Concrete Annexure

7/28/2019 Concrete Annexure

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SDL/ QST Concrete Annexure

1 04/08/2009

Sobha Developers Ltd.

Department of Quality Safety & TechnologyDepartment of Quality Safety & TechnologyDepartment of Quality Safety & TechnologyDepartment of Quality Safety & Technology

(Valid from 01-Aug-2009, until further notice)

Prepared byPrepared byPrepared byPrepared by Approved byApproved byApproved byApproved by

Mr. Venkatesh MMr. Venkatesh MMr. Venkatesh MMr. Venkatesh M Mr. Olaf WagnerMr. Olaf WagnerMr. Olaf WagnerMr. Olaf WagnerManagerManagerManagerManager QSDQSDQSDQSD SVPSVPSVPSVP ---- QSTQSTQSTQST


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CONTENTS

S.No Description Page No.

CONCRETE 5

A INGRADIENTS OF CONCRETE 5

I Cement 5

1 Types of Cement 5

2 Ordinary Portland Cement 6

3 Blended Cement 7

4 Storage of Cement 9

5 Test of Adulteration 9

II Mineral Admixtures 10

1 Limits of Mineral Admixtures to be used with Cement 10

2 Requirements of fly ash for use as pozzolana and admixture 11

III Aggregates 12

1 Classification of Aggregates 12

2 Grading of Aggregates 12

3 Quality of Aggregates 13

4 Deleterious materials 15

5 Bulking of Sand 15

6 Storage of Aggregates 16

IV Water 17

1 Typical limits for solids in water 17

V Chemical Admixtures 18

1Physical requirements for accelerating, retarding, Water-reducing and air entraining

admixtures

19


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B DURABILITY OF CONCRETE 20

1 Environmental exposure conditions 20

2Minimum cement content, Maximum water Cement ratio, Minimum grade of concrete forDifferent Exposures with normal weight aggregates of 20mm nominal maximum size

21

3 Limits of Mineral Admixtures to be used with cement 21

I Maximum Cement Content 22

1 Adjustment to Minimum Cement content other than 20mm Nominal Maximum size. 22

II Grade of Concrete 22

III Carbonation and Chlorides in concrete 23

1 Limits of Chloride content of concrete 23

IV Sulphates in Concrete 23

1 Requirements for Concrete Exposed to Sulphate Attack 24

V Cover to Reinforcement 25

1 Nominal cover to meet durability requirements 25

VI Cover for Fire Resistance 26

1 Nominal cover to meet specified period of Fire Resistance 26

C CONCRETE MIX DESIGN 27

1 Slump suitable for different placing conditions 27

I Guidelines for Concrete Mix Proportioning 28

1 Data for Mix Proportioning 28

2 Target strength for Mix proportioning 28

a Selection of Mix proportions 29

1 Selection of Water Cement Ratio 29

2 Selection of Water content 30

b Calculation of Cementitious Material Content 30

1 Estimation of Coarse Aggregate proportion 30

2 Estimation of Fine Aggregate proportion 31

3 Combination of Different Coarse Aggregate Fractions 31

c Trial Mixes 31


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D AN ILLUSTRATIVE EXAMPLE OF CONCRETE MIX PROPORTIONING 32

E MAKING GOOD CONCRETE 36

F LABORATORY MANUAL FOR QUALITY CONTROL OF CONCRETE 37

I List of Laboratory Testing for Quality concrete 37

a Cement 38

1 Specific Gravity of Cement 38

2 Fineness of Cement 39

3 Standard Consistency and Setting time 41

4 Compressive Strength of Cement 44

b Aggregates 47

1 Specific Gravity & Water Absorption of Fine Aggregate 47

2 Specific Gravity & Water Absorption of Coarse Aggregate 49

3 Unit Mass of Concrete Aggregate 51

4 Moisture Content of Concrete Aggregate 52

5 Fineness Modulus & Grain Size distribution 53

6 Silt Content 56

7 Bulking of Fine Aggregate 57

8 Flakiness & Elongation indices of Coarse Aggregates 58

c Concrete 61

1 Slump test 61

2 Strength of Cement Concrete 63


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CONCRETE

The concrete is the most important construction material, which is manufactured at site. It is a composite productobtained by mixing cement, water and an inert matrix of sand and gravel or crushed stone. It undergoes a number ofoperations such as transportation, placing, compacting and curing. The distinguishing property of the concrete is its ability

to harden under water. The ingredients of the concrete can be classified into two groups namely, active and inactive. Theactive group consists of cement and water whereas inactive group comprises of fine and coarse aggregates.

The cement commonly used is Portland cement, and the fine aggregates and coarse aggregates, are those obtainable,

usually from nearby sand, gravel or rock deposits. In order to obtain a strong, durable and economical concrete mix, itis necessary to understand the characteristics and the behavior of Ingredients.

