UNIT-2

SERVICEABILITY AND DURABILITY OF CONCRETE

QUALITY ASSURANCE FOR CONCRETE CONSTRUCTION

INTRODUCTION

• Quality assurance scheme is management system

• Increase confidence that a material,product(or)service will confirm to special requirement policies designed responsibilities and

requirements the owner Controlling to pre determined requirements actives which influence quality

Quality assurance for concrete structures

• Types of structures guidelines as to permissible loading

• Periodic inspections maintenance cannot be ignored ,possible anticipated durability serviceability (or) functional efficiency

• Detail at time at final inspection and use of the structures

Need for quality appearance

• Construction and use of a concrete structures• Client requires• Designer depends• Material producer• Building contactor• Finally the user is rewards by a functional

efficient structure a good appearance

Causes of design faults

• Mis interpretation of the client needs• Lack of good communication between

members• Production ,inadequate and impressive

speciation's• Design standard (or) codes of practices• Use of incorrect or out of data

Causes of design faults in construction

• Mis interpretation of design drawings or speciation's

• Lack of effective communication with suppliers and sub contractors

• Inefficient co-ordination of sub contracted work

• Inadequate on site supervision• Poor workmanship

ACI committee

• Freezing • Aggressive chemical exposure• Abrasion• Corrosion of steel and other embedded

material• Chemical reactions of aggregate

PROPERTIES OF CONCRETE

Strength of concrete

• The strength of the concrete is resistance and rupture

• It may be measured in a number of way such as strength in compression strength in tension strength in shear in flexureAll these indicate strength with reference

particular method of testing

Permeability of concrete

• Volume change and cracking of concrete and durability of concrete structures

• Primary responsible for affecting durability ,permeability of concrete

• Concrete resists external attack• Aggregate of low permeability into cement paste at reducing

permeability of the system• Large size of aggregate increase the permeability• Air entrainment makes the concrete process upto 6%makes of

concrete• Crushed silica decrease the permeability

Thermal properties

• To study of thermal properties of concrete is an dealing with durability of concrete

• Concrete material used all climatic regions all land of structures

• Properties of concrete are thermal conductivity thermal diffusivity specific heat coefficient of thermal expansion

• Thermal conductivity material conduct heat it is measured joule per second per square meter values of

conductivity of concrete made with different aggregate limestone – 3.2 sandstone -2.9Thermal diffusitivity it represent the rate which temperatureChange concrete massDiffusitivity =conductivity/cpWhere c =specific heat p =density of concrete range of diffusitivity =0.002 to 0.006m^2/h

• Specific heat quality of heat required to raise the

temperature unit mass of a material by one degree centigrade ranges of concrete 840 to 1170

Coefficient of thermal expansion ratio between change in unit length per

degree change in temperature

Cracking

• Cracking will occur the tensional strain which occur exceeds the tensional strain capacity of concrete

• Tensional strain capacity of concrete varies the age of rate of application of strain

Effects of cracking

• Immediate structural distresslong run to a reduction of through corrosion of steel

• Mal function of the structure as evidence • Cracks leading structural failure• Cracks causing corrosion• Cracks affecting function• Cracks affecting appearance

Cracks in concrete`

Before hardening• Drying plastic shrinkage settlement shrinkage bleeding curingConstructional cracks formwork excess vibration finishingEarly first damage

After hardening• Un sand material• Long term drying shrinkage• Thermal• Moisture movement• Tensile zone• Structural design

deficiencies• Chemical• Corrosion of reinforcement

Types of crack

• Delayed curing• Formwork movement• Excess vibration• Sub grade settlement• Finishing• Early frost damage• Unsound materials\

Cracking in plastic concrete• The removal of water from

the top surface by evaporation exceeds the rate at which bleed water is coming to the surface

• Early shrinkage of concrete

Cracking in hardened concrete• Structural response to

applied loads and external displacement

• The interstice nature of the concrete and is constituent materials

EFFECT DUE TO CLIMATE

Concrete can be protected from freeze-thaw by the

entertainment of appropriate quantities of air distributed

through the cement paste, with spacing between bubbles

of not more than about 0.4mm

For effective protection air entraining agents must be

added to the mix

The amount of air required is between 4-8% depending

on size of aggregate

FREEZING AND THAWING

If the concrete has been made more dense without any

capillary pores , the resistance to freeze and thaw will exist

without any air entrainment.

