTREME FIBRES IN PSCGIRDERS, IN SERVICE CONDN.

AVOID CURTAILING CABLES INTHE DECK SLAB. THE BLISTERS IFUNAVOIDABLE SHOULD BEPROVIDED IN NON-CRITICAL

ZONES


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CONTINUED-3

PROVISION FOR ADDL. PRESTRESSFOR FUTURE REQUIREMENT

PROVISIONS TO BE KEPT FORMAINTAINABILITY OF BRIDGES

CONCEPT OF MAINTENANCE

MANUAL


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CHEM. IMPURITIES IN

AGGREGATESS.NO. CHEMICA-

LSFINE AGG. COARSE

AGGR.

(I) Cl (MAX.) 0.04% BYWT.

0.02% BYWT

(II) SO3 (MAX) 0.4% BYWT

0.4% BYWT.


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TOTAL CHLORIDE

CONTENT IN CONCRETEEXTREME/V.SEVERE ENV.

SEVERE/MODERATE/MILD

PSC 0.06% BY WT.OF CEMENT

0.10% BY WT.OF CEMENT

RCC 0.15% BY WT.OF CEMENT

0.15% BY WT.OF CEMENT


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AGGREGATES

ORGANIC IMPURITIES BE ABSENT

CLAY& SILT UPTO 75 MICRON TO BE

ABSENT OR CONTROLLED MARINE AGGREGATE IF USED

SHOULD BE WASHED BEFORE USE

WATER SOLUBLE CHLORIDES ANDSULPHATES TO BE AVOIDED


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ADMIXTURES

THESE SHOULD BE CHLORIDEFREE

SHOULD NOT BE AIR ENTRAINIGTYPE IN PSC WORK

EXCESSIVE QTY OF SUPER-

PLASTICISER CAN LEAD TOSEGGREGATION

GROUTING ADMIXTURES SHOULDBE FREE FROM Cl-,So4-,So3-,No3-


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MAINTAINABILITY

AMENABLE TO INSPECTION ANDATTENTION , IF REQD.

CLOSED SECTIONS SHOULD BEPROVIDED WITH SYSTEM OF

PROPER LIGHTING

WELL DEFINED SCHEME ANDSCHEDULES OF INSPECTIONS


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QUALITY CONTROL

A WELL DEFINED QC/QA SYSTEM WITHCHECK LISTS FOR VARIOUS ACTIVITIESOF DIFFERENT STAGES AND POINTED

RESPONSIBILITY OF OFFICERS AND STAFFIS THE ONLY ANSWER

HIGHEST OFFICER INCHAGE OF PROJECTSHOULD BE COMMITTED TO QC/QA


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PERMEABILITY TEST

DEPTH OF PENETRATION OFMOISTURE SHOULD NOT EXCEED

25 MM.

THIS TEST IS MANDATORY FOR

BOTH RCC & PSC STRUCTURES INSEVERE ,V.SEVERE & EXTREMEENV.


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Corrosion of Concrete-

Carbonation The diffusion of atmospheric CO

2in the gaseous phase

of the concrete pores and reacts in following two ways.

The dissolution of solid Ca(OH)2from cement gel into the

pore water and reaction of dissolved CO2with dissolved

Ca(OH)2in the pore water.

The reaction of dissolved CO2 with CSH.


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CarbonationCa(OH)

2+ 2CO

3> CaCO

3+ 2H

2O

3CaO2SiO23H

2O + 3CO

2> 3CaCO

32SiO

23H

2O

The pH-value decreases to less than 9,which normally is insufficient to protect

the reinforcement against corrosion.


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CarbonationX= K T

Where X is measured in mm and T

in years

K is function of concrete strength

Above relation is for RH 50%


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Carbonation


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Depth of Carbonation

Strength of Concrete


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Chlorides Mix Water

Aggregates

Admixtures (Accelerators)

Curing water

Surrounding soil Sea water


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Corrosion of Concrete-Critical

Chloride Content


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Alkali Aggregate Reaction

Probable Area Anywhere on structure

Probable Locations Damp area, shows gel type or dried resin type deposit in

cracks Cause

Reactive silicates and carbonates in aggregates reactingwith Alkali in cement

Remedy Use proper aggregates, Use Portland Blast Furnace Slag

cement, Keep water away

Time of Appearance

More than five years


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Alkali Aggregate Reaction


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Sulphate Attack

Sulphate salts from surrounding soil react with

C3A . No deposits like those in Alkali- Aggregate

reaction

Use low C3A cement, Portland Blast Furnace Slag

cement

After two years


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Sulphate Attack

High concentrations of sulphate ions(SO

4--) + Ca(OH)

2+ 2H

2O ->

CaSO42H

2O + 2OH- + expansion

Low Sulphate ion concentration

Calcium Aluminate Hydrate + CaSO42H

2O ->

3CaOAl2O

3CaSO

432H

2O (ettringite) +expansion

Magnesium and Ammonium Sulphate(Serious)

MgSO4reacts with Calcium Aluminate Hydrate

MgSO4+ Ca(OH)

2->

CaSO4+ Mg(OH)