A. INGRADIENTS FOR CONCRETE

I. CEMENTPortland cement is a hydraulic binder and a finely ground inorganic material. When mixed with water, it forms a paste

which sets and hardens by means of hydraulic reactions.

1. TYPES OF CEMENTThere are various types of cement in use and as per IS 456:2000, Indian Standard code of practice for plain andreinforced concrete permits the use of 10 different types of cement.

SL NO. TYPES OF CEMENT REFERENCE

1 33 Grade ordinary Portland cement IS 269



4 Rapid hardening Portland cement IS 8041

5 Portland Slag Cement IS 455

6 Portland Pozzolana cement (fly ash based) IS 1489 (part 1)

7 Portland Pozzolana cement (Calcined clay based) IS 1489(part 2)

8 Hydrophobic cement IS 8043

9 Low heat Portland cement IS 12600

10 Sulphate resisting Portland Cement IS 12330


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2. ORDINARY PORTLAND CEMENTOrdinary Portland cement is a product obtained by intimately mixing together calcareous (limestone, chalk, etc) andargillaceous (clay, shale,etc) materials, with or without other materials containing silica, alumina, or iron oxide,

burning them at a high temperature, and grinding the resulting intermediate product, clinker with gypsum. Afterburning, no material other than gypsum is added.

Grades of Ordinary Portland Cement (OPC)

The Bureau of Indian Standards has classified OPC into three grades for producing different grades of concrete tomeet the demands of the construction industry. The classification is made on the basis of Compressive strength at 28days as:

33 grade Ordinary Portland Cement43 grade Ordinary Portland Cement53 grade Ordinary Portland Cement

The grade indicates compressive strength of the cement in N/mm2 at 28 days. Since higher grades of concretenecessitate the use of higher strength of cement at 28 days, use of 33 grade cement has dropped during the last

decade.

Both 43 grade and 53 grade cement can be used for producing higher grades of concrete.

Table 1: Physical and Chemical properties of various grades of Ordinary Portland cement

TYPE OF CEMENT 33 GRADE 43 GRADE 53 GRADE

PHYSICAL PROPERTIES

Minimum compressivestrength,N/mm2

3 day 16 23 27

7 day 22 33 37

28 day 33 43 53

Fineness

Minimum specific surface, m2/kg 225 225 225

Setting time, minutes

Initial, minimum 30 30 30

Final, maximum 600 600 600

Soundness, expansion

(Le chatelier test, mm), maximum 10 10 10

Autoclave test MgO, percent, maximum 0.8 0.8 0.8

CHEMICAL PROPERTIES

Loss on ignition, percent, maximum 5.0 5.0 4.0

Insoluble residue, percent, maximum 4.0 2.0 2.0

Magnesia Mgo, percent Maximum 6.0 6.0 6.0

Lime saturation factor (LSF) .66-1.02 .66-1.02 0.8-1.02

Ratio, AF, minimum 0.66 0.66 0.66


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3. BLENDED CEMENTSBlended cements or composite cements are those cements in which a mineral additive has been added to Portland

cement. Blended cement is a hydraulic cementitious product, similar to ordinary Portland cement, but due to theaddition of blending material it has certain improved properties compared to OPC.

Portland Pozzolana Cement (PPC)

Portland Pozzolana Cement (PPC) is manufactured either by grinding intimately together Portland cement clinker,gypsum and a pozzolana such as fly ash, or by intimately and uniformly blending Portland cement and fine pozzolana.The BIS has differentiated PPC based on the pozzolana added to the mix. Thus IS 1489 (part 1) is Portland pozzolanacement (fly ash based).According to the latest amendment in July 2000, the proportion of fly ash as a pozzolana usedcan vary between 15 and 35 percent by weight of cement, as stipulated by IS 1489 (part 1) 1991.

Increased impermeability, lower heat of hydration, lower plastic shrinkage, reduced alkali-aggregate expansion andimproved resistance to aggressive chemical agents and corrosion are some of the major benefits to be derived fromthe use of PPC. The use of PPC is, thus desirable for enhancing durability in different construction jobs, specially forstructures subjected to aggressive environments. In mass concrete construction, PPC concretes have shown rather

better behavior in respect of cracking than OPC concretes because of lower heat of hydration.

Portland Blast furnace Slag Cement (PBSC)

Portland blast furnace slag cement is an intimately ground mixture of Portland cement clinker and granulated blast

furnace slag, either inter ground or ground separately and blended together. The granulated blast furnace slag is anon-metallic product obtained by rapidly chilling or quenching in water the molten tapped from the blast furnace of a

steel plant. As per the latest amendment to IS 455 in May 2000, the slag constituent should not be less than 25percent nor more than 70 percent of the Portland cement. PBSC generally has higher fineness, lower heat ofhydration, lower permeability and better resistance to chemical attack and corrosion than OPC.

