durabilityofconcrete-140827033215-phpapp01.ppt

Quality Control in Concrete and Durability factors : An overviewby

byRAJESH PRASAD, CPM/M, RVNL. KOLKATA

INTRODUCTIONConcrete the man made rock is the most widely used construction material.More than 80,000 crores cum of concrete are poured every year.India has an installed capacity of 200 million tonnes of cement.Some Structures are designed with life of 100 years.So it is necessary that the concrete used is durable.

Quality*Definition : Conformance to requirements expressed & implied.Objective : Total customer (both internal & external) satisfaction.Performance standard : ZERO DEFECTS.

System of causing Quality*DIRFT (DO IT RIGHT THE FIRST TIME)Process oriented & Not Inspection oriented approach.Prevention and not appraisal.MBWA and not MBTA (Management by Wandering Around and not Management by Talking Around.)KAIZEN slow but continuous improvement.

Quality

*Measure : The measurement of quality is the Price of non-conformance.Responsible for non- quality : Seniors are the sinners.

Quality

DurabilityDefinition

A durable concrete is one that performs satisfactorily in the working environment during its anticipated exposure conditions during service (IS 456-2000)Durability of concrete is its ability to resist weathering action, chemical attack, abrasion or any other process of deterioration (American Concrete Institute). When exposed to environment durable concrete is likely to retain its original form, quality and serviceability during its lifetime. Durable Concrete envisage limits for maximum water cement ratio, minimum cement content, cover thickness, type of cement used and presence of amount of chloride and sulphates in concrete. ( IS-SP-28)As Low permeability as possible under situation. (IS-SP-23)

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Consequences of Improper Quality and Inadequate DurabilityLoss of strength of concreteConcrete liable to be easily affected by deterrentsCorrosion of rebars Loss of serviceabilityUnpleasant appearanceDanger to persons and propertyExpensive repair costsPoor perception of concrete as a materialPoor perception of agencies involvedReduction of service lifeExternal agencies like weathering, attack by natural or Industrial liquids, Gases, bacterial Growth etc.Alkali- aggregate reaction.Ingression of moisture/air facilitating corrosion of steel and cracking concrete cover.

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Consequences of Inadequate Durability*

Consequences of Inadequate Durability*

Consequences of Inadequate Durability*

Factors Influencing Durability of Concrete (IS: 456-2000)The Environment Type and quality of constituent materialsCement content and W/C ratio of concreteWorkmanship especially in compaction curing it is very importantCover to embedded steelShape and size of the member*

Factors Affecting DurabilityDurability depends on two main factorsThe concrete system &The service environment

a) Concrete system is based on Quality and quantity of materials used and Processes involved in manufacture of concrete.

b) Service environment affects concrete by way of Physical actions andChemical actions on concrete.

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Factors Affecting Durability*DURABILITYThe Concrete SystemAggressiveness of the EnvironmentMaterialsProcessPhysicalChemicalBinder typeBinder contentAggregatesAdmixtureMix designMixing TransportingCompactionCuringTemperatureworkmanshipAbrasionErosionCavitationFreeze-thawDissolutionLeachingExpansionAlteration

MATERIALS*

Selection of Good Quality Materials(Conforming to relevant IS codes)Cement (from Reputed Manufacturers)Sand (River / Crushed, Silt < 5%)Aggregates (Cubical in shape, Innocuous)Water (Tested) with PH value ranging 6to 8Admixture (From Reputed Manufacturer) Compatibility of cement and plasticizer (PC based or Naphtha based) and 3rd generation superplasticiters of Polycarboxylates base, Polyacrylates based or Monovinyl alcohols based*

UNSOUND MATERIALS*

UNSOUND MATERIALSCement or aggregate is considered unsound when they cause unacceptable volume change, hardened concrete or mortar which causes cracks and affects durability.Aggregates containing certain materials such as shale, clay lumps, coal, iron pyrites etc show unsoundness later when concrete undergoes wetting and drying or freezing and thawing.More moisture absorption in aggregate (CA1 or CA11) is often used as a rough index for unsoundnessCement parameters that impact soundness are free lime, MgO & excess gypsum*

*Water - Permissible Limits for Solids. IS 456:2000 Table-1

Sr. No.Tested as per Permissible Limit, Maxi)OrganicIS 3025 (Part 18)200 mg/lii)Inorganic IS 3025 (Part 18)3000 mg/liii)Sulphates (as SO3)IS 3025 (Part 24)400 mg/liv)Chlorides (as CI)IS 3025 (Part 32)2000 mg/l for concrete not containing embedded steel and 500 mg/l for reinforced concrete workv)Suspended matterIS 3025 (Part 17)2000 mg/l

