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CONCRETE

TECHNOLOGY

BY Deepak G. Talekar

M.E. (Geotech), B.E. (Civil), C. Engg, AMIE (I), MISTE

Mob: 9449500044

Email : deepakgtalekar@gmail.com

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CONCRETE :

• Mixture of cement, sand, pebbles or crushed rock (Aggregates) and water.

• When it is placed in forms & allowed to cure it becomes hard like a stone.

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• The hardened concrete may also be considered as an artificial stone in which the voids of larger particles (coarse aggregates) are filled by the smaller particles (fine aggregates) and the voids of fine aggregates are filled with cement.

• The Strength, durability and other characteristics of concrete depends upon the properties of (a) ingredient, (b) proportions of mix (c) method of compaction (d) placing and curing.

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Factors affecting the performance of concrete

• Cement composition quality

• Size, shape and grading of aggregates

• Quantity of moisture in aggregates.

• Chemical admixtures properties.

• Water-cement ratio.

• Mixing of concrete.

• Quality of form work.

• Placing and curing of concrete.

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PROPERTIES OF CONCRETE

1. It has high Compressive strength. 2. It is free from corrosion – no effect of

atmospheric agent and it hardens with age. 3. It is Cheaper than the steel. 4. It binds perfectly with steel 5. It resist the tensile load (RCC). 6. It resist tortional effects. 7. It resist vibration. 8. It resist abrasion. 9. It is water-proof. 10. It is easy to prepare or fabricate in to any size

and shape.

Properties of fresh Concrete

• It can be handled and mixed

• Can be moved from one place to another

• It can be compacted to remove all air.

• It can be leveled to give smooth surface

• It can be placed where it will be harden

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Properties of plastic concrete

• Workability

• Segregation :Segregation of concrete can be defined as separation of coarse aggregates from mortar resulting non-uniform mix. It leaves voids in the concrete causing honeycombing and thus reduces the strength. Segregation is caused due to over vibration, dropping wet concrete from considerable height, passing long chutes along a slope etc. It can be prevented by ensuring a certain minimum proportion of finer materials, proper grading of aggregates and by correct handling, placing and compacting of concrete.

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• Bleeding :Bleeding is also known as water gain. Bleeding is a form of segregation in which water in a concrete mix rises to the surface during its placement. Bleeding is due to more water present than the require quantity for cement paste. It makes concrete porous, weak and non-durable. Bleeding can be prevented by controlling the water content, using finely ground cement and controlling compaction. Addition of pozzolana or aluminum powder reduces bleeding.

• Consistency: Consistency is an indication of workability. It shows the relative mobility or the ability of wet to fresh concrete to flow.

• Mobility: mobility is the ease with which concrete can flow in to the formwork around steel reinforcement .

• Compactability : Compactability is the ease with which concrete can be compacted to make the concrete dense.

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Properties of hardened concrete

• Strength: It has high very high compressive strength and when reinforced with steel, it takes tensile load also.

• Durability: It is durable

• Impermeability: Concrete is water proof material.

• Creep of concrete: concrete under stress undergoes a gradual increase in strain with time. Such deformation is called creep of concrete.

• Shrinkage of concrete: Loss of moisture by evoporation

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INGREDIENTS OF CONCRETE

• CEMENT : Ground material – Adhesive & Cohesive properties: Binding medium.

• AGGREGATES: Coarse aggregates and Fine aggregates

• WATER

• STEEL ( In case of RCC)

• ADMIXTURES (Optional)

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Cement

• Raw materials required for manufacture of

Portland cement are calcareous materials (lime stone or chalk) and argillaceous material (shale or clay).

• Manufacture: girding the raw materials, mixing them intimately in certain proportions and burning them in kiln at 1300 to 1500 degree centigrade. At this temperature, the material sinters and partially fuses to form nodular shaped clinker. The clinker is cooled and ground to fine powder with addition about 3 to 5% gypsum. – Portland cement.

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• There are two process known as wet and dry process depending upon whether the mixing and girding of raw material is done in wet or dry condition.

• For many years wet process remain popular because of the possibility of more accurate control in the mixing of raw materials. The technique of intimate mixing was not available.

• Wet process require more fuel.

• It require 35 to 50% water for slurry.

• With modern development, compressed air is used in Dry process.

• Dry process require less fuel.