Portland slag Cement can be used for all construction jobs in place of ordinary Portland cement, but its specialproperties render its adoption highly desirable fro marine structures involving large masses of concrete such as dams,

retaining walls, and bridge abutments, and for structures exposed to sulphate bearing soils such as foundations androads.

Benefits of Blended Cements

The use of blended cement improves the properties of both, fresh and hardened concrete. These can be as a resultof the extended hydration of the cement-pozzolana mixture, reduced water demand, and due to the improvedcohesion of the paste. Another important benefit is the improvement in durability resulting from the lower

permeability and improved microstructure of the concrete. This arises from the reduction in pore size of the cementpaste and the refinement of pore structure of the cement paste as well as improvements in the properties of theinterfacial zone between he cement paste and the aggregate/inerts.


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Table 2: Physical and Chemical properties of blended cement (PPC and PBSC)

Type of cement PPC PBSC

Physical properties

Minimum compressivestrength,N/mm2

3 day 16 167 day 22 22

28 day 33 33

Fineness

Minimum specific surface, m2/kg 300 225

Setting time, minutes

Initial, minimum 30 30

Final, maximum 600 600

Soundness, expansion

(Le chatelier test, mm), maximum 10 10

Autoclave test MgO, percent, maximum 0.8 0.8Additives, percent by weight of cement

Fly ash 15-35

GGBS 25-70

Chemical properties

Loss on ignition, percent, maximum 5.0 5.0

Insoluble residue, percent, maximum # 4.0

Magnesia Mgo, percent Maximum 6.0 8.0

Sulphur, percent, maximum as sulphuricanhydride (SO3)

3.0 3.0

#- x + (4.0(100-x)/x) where x is the declared percentage of pozzolana in PPC.


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4. STORAGE OF CEMENTSince cement is a very finely ground hygroscopic material: i.e. it readily absorbs moisture every precaution should betaken to ensure that the cement is kept free from contact with moisture in any form. The storage shed should have a

pucca floor raised at least 150mm above ground level, and it should be provided with air tight doors and windows.It is a good practice that cement is moved in and out of the godowns in the first-in-first-out method. The drainagesystems on the roof and around the godown should be well maintained, specially during the monsoon months.

At site, the cement bags should be kept on a raised platform and covered with a tarpaulin.Cement stored for a long time tends to deteriorate and an indicative rate of its deterioration is given.

Table 3: Possible reduction in strength of concrete made with stored cement

PERIOD OF STORAGE OFCEMENT

MINIMUM EXPECTED REDUCTIONS IN STRENGTHAT 28 DAYS (%)

Fresh 0

3 months 20

6 months 30

1 year 40

2 years 50

5. TEST FOR ADULTERATIONA sample of doubtful cement should be burnt for about 20 minutes on a steel plate heated on a stove. An adulterated

sample will change in colour; unadulterated cement, on the other hand, will remain unchanged.

Small pats of about 50 X 50 X 20 mm size should be made. If the cement is adulterated, the pats can be broken

easily with the pressure of fingers the next day.

It is, however, always advisable to send a sample to a laboratory for analysis and tests whenever there is doubt

regarding the quality of cement.


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II. MINERAL ADMIXTURESMineral Admixtures are finely divided siliceous materials which are added to concrete in relatively amounts. They canbe broadly divided into two groups, namely,

1. Reactive mineral admixtures, which could be either pozzolonic(for example, low calcium fly ash, silica fume),or cementitious (for example, ground granulated blast furnace slag), or both cementitious and pozzolonic (for

example, high calcium fly ash)2. Inert mineral admixtures, which have no cementitious or pozzolonic value and are generally added as a fillermaterial (for example, silica flour, limestone powder, etc.).

When the materials from the first group comprising of reactive mineral admixtures are used to partially replacement,

they react with the calcium hydroxide in the hydrated cement paste to form complex compounds which result in areduction in permeability, improvement in the ultimate strength, water tightness and durability, besides impartingeconomy to the mix. However, these admixtures need to be uniformly blended while mixing the concrete.

Incidentally, blended cements such as PPC and PBSC contain mineral admixtures as per relevant Indian standards.They are manufactured under controlled conditions in a factory and contain these admixtures uniformly. Thesecements are most suitable for site as well as ready mixed concrete.

The IS 456:2000 permits the use of the following mineral admixtures, provided uniform blending with

cement is ensured:

1. Fly Ash2. Ground Granulated Blast-furnace Slag (GGBS)3. Silica Fume4. Rice Husk Ash5. Metakaolin.

The use of mineral admixtures directly at site in concrete is still in its infancy in India and is mainly restricted to theready mixed concrete. Excepting silica fume, none of these admixtures are readily available commercially in themarket. While the specifications of silica fume, rice husk ash and metakaolin are yet to be formulated by the Bureauof Indian Standards, fly ash conforming to Grade I of IS 3812 and GGBS conforming to IS 12089 may be used as partreplacement of ordinary Portland cement provided uniform blending with cement is ensured.

