Strength and durability of concrete - Repair and rehabilitation of structures(RRS)

DEPARTMENT OF CIVIL ENGINEERING
CE6021-REPAIR AND REHABILITATION OF
STRUCTURE
UNIT II – STRENGTH AND DURABILITY OF
CONCRETE
PRESENTATION BY
SHANMUGASUNDARAM N
ASSISTANT PROFESSOR
1/35CE6021-RR/unit 2 by,Shanmugasundaram.N
12/4/2020

UNIT II
STRENGTH AND DURABILITY OF CONCRETE
Quality assurance for concrete – Strength, Durability and
Thermal properties, of concrete - Cracks, different types,
causes – Effects due to climate, temperature, Sustained
elevated temperature, Corrosion - Effects of cover
thickness.
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PURP OSE OF THIS TOPIC
Top 5 Worst Quality Failures in Construction.mp4
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Strength of concrete
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Durability of concrete
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Quality assurance for concrete
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INTRODUCTION
 Maintenance of standards of quality of manufactured goods
 It is a management system
 It increases the confidence that a material used in construction
Quality management system: (QMS)
 Quality Assurance - Organization
 Quality Control
 Quality audit – Reviewing and feedback
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MECHANISMS IN A QUALITY MANAGEMENT SYSTEM
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QUALITY
ASSURANCE -
ORGANIZATION
Quality
Control
QUALITY AUDIT
– REVIEWING
AND FEEDBACK
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Quality assurance
Quality management system: (QMS)
 Planning, Engineering, Procurement, construction, Inspection.
Planning:
 Owner formulates Quality assurance policy and develops QA
plan.
Engineering:
 The consultant developed his own design QA programmer
and that of prospective contractors.
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Quality assurance
Procurement:
 Suppliers developed and submit the own QA programmer
and QC method.
Construction:
 Contractors developed and submit the quality assurance
programmer and QC methods.
Inspection:
 The testing agency developed the QA programmer.
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COMPONENTS OF QUALITY ASSURANCE
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STANDARDS
PRODUCTION CONTROL:
COMPLIANCE CONTROL
TASKS & RESPONSIBILITIES
GUARANTEES FOR USERS
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COMPONENTS OF QUALITY ASSURANCE
 STANDARDS : To define important criteria, method of assessment, level
of acceptance
 PRODUCTION CONTROL: Done by each of the parties to conform to
its own quality standards.
 COMPLIANCE CONTROL : Applied to materials, structural & non-
structural members inspection records
 TASKS & RESPONSIBILITIES : For each activity – each parties need
to be established
 GUARANTEES FOR USERS
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QUALITY CONTROL:
 It implements the quality plan by those actions necessary for
conformance to established requirements.
 It is the system of procedure and standard by which a
contractor. Product manufacturer material process or are the
like monitor the properties of finished work.
 QC is the responsibility of the contracting organization and
also responsible for a QC activities related to its sub
contractor.
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QUALITY CONTROL: (Uses)
 Performing design
 Purchasing
 Fabrication
 Production of concrete and
 Other construction activities for the contractual
responsibilities.
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QUALITY CONTROL: (Uses)
 Identification of agencies and personal responsible for
implementing,
 Managing and documenting the QC programmer.
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QUALITY AUDIT: (INSPECTION CHECK)
 This is a system of tracking and documentation of
quality assurance and QC programs.
 Quality audit covers both the design as per as the
construction phase.
 The concept of quality management encompasses the total
project and element of the project.
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QUALITY AUDIT: (INSPECTION CHECK)
 The system on methodology of implementing concept of
quality management depends on available materials
and construction technology.
 An integrated systematic implementation of QMS is
extremely beneficial.
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 ORGANIZATION: Definition of responsibilities &
relationships for the total construction project.
 AUDITING: The ability to demonstrate that the tasks defined
under responsibilities are continually being executed according
to stated methods.
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 REVIEWING: Continuous checks on process methods &
action procedures adopted if stated requirements are not being
met.
 FEEDBACK: Elucidation in measurable terms of causes of
errors that generate defects, in order that processes can be
changed so as to reduce nonconformance.
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NEED FOR QUALITY ASSURANCE
 To promote next generating scheme
 For reputation & professional satisfaction
 Quality of work for future sales
 Sampling testing documentation and material qualification.
 Preparation submission and maintenance of records at all stages.
 To procure future contracts
 Trouble free use & low maintenance cost
 Good performance & appearance
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DESIGN FAULTS IN CONCRETE CONSTRUCTION
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 Misinterpretation of the client’s needs
 Lack of good communication between members of the
design team
 Misinterpretation of design standards or codes of practice
 Use of incorrect or out-of-date data
 Imprecise specification
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 Misinterpretation of design drawings or specifications
 Lack of effective communication with suppliers &
subcontractors
 Inadequate on-site supervision
 Poor workmanship due to inadequate skills
 Failure to understand the design principles
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REASONS FOR POOR QUALITY CONSTRUCTION.
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REASONS FOR POOR QUALITY CONSTRUCTION
 Poor materials
 Poor architectural or structural design