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HYDRATION OF CEMENT

• Anhydrous cement does not bind fine and coarse aggregate. It acquires adhesive properties only when mixed with water. The chemical reactions that takes place between cement and water is referred as hydration of cement.

• The reaction of cement with water is exothermic. The reaction liberates a considerable quantity of heat ( Heat of Hydration).

•

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TYPES OF CEMENT • Ordinary Portland cement : Three grades

– 33 grade (The compressive strength at 28 days 33N/mm2) – 43 grade (The compressive strength at 28 days 43N/mm2) – 53 grade (The compressive strength at 28 days 53N/mm2)

• Portland pozzolana cement : It is produced by girding together a mixture of 60 to 80% portland cement and 20 to 40% pozzolana (such as volcanic ash or pumice or an burnt cla or shale). It has higher resistance to chemical disintegration and sulphate attack.

• Rapid hardening portland cement: This has high content of tricalsium silicate. The chemical composition of this cement is same as OPC but more finely ground. Its 3days strength is nearly equal to 7 days strength of OPC. – It is used in pre-fabricated concrete construction, – Where form work is required to be removed early for re-use

elsewhere. – Road repair works

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• Sulphate resisting cement: – It is used in marine condition

– It is used in foundations where soil is infested with sulphates

– Used to fabrication of pipes which are likely to be buried in soil.

– Used in construction of sewage treatment works.

• Quick setting cement: It is sets quickly. This property is achieved by reducing the gypsum content. It is used in grouting operations.

• Super sulphate cement

• Low heat cement

• Coloured cement

• High alumina cement

• Acid resisting cement

• Blast-furnace cement

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TEST ON CEMENT FIELD TEST and LABORATORY TEST

FIELD TEST: Minor works.

• Colour: greenish grey.

• Presence of Lumps :No visible lumps.

• Physical properties : Pinch of cement & feel between the fingers- smooth and not gritty

feeling.

Keep Hand-Cool feeling.

Take hand full of cement – throw it on a bucket full of water - particles should float for some time and then sink.

• Strength :Cake : Bucket of water- shape should not disturbed after 24 hrs.

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Laboratory Test: The following tests are usually conducted in the

laboratory:

• Fineness test

• Setting time test

• Strength test

• Soundness test

• Heat of hydration test

• Chemical composition test

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Fineness test : • The Fineness of cement is a measure of the size of the

particles of cement and it is expressed in specific surface of cement.

• For a given weight of cement, the surface area is more for finer cement than for a coarser cement.

• Finer the cement higher the rate of hydration and faster the development of strength.

• If the cement is ground beyond the limits, prehydation takes place due to atmospheric moisture and deterioration takes place.

• Fineness of cement is tested in two ways. By Seiving (Calculated from particle size distribution)

By Air permeability method (total surface area of all the particles in one gram of cement)

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Setting Time:

Initial setting time :Time at which the cement paste losses its plasticity.

( should not be less than 30 min for OPC)

Final setting time : Time to reach the stage , the paste becomes hard mass.

( should not be more than 600 min for OPC)

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Soundness : • Cement after setting shall not undergo any

appreciable change in Volume.

• The expansion causes disintegration and severe cracking.

• The unsoundness due to free lime and magnesia in the cement.

• After the setting of cement,, moisture penetrates in to the free lime resulting in its hydration. Since slaked lime occupies a larger volume, the expansion takes place resulting severe cracking.

• The soundness should not be more than 10mm.

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Compressive Strength

• Important properties of cement

• Conducted on standardized aggregates under carefully controlled conditions.

• Cement mortar cube (1:3) having area of 50 cm2 & Tested under CTM.

• For OPC : 16 N/mm2 3 day of Curing

22 N/mm2 7 days of Curing

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CHEMICAL COMPOSITION TEST :

• Ratio of % of alumina to iron oxide –not less than 0.66 & not greater than 1.02

• Total loss of ignition : should not be greater than 4%.

• Total sulphur content : should not be greater than 2.75%

• Weight of insoluble residue : should not be greater than 1.5%

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CONSISTENCY TEST

• To determine the % of water required to conduct other test.

• Vicat apparatus.

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ROLE OF AGGREGATES

• Aggregates are important constituents in concrete. • They give body to the concrete, reduce shrinkage and

effect economy • They occupy 70 to 80% of the volume of concrete. • Aggregates are cheaper than cement and gives stability

and durability to the concrete. • The aggregate is used primarily for the purpose of bulk

to the concrete. • To increase the density of the concrete, two or more

sizes of aggregates are used. • Fine aggregates help to produce workability and

uniformity in mixture. • The fine aggregates hold the coarse aggregates with the

help of cement paste. Due this plasticity it prevents segregation.