Particular form of frost action is known as D-cracking or

Durability Cracking

Caused by the coarse aggregate and air-entrainment, which

does not therefore provide protection

Carbon dioxide from air penetrates into concrete an reacts

with calcium hydroxide to form calcium carbonates

One of the reason for corrosion of reinforcement

Carbonated concrete is less permeable

Alkalinity of the concrete reduced when carbonation takes

place therefore protection against corrosion gets reduced

So its important to ensure quality and thickness of concrete

cover

CARBONATION

Factors affecting Rate of Carbonation

The level of pore water

Grade of concrete

Permeability of concrete

Whether the concrete is protected or not

Depth of cover

Time

Highest rate of carbonation occurs at

relative humidity of between 50-70%

Effects Due to Temperature

Removal of evaporable water

Removal of combined water

Alteration of cement paste

Disruption from disparity of expansion and resulting

thermal stress

Alteration of aggregate

Change of the bond between aggregate and paste

Effect due to Chemical Attack

High porosity and hence permeability and absorption

Improper choice of cement type for the conditions of

exposure

Inadequate curing prior to exposure

Exposure to alternate cycles of wetting and drying and to a

lesser extent heating and cooling, with allowance for the fact

that higher temperatures increases reactivity

Increased fluid velocity

Expansive reactions of any sort which may cause

cracking and any other physical phenomena, which

lead to greater exposure of reactant surfaces

Suction forces

Unsatisfactory choice of shape and surface to

volume ratios of concrete sections

• A concrete is said to be durable if it withstands the conditions for which it has been designed, without deterioration over a period of years

• Resistance of a concrete to variety of physical or chemical attacks due to external causes or by the internal causes

Durability of a structures

CORROSION

Definition of Corrosion

Reinforced concrete – weakness

Characteristic of concrete

Stages of corrosion

Corrosion of steel

reinforcement

Principles and mechanism of

Corrosion

Causes of corrosion in reinforced concrete

Carbonation

Chloride attack

Factors Influencing Corrosion

Effects due to

corrosionDamages induced by corrosion

Preventive methods

corrosion rate

monitoring

Corrosion is the deterioration of materials by chemical interaction with their environment.

The term corrosion is sometimes also applied to the degradation of plastics, concrete and wood, but generally refers to metals.

Definition of Corrosion

Reinforced concrete - weakness

• Statics indicates that 40% of structure fails due to corrosion of reinforcement

• susceptible to environmental attack– deterioration accelerates under

humid conditions– corrosion leads to spalling of

concrete– reinforcement is exposed– bond reduces– strength reduces

Characteristic of Concreteconcrete provides chemical protection to the

steel with the formation of highly alkaline pore solution.

The highly alkaline in the concrete promotes the formation of an adhering passive film in the surface of the steel, which protects it from corrosion.

Characteristic of concrete

Corrosion

Stages of corrosion

• Rust staining • Bulging of cover (collection of rust products)• Micro cracks• Macro cracks• Spalling of cover concrete

Corrosion of steel reinforcement

Corrosion of steel reinforcement Penetration of unfavourable chemical species

can destroy the protective environment and eventually cause corrosion of the steel.

Significant chemical species which can break down the passive film on the steel are carbon dioxide and chlorides.

• Concrete is a high alkalinity material. • The pH of new concrete is 12 to 13.• In this range of alkalinity, embedded steel is protected

from corrosion by a passivating film ( gamma iron oxide film) bonded to the reinforcement surface.

• However when the passivating film is disrupted, corrosion may take place.

• Reinforcement corrosion can get initiated through one or more effects from the environment.

Principles and mechanism of Corrosion

Causes of corrosion in reinforced concrete

• Corrosion Due to Carbonation• Corrosion Due to Chloride Ion Penetration

Carbonation CO2 from air penetrates into concrete In the absence of moisture CO2 is non reactive In the presence of moisture CO2 diluted carbonic acid it reacts with Ca(OH)2 to form CaCO3

shrinkage It also reduces alkalinity of concrete detoriates passivating film corrosion of steel reinforcement

chloride attack

• Sulphate attacks the concrete, chloride attacks the steel

• Sources of chloridecementwaterAggregateSometimes from Admixtureproviding from marine atmosphere

Chloride attack

• Amount of chloride required to initiate corrosion depends on the pH of pore water

• pH < 11.5 corrosion occur without chloride• pH > 11.5 chloride is needed for corrosion• Concrete contains chloride

In insoluble form (chlorialuminates)does not cause corrosion

In soluble form causes corrosion

• Electrochemical process (transfer of electrons as a result of chemical Reactions)