 Poor detailing of reinforcement
 Poor workmanship
 Cement content – It should be minimum of 300 kg per cubic
meter of concrete
 Excess water to cement ratio – It should not exceed about
50% of the weight of cement.
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REASONS FOR POOR QUALITY CONSTRUCTION
 Inadequate compaction of concrete
 Inadequate curing of concrete
 Inadequate cover to reinforcement
 poor or no supervision
 Lack of technical knowledge of the building contractor and
his supervising team
 Poor maintenance
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PREMATURE DETERIORATION OF CONCRETE
 Freezing & thawing
 Aggressive chemical exposure
 Abrasion PREMATURE =அகால
 Corrosion of steel
 Chemical reactions of aggregates
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Freezing & thawing
Deterioration of concrete from freeze thaw actions may occur when the
concrete is critically saturated, which is when approximately 91% of its pores
are filled with water. When water freezes to ice it occupies 9% more volume
than that of water
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Corrosion of steel
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Abrasion
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Chemical reactions of aggregates
The alkali–silica reaction (ASR), more commonly known as
"concrete cancer", is a swelling reaction that occurs over time
in concrete between the highly alkaline cement paste and the
reactive non-crystalline (amorphous) silica found in many
common aggregates, given sufficient moisture.
https://en.wikipedia.org/wiki/Alkali%E2%80%93silica_reaction
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PROPERTIES OF CONCRETE:
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PROPERTIES OF CONCRETE:
Strength of concrete.
Permeability of concrete.
Durability of concrete.
Thermal property of concrete.
Micro cracking of concrete.
Stress and strain characteristic of concrete.
Shrinkage and temperature effects.
Creep of concrete.
Acid attack fire resistance, efflorescence.
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CONCRETE PROPERTIES
STRENGTH
 The strength is usually specified as characteristic strength which is the
strength determined by testing at a fixed age samples of concrete.
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CONCRETE PROPERTIES
 Compressive Strength: Three types of test specimen
 Cube:150mm X 150mm or 100mm X 100mm Cylinder: 150mm dia
and 300mm ht
 Prism: 100mmX100mmX500mm
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 Compressive Strength: Test specimen are cast, cured & tested as per
standards.
 Compressive strengths given by different specimens for the same
concrete mix are different
 (fck)cy = 0.8(fck)cube
 ft = t/(a+bt) * f28 a=4.7,b=0.833
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 Flexural Strength
◦ Determination of this test is essential to estimate the load at which
the concrete member may crack.
◦ Specimen size:150X150X700mm over 600mm span
100X100X500mm over 400mm span
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 Flexural Strength=0.7(fck)1/2
Results are affected by
 Size of the specimen
 Casting
 Curing
 Moisture conditions
 Rate of loading
 Manner of loading
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Flexural Strength Test
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Flexural Strength Test
Flexural Failure of Reinforced Concrete Beam I
Flexure Strength I Concrete Laboratory
Testing.mp4
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Tensile strength
Splitting tensile strength:
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Splitting tensile strength:
Split Cylinder Testing (ASTM C496).mp4
Brazilian Test - Tensile Failure of Concrete in Slow Motion.mp4
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 Tensile strength:
◦ Splitting tensile strength:
Direct compressive force is applied to a concrete
specimen in such a way that the specimen fails due
to tensile stresses induced in the specimen.
 σsp = 2P/(П*d*l)
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Factors affecting strength of concrete
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1
• Size of the test specimen
• Size of aggregate & type of aggregate
2
• Support conditions of the specimen
• Moisture conditions
3
• Types of testing machine
• Type of cement
4
• Degree of compaction
• Type of curing & temp of curing & Nature of loading
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Thermal properties of concrete
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Thermal properties of concrete:
 Thermal conductivity is a measure of the ability of the
concrete. To conduct heat and it measure.
 Thermal conductivity depends upon the composition of
concrete.
 The structural concrete containing norm aggregate,
conduct heat more readily then light weight concrete.
 Lower the water content of the mix the higher
conductivity of a harden concrete.
 The density of the concrete does not appreciable affects
the conductivity of the ordinary concrete.
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Age
Water/cement ratio
Thermal
expansion and
diffusivity of cement
paste
Aggregates
and concrete are
discussed
Temperature and
moisture content
on specific heat
Properties vary with
age, temperature and
humidity
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Thermal properties of concrete depends on
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Thermal diffusivity: (விரவல்தன்மை)
 Thermal diffusivity is a measure of the rate at which
temperature change within the mass take place.
 𝐷 = k/𝑠𝑑
 D= Diffusivity, d=Density, s=Specific head, k=Thermal
conductivity
 The range of diffusivity of concrete is between 0.002 to 0.006
m3/h.
Specific heat
 The specific heat gives the heat capacity of concrete.
 It increases with the moisture content of concrete.
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Co-efficient of Thermal expansion:
 The co-efficient of thermal expansion of concrete depends on
the composition of mix and on the value of the co-efficient
of expansion of cement pasted and aggregate.
 The value of co-efficient of thermal expansion varies from of
9X10-6 /c ̊
 Thermal properties of aggregate affect the performance of
concrete.
 The co-efficient of expansion of aggregate leads to higher