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CLASSIFICATION OF AGGREGATES

• BASED ON GEOLOGICAL ORIGIN

NATURAL AGGREGATES : SAND, GRAVEL, CRUSHED ROCK

ARTIFICIAL AGGREGATES : CLEAN BROCKEN BRICKS & AIR-

COOLED FRESH BLAST-FURNACE SLAG (30 TO 35 Mpa)

• ACCORDING TO SIZE

FINE AGGREGATES : PASSES THROUGH 4.75MM SIEVE AND

RETAINED ON A 75µ SIEVE (SAND, CRUSHED STONE SAND)

COARSE AGGREGATES :PASSES THROUGH 80MM SIEVE

AND RETAINED ON A 4.75MM SIEVE (CRUSHED GRAVEL/STONE)

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• ACCORDING TO SHAPE

1. ROUNDED AGGREGATES (RIVER PEBBELES –

32-33% VOIDS, MIN CEMENT PASTE TO MAKE GOOD CONCRETE, INTERLOCKING IS POOR)

2. IRREGULAR AGGREGATES (35 TO 38%OF

VOIDS, MORE CEMENT PASTE TO MAKE GOOD CONCRETE, INTERLOCKING IS BETTER)

3. ANGULAR AGGREGATES : SHARP, ANGULAR

AND ROUGH PARICLES, 38 TO 40% OF VOIDS, MORE CEMENT, GOOD BOND)

4. FLAKY AND ELONGATED AGGREGATES ( LEAST DIM IS LESS THAN 3/5TH OF ITS MEAN DIM-FLAKY

AND GREATEST DIM IS GREATER THAN 9/5TH ITS MEAN DIM)

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• BASED ON UNIT WEIGHT NORMAL WEIGHT AGGREGATE

: Commonly used aggregates such as sand and gravel, crushed rock whose Sp. Gravity 2.5 to 2.7 produce the concrete ρ=23KN to 26 KN/m3

1) HEAVY WEIGHT AGGREGATE

: Heavy weight aggregates Sp. Gravity 2.8 to 2.9 such as magnetite, Barytes and scrap iron. Used to construct Nuclear Plant

2) LIGHT WEIGHT AGGREGATE

: Bulk density about 12KN/m3 used for Light weight structures. Diotomite, Pumice, Volcanic cinder etc.

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TEST ON AGGREGATES

• Crushing value test: Resistance to crushing under gradually applied comp. load.

• Impact Value test : resistance to toughness of the material. • Abrasion Value test : resistance to wear ( e.g. Loss Angeles

Test) • Bulk Density (Unit weight): Information about the shape and

grading. • Specific gravity : Used for Mix design. Sp. Gr.=2.6 to 2.8. • Moisture content of Aggregates: Important in Control of Quality

i.e. workability & strength. • Sieve Analysis Test : To find the particle size distribution. • Flakiness Index & Elongation Index : Least dim is less than

3/5th of its mean dim-flaky and greatest dim is greater than 9/5th its mean dim)

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PHYSICAL PROPERTIES OF AGGREGATES

1. Crushing value : Resistance to crushing under gradually applied comp. load.

2. Impact Value : Resistance to toughness of the material.

3. Abrasion Value : resistance to wear ( e.g. Loss Angeles Test)

4. Bulk Density (Unit weight): Information about the shape and grading.

5. Specific gravity : Used for Mix design. Sp. Gr.=2.6 to 2.8.

6. Moisture content of Aggregates: Important in Control of Quality i.e. workability & strength.

7. Sieve Analysis : To find the particle size distribution 8. Soundness : Resistance to climatic changes ( Heating,

cooling, freezing, wetting & drying etc) 9. Durability : They are more durable.

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Maximum size of aggregate:

1. In general, the size of aggregates is larger, the smaller the cement content requirement.

2. This will also reduce the heat of hydration which reduces the thermal and shrinkage cracks.

3. The water-cement ratio can be decreased which increases the strength.

4. In general, for strength up to 20 MPa aggregates up to 40mm may be used and for strengths above 30 MPa, aggregates up to 20mm may be used.