Impact of W/C RatioOn DurabilityPermeability is the contributory factor for volume change and higher W/C ratio is the fundamental cause of higher permeability.Use of higher W/C ratio permeability volume change cracks disintegration failure of concrete is a cyclic process in concrete.For a durable concrete, use of lowest possible W/C ratio is the fundamental requirement to produce dense and impermeable concrete.Modern superplasticizers of Polymer base are so efficient that it is now possible to make flowing concrete with a W/C as low as 0.31 or even as low as 0.29 with increased slump more than 250mm.*

Permeability Vs W/C Graph*

PROCESSES*

Workmanship for Durable ConcreteBatchingMixingTransportationPlacingCompactionFinishingProtectionCuring*

Compaction of ConcreteEnsuring suitable workability employing appropriate placing and compaction equipment Adequate compaction without segregation1% voids reduces strength by 5%

Criticality of CuringExtremely important if the water-cement ratio is low & cement content is high.

If the cement has a high rate of strength development

Ambient temperature during placing is high and day is windy

If the concrete contains GGBFS or Pulverized Fly ash (PFA)

Recommended Moist Curing (IS 456: 2000)Normal Weather Conditions

Harsh Weather Conditions (Hot and Dry)

*OPC Based Concretes-7 Days*Blended Cements based concretes-10 Days

*OPC Based Concretes-10 Days*Blended Cements based concretes-14 Days

Cracks on concrete surface due to inadequate curing

ENVIRONMENT

Environment can be classified asPhysical Temperature, Moisture, alternate wetting and drying, freezing and thawing

b) Chemical Acidic, gaseous, alkaline, corrosive

PHYSICAL ENVIRONMENTS ATTACK AFFECTING DURABILITY

Physical Environment impactsTemperature

Significantly affects rate of hydration of cement.Leads to Plastic shrinkage cracks in fresh concreteVolume changes and cracking especially in mass concreteSpalling and disintegration of concrete at higher temperatures > 250C (3000c as per A.M. Neville P-387) Variation in ambient temperature causes secondary stresses in structures

Physical Environment impactsMoisture Shrinkage on drying, consequent volume change and crackingInduces corrosion of steelActs as carrier of chemicals inside the body of concreteCauses efflorescence and deposition of Ca(Cao+2H2 0= Ca (OH)2 +H2 0 OH)2 on surfaceSeepage / Leakages cause inconvenience to occupants and deteriorates structures due to permeable concrete.

Alternate wetting and dryingCauses secondary stresses in the structuresAccelerates corrosion of steel and Chemical attack on concrete

Freezing and Thawing Leads to expansion of concrete and cracking Ice-melting salts cause erosion of concrete

Physical Environment impacts

CHEMICAL ENVIRONMENT ATTACK AFFECTING DURABILITY

Chemical ActionWhen we are dealing with durability, chemical attack which results in volume change, cracking and consequent deterioration of concrete become a major cause of concernTypes of Chemical attackSulphate attack Alkali aggregate reactionChloride ion attack - CorrosionCarbonationAcid AttackEffect on concrete in Seawater

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1. Sulphate attackSulphate attack denotes an increase in the volume of cement paste in concrete or mortar due to chemical action between the products of hydration of cement and solution containing sulphate, and also sodium, magnesium and Cholorides.In hardened concrete, calcium aluminate hydrate (C-A-H) can react with sulphate salt from outside, product of reaction is calcium sulphoaluminate, which can cause an increase in volume up to 227%Rate of sulphate attack increases with a saturated sulphate solution. A saturate solution of magnesium sulphate can cause serious damage to concrete with high w/c ratio.

Sulphate attackMethods of controlling sulphate attackUse SRC (sulphate resisting cement)Quality concrete - low w/c ratio, well designed and compacted dense concreteUse of air-entrainmentUse of puzzolanaHigh pressure steam curingUse of high alumina cement

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2. Alkali - Aggregate ReactionAlkali from cement, reacts with reactive silica (of aggregates) to form alkali-silica gel of unlimited swelling type. The continuous growth of silica gel exerts osmotic pressure within the concrete. This manifests into cracking and bulging of concreteOccurrence is due to :High alkali content in cement (more than 0.6%)Reactive silica in aggregateAvailability of moisture

Alkali - Aggregate Reaction*Alkali-aggregate reaction (AAR) is basically a chemical reaction between the hydroxyl ions in the pore water within concrete and certain types of rock mineralsSince reactive silica in the aggregate is involved in this chemical reaction it is often called alkali-silica- reaction (ASR).It is recognized as one of the major causes of cracking of concrete. The reaction produces what is called alkali-silica gel of unlimited swelling type under favorable conditions of moisture and temperature. The crack width can range from 0.1mm to as much as 10mm.