1. Limits of Mineral Admixtures to be used with cement : Table 4Sl NO. MINERAL ADMIXTURE % TO BE USED REFERENCE

1 Fly Ash (PFA) 15 - 35IS 1489 (Part 1) 1991

Amendment No.3, July 2000

2 Slag (GGBS) 25 - 70IS 455 -1989

Amendment No.4, May 2000

3 Silica Fumes 05 - 10 IS 456 - 2000


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2. Requirements of Fly Ash for use as pozzolana and Admixture : Table 5Characteristic

Requirement of Fly AshGrade I

Physical Requirements

Fineness, minimum specific surface, m2/kg 320

Lime reactivity, average compressive strength, N/mm2,Minimum

4.0

Minimum compressive strength, at 28days, N/mm2,minimum

Not less than 80 percent of thestrength of corresponding plain

cement mortar cubes

Drying shrinkage, percent, maximum 0.15

Soundness expansion, Autoclave test, percent, maximum 0.8

Chemical Requirements

Silicon dioxide(Sio2) plus aluminium oxide(Al2O3)plusiron oxide(Fe3O2), percent by mass, minimum

70.0

Silicon dioxide(SiO2), percent by mass, minimum 35.0

Magnesium oxide(Mgo), percent by mass, maximum 5.0

Total sulphur as sulphur trioxide(SO3), percent by mass,maximum

2.75

Available alkalis as sodium oxide (Na2O), percent by

mass, maximum1.5

Loss on ignition, percent by mass, maximum 12.0


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III. AGGREGATESAggregates constitute nearly 70 to 75 percent of the total volume of concrete and are essentially inert in nature.A large number of properties of concrete are governed by them. Aggregates have two prime functions: namely,to provide concrete with a rigid skeletal structure and reduce the void space to be filled by the cement paste.The characteristics of aggregates are dependent upon three main features, namely, the mineralogical composition

of the parent rock, exposure conditions to which the rock has been subjected to and the type of equipment andprocesses used in producing aggregates. Most natural rocks, whether massive or broken down by nature, aresuitable for making concrete. In India, the rock types that are most generally used in concrete include: Basalt,Granite, limestone, Sandstone, etc. Crushed rock is the commonly used coarse aggregate in the country, althoughgravel is also used wherever available economically. For fine aggregate, river sand is used on a large scale.

IS 456:2000 specifies that aggregates shall comply with the requirements of IS 383. Preference shall be given tonatural aggregates.

1. Classification of AggregatesAggregates are commonly classified into two sizes, fine and coarse; the dividing line being the 4.75 mm IS sieve.Where, however, the aggregate is a mixture of fine and coarse particles as it comes from the pit, riverbed,

foreshore, quarry or crushing plant it is termed as all-in aggregate.Aggregates can also be classified into two more ways. Depending on the source, they could either be naturallyoccurring (gravel, pebbles, sand, etc) or synthetically manufactured (bloated clay aggregates, sintered fly ashaggregates, etc). Further depending on the bulk density, aggregates can either be normal weight (1400 to 1600

kg/m3), light weight (less than 1200 kg/m3), or heavy weight (above 2000 kg/m3).

2. Grading of AggregatesThe distribution of the sizes of aggregate particles is called grading. Grading is an important property of

aggregate for concrete in view of its effect on the packing, and thus voidage, which will in turn influence thewater demand and cement content of concrete. Uniformity of grading within and between consignments is mostvital.

Grading is usually described in terms of cumulative percentage by mass of aggregate passing particular IS sieves.As mentioned earlier, aggregates are classified into two sizes, Fine and Coarse; the dividing line being the 4.75

mm IS sieve.

Coarse Aggregatesare described either as graded, that is having more than one size of particles, or singlesized, that is mainly retained between two adjacent sieves in the upper part of the list.

Table 6: Grading limits for single-sized coarse aggregates(Ref: Clause 4.1 and 4.2 of IS 383:1970)

Percentage passing for single sized aggregate of nominal sizeIS Sieve

63 mm 40 mm 20 mm 16 mm 12.5mm 10 mm

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 -

12.5mm - - - - 85-100 100

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

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


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Fine Aggregate,depending on its fineness modulus (FM), is divided into three categories, namely,

Table 7: Fineness modulus

Fine Aggregate Fineness modulus(FM)

Fine 2.2 to 2.6

Medium 2.6 to 2.9

Coarse 2.9 to 3.2

Table 8: Grading Limits for Fine Aggregates(Ref: Clause 4.3 of IS 383:1970)

Percentage PassingIS Sieve designation

Zone I Zone II Zone III Zone IV

4.75 mm 90 - 100 90 - 100 90 - 100 95 - 100

2.36 mm 60 95 75 100 85 100 95 - 100

1.18 mm 30 70 55 90 75 100 90 100

600 micron 15 34 35 59 60 79 80 100

300 micron 05 20 08 30 12 40 15 50

150 micron 0 - 10 0 - 10 0 - 10 0 - 15

Note: 1 for crushed stone sands, the permissible limit on 150-micron IS sieve is increased to 20 percent.Note: 2 it is recommended that fine aggregate conforming to Grading zone IV should not be used in reinforced

concrete unless tests have been made to ascertain the suitability of proposed mix proportions.

