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SEMINAR BY : RAGHUNATH.R

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1. Understanding concrete materials

Cement

Cement Replacement Materials

Sand

Aggregates

Water

Admixtures

2. Understanding concrete

Fresh concrete

Hardened concrete

CONTENTS

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OTHER CONCRETES : High strength concrete High performance concrete Light-weight concrete High-density concrete Aerated concrete No-fines concrete Sulphur-infiltrated concrete Fibre-reinforced concrete Polymer concrete Roller compacted concrete Ferrocement Self compacting concrete.

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Expectations?

Should acquire desired strength ( Design strength)

Should be workable

Should be durable

CONCRETE

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By careful selection of ingredients.

By careful proportioning of all the ingredients. (cement, water, sand and coarse aggregates)

By proper mixing.

By proper placing, compacting and protecting when it is green.

By adequate curing.

HOW TO ACHIEVE

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Cement was invented by Joseph Aspdin of U.K. in 1824.

What is cement ?

Cement is a fine powder which sets and hardens when mixed with water.

It’s a binding material

Can be produced in controlled conditions.

Early strength.

CEMENT

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Raw materials

Limestone

Hematite

Bauxite

Clay … etc.

Oxides required in raw material

Lime

Silica

Alumina

Iron-oxide

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Lime

Silica

Allumina

Iron Oxide C4AF

C3S

C2S

C3A

COMPOSITION OF PORTLAND CEMENT

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Sl. No.

Compounds Composition as percent

1 C3S 45 -55 %

2 C2S 25-35 %

3 C3A 5-14 %

4 C4AF 9 -15 %

5 Free lime 0.5-1.5%

EXTENT OF CHEMICAL COMPOUNDS IN CEMENT

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1. C3S :

High early strength (1,3,7 days),

Early removal of formwork,

Reduces cement consumption in concrete

2. C2S :

Low heat of hydration,

Contributes to ultimate strength (28 days strength)

EFFECT OF MAJOR COMPOUNDS ON CEMENT PERFORMANCE

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3. C3A Reduced permeability in concrete

Enhanced durability

Develops high ultimate strength.

Generates low heat of hydration.

Greater volumetric stability

Moderate sulphate resistance properties.

Less cracking tendency

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What is hydration of cement ?

The reaction between water and cement is called hydration of cement.

This reaction is exothermic i.e. heat is evolved during the course of hydration

It is called heat of hydration

HYDRATION OF CEMENT

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Hydration of cement (exothermic)This heat is called heat of hydration

It is desirable to know the heat producing capacity of cement in order to choose the most suitable cement for a given purpose

High degree of fineness of cement increases the rate of heat of hydration but not the total heat of hydration.

HEAT OF HYDRATION

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Main physical parameters are

Fineness

Consistency

Setting time

Compressive strength

TESTING OF CEMENT

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BLAINE AIR PERMEABILITY APPARATUS

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COMPRESSIVE TESTING MACHINE

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Check that bags are fresh and machine stitched.

Indian standards mark

Check the manufacturing week on the bag.

There should be no lumps .

Colour of the cement is uniform. Feels cool when hand is inserted. Check that an handful of cement when thrown in a

bucket of water floats for some time and then settles down.

FIELD TESTS

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There are many types of cement to suit every need.

1. Ordinary Portland cement (OPC)2. Portland Pozzolana cement (PPC)3. Rapid Hardening Portland cement4. Portland Slag cement (PSC)5. Sulphate resisting Portland cement

(SRC)6. Low heat Portland cement7. Hydrophobic cement.8. Oil well cement9. White cement

TYPES OF CEMENT

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The type of cement selected should be appropriate for the intended use

Some of the major factors which effect the selection of cement are

Functional requirement of the structure, design parameters

Speed of construction

Durability characteristics

Environmental condition

SELECTION OF CEMENT

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Used for general civil construction works.

Now-a-days this variety is generally not produced

OPC 33 GRADE

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Now-a-days 43 grade is being used widely for general construction work.

However, 43 grade OPC is gradually being replaced by blended cements.