co-efficient of expansion for the concrete.
 The properties of concrete which have bearing on expansion
and contraction on heating and cooling.
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Cracking:
 Before hardening
 After hardening
Before hardening:
Drying:
 Plastic shrink age, Settlement shrinkage, Bleeding, Delayed
caring.
Constructional:
 Formwork movement, Excess vibration, sub grade settlement,
 Finishing.
 Early frost damage
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Cracking of concrete
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Before hardening
After hardening
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Before
Hardening
After
Hardening
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Before
hardening
Drying
Constructional
Early frost
damage
After
hardening
Unsound
materials
Thermal
Chemical
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Before
hardening:
Drying
Plastic
shrinkage
Settlement
shrinkage
Bleeding
Delayed
caring
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Before
hardening:
Constructional
Excess
vibration
sub grade
settlement
Finishing
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3.Early frost damage
2.
Frost - பனி
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After Hardening
Unsound materials:
 Cement, aggregate, excess silt, Mud and Dust
Thermal:
 Heat of hydration, External temperature, Joints in concrete, elevated
temperature, Freezing, Moisture moments, Transition zone, Biological
process, structural design deficiency.
Chemicals:
 Sulphate attack, Alkali aggregate attack.
 Acid attack, Sea water, Carbonation, Fluorides attack corrosion of
reinforcement.
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After
Hardening:
Unsound
materials
Cement
Aggregate
Excess
silt
Mud and
Dust
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1.
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After
Hardening:
Thermal
Heat of
hydration External
temperature
Joints in
concrete
Elevated
temperature
structural
design
deficiency
Biological
process
Transition zone
Moisture
moments
Freezing
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2.
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After
Hardening:
Chemicals
Sulphate
attack
Alkali aggregate
attack
Acid attack
Sea water
Carbonation
Fluorides
attack
corrosion of
reinforcement.
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Pre Hardening
Constructional movement
1. Sub grade.
2. Settlement sub grade.
3. Moisture changes in sub grade.
4. Control of sub grading.
5. Formwork
6. Movement of formation.
7. Swelling of wood.
8. Construction of adequate forms.
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Settlement Shrinkage:
Reinforcement
Settlement of concrete during setting
Settlement of around obstructions mix to fluid
Dense mixers with low water content
Adequate compaction of low lift
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Setting shrinkage:
 Plastic shrinkage
 Chemical reaction
 Cracks occurs soon after placing
 under moist condition
Drying shrinkage:
 Drying shrinkage
 Rapid drying while setting occurs
 Cracking of exposed surface due to high wind, low humidity
 Temperature differences
 Proper protection
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After hardening
Drying shrinkage:
Loss of water
Cracking of buildings slabs and walls
Dense mixes with low cement and water content adequate curing
Temperature: Internal:
Differential expansion and contraction
Heat of hydration of cement
Aggregate of abnormal thermal expansion
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Chemical action:
Concrete and steel
Expansion of internal mass resulting in cracking of external skin
Reactive aggregate
Corrosion of reinforcement
How alkali cement and non-reactive aggregate
Thick and dense layer at productive concrete
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Temperature: Internal:
Low heat cement and control of temperature rise
Aggregates of normal thermal expansion
Differential expansion and contraction
Heat of hydration of cement
Aggregate of abnormal thermal expansion
Aggregates of normal thermal expansion
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External:
Climate changes, frost action
Large slabs (or) walls without adequate joints
Spalling of surface
Adequate expansion, contraction joints
Air entrainment and sound concrete
Structural failure:
Excessive tensile stress due to load
Building settlement, excessive load , vibration earthquakes and insufficient
reinforcement
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Effects of temperature:
Fire resistance
Freezing and thawing
Effects of salts
Moisture movement
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Fire resistance:
 Concrete though not a refractory material is in combustible and as good fire
resistance.
 The heating of reinforcement aggravates the expansion of both laterally
and longitudinally of the reinforcement bars, resulting in loss of strength of
reinforcement.
 The effect of increase in temperature on the strength of concrete is not much up
to a temperature of about 250 C0 but above 300c0 loss of strength take place.
 The hardened concrete contains calcium hydroxide, If this calcium oxides
gets wetted, the calcium by droxideallombired by an expansion is volume.
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Fire resistance:
 Portland blast furnace slack cement is found to be more resistance to the fire in
this regard.
 In mortar and concrete and aggregate undergo a progressive expansion on heating.
 This expansion as a disruptive action on the stability of concrete.
 The best fire resistance aggregates among the igneous rocks are the basalts and
dolomites.
disruptive -சீர்குலலக்கும்
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Fire resistance:
 Limestone expander sturdily until temperature of about 900
C0
 It has been found that dense limestone is considered as a
good fire resistance aggregates.
 Broken bricks also form a good aggregate in respect of fire
resistance.
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Freezing and Thawing:
 The lack of durability of concrete on account of freezing and thawing
action of frost is not of great importance to Indian conditions.
 Frost action is one of the most powerful weathering actions on the