Corrosion = Iron + Oxygen + Moisture• Difference in electrical potential along steel

reinforcement in concrete, an electrochemical cell is set up

• One part of steel anode• Another part of steel cathode• pore water Electrolyte

Electrochemical corrosion in the presence of chloride

Reactions in electrode

• The anode is the site of the oxidation of the steel. The reaction at the anode is expressed as:

Fe → Fe2++ 2e-

• The cathode is the site of the reduction reaction. The liberated electrons are used at the cathode

• Positively charged ferrous ions at anode passes into the solution

• Negatively charged free electrons passes through steel into cathode

Corrosion in steel

• Anode Reaction Fe → Fe2++ 2e-

• Cathode Reaction 2e- + H2O + ½ O2 → 2 OH-

H2O H2OO2 O2

Cl- Cl-

OH- OH-Cathode Cathode

Anodee- e-

Fe2+

rust rustCl-

Cl-

Cl-

Cl-

Cl-Cl-

Cl-

• These electrons are absorbed by electrolyte and react with water and oxygen to form hydroxyl ion Fe2+ + 2OH- → Fe(OH)2 {Ferrous hydroxide}

4Fe(OH)2 + O2 + 2H2O → 4Fe(OH)3 {ferric oxide} 2Fe(OH)3 → Fe2O3•H2O + 2H2O

Fe2O3•H2O {hydrated ferric oxide}

Patch Accelerated Corrosion

Chloride-Free Patch

Potential Difference Between Patch and Chloride Contaminated Concrete Results in Accelerated Corrosion

Chloride Contaminated Concrete

© Vector

Effect due to cover thickness

• Cover thickness is the physical production• If larger cover thickness is provided then the time

taken for the penetration of chemicals and other agent is high

• If thickness of cover is less the penetration will occur in short period

As per IS

S.No Exposure conditions Nominal concrete cover in mm not less than

1 Mild 20

2 Moderate 30

3 Severe 45

4 Very severe 50

5 Extreme 75

As per IS 456-2000nominal cover to meet durability requirement

Factors Influencing Corrosion

• Cover thickness• Quality of concrete in the cover region• Environmental conditions• pH value of concrete • Chloride level in concrete• Presence of cracks

• the cross sectional area of the reinforcement is reduced, which in turn reduces the load carrying capacity of the steel

• products of the corrosion, iron oxide (rust), occupy a volume about 6 times the volume of the original steel depending upon the oxidation rate.

• This increase in volume leads to cracking and ultimately spalling of the concrete.

• produces internal stresses in concrete

Effects due to corrosion

cracking

Damages induced by corrosion

Spalling

delamination

Prevention of Metal Corrosion

• Use of concrete with low permeability• Use of properly proportioned concrete having low

W/C ratio• Use of good workmanship in placing the concrete• Curing the concrete properly• Providing adequate cover to the steel reinforcement• Limiting chlorides in the concrete mix• Providing good drainage to prevent water from

standing on the concrete

Preventive methodsTo Prevent Corrosion Following methods areadopted Metallurgical method Corrosion inhibitors Coatings to reinforcement Coatings to concrete Cathodic protection Design & Detailing

• Steel is made to be more corrosion resistant by altering its structure through metallurgical process

• This can improve mechanical and corrosion resistant property of steel

• Stainless steel can be used

Metallurgical method

• This is chemical method• Chemical inhibitors

Nitrites (calcium nitrite)PhosphatesBenzoates

• Inhibitors are mixed with concrete during mixing

corrosion inhibitor

Corrosion Inhibitors

• In the oil production and processing industries, inhibitors have always been considered to be the first line of defense against corrosion.

• Rules, equations or theories to guide inhibitor development or use are very limited.

• Reducing the movement or diffusion of ions to the metallic surface

• Increasing the electrical resistance of the metallic surface.

• Types:Cathodic Inhibitors - Amine based salts (NH2)Anodic Inhibitors - Nitrite based salts (NO2)passivating InhibitorsOrganic InhibitorsPrecipitation InhibitorsVolatile Inhibitors

types of inhibitors

Advantages:• Initial lab testing showed promise for reducing

corrosion potentials.

Disadvantages:• Field testing has shown low bond strengths, no

reduction in corrosion potential. • High cost to apply

advantage and disadvantage

Coating to reinforcement•Coating should withstand pouring of concrete and compaction by vibrating needle

•to provide a durable barrier to aggressive materials

• The principle involved in the cathodic protection is to force the metal to behave like a cathode.