OPC 43 GRADE

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Used in RCC and pre-stressed concrete of higher grades,

Cement grouts,

Instant plugging mortars etc,

Where initial higher strength is the criteria.

OPC 53 GRADE

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Pozzolana: which will in finely divided form and in the presence of moisture react with calcium hydroxide to form compounds possessing cementicious properties.

PPC makes concrete more impermeable.

Denser as compared to OPC.

The long term strength of PPC is higher compared to OPC,

Contd…

PORTLAND POZZOLONA CEMENT

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PPC produces less heat of hydration

Offers greater resistance to the attack of aggressive waters than normal OPC.

PPC is ideally suited for

Domestic construction like plastering, brickwork,

Mass concreting works like dams, large foundations etc

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PSC provides better protection against chloride and sulphate attack.

PSC is preferred over OPC for usage in constructions where the structures are susceptible to sulphate and chloride attack,

e.g. Marine structure- or structures near the sea, sewage disposal treatment works, water treatment plants

PORTLAND SLAG CEMENT

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SRC can be used wherever OPC/PPC/PSC is used

It is advantageous for foundations, piles, basements, underground structures, sewage and water treatment plants and coastal works, where sulphate attack due to water or soil is anticipated.

SULPHATE RESISTING PORTLAND CEMENT

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Low heat Portland cement is particularly suitable for making concrete for dams

Many other types of water retaining structures

Bridge abutments

Massive retaining walls,

Piers, Slabs etc

LOW HEAT PORTLAND CEMENT

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The Rapid hardening cement is used for repair and rehabilitation works and

Where speed of construction and early completion is required due to limitations of time, space, or other reasons

RAPID HARDENING CEMENT (RHC)

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Special requirement for high rainfall areas to improve the shelf life of cement.

The cement particles are given a chemical coating during manufacturing,

Provides water repelling property ,

Cement is not affected due to high humidity

Can be stored for a longer period,

Due to abundant availability of cement in all parts of the country, this Cement is rarely produced these days.

HYDROPHOBIC PORTLAND CEMENT

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White Portland cement is made from raw materials containing very little iron oxide and manganese oxide.

Burning in the kiln is done with furnace oil or gas instead of coal.

Limited quantities of certain chemicals , which improve whiteness of cement, are added during manufacturing.

This type of cement is generally mean for non-structural works.

It is used for architectural purposes such as mosaic tiles, wall paintings, and for special effects.

WHITE CEMENT

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This is a special kind of cement for use in the drilling of oil wells to fill the space between the steel lining tubes and the wall of the well.

It sets slowly in order to give the slurry made with it sufficient time to reach the large depths of the wells.

However, once set, it develops strength rapidly and remains stable at high temperatures.

OIL WELL CEMENT

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SL. No. Age in months Loss of

strength in %

1 3 Nil to 10

2 6 20-30

3 12 30-40

CEMENT LOSES STRENGTH AS IT AGES

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CEMENT REPLACEMENT MATERIALS

FLY ASH It is finely divided residue resulting from the

combustion of powdered coal and transported by the flue gases and collected by electrostatic precipitator ( Thermal Power plants)

Mostly used pozzolonic material

Contributes to environmental Pollution control

Reference IS-3812

Contd…

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Savings in cement

Reducing heat of hydration

Reducing water demand

Spherical shape and smooth surface of flyash helps to reduce the inter-particle friction and thus facilitates mobility.

Reduce Bleeding and drying shrinkage.

Fly ash particles plasticize cement paste and improves flowability and rheology of the mix.