durability of concrete.
 The durability of concrete is affected by alternative wetting and
drying, heating and cooling.
 Freezing is one of the very important factors affecting the durability
of concrete in the cold countries.
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 It is very well known that fresh concrete should not be subjected
to freezing temperature.
 Fresh concrete contains considerable quantity of free water.
 The fully harden concrete is also damaged particularly to the
effect of alternate cycle of freezing and thawing.
 A freezing starts at a surface in the largest cavities and gradually
extend to smaller cavities.
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 The resistance of concrete to frost action depends on the
strength of the paste, water cement ratio, type of aggregate, age
of concrete, duration and extend to which the concrete is
subjected to freezing action.
 The fine air bubbles entrained in the body of the concrete will
act as a better to relive the pressure created by freezing.
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Effect of salts:
 Chemicals used for snow and Ice clearance can cause and
aggravate surface in scaling.
 The formation of salt crystals in concrete may contribute to
concrete scaling and deterioration layer by layer.
 In cold region in the winter, sodium chloride or calcium
chloride is used for de-icing snow clearance on concrete road.
 The use of air entrainment makes the concrete road more
resistance to surface scaling on account of frost action.
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Moisture (moment) movement:
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Moisture (moment) movement:
 The concrete member is outdoor condition such as pavement,
bridge decks, transmission poles; water tank, swimming pool
etc. are subjected to alternative wetting a drying condition,
under goes expansion and shrinkage.
 The exposure of concrete to repetitive expansion and
shrinkage or repetitive stress and tensile stress which may
cause fatigue in concrete and affect the durability of concrete.
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Effects of chemical action:
Sulphate attack:
 Most soil contains some sulphate in the form of calcium,
sodium, magnesium and ammonium sulphate.
 Sulphate attack is a common occurrence in natural industrial
situation.
 In calcium sulpho-aluminate forming within the frame work
of hydrated cements paste.
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Methods of controlling sulphate attack:
Use of sulphate resisting cement.
Quality concrete.
Use air entrainment.
Use of pozzolona cement.
High pressure steam curing.
High alumina cement.
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Alkali aggregate reaction:
Hydroxyl ions in the pore water within concrete.
Alkali silica reaction in the aggregate.
Alkalis come from sand containing sodium.
 Chlorides, admixtures, mixing of water, sea water penetration, fly ash,
blast furnace slag.
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Acid attack:
 Concrete is not fully resistance to acids.
 Portland cement concrete depending upon the oxalic acid and phosphoric
acid.
 With the sulphuric acid, calcium sulphate, calcium aluminates, calcium
sulpho-aluminate which on crystallization can cause expansion and
disruption of concrete.
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Concrete in sea water
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Concrete in sea water:
Off-structure.
The sea waters subjected to chloride.
Corrosion of steel.
Salt weathering.
Abrasion by sand.
Sea water contains some amount of co2.
Calcium hydroxide and calcium sulphates soluble in sea water.
The rate of chemicals attack is increased in temperature zone.
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Carbonation
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Carbonation:
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Carbonation:
 Carbonation of concrete is a process by which carbon-dioxide
from the air penetrates into concrete and reacts with calcium
hydroxide. To form calcium carbonation.
 Carbonic acid which attack the concrete.
 The carbonation of concrete is one of the main reasons for
corrosion of reinforcement.
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Rate of carbonation
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• Depth
of cover
• Protecting
coat is
required for
long span
bridge
girder, fly
over,etc..
• Deep of
cover.
Grade of
concrete.
Level of pore
water
A concrete is
protector or
not.
Permeability
of concrete.
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Effects of corrosion:
Strength will reduce.
Structures will failure.
Eccentricity.
Cracks, spalling of concrete.
The cross section of reinforcement progressively reduces.
Determination of cover.
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Control the corrosion of steel reinforcement
CE6021-RR/unit 2
Control
Metallurgical
ecological
Corrosion
inhibitors
Cement
coating,
Sealing,
Fusion bond,
Epoxy coating
Galvanized
reinforcement,
cathodic
protection.
De-rusting,
Phosphating,
Coating to
concrete
Coating to
reinforcement
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To control the corrosion of steel reinforcement:
Metallurgical ecological method.
Corrosion inhibitors.
Coating to reinforcement.
De-rusting, Phosphating, Coating to concrete.
Cement coating, Sealing, Fusion bond, Epoxy coating.
Galvanized reinforcement, cathodic protection.
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 Metallurgical method: - உலலாகவியல்
Steel can be made more corrosion resistance by altering its structure
through metallurgical process.
There are many situation were stainless steel reinforcement are used for
long term durability of concrete structure.
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Corrosion inhibitors:
 Corrosion can be prevented by chemical methods by using certain
corrosion inhibiting chemicals such as Nitrates, Phosphate, Benzoates,
etc.,
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Corrosion inhibitors:
 A most widely used admixture is based on calcium Nitrates. It is added to
the concrete during mixing of concrete.
 The steel is protected by a layer of ferric oxide on the surface of the steel.
CE6021-RR/unit 2