3. Quality of AggregatesThe aggregates used to make concrete must be clean, dense, hard, durable, structurally sound, capable ofdeveloping good bond with cement, weather-resisting, and unaffected by water. Most of the aggregates available incountry have adequate strength and other properties for using in concrete.

The properties of the concrete depend upon the quality of the aggregates- their strength, water absorption, shapeand texture, the maximum size of aggregate, etc.

Typical Bulk density, specific gravity, approximate water absorption of different types of aggregates and the limitingvalue of its mechanical properties are mention below.


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Table 9(a): Aggregates: Bulk density and Specific gravity

Bulk Density, Kg/m3

River Sand

Fine 1440

Medium 1520

Coarse 1600

Beach or river shingle 1600

Broken stone 1600

Stone screenings 1440

Broken Granite 1680

Specific Gravity

Trap 2.9

Granite 2.8

Gravel 2.66

Sand 2.65

Table 9(b): Aggregates: Limiting values of mechanical properties(Ref: IS 383:1970)

Properties For wearing surfaces (%)Other than for wearing

surfaces (%)

Crushing value 30 45

Impact value 30 45

Abrasion value 30 50

Table 10: Approximate water absorption of aggregates, by weight

Average sand 1.0 percent

Pebbles and crushed limestone 1.0 percent

Trap rock and granite 0.5 percent

Porous sand stone 7.0 percent

Very light and porous aggregates may absorb asmuch as

25 percent by weight


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4. Deleterious MaterialsImpurities in aggregates are undesirable as they may hinder the hydration of cement and prevent adhesion of theaggregates with the cement paste, reducing strength and lower durability. The limits of allowable deleteriousmaterials as given in IS: 383:1970

Table 11: Limits of Deleterious Materials(Ref: Clause 3.2.1 of IS 383:1970)

Fine aggregates Coarse aggregatesDeleterious substances

Uncrushed Crushed Uncrushed Crushed

Coal and lignite 1.00 1.00 1.00 1.00

Clay lumps 1.00 1.00 1.00 1.00

Material finer than 75-micron

IS sieve3.00 15.00 3.00 3.00

Shale 1.0 - - -

Total of percentages of alldeleterious material 5.0 2.00 5.00 5.00

5. Bulking of SandSand as delivered sometimes contains moisture which causes a film of water on the surface of the particles, fluffingthem apart. This is called bulking which will have to be taken into account while batching the mix.

Tables show the bulking of sand for various moisture contents and the approximate quantity of surface water in akilolitre of average aggregates.

The values given in the table are applicable to nominal mixes only, particularly when no data about the surface wateris available.

Table 12: Bulking of sand for various moisture content

Percentage bulking inMoisture,percent Fine sand Medium sand Coarse sand

1 16 8 6

2 26 16 12

3 32 22 15

4 36 27 17

5 38 29 18

6 37 28 18

8 35 26 16

10 32 22 12

12 28 19 8

15 22 12 2

17 18 7 0

20 9 0 0

27 0 0 0


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IV. WATERThe purpose of water in concrete is three-fold. Water distributes the cement evenly, so that every particle of theaggregate is coated with it and brought into intimate contact with it and brought into intimate contact with its neighbor.It reacts chemically with cement, the reaction being called hydration of cement, and brings about the setting andhardening of cement. Water also lubricates the mix and gives it the workability required to place and compact it

properly. Ponding of the freshly hardened concrete with water is a widely prevalent practice in the country.

Water used for mixing concrete should be free from Oil, acids, and alkalis, salts, sugars, organic materials, or any othersubstances that may be deleterious to concrete. Generally it should be of potable quality.

The PH value of water shall not be less than 6. Sea water is not recommended for reinforced and pre-stressed

concrete, but can be used only under unavoidable circumstances for plain concrete.

It is well known that the Chloride and Sulphate contents of water have a major influence on the durability of concrete.In the latest revision of IS 456:2000, the permissible limits of these harmful agents have been made stringent. ThePermissible limits for solids in water are given in the table.

1. Typical Limits for solid in water : Table 14(Ref IS 456:2000 clauses 5.4)

SolidsPermissible limits,

max, mg/l

Organic 200

Inorganic 3000

Sulphates (as SO3) 400

Chlorides (as Cl)

For plain concrete 2000

For reinforced concrete 500

Suspended matter 2000

In case of doubt regarding the development of strength the following test are specified in IS 456:2000.