Contributes to strength

Contd…

ADVANTAGES OF FLY ASH

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CEMENT + C-S-H Gel + Ca(OH)2

WATER FLYASH C-S-H Gel

SECONDARY HYDRATION OF FLY ASH

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PETROGRAPHIC VIEW OF FLY ASH

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FLYASH-PARTICLE PACKING EFFECT

FLYASH

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Cement Flyash

BALL BEARING EFFECT

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Trapped Water

DISPERSION OF CEMENT PARTICLES WITH FLY ASH

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Condensed Silica Fume is a by product of ferro-Silicon alloy industry and it is the dust which is collected from furnace exhaust system

Fineness of silica fume is @ 15000 m2/kg as against 280 to 290 m2/kg of Cement

Contributes significantly to compressive strength due to micro-filler effect and excellent pozzolanic properties

Leads to increase in density and reduction of permeability in concrete

It’s use is must for manufacturing of concrete above M50

Contd…

SILICA FUME (Micro Silica)

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SILICA FUME

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Aggregate is the word used to describe any inert material . Usually rock derivative generally between 50mm down to

75 micron used to produce concrete . It is divided into coarse aggregate and fine aggregate Those which are 4.75mm to 50mm are classified as coarse

aggregates Those below 4.75mm to 75 micron as fine aggregates Except for mass concrete in dams etc. which may contain

upto 150mm size aggregate, the maximum size of aggregate is normally 20mm inmost cases

But it may be 40mm for plain concrete or massive works.

AGGREGATES

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Specific gravity: it should have good crushing strength and density

Surface texture: it should be slightly rough but not honeycombed

Particle shape : it should be angular, should not be flaky or elongated.

Porosity : it should have very low water absorption

PROPERTIES OF COARSE AGGREGATES

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Water demand, Workability Cohesion of concrete in plastic state Strength, Density, Durability Porosity of hardened concrete

Stability : it should be chemically inert.

Impurities: it should be free from impurities (like mica, silt, clay)

Compactness: it should be graded, then only the voids can be less.

PROPERTIES OF AGGREGATE EFFECT

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Specific gravity implies the absolute weight per unit volume of aggregates

A low specific gravity may indicate

high porosity

poor durability

low strength.

Specific gravity of aggregates is used in arriving at mix design

Generally the specific gravity of good aggregates is greater than 2.5

SPECIFIC GRAVITY

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Surface texture reveals how grainy or smooth the surface of the aggregate is.

It indicates bonding strength and porosity. Higher the smoothness of the particle, lesser is

the bonding between aggregate and cement matrix.

Experiments have shown that rough textured aggregates develop higher bond strength than smooth textured aggregates,

This property is especially considered while producing high strength concretes.

SURFACE TEXTURE

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Particle shapes are classified as Irregular Rounded Flaky Angular Aggregates should be as much cubical as

possible in shape

PARTICLE SHAPE

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Grading of aggregates means particle size distribution of the aggregates.

Principle of grading is that smaller size particles fill up the voids left in larger size particles.

GRADING

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IS sieve Designatio

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Percentage passing for single size aggregate of nominal size by weight

63 mm 40mm 20 mm 16 mm 12.5 mm

10 mm Remarks

80 mm 100 - - -

63 mm 85-100 100 - -

40 mm 0-30 85-100 100 -

20 mm 0-5 0-20 85-100 100

16 mm - - 85-100 100

12.5 mm - - - 85-100 100

10 mm 0-5 0-5 0-20 0-30 0-45 85-100

4.75 mm 0-5 0-5 0-10 0-20

2.26 mm - - - 0-5

GRADING OF COARSE AGGREGATE

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Indian standards divides the sand into four zones

zone-I to zone-IV based on the sieve analysis Sand falling in zone-I is coarse and that falling

in zone-IV is fine. Sand falling in zone IV shall not be used for

reinforced concrete work. Fineness modulus for sand : ranges from 2.2

to 3.2, higher value indicates coarser grading

SAND

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IS sieve designation

Percentage passing

Zone-I Zone-II Zone-III Zone-IV

10 mm 100 100 100 100

4.75 mm 90-100 90-100 90-100 90-100

2.36 mm 60-95 75-100 85-100 95-100

1.18 mm 36-70 55-90 75-100 90-100

600 microns 15-34 35-59 60-79 80-100

300 microns 5-20 8-30 12-40 15-50

150 microns 0-10 0-10 0-10 0-15

Remarks Very coarse Coarse Medium Fine

REQUIREMENT OF FINE AGGREGATES

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Water helps in dispersing the cement evenly

Quality of water for making concrete and for curing

Water should be free from salts, oils, acids, alkalis, sugar and organic materials

pH value shall not be less than 6

Sea water is not suitable for making concrete

WATER

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SL. No.