• It consist of application of impressed current to an concrete above steel reinforcement.

• This serves as anode and steel serves as cathode• Steel is connected to negative terminal of DC source• When current is applied external anode will get corroded• So the cathode is prodected from corrosion

Cathodic production

• In this method the negatively charged chloride ions which are causing damages to the passivating film are drawn away from the vicinity of steel towards anode

• In anode chloride ions are converted to chlorine gas because of oxidation process

• The environment around the steel reinforcement reverts back to alkaline condition which products the steel

• Cathodic protection is a technique by which the electrical potential of the steel is increased to a level at which corrosion cannot take place.

Cathodic protection is used to protect :

• Pipelines

• Storage tank bases

• Harbour structures

• Steel sheet, tubular and foundation pilings

• Offshore platforms, floating and sub sea structures

• Ship’s tanks

Applications of Cathodic production

• Design errors may be divided into two general types:

those resulting from inadequate structural design.

those resulting from lack of attention to relatively minor design details.

design errors

• Mechanism:The concrete is exposed to greater stress than it is capable of

carrying or it sustains greater strain than its strain capacity.• Symptoms:

Visual examinations of failures resulting from inadequate structural design will usually show one or two symptoms.

1) Errors in design resulting in excessively high compressive stresses will result in spalling. Similarly, high torsion or shear stresses may also result in spalling or cracking.

2) High tensile stresses will result in cracking. To identify inadequate design as a cause of damage, the locations of the damage should be compared to the type of stresses that should be present in the concrete.

In adequate structural design

Inadequate design is best prevented by thorough and careful review of all design calculations.

Prevention

• While the structure may be adequately designed to meet loadings and other overall requirements, poor detailing may result in localized concentrations of high stresses in concrete.

• These high stress may result in cracking that allows water or chemicals access to the concrete.

• In other case, poor design detailing may simply allow water to pond on a structure resulting in saturated concrete.

Poor design detailing

• Generally, poor detailing does not lead directly to concrete failure, rather it contributes to the action of one of the other causes of concrete deterioration.

Abrupt change in section:It may be cause stress concentrations that

may result in cracking.Insufficient reinforcement at reentrant corners and

openings:The best prevention is to provide additional

reinforcement in areas where stress concentrations are expected to occur.

Inadequate Provision for Deflection:Deflection in excess of those anticipated may

result in loading of members or selection beyond the capacities for which they are designed.

Typically, these loadings will be induced in walls or partitions resulting in cracking.

Inadequate Provision for Drainage:Poor attention to the details of draining a

structure may result in the ponding of water. It results in leakage or saturation of concrete.

Insufficient travel in expansion joints:Inadequately designed expansion joints may

result in spalling of concrete adjacent to the joints.

In compatibility of materials:The use of materials with different

properties adjacent to one another may result in cracking or spalling.

Failure to follow the specified procedures and good practice or outright carelessness may lead to a number of conditions that may be grouped together as construction errors.

Typically, most of these errors don't lead directly to failure or deterioration of concrete. Instead, they enhance the adverse impacts of other mechanisms.

Construction errors

• Adding water to concrete• Improper alignment of formwork• Improper consolidation• Improper curing• Improper location of reinforcing steel• Premature removal of shores or reshores• Settling of the concrete• Setting of the sub grade• Vibration of freshly placed concrete• Improper finishing of flatwork

corrosion rate monitoring

Non-destructive corrosion rate monitoring

• Electrochemical methods1. Static measurements

– Half-cell potential measurements– Hand held equipment– Embedded reference electrodes Corrosion macro cell current

measuring Electrochemical noise

2. Polarization measurements– Linear polarization method– Hand held equipment– Embedded linear polarization sensors– Electrochemical impedance spectroscopy– Localized electrochemical impedance spectroscopy– Galvanostatic pulse method– Scanning reference electrode method

• Nonelectrochemical methods1. Visual inspection2. Seismic method3. Infrared thermography4. Acoustic emission5. Radiography and radiometry Radar6. Electrical resistivity of concrete7. Electrical resistance method8. Optical fibber sensors Magnetic technique9. Microwave based Thermoreflectometry

POLARIZATION TEST SET-UP

Specimens are ready for polarization test

Polarization Test Setup

Specimens shows after crack initiation and propagation under polarization test

Experimental set up

Regulated DC supply

Fibre reinforced tub

RCC Beam

Salt solutionStainless steel plate

Steel bar

Half Cell Potential (HCP)

Schematic showing the half cell potential measurement technique

THANK YOU