Alkali - Aggregate Reaction*Alkali content (K2O and Na2O) or what is called soda equivalent. This is calculated as the actual Na2O content plus 0.658 times the K2O content of the clinker. It should be less than 0.6 percent by mass of cement.Alkalis from all these sources must be included in finding the total alkalis. British standard 5328 : part 1 : 1091 specifies a maximum of 3.0 kg of alkalis (expressed as soda equivalent) in 1 m3 of concrete in case of alkali reactive aggregates are used.

Alkali - Aggregate ReactionUse of pozzolana, slag or silica fumeControl on service condition, limiting degree of saturation of concreteRemedial Measures:Use non-reactive aggregates from alternate sourcesUse low-alkali cementReduce cement content in concrete

3. Chlorides in ConcreteChlorides in concrete increases risk of corrosion of steel (Electrochemical reaction) (IS 456:2000)Higher Chloride content or exposure to warm moist conditions increase the risk of corrosionTo minimize the chances of corrosion, the levels of chlorides in concrete should be limitedTotal amount of chloride content (as Cl) in concrete at the time of placing is provided by IS 456:2000

Methods of Controlling Chlorides*Chlorides in cement to be less than 0.1 % max ( or 0.05% max for prestressed works)Chlorides in water to be less than 2000 mg/ltr for PCC and below 500 mg/ltr for RCCChlorides in aggregates are generally not encountered but, its a good practice to wash sand containing salt more than 3%Chloride traces are also found in chemical admixtures. Chloride free admixtures should be generally preferred.

CorrosionCorrosion is an electro-chemical process Basic Mechanism :Different areas of the same steel bar become anode and cathode. The electrical connection being maintained by pore water, which acts as electrolyte

At the anode, steel releases electron and takes the ionic form Fe 2e- + Fe2+

At the cathode, water in presence of oxygen and the released electron forms hydroxyl ions (OH)-2O2 + H2O + 2e- 2(OH)-

Fe++ + 2(OH)- Fe(OH)2 Iron Hydroxide (Rust)2H2O+O24e-=4 (OH-)

Example of Delamination of Concrete cover

Corrosion

Crack formed due to bursting pressure on account of rusting of reinforcements

Methods of Controlling Corrosion*Limit the chlorides in water, cement, superplastizers, etc to acceptable levelsProvide proper cover as per IS normsCover blocks also need to be of good qualityConcrete should be properly compactedMake dense, impermeable / waterproof concreteHave protective coatings wherever suitableEnsure proper & timely maintenance of structures

4. Carbonation of ConcreteMechanism : Carbon dioxide from the air reacts with calcium hydroxide to form calcium carbonatesIn the presence of moisture, carbonic acid is formed which reduces the alkalinity of concretepH value of concrete reduces from 12.5 to 9, thus destroying the protective layer and exposing the steel to corrosionRate of Carbonation depends upon relative humidity, grade of concrete, permeability of concrete, depth of cover and timeNearly 1 mm carbonation is reported per year in normal M-20 grade of concrete

Measurement of Depth of CarbonationPink color indicates that Ca(OH)2 is unaffected by carbonation. The uncolored portion indicates that concrete is carbonated

CarbonationCarbonation of concrete is a process by which carbon dioxide from the air penetrates into concrete and reacts with calcium hydroxide to form calcium carbonates. In actual practice, CO2 present in atmosphere permeates into concrete and carbonates the concrete and reduces the alkalinity of concrete. When all the Ca(OH)2 has become carbonated, the pH value will reduce upto about 8.3. In such a low pH value, the protective layer gets destroyed and the steel is exposed to corrosion.

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CarbonationThe highest rate of carbonation occurs at a relative humidity between 50 and 70 percent.Protective coating is required to be given for long span bridge girders, flyovers, Industrial structures and chimneys. Such as plastic paints (Impermeable)Deep cover plays an important role in protecting the steel from carbonation.

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Steel in Passivity condition*Concrete is under continuous attack by aggressive environmental agencies.Good concrete and sufficient cover is the answer for durabilitySteel in passivity condition

5. Acid attack *Concrete is not fully resistant to acids depending upon the type and concentration of acid. Oxalic acid and phosphoric acids are harmless. The most vulnerable part of the cement hydrate Is Ca(OH)2, but C-S-H gel can also be attacked.Concrete can be attacked by liquids with pH value less than 6.5.