Description Tested as per Permissible limit (max) mg/l

1 Organic IS-3025(part-18) 200

2 Inorganic IS-3025(part-18) 3000

3 Sulphates (as SO3)Sulphates (as SO4)

IS-3025(part-24) IS-3025(part-24)

400500

4 Chlorides (as Cl) IS-3025(part-32) 2000 for concrete not containing embedded steel

1000 mg/l for RCC work

5 Suspended matter IS-3025(part-17) 2000

PERMISSIBLE LIMITS FOR SOLIDS IN WATER

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Admixtures are materials mostly chemicals that are added in small quantities during the preparation of concrete to impart certain specific properties to it.

The requirements may be

Improving the workability of concrete during placing

Retarding or accelerating setting

Improving the impermeability and water tightness of the cast concrete.

Imparting corrosion inhibition etc

Entraining air in concrete

There is much difference between the terms ‘additive’ and ‘admixture’

ADMIXTURES

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Compatibility test by Marsh Cone Apparatus

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DEFLOCULATION OF CEMENT PARTICLES

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DISPERSION OF MECHANISM

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EFFECT OF SUPER PLASTICISERON WORKABILITY

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SLUMP : Collapse

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EFFECT OF SUPER PLASTICISERON WORKABILITY

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PUMPABLE CONCRETE

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FRESH CONCRETE

Fresh concrete is a freshly mixed material which can be moulded into any shape.

Workability: Workability is the ease with which fresh concrete can be mixed, transported, placed and compacted in the moulds or forms

Apart from water-cement ratio the concrete has to be compacted well to get the required strength

UNDERSTANDING CONCRETE

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It is the science of the deformation and flow of materials and is concerned with relationships between stress, strain, rate of strain and time.

The term Rheology deals with the materials whose flow properties are more complicated than those of fluids ( liquids or gases)

RHEOLOGY OF CONCRETE

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Factors affecting workability: Water content

Mix proportions

Size of aggregates

Shape of aggregates

Surface texture of aggregate

Grading of aggregate

Use of admixture

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Segregation: Segregation can be defined as the separation of

the constituent materials of concrete.

Bleeding: Sometimes referred as water gain

It’s a particular form of segregation due to highly wet mix

If water cement ratio is more than 0.7

Badly proportioned and insufficiently mixed concrete

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While traversing from bottom to top

Bleeding channels responsible for permeability

It may be interrupted by aggregates (flaky)

It may be interrupted by reinforcement

Reduces bond between reinforcement, aggregate and paste

Remedy— re-vibration, delayed finishing

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Cement – 3.15

Coarse aggregate – 2.70

Sand – 2.60

Water – 1.00

Fly ash – 2.15

Silica Fume - 2.20

SPECIFIC GRAVITY

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Compaction of concrete is the process adopted for expelling the entrapped air from the concrete.

The entrapped air in the form of voids reduces the strength of concrete.

For every 1% of entrapped air, the strength of concrete falls about 5% to 6%.

COMPACTION

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Hand compaction

Tamping

Ramming : generally permitted for unreinforced foundation concrete

RCC should never be rammed

Compaction by vibration: common needle vibrator dia is 25mm to 40mm

External vibrators

Surface vibrators

METHODS OF COMPACTION

Contd…

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When inserting a needle vibrator, allow it to penetrate the bottom of the layer as quickly as possible.

If it is done slowly, the upper part of the concrete will get compacted and prevent the air in the bottom layer from escaping.

The vibrator should be left in the concrete for about 10 sec. and then withdrawn slowly. If it is withdrawn fast, a hole will be left in the concrete.

PRECAUTIONS

Contd…

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The vibrator should be inserted again at a distance of not more than 50 cm from its last position.