1. Average 28 day compressive strength of at least three cubes (150mm) prepared with the water proposed to beused shall not be less than 90 percent of the average strength of cubes prepared with distilled water as per IS516.

2. The initial setting time shall not be less than 30 min and shall not differ +/- 30 min from that of the cubes castwith distilled water as per IS 4031 (part V).


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V. Chemical AdmixturesChemical admixtures are sometimes called the fifth ingredient of concrete, other than cement, coarse and fineaggregates and water. They are inorganic or organic materialssolid or liquidwhich when added to the normalcomponents of a mix (either concrete, mortar or paste), interact with the cementitious system through chemical,

physical or physico-chemical means, modifying one or more properties of the mix in the fresh, setting, hardening orhardened state.

A number of advantages can be derived with the use of admixtures. For example, in the fresh state of concrete,depending on the type of admixture used, they can increase the workability without increasing the water content,reduce or prevent settlement, modify the rate and /or capacity of bleeding, reduce segregation and reduce slump

loss, retard or accelerate the time of initial/final setting.

Aside from altering the properties of the fresh mix, they can retard or reduce heat evolution during early hardening,accelerating the rate of strength development at early ages, increase the compressive strength of concrete, improvedurability, control alkali-aggregate reactivity, produce aerated concrete, improve bond between old and new concrete

inhibit corrosion of reinforcement, produce coloured concrete/mortar, etc.

Chemical admixtures can be classified according to the purpose they are used, or according to the type of materialsconstituting them.

Commonly-used admixtures are:1. Water reducing /plasticizing admixtures2. Set controlling admixtures, or retarders3. Air entraining admixtures4. Accelerating admixtures5. High range water reducing, or super plasticizing admixtures.Besides the above, other types of admixture are also used. These include Grouting admixtures, pumping aids,bonding admixtures, expansion-producing admixtures, fungicidal, germicidal and insecticidal admixtures, etc.

Commercially available admixtures may contain materials that separately belong to one or more groups. For example,a water-reducing admixture may be combined with a retarding admixture, and so on. The effectiveness of an

admixture depends upon such factors as type, brand and amount of cement; water content; aggregate shape,grading and proportions; mixing time; slump; and temperatures of concrete and air.

Trial mixes should be made with the admixture and the job materials at temperatures and humidity anticipated on thejob. In this way the compatibility of the admixture with other job materials, as well as the effects of admixtures onthe properties of the fresh and hardened concrete, can be observed. The amount of admixture recommended by the

manufacturer, or the optimum amount determined by laboratory tests should be used.


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1. Physical requirement for the main types of admixtures as given in IS 9103:1999are given in the table: Table 15

Requirement AA RA WRA AEA NSA RSA

Water content, percent of control sample,maximum

- - 95 - 80 80

Time of setting, allowable deviation fromcontrol sample, hours:

Initial Maximum -3 +3 +/-1 - - +4

Minimum -1 +1 - - +1.5 +1

Final Maximum -2 +3 +/-1 - +/-1.5 +/-3

Minimum -1 +1 - - - -

Compressive strength, percent of controlsample, minimum:

1-day - - - - 140 -

3-day 125 90 110 90 125 125

7-day 100 90 110 90 125 12528-day 100 90 110 90 115 115

6-month 90 90 100 90 100 100

1-year 90 90 100 90 100 100

Bleeding, percent increase over control

sample, maximum

5 5 5 5 5 5

Loss of workability - - - - * **

Air content, percent, maximum, overcontrol

- - - - 1.5 1.5

Notes:AA: Accelerating admixture; RA: Retarding Admixture;WRA: Water-reducing admixture;AEA: Air entraining admixture;

NSA: Super plasticizing admixture (normal);RSA; Super plasticizing admixture (retarding)

*At 45 min the slump shall not be less than that of control mix concrete at 15 min**At 2 hour, the slump shall not be less than that of control mix concrete at 15 min.


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B. DURABILITY OF CONCRETE

Durable concrete can be defined as one that is designed, constructed and maintained to perform satisfactorily in theexpected environment for the specified life of the structure without undue maintenance. The materials and mixproportions chosen should be such as to maintain the integrity of the concrete and to protect the embeddedreinforcement.

The principal causes of deterioration of concrete have been identified as: Carbonation, corrosion ofreinforcement, sulphate attack and alkali-aggregate reaction. Generally, the concrete suffers from more thanone cause of deterioration, which is generally seen in the form of cracking, spalling, loss of strength, etc. It is nowaccepted that the main factors influencing the durability of concrete is its impermeability to the ingress of oxygen,water, carbon dioxide, chlorides, sulphates, etc. Impermeability is dependent on the constituents and workmanshipused in making the concrete.

