G.GUNA SRVEC 1

SEMBODAI RUKMANI VARATHARAJAN ENGINEERING COLLEGESEMBODAI 614 809

DEPARTMENT OF CIVIL ENGINEERING

CE 6002 – CONCRETE TECHNOLOGYUNIT – Iv

Fresh and hardened properties of concreteG.GUNA S.R.V.E.C

CONTENTS

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1. WORKABILITY OF CONCRETE2. Fresh and hardened concrete3. Videos based on:

1. Compressive test2. Concrete slump test3. Compaction factor test4. Youngs modulas test5. Flexural tensile test

Workability of Concrete

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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.

Workability is the property of concrete which determine the amount of useful internal work necessary to produce full compaction.

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Factors affecting WorkabilityWater contentMix ProportionsSize of AggregateShape of AggregateSurface texture of AggregateGrading of AggregateUse of Admixtures

Measurement of Workability

Slump TestCompacting Factor TestFlow TestKelly Ball TestVee Bee Test

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Slump Test

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Compacting Factor TestConcrete is filled in top hopper 1 meter highAllowed to drop in second hopperConcrete is dropped from second hopper into cylinder and leveledWeighed and emptiedFilled with fully compacted concrete and weighed againRatio of fallen weight to fully compacted concrete is compacting factor

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Vee Bee Test 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.

Time in second to achieve state of concrete shown below is called Vee Bee

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Conical mould is filled with concrete and placed in centre of board.Board is raised and dropped 15 timesSpread of concrete is measured and is called Flow

Flow

Test

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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 needleFinal 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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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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Workability :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 flowII) 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 ofcohesiveness and plasticity of the paste.

 

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PROPERTIES OF HARDENED CONCRETE

The principal properties of hardened concrete which are of practical importance can be listed as:

1) Strength2) Permeability & durability3) Shrinkage & creep deformations4) 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 loads2) Compressive strength is easily obtained3) It is a good measure of all the other properties.

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STRENGTH OF CONCRETE The strength of a concrete specimen prepared, cured

and tested under specified conditions at a given age depends on:

1. w/c ratio2. 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:

1. The penetration of some aggresive solution may result in leaching out of Ca(OH)2 which adversely affects the durability of concrete.

2. The moisture penetration depends on permeability & if concrete becomes saturated it is more liable to frost-action.

3. In some structural members permeability itself is of importance, such as, dams, water retaining tanks.

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DURABILITY

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 ATTACKGround 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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CORROSIONElectrochemical 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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Compressive Strength Test

Flexural Strength TestCompaction Factor Test

Young's Modula's Test

Slump test

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THE END……