The vibrator should not be allowed to touch the face of the form work or the reinforcement to prevent the reinforcement from losing bond with concrete

Do not stop the vibrator when the needle is in the concrete.

Do not over vibrate or under vibrate

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The rate of levelling should not be less than the rate placing of concrete

FINISHING OF CONCRETE

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Effect of Water-Cement ratio Effect of maximum size of aggregate on

strength Grades of concrete: Concrete in construction is specified by

grade like M20,M25 etc. Usually increments of five.

M20 means the specified crushing strength is 20 N/mm2

STRENGTH OF CONCRETE

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CURING

Why Curing ?

To prevent loss of moisture from the Concrete due to combined effect of hot sun and drying wind

Creation of conditions for promotion of uninterrupted and progressive hydration of cement during the period immediately after placing

Curing does not mean only application of water

HARDENED CONCRETE

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1. WATER CURING2. MEMBRANE CURING3. APPLICATION OF HEAT (Steam Curing)4. ACCELERATED CURING

WARM WATER METHOD (1h+1.5 h +20 h+1h) BOILING WATER METHOD ( 23h+3.5h+2h)

CURING METHODS

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Sampling Criteria Cube Testing Acceptance Criteria Non Destructive Testing of Concrete

1. Rebound Hammer Test

Core Test

COMPRESSIVE STRENGTH

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OTHER CONCRETES : High strength concrete High performance concrete Light-weight concrete High-density concrete Aerated concrete No-fines concrete Sulphur-infiltrated concrete Fibre-reinforced concrete Polymer concrete Roller compacted concrete Ferrocement Self compacting concrete.

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HIGH STRENGTH CONCRETE

CONCRETE GRADE FROM M60 ONWARDS REGARDED AS HIGH STRENGTH CONCRETE

FOR HIGH STRENGTH CONCRETE DESIGN STANDARDS GIVEN IN THE CODE IS-456-2000 MAY NOT BE APPLICABLE

THEY HAVE TO BE OBTAINED FROM SPECIFIED LITERATURES OR BY EXPERIMENTAL RESULTS

SPECIAL CONCRETES

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POSSESSING

1. HIGH WORKABILITY

2. HIGH STRENGTH

3. HIGH DENSITY

4. HIGH DIMENSIONAL STABILITY

5. LOW PERMEABILITY

6. RESISTANCE TO CHEMICAL ATTACK

HIGH PERFORMANCE CONCRETE

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NORMAL CONCRETE

HEAVY SELF WEIGHT

(DENSITY 2200 to 2600 KG/M3)

UN-ECONOMICAL

LIGHT WEIGHT CONCRETE

DENSITY (300 to 1850 KG/M3)

LOW THERMAL CONDUCTIVITY

LIGHT WEIGHT CONCRETE

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DENSITY 3360 TO 3840 KG/M3 EVEN 5280 KG/M3 USING IRON AS BOTH F.A. AND C.A

DENSITY 50% HIGHER THAN THE CONVENTIONAL CONCRETE

USED AS A SHIELDING MATERIAL FOR PROTECTION FROM RADIATION

HIGH DENSITY CONCRETE

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It is made by introducing air or gas into the slurry composed of cement and finely crushed sand by alluminium powder.

Uniformly cellular structure is formed.

Also called as gas concrete, foam concrete, cellular concrete

AERATED CONCRETE

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By Omitting fine aggregate fraction

Made by cement, water and single sized coarse aggregates

Having large voids and hence light in weight

Applications Temporary structures

In external walls for Thermal insulation

Rough texture gives good base for plastering

Free from dampness because of low capillary action on account of large voids

NO-FINES CONCRETE

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RMC PLANT

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CONVEYOR BELT

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DOUBLE SHAFT MIXER

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RMC PLACEMENT THROUGH BOOM PUMPS

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Properties of Concrete by Naville

Concrete Technology by M.S. Shetty

Concrete Technology by Gambhir

Literature from ACC Cement and RMC

Literature from Birla Cement and RMC

Literature from RMC India

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