IS 456:2000 identifies various factors influencing durability as:

1. Environment2. Cover to the embedded steel3. Type and quality of constituent materials4. Cement content and water cement ratio5. Workmanship to obtain full compaction and efficient curing6. Shape and size of members.IS 456:2000 classifies the general Environment in which the concrete will be exposed into five levels of severity---mild, moderate, severe, very severe and extreme. The code has also specified the values of minimum and maximumcement content, maximum free water cement ratio and the grades of concrete for different exposure conditions.

These values are applicable for those mixes having 20 mm nominal size aggregate. For other sizes of aggregates, thevalues need to be changed as given in the table.

It is to be noted that the minimum specified grade for reinforced concrete is M20. Incidentally, the grades of concrete

have been classified into three different categories in IS 456, namely,

1. Ordinary concrete2. Standard concrete3. High strength concrete

1. Environmental Exposure Conditions : Table 16(Reference IS 456:2000 Table 3)

Sl No. Environment Exposure Conditions

1 MildConcrete surfaces protected against Weather or aggressive conditions, exceptthose situated in coastal area.

2 Moderate

Concrete surfaces sheltered from Severe rain or freezing whilst wetConcrete exposed to condensation and rainConcrete continuously under waterConcrete in contact or buried under non-aggressive soil/ground waterConcrete surfaces sheltered from saturated salt air in coastal area

3 Severe

Concrete surfaces exposed to severe rain, alternate wetting and drying oroccasional freezing whilst wet or severe condensation.Concrete completely immersed in sea water

Concrete exposed to coastal environment

4 Very SevereConcrete surfaces exposed to sea Water spray, corrosive fumes or severefreezing conditions whilst wetConcrete in contact with or buried under aggressive sub-soil/ground water

5 ExtremeSurface of members in tidal Zone

Members in direct contact with liquid/solid aggressive chemicals


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2. Minimum Cement Content, Maximum Water-cement ratio and Minimum grade of concrete forDifferent Exposures with normal weight aggregates of 20mm nominal maximum size : Table 17

(Reference IS 456:2000 Table 5)

Plain concrete Reinforced Concrete

S.No ExposureMinimumcementcontentKg/m3

MaximumFree

water-cementratio

MinimumGrade of

Concrete

MinimumcementcontentKg/m3

MaximumFree

water-cementratio

MinimumGrade of

Concrete

1 Mild 220 0.60 - 300 0.55 M 20

2 Moderate 240 0.60 M 15 300 0.50 M 25

3 Severe 250 0.50 M 20 320 0.45 M 30

4 Very Severe 260 0.45 M 20 340 0.45 M 35

5 Extreme 280 0.40 M 25 360 0.40 M40

NOTE:

Cement content prescribed in this table is irrespective of the grades of cement and it is inclusive of additions(Mineral Admixture). The additions such as fly ash or ground granulated blast furnace slag may be taken intoaccount in the concrete composition with respect to the cement content and water-cement ratio if the suitabilityis established and as long as the maximum amounts taken into account do not exceed the limit of pozzolona (flyash) and Slag (GGBS).

3. Limits of Mineral Admixtures to be used with cement : Table 18S. No. Mineral Admixture % to be used Reference:

1 Fly Ash (PFA) 15 - 35

IS 1489 (part 1) 1991

Amendment No.3, July 2000

2 Slag (GGBS) 25 - 70IS 455 -1989

Amendment No.4, May 2000

3 Silica Fumes 05 - 10 IS 456- 2000


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I. Maximum Cement ContentCement content not including fly ash and ground granulated blast furnace slag in excess of 450 kg/m3 should notbe used unless special consideration has been given in design to the increased risk of cracking due to dryingshrinkage in thin sections, or to early thermal cracking and to the increased risk of damage due to alkali silicareactions.

1. Adjustments to Minimum Cement contents for AggregatesOther than 20mm Nominal Maximum size: Table 19

Sl No.Nominal Maximum Aggregate

size mmAdjustments to Minimum Cement

content in kg/m3

1 10 +40

2 20 0

3 40 -30

II.Grades of Concrete: Table 20(Ref: IS 456:2000 Table 2)Group

Gradedesignation

Specified characteristics compressive

strength of 150 mm cube at 28 days,N/mm2

M 10 10

M 15 15Ordinary Concrete

M 20 20

M 25 25

M 30 30

M 35 35M 40 40

M 45 45

M 50 50

Standard concrete

M 55 55

M60 60

M65 65

M70 70

M75 75

High strength concrete

M80 80

Notes:1. In the designation of concrete mix, M refers to the mix and the number to the specified compressive strength

of 150 mm size cube at 28 days, expressed in N/mm2.2. For concrete of compressive strength greater than M55, design parameters given in the standard may not be

applicable and the values may be obtained from specialized literature and experimental result.