2+ volume expansion


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Corrosion of Steel

Electrochemical corrosion

Galvanic corrosion

Atmospheric corrosion


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Electrochemical corrosion


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Corrosion of Steel Rebars

Electro-chemical process of corrosion


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Chemical Reaction - Rusting

At Anode

Fe Fe2+ + 2e-

At Cathode

2e- + H2O + O2 2(OH)

At AnodeFe2+ + 2(OH) FeO.H2O Rust


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Volume of Rust

FeO

Fe(OH)2

Fe3O4

Fe(OH)3

Fe(OH).3nH2O

1 2 3 4 5 6

Volume

Fe2O3


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Galvanic corrosion

More anodic metal releases ions when

two different metals are in electrical

contact in moist atmosphere


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Atmospheric corrosion High humidity level ( > 65 %)

The corrosion velocity is doubled for every10oC increase in temperature.

Air pollution

SO2in air

The sulphur dioxide creates H2SO

3which

is oxidized to sulphuric acid (H2SO4)

which increases the corrosion velocity.

Correction to CBC


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Correction to CBCEnvironment

Exposure condition

Moderate Concrete surface protected against weather or aggressive conditions.Concrete surface sheltered from severe rain or freezing whilst wetconcrete exposed to condensation. Concrete structure continuouslyunder water, Concrete in contact with non-aggressive soil/groundwater.

Severe Concrete surface exposed to severe rain, alternate wetting and dryingor occasional freezing or severe condensation. Concrete exposed toaggressive sub soil/ground water or coastal environment.

Extreme Concrete surface exposed to sea water spray, corrosive fumes orsevere freezing conditions whilst wet. Concrete structure surfacesexposed to abrasive action, surface of members in tidal zone. Allother exposure conditions which are adverse to exposure conditionscovered above.


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Existing Provisions CBC

Minimum Grade of Concrete

Environment PCC RCC PSC

Mild M - 10 M 15 M 35

Moderate M - 10 M 20 M 35

Severe M - 15 M 20 M 45

Very Severe M - 15 M 25 M 50

Extreme M - 20 M - 30 M - 50


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MINIMUM COVER TO REINF.

Cl.15.9.8.1 OF CBCType ofStructure

ExtremeEnviron.

VerySevere

Severe Moderate/Mild

SLAB 50 50 25 25

BEAM/GIRDER

60 50 40 35

COLUMN75 75 75 50

WELL/PILE/Foot

75 75 75 50


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Correction to CBC Cover to

reinforcementType of

StructureExtreme Severe Moderate

Slab 50 35 25Beam/Girder 60 50 35

Column 75 75 50

Well/ pile &footing

75 75 50


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Minimum Cementitious MaterialKg/m3


Mild 210 300 350

Moderate 250 300 400

Severe 250 350 430

Very Severe 300 400 440

Extreme 300 400 440


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MINIMUM CEMENT

CONTENT Cl.5.5.4 OF CBCExposure PCC(Kg/m3)

RCC(Kg/m3)

PSC (Kg?m3)

MILD 300 350 400

MODER. 350 400 400

SEVERE 350 400 430

VERY

SEVEREExtreme

400

400

430

430

430

440

Cement Content shall not exceed 530 Kg/M3


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Correction to CBC

Exposureconditions

Minimum cementitiousmaterial content kg/m3

PCC RCC PSC

Moderate 240 300 400

Severe 250 350 430Extreme 300 400 440


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MAXM. W/C RATIO

Cl.5.4.2OF CBCExposure condition Max. W/C Ratio

MILD 0.50

MODERATE 0.45

SEVERE 0.40

VERY SEVERE 0.40


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Maximum Water Cement Ratio


Mild 0.55 0.50 0.45

Moderate 0.50 0.50 0.40

Severe 0.50 0.45 0.40

Very Severe 0.50 0.45 0.35

Extreme 0.45 0.40 0.35


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Correction to CBC

Environme

nt

Maximum Water-CementRatio

(PCC) (RCC) (PSC)

Moderate 0.50 0.45 0.40Severe 0.45 0.40 0.40

Extreme 0.40 0.35 0.35


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MINIMUM GRADE OF CONC.

Cl.5.4.3 OF CBCExposurecondition

PCC RCC PSC

Mild/Moderate M 25 M 35

SEVERE M 25 M 30 M 50

Extreme/V.Severe/severe

M 30 M 30 M 50


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Correction to CBC Minm grade

of ConcreteFor Important Bridges and PSC workStructuralMember

Moderateexposure

Severeexposure

ExtremeExposur

ePCC Member M-25 M-30 M-35

RCC Member M-30 M-35 M-40

PSC Member M-35 M-40 M-45

For Bridges not covered above

PCC Member M-15 M-20 M-25

RCC Member M-20 M-25 M-30


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OTHER REQTS FOR

DURABILITY PROPER DRAINAGE

ARRANGEMENTS

COVER BLOCKS IN THE SAMEGRADE OF CONCRETE

BINDING WIRES TO BEGALVANISED

PROTECTIVE COATINGS TO REINF.AND CONCRETE SURFACE


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Documents

Durability Modified