1. CE 6002 – CONCRETE TECHNOLOGY
SEMBODAI RUKMANI VARATHARAJAN ENGINEERING COLLEGE
SEMBODAI
DEPARTMENT OF CIVIL ENGINEERING
CE 6002 – CONCRETE TECHNOLOGY
UNIT – Iv
Fresh and hardened properties of concrete
G.GUNA S.R.V.E.C
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2. CONTENTS WORKABILITY OF CONCRETE Fresh and hardened concrete
Videos based on:
Compressive test
Concrete slump test
Compaction factor test
Youngs modulas test
Flexural tensile test
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3. Workability of Concrete
Workability is the property of concrete which determine the amount of useful internal work necessary to produce full compaction.
Requirement of Fresh Concrete
It must be easily mixed and transported.
It must be uniform throughout a given batch, and between batches.
It must keep its fluidity during the transportation period.
It should have flow properties such that it is capable of completely filling the forms.
It must have the ability to be fully compacted without segregation.
It must set in a reasonable period of time.
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4. Factors affecting Workability
Water content
Mix Proportions
Size of Aggregate
Shape of Aggregate
Surface texture of Aggregate
Grading of Aggregate
Use of Admixtures
Measurement of Workability
Slump Test
Compacting Factor Test
Flow Test
Kelly Ball Test
Vee Bee Test
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5. Slump Test
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6. Compacting Factor Test
Concrete is filled in top hopper 1 meter high
Allowed to drop in second hopper
Concrete is dropped from second hopper into cylinder and leveled
Weighed and emptied
Filled with fully compacted concrete and weighed again
Ratio of fallen weight to fully compacted concrete is compacting factor
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7. Vee Bee Test
Time in second to achieve state of concrete shown below is called
Vee Bee
Slump cone test is performed in a closed cylinder of 300 mm dia.
Perspex plate is placed on top.
Vibration are applied at standard rate till plate is fully in contact.
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8. F l o w T e s t
Conical mould is filled with concrete and placed in centre of board.
Board is raised and dropped 15 times
Spread of concrete is measured and is called Flow
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9. Setting Time Of Concrete
Setting of concrete is caused by water cement reaction.
Setting time of cement and concrete do not coincide.
Initial and final setting times are arbitrarily defined by method of penetration of needle
Final set of concrete do not mean complete loss of workability.
Initial set represent time after which concrete can not be mixed placed and compacted properly.
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10. Properties of Fresh Concrete: Properties at Early Ages :
Properties of fresh and hardened concrete
The potential strength and durability of concrete of a given mix proportion is very dependent on the degree of its compaction. It is vital, therefore, that the consistency of the mix be such that the concrete can be transported, placed, and finished sufficiently early enough to attain the expected strength and durability.
Properties of Fresh Concrete:
The first 48 hours are very important for the performance of the concrete structure.
It controls the long-term behavior, influence f'c (ultimate strength), Ec (elastic modulus), creep, and durability.
Properties at Early Ages :
Workability
Slump Loss
Segregation/Bleeding
Plastic Shrinkage
Time of Set
Temperature
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11. Workability : Slump Test: Consistency:
Definition: Effort required to manipulate a concrete mixture with a minimum of segregation.
It is not a fundamental property of concrete.
I) consistency (slump)-- easy to flow
II) cohesiveness --tendency to bleed and segregate
Slump Test:
Slump test is a test conducting before concrete to
be used for casting. The purpose of slump test
Is to determine the water content in concrete and its workability
Consistency:
Consistency or fluidity of concrete is an important component of workability and refers in a way to the wetness of the concrete.
However, it must not be assumed that the wetter the mix the more workable it is. If a mix is too wet, segregation may occur with resulting honeycomb, excessive bleeding, and sand streaking on the formed surfaces.
On the other hand, if a mix is too dry it may be difficult to place and compact, and segregation may occur because of lack of
cohesiveness and plasticity of the paste.
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12. PROPERTIES OF HARDENED CONCRETE
The principal properties of hardened concrete which are of practical importance can be listed as:
1) Strength
2) Permeability & durability
3) Shrinkage & creep deformations
4) Response to temperature variations
Of these compressive strength is the most important property of concrete.
Of the abovementioned hardened properties compressive strength is one of the most important property that is often required, simply because;
1) Concrete is used for compressive loads
2) Compressive strength is easily obtained
3) It is a good measure of all the other properties.
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13. STRENGTH OF CONCRETE 1. w/c ratio 2. Degree of compaction
The strength of a concrete specimen prepared, cured and tested under specified conditions at a given age depends on:
1. w/c ratio
2. Degree of compaction
COMPRESSIVE STRENGTH
Compressive Strength is determined by loading properly prepared and cured cubic, cylindrical or prismatic specimens under compression.
PERMEABILITY OF CONCRETE
Permeability is important because:
The penetration of some aggresive solution may result in leaching out of Ca(OH)2 which adversely affects the durability of concrete.
The moisture penetration depends on permeability & if concrete becomes saturated it is more liable to frost-action.
In some structural members permeability itself is of importance, such as, dams, water retaining tanks.
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14. Factors Affecting Durability: External → Environmental
A durable concrete is the one which will withstand in a satisfactory degree, the effects of service conditions to which it will be subjected.
Factors Affecting Durability:
External → Environmental
Internal → Permeability, Characteristics of ingredients, Air-Void System...
SULFATE ATTACK
Ground water in clayey soils containing alkali sulfates may affect concrete.
These solutions attack CH to produce gypsum. Later, gypsum and calcium alumina sulfates together with water react to form “ettringite”.
Formation of ettringite is hardened cement paste or concrete leads to volume expansion thus cracking.
Moreover, Magnesium sulfate may lead to the decomposition of the C-S-H gel.
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15. CORROSION
Electrochemical reactions in the steel rebars of a R/C structure results in corrosion products which have larger volumes than original steel.
Thus this volume expansion causes cracks in R/C. In fact, steel is protected by a thin film provided by concrete against corrosion. However, that shield is broken by CO2 of air or the Cl- ions.
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16. Compressive Strength Test
Flexural Strength Test
Compaction Factor Test
Young's Modula's Test
Slump test
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17. THE END……
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