Coating to reinforcement:
 The object of coating to steel bar is to provide a durable barrier to
aggressive material such as chlorides.
 The coating should be robust to with stand fabrication of reinforcement
cage and pouring of concrete and compaction by vibration needle.
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De – rusting: Removing Rust in Less Than 3 Minutes.mp4
 The reinforcement is cleaned with a de-rusting solution.
 This is followed without delay by cleaning the rods with wet
waste cloths and cleaning powder.
 The rods are then rinsed in running water and air dried.
Phosphate
 Phosphate is applied to the surface And in inhibitors solution
is then brushed over the phosphate surface.
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Cement coating
 Slurry is made by mixing the inhibitor solution with water
and cement and applied on the bar.
 The sealing solution is brushed after the rods are air cured.
 The sealing solution as an inside curing effect.
 The second coat of slurry is then applied and the bars are air
dried.
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Sealing: (solution)
 Two coats of sealing solution are applied to the bars in order
to seal the micro pores of the cement coat and to make it
impermeable to corrosive salt.
Epoxy coating:
 Epoxy coating.mp4
 It is one of the effective method of coating the debars.
 Carrying out in a factory and not at site of work
CE6021-RR/unit 2

Epoxy coating:
 The plant are designed to coat the straight bars is a continuous
process.
 The epoxy powder particles are deposited evenly on the surface
of the bars.
 The epoxy coated bars have an excellent protection to
corrosion in aggressive environment.
 After treatment, cutting and bending may injure the steel.
 The coating may get damaged during vibration of concrete.
CE6021-RR/unit 2