5. According to IS 456-2000, the maximum size of aggregates should not be greater than one-forth the thickness of member or 5mm less than the clear cover.

6. In practice for columns, slab, beam, lintel, aggregates up to 20mm is used.

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Grading of Aggregates: • The particle size distribution of an aggregates as

determined by seive analysis is termed as grading of the aggregates.

• If the aggregates are of uniform size, the compacted mass will contain more voids.

• If the aggregates are of various size, the compacted mass will contain less voids.

• The particle size distribution of a mass of aggregate should be such that the smaller particles fill the voids between the larger particles.

• Therefore proper grading produces dense concrete which gives more strength.

• Grading also affect the workability which controls water, cement requirement, segregation and influences the placing and finishing of concrete.

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Sizes of Aggregates used for different purposes

• 12mm to 20mm size are used for heavily loaded RCC works, precast members and heavily reinforced members.

• 20 mm size is used for water retaining structure, precast product, bridges, columns and sewer construction.

• 25mm size is used for Footpath and road works

• 12 to 40mm size are used for all general works

• 25 to 50mm size are used for mass concreting in culverts, retaining walls.

• 12mm to 20 mm size are used for bitumen hot mix for roads.

• 40mm size is used for concrete bed for foundation in buildings.

• 10mm and 20mm size are used for slab, beam, lintel, column etc..

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Grading Limits

• As per IS 383-1970 the sands are divided in to 4 zones as zone I, II, III and IV according to the percentage passing through 600 micron seive.

• The following values of fineness modulus may be taken as guidance. Type of sand Fineness modulus

Fine sand 2.2-2.6

Medium sand 2.6-2.9

Coarse sand 2.9-3.2

• Any sand having fineness modulus more than 3.2 will not be suitable for making satisfactory concrete.

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Free moisture forms a film around each particle. This film of moisture exerts what is known as surface tension which keeps the neighbouring particles away from it. This causes bulking of the volume.

Bulking of Sand : The increase in the volume of a given mass of fine aggregates (sand) caused by the presence of moisture is known as bulking.

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The surface tension depends upon the percentage of moisture and particle size of the fine aggregates.

It is interesting to note that the bulking increases with the increase in moisture content up to a certain limit and beyond that the further increase in the moisture content results in the decrease in the volume and at a moisture content representing saturation point, the fine aggregates shows no bulking.

Incr

ea

se in v

olu

me,

%

Moisture content

Fine sand

Medium

Coarse sand

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1) If the sand is measured by volume and if no allowance is made for bulking, the mix will be richer than that specified because for a moist sand occupies a considerable larger volume than the dry sand for same mass.

2) This results in a mix deficient in sand increasing the chances of the segregation and honeycombing.

3) The yield of concrete is also reduced 4) It is necessary in such a case, to increase the

measured volume of the sand by percentage bulking.

5) If no allowance is made in sand, the strength of concrete will be reduced.

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Workability

Workability is the property of the fresh concrete which determines the ease and homogeneity with which it can be mixed, placed, compacted and finished.

1. The mix should be able to produce a homogeneous fresh concrete from the constituent material after proper mixing.

2. The mix should be stable i.e. it should not segregate during transportation and placing

3. The mix should be cohesive and should able to go around the reinforcement.

4. The mix should be amenable to proper and thorough compaction in to dense concrete with minimum voids.

5. The mix should be able to attain good surface finish without honeycombing.

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Factors affecting the workability

1. Water content : Water content in a given volume of concrete, will have significant

influence on the workability.

The higher the water content per cubic meter of concrete, the higher will be the fluidity of concrete.

But adding more water may lead corrosion to steel and concrete become poor with less strength.

2. Mix proportions : Aggregate-cement ratio is an important factor influencing

workability.

The higher the aggregate-cement ratio lower the workability.

3. Size of aggregates : The bigger the size of aggregate, the less is the surface area

and hence give higher workability.

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Factors affecting the workability

4. Shape of aggregates: An angular, elongated or flaky aggregate will have lesser

workability than rounded or cubical aggregates.

5. Surface texture of aggregate: The rough surface texture aggregate will have poor workability

and smooth surface aggregate will have higher workability.

6. Grading of aggregate: The better the grading, voids will be lesser and hence higher

the workability.

7. Use of admixtures: This is very important factor which affect workability.

The plasticizers and superplastisizers are used to boost the workability.

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How do you measure workability?

The following test are made to measure the workability.