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III. Carbonation and chlorides in concreteGenerally, impermeable concrete provides adequate protection to reinforcing steel. However, the atmospheric carbondioxide can react with the products of hydration resulting in the process of carbonation, which on reaching the

reinforcing steel makes it vulnerable to corrosion. This process may take a few years, or even decades, depending on

a host of factors, such as depth of cover, its permeability, level of CO2, type of cement and/or additive used, etc.

Another major source of corrosion is the presence of chlorides in the concrete. The chlorides may get introduced intothe concrete through the chlorides present in any of the ingredients, such as cement, aggregates, water, admixtures,etc, or through an external source into the hardened concrete.

IS 456:2000 lays down the limits of the chloride content (as Cl) in concrete at the time of placing.

1. Limits of Chloride content of concrete : Table 21(Ref: IS 456:2000 Table 7)

Sl No. Type or use of concrete

Maximum total acidsoluble Chloride content

expressed as kg/m3 ofconcrete

1Concrete containing metal and steam cured at

elevated temperature and pre-stressed concrete0.4

2Reinforced concrete or plain concrete containing

embedded metal0.6

3Concrete not containing embedded metal or any

material requiring protection from chloride3.0

IV. Sulphates in ConcreteSulphate attack can originate from ground water, soils, sea water or industrial effluents. The reaction depends on theconcentration of sulphate ions present in sulphate solutions (that is, sodium, potassium ammonium or magnesium), C3Acontent of the cement and the quality of the concrete. Sulphates convert the free lime in the hardened concrete to

calcium sulphate, and the hydrates of calcium aluminates and ferrites to calcium sulphoaluminates or sulphoferrites.These conversions occupy more than double the solid volume, which results in disruption, expansion and cracking of theconcrete.IS 456:2000 stipulates that the total water soluble sulphate content of the concrete mix, expressed as SO3 should notexceed 4 percent of the mass of cement in the mix. The standard also gives recommendations for the type of cement,

maximum free water cement ratio, minimum cement content required at different sulphate concentrations in near neutral

ground water having a pH of 6 to 9.


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1. Requirements for Concrete Exposed to Sulphate Attack : Table 22(Ref: IS 456:2000 Table 4)

Concentration of sulphates,expressed as SO3

Dense fully compacted

concrete made with 20mmnominal Max. sizeaggregatesSl

No.Class

TotalSO3 %

SO3 in 2:1water: SoilExtract, g/l

In Groundwater, g/l

Type of Cement

Min.cementcontent

Max. freewater-cement

ratio

1 ITraces(


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V. Cover to reinforcement

It is observed that inadequate cover to the reinforcement is one of the major factors leading to early deterioration ofreinforced and prestressed concrete structures. Provision of appropriate cover to all reinforcements and ensuring that thequality of the cover concrete including that of the cover blocks is same as that of the core concrete to go a long way inmitigating the problem of early deterioration. IS 456:2000 gives detailed guidelines on provision of cover.

The code defines nominal cover as the design depth of concrete cover to all reinforcement, including links. In order to

meet durability requirements, the cover for normal weight concrete, including links as specified by the code is given inbelow table.

1. Nominal cover to meet durability requirements (Ref: Table 16, IS 456:2000): Table 23

Exposure

Nominal cover not less than

( mm)

Mild 20

Moderate 30

Severe 45

Very Severe 50

Extreme 75

Notes:

1. For main reinforcement up to 12 mm diameter bar for mild exposure conditions, normal cover may be reduced by5 mm.

2. For Exposure conditions of severe and very severe, cover may be reduced by 5 mm, where concrete grade isM35 and above.

3. Unless specified otherwise, actual concrete cover should not deviate from the required nominal cover by +10mm.

The code specifies that for longitudinal bar in a column nominal cover shall not be less than 40 mm, or less than the

diameter of the bar. In those columns of minimum dimension of 200 mm or less, where the reinforcing bars do notexceed 12 mm diameter, a nominal cover of 25 mm may be used. For footings minimum cover shall be 50mm.


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VI. Cover for Fire resistance:For the first time, IS 456 has specified cover for fire resistance. The nominal cover of normal weight aggregate concrete

shall be provided to all reinforcement, including links to meet fire resistance as specified in Table.

1. Nominal cover to meet specified period of fire resistance: Table 24(Ref: Table 16A of IS 456:2000)

Nominal cover

Beams Slabs RibsFire

resistance,hr

Simplysupported

ContinuousSimply

supportedContinuous

Simplysupported

continuous

Columns

0.5 20 20 20 20 20 20 40

1.0 20 20 20 20 20 20 40

1.5 20 20 25 20 35 20 40

2.0 40 30 35 25 45 35 40

3.0 60 40 45 35 55 45 40

4.0 70 50 55 45 65 55 40

Note:

1. The nominal covers given relate specifically to the minimum member dimensions given in fig