Galvanized reinforcement:
 Galvanized reinforcement consists of dipping of steel bar in
molten zinc.
 The coating of zinc bonded to the surface of steel.
 The zinc surface reacts with the calcium hydroxide in the
concrete to form a passive layer and prevent corrosion.
Hot Dip Galvanizing- Dipping Process....... in action.mp4
CE6021-RR/unit 2

Cathodic protection:
 Cathodic protection is one of the effective, well known and
extensively used methods for preventing of corrosion in
concrete method.
 It is high case and long term monitoring required for this
method.
 The catholic protection comprises of application current to an
elected laid on the concrete above steel reinforcement.
CE6021-RR/unit 2

Cathodic protection: CATHODIC PROTECTION
PRINCIPLE FOR CONCRETE STRUCTURES.mp4
CE6021-RR/unit 2

Cathodic protection:
CE6021-RR/unit 2

Coating to concrete: (purpose)
Environmental pollution.
Industrial fumes and contamination of ground.
The reduction in depth of carbonation of the protected
concrete.
CE6021-RR/unit 2

Design and cover thickness and cracking:
The structural designer should take all precaution in
designing and detailing with respect to spacing between
reinforcement.
CE6021-RR/unit 2

 To facilitate vibration of concrete.
 To given proper cover to the steel reinforcement.
 To restrict the crack width etc.
 The first object is achieved the stipulated minimum strength and
durability.
 The second object is making the concrete in the most economical
manner.
CE6021-RR/unit 2

 A permeability of concrete is governed by the quality and
continuity of the waste.
 Design of concrete mix needs not only the knowledge of
material property and properties of concrete in plastic condition.
CE6021-RR/unit 2

Mix proportion:
Water cement ration.
Cement content.
Cement aggregate ratio.
Gradation of aggregate.
Consistency.
Cover thickness:
 The nominal cover is applicable to all steel reinforcement
including links.
CE6021-RR/unit 2

Cover thickness:
 In the column of min dimension of 200mm, whose reinforcing
bar do not exceed 12mm, a nominal cover of 25mm may be
used.
 The nominal concrete cover in mm not less than mild steel
20mm, moderate steel 30mm, severe steel 45mm, very sever
50m, extreme 75mm.
CE6021-RR/unit 2

Errors in construction:
Poor workman ship.
Vibrator is not applicable.
Laying and patching, curing.
Poor formwork.
Delay processing work
Mix proportion (ratio)
Improper mix design of concrete.
CE6021-RR/unit 2

112/3
5
CE6021-RR/unit 2
THANK YOU
12/4/2020

Strength and durability of concrete - Repair and rehabilitation of structures(RRS)

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