1) Slump test (Collapse=150-255mm, Shear=25-150, True=

2) Compaction factor test

3) Flow test

4) Kelly ball test

5) Vee Bee Consistometer test.

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WATER

• Water required for hydration

• For mixing & Curing- Free from impurities

• Potable water is used

• In case of doubt, water should be tested.

• The PH between 6 to 8

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Effect of impurities in Water

• Suspended particles: as per IS 456-2000, 2000 mg/lit • Miscellaneous Inorganic salts : manganese, tin, zinc,

copper & lead reduces the strength of concrete • Salt in sea water : ( 3.5% dissolved salt, 78% NaCl2,

15% MgCl2 & MgSo4):Reduces the Ultimate strength of concrete.

• Acid and Alkalies: Industrial waste water consist of acid and alkalies.

• Algae : Reduces the bond, reduces the strength. • Sugar : If quantity more then 0.2%, setting time

accelarated. • Oil contamination :Effect on strength

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Water-Cement Ratio

The water–cement ratio is the ratio of the volume of water mixed in concrete to the volume of cement used in a concrete mix

Significance of water-cement ratio: • A lower water-cement ratio leads to higher strength and

durability, but may make the mix more difficult to place. Placement difficulties can be resolved by using plasticizers or super-plasticizers.

• If the amount of water is less than the optimum water decreases the strength, since water may be insufficient for hydration.

• If the amount of water is more than the optimum water, increases the workability but decreases the strength.

• The use of excessive water also increases the shrinkage and decreases the density and durability.

CURING OF CONCRETE

• The concrete surface are kept wet for a certain period after placing of concrete so as to promote the hardening of concrete is called curing of concrete.

Methods of curing:

• Water curing

• Membrane curing

• Application of heat

• Spraying of water

• Steam curing

• Ponding with water

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Concrete Mix Design (Proportioning): Concrete mix design is a process of proportioning or determining the various ingredients such as cement. aggregate, water and admixtures (if used) with the object of producing concrete of certain minimum strength and durability as economically as possible.

Objectives of proportioning: 1. To meet with the strength requirement as measured by

compressive strength. 2. To meet with durability requirement. 3. To achieve workability ( can be mixed, transported and

compacted as efficiently as possible). 4. To achieve economy. Nominal mix : These are the proportion of standard mix for

concrete of grade M20 or lower. For example, – M20 Mix, Proportion : 1:1.5:3 – M15 Mix, Proportion : 1:2:4

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Factors influencing the choice of Mix Proportions

• Grade designation ( characteristic compressive strength)

• Type and grade of cement

• Size of aggregate

• Grading of aggregates

• Water-cement ratio

• Workability

• Durability

• Quality control

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Mix Design Methods

a) Indian Standard Mix design method ( IS 10262-1982)

b) Arbitrary proportion

c) Fineness modulus method

d) Maximum density method

e) Surface area method

f) Indian Road Congress, IRC 44 method

g) High strength concrete mix design

h) Mix design based on flexural strength

i) Road note No. 4 (Grading curve method)

j) American Concrete Institute (ACI method)

k) British DoE method

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Mix Design Procedure as per BIS 10262-1982)

The following basic data are required to be specified for design of concrete mix.

• Characteristic compressive strength of concrete, fck at 28 days.

• Degree of workability. • Limitations of water-cement ratio. • Type and maximum size of aggregate to be

used. • Standard deviation.

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The step-by-step procedure for mix proportioning is as follows:

1) Target mean strength for mix design: The target mean compressive strength (ft) at 28 days is given by

ft = fck + kS,

where

fck=characteristic compressive strength at 28 days.

S=standard deviation

k=Statistical value depending on expected proportion of low result (5%) k=1.65 as per IS 456-2000.

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2) Selection of free Water-Cement Ratio: The water-cement ratio for the target mean strength is chosen from figure below. The water-cement ratio so chosen is checked against the limiting water-cement ratio for the requirements of durability.

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3. Selection of free water content and % of fine aggregate:

a) The approximate amount of entrapped air is selected for the maximum size of the coarse aggregate to be used ( Table 41 of SP23).

b) Adjustment in values of water content and sand percentage is applied as per table 44 of SP23.

4. Selection of cement content : The cement content is calculated from water-

cement ratio and checked with minimum cement

content with durability.

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5. Computation of absolute volume of aggregate:

Where V = absolute volume of fresh concrete minus entrapped air in m3

W = mass of water in Kg.