Acid attack *But the attack is severe only at a pH value below 5.5.At a pH value below 4.5, the attack is very severe.Cement compounds are eventually broken down and leached away. If acids are able to reach the reinforcing steel through cracks corrosion can occur leading to further cracking

COVER TO REINFORCEMENT*

Cover to Reinforcement(IS 456 2000)*Note :For main reinforcement upto 12 mm dia bar for mild exposures, the nominal cover may be reduced by 5 mmUnless specified otherwise, actual concrete cover should not deviate from the required nominal cover by +10mm or 0mm

Exposure ConditionMin Nominal cover (mm)Mild20Moderate30Severe45Very Severe50Extreme75

Effect of Other materialsMineral Oil usually effects only fresh concrete in their hardening process (petrol, petroleum distillates etc)Organic Acid have corrosive effect Vegetable & Animal oils & Fats causes deterioration of concrete surfaces due to their corrosive actionAction of Sugar has retarding effect on fresh concrete; has gradual corrosive effect on hardened concrete Action of Sewage concrete sewers running full remain unaffected; but in partially filled sewers where hydrogen sulphide gas is evolved & sulphuric acid is formed, concrete above sewage level gets affected due to corrosive action of such acids*

Fire ResistanceThe fire resistance is not only dependent upon the type of concrete but also on the thickness of cover to reinforcement.Effect of temperature on the strength of concrete is not much upto a temperature of about 250oCAbove 300oC definite loss of strength takes place.Portland blast furnance slag cement is found to be more resistant to the action of fire.Light weight concrete stand up better to fire than ordinary concrete.*

Fire ResistanceBest fire resistant aggregates amongst the igneous rocks are, the basalts and dolerites less amount of silica.Since then decomposition takes place only at a very high temperature of 900oC , Limestone is considered as a good fire resistant aggregate.Serious reduction in strength occurs at a temperature of about 600oC.*

Constraints/Issues for Concrete in Aggressive EnvironmentContaminants in soil/water like sulphates, chlorides, effluents, etc. highly affect the durability of concrete (limitation of SRC)Heavy reduction in the headroom space due to large depths of the beamLimitation of OPC leading to weak micro -pore structureLarge dimension of columns in particular, leads to space constraints.

Why is Quality necessary?Intense Competitive Environment

Entry of Foreign Goods and Services

Increased Customer Consciousness

Earning Profit instead of making profit

Organizations survival / progress depends on it

Safety vs. OperationQuality vs. Progress

In our day to day work COM gets a lot of importance.Safety comes after Operation.Similarly Quality comes after Progress.. I am CSOI am COMBoth are PHODs/CHODsWith different duties and responsibilities Operation vs safety

Good PhysiqueRegular Check upsPreventive Measures & MedicinesProper & Timely Cure & RestorationGood ConstructionRegular InspectionsPreventive Measures & MaterialsProper & Timely Repairs & Restoration

This ROB constructed 14years back, was partly closed in 2007

Distress in Concrete Slab at Bagha jatin ROB

GHPR Swimming PoolPoor Quality & incomplete work by RITES as like this.After construction & commissioning

Construction Process Analysis What we think it is

What it really is ( Hidden )What it should beWhat it could be

5 Gaps in Service Quality Gap 1: Consumer Expectation- Management Perception

Gap 2: Management Perception-SQ Specification

Gap 3: SQ Specification- Service Delivery

Gap 4: Service Delivery- Perceived Service

Gap 5: Perceived Service- Consumer Expectation

5-S.Seiri - Remove unnecessary items

Seiton- Keep necessary things properly

Seiso - Clean workplace thoroughly

Seiketsu - Maintain high standards regularly

Shitsuke - Maintain self-discipline

Quality work does not mean the work to stop or standstill

Give wider publicity about Quality and consequences of poor quality.Quality consciousness

This is a quality project..

Never disrespect contractorsListen to them but ensure quality

I can straightway say there is a huge mistake I dont know whether its human error or an error in our judgment but we did not follow QAP properly.QualityAudit

Durability of Structures

Blacklisted Contractors

Poor quality is always exposed at sometime.

RVNL OFFICE

RVNL PIU

Are You Lonely and Worried for quality and durability of Concrete??Dont like working on your own?Hate making decisions?Then call A MEETING!!You can

SEE people DRAW flowchats FEEL important IMPRESS your colleaguesAnd must discuss on quality related issues for Project Implementation.MEETINGSThe practical alternative to work.

Concluding RemarksStrength and durability are two important properties of concrete.Concrete is a long lasting material provided adequate care is taken inSelection of ingredients - Right type of materials & right concrete for appropriate end applicationsMix design, batching, mixing, transporting, placing, compaction, finishing, protection & curingReinforcement detailing and adequate cover Good quality form workMaintenance and upkeep

Concrete is a dependable construction material and it should not be abused to the limits. It should be used with understanding, love and care.

Quality of Food is important for him. Quality of Construction is important for us.

It was a presentation byRajesh Prasad

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