C = mass of cement in Kg.

Sc= specific gravity of cement.

p = ratio of fine aggregates to total aggregates.

fa, Ca = total masses of fine and coarse aggregates respectively.

Sfa, Sca = specific gravity of FA and CA.

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6. Adjustment for Aggregates moisture and determination of final proportions

7. Preparation of trial batches and Testing • 150mm size cubes tested under compression

testing machine after 28 days of moist curing.

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Compaction of Concrete

• The process of removal of entrapped air and of uniform placement of concrete to form a homogeneous dense mass is termed compaction.

• If concrete is not compacted, the concrete may be porous, non-homogeneous and strength may be reduced.

• The presence of even 5% voids in hardened concrete due to improper compaction may reduce its compressive strength up to 35%.

• Due to improper compaction, the moisture may penetrate in to the concrete and corrode the steel.

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Compaction methods:

1. Hand compaction : Concrete is compacted by Rodding, temping or

ramming for less important works.

2. Compaction by mechanical vibrators: – Vibration is most commonly used method of

compaction of concrete, which reduces the internal friction between the different particles of concrete and thus consolidates the concrete in to a dense, and compacted mass.

– The quality of concrete may be improved – It reduces the compaction time and energy. – The concrete with dense reinforcement can be

compacted easily. – Vibrators are used to achieve high strength concrete

with low water cement ratio.

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3. Centrifugation or spinning

4. High pressure and shock.

Types of Vibrators:

1. Immersion or Needle vibrators a) These vibrator are most commonly used.

b) Its one end consists of a steel tube having an eccentric vibrating element and other end to the electric motor or diesel engine.

c) They are available in sizes varying from 40 to 100mm in diameter.

d) These vibrators are used for footings, columns, slab, beams etc.

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2. External or Shutter vibrators: These vibrators are attached to the formwork and external centering of walls, columns, retaining walls, water tank and any thin RC members.

3. Surface vibrators: Used for thin RC members such as slab, roof slab etc..

4. Vibrating table : This is operated by electrical motors and used in the laboratory for test specimen and precast members.

5. Vibratory roller: These are used for construction of dam and pavements.

JOINTS IN CONCRETE

• Construction joint: The construction joints are provided at locations where the construction is stopped either at the end of the day or for any other reason. It is provided to ensure proper bond between old and new work. The position of construction joint should be preplanned before concreting is started.

• Expansion joints: Concrete is subjected to volume changes due to change in temperature. i.e. roof slab subjected to expansion and contraction during day and night. The building longer than 45m are generally provided with one or more expansion joints.

• Contraction joints: Concrete undergoes shrinkage which results in cracks. To avoid these cracks, contraction joints are provided at 5 to 10 m.

• Isolated joint : These joints are provided when floor slab meets with column or wall.

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MATERIALS FOR REINFORCED CONCRETE

CONCRETE: Grades of concrete: • The Indian standard Code IS:456-2000 specifies that the concrete

mix proportions should be selected so as to ensure the workability of fresh concrete and durability of hardened concrete.

• The proportion of desired mix is determined by mix design or nominal mix.

• The code specifies that the design mix should be preferred then nominal mix because the design mix gives better performance then nominal mix.

• For reinforced concrete work, most commonly used grades of concrete are M-20 to M-30. IS 456-2000 specifies the minimum grade of concrete as M-20. M-10 and M-15 are used for plain concrete works ( concrete bed, etc.)

Tensile strength of concrete:

• The tensile strength of concrete is expressed in terms of flexural strength.

flexural strength: fcr=0.7√fck N/mm2

fck = Characteristic compressive strength in N/mm2

Modulus of elasticity of concrete:

• The modulus of elasticity of concrete is required to calculate the deflections of structural member it it depends upon fck.

Ec=5000 √fck N/mm2

Shrinkage of concrete:

The total shrinkage of concrete depends upon the constituents of concrete, size of member and environmental conditions. The approximate value of the total shrinkage strain in concrete for design purposes may be taken as 0.0003.

Creep of concrete:

Concrete under the action of sustained loading, continue to deform with time. This time-dependent deformation due to elasto-plastic properties of concrete is known as creep.

Durability of concrete: Durability of concrete is depends upon various factors such as type of environment, cement content, w/c ratio,workmanship, cover to the reinforcement, shape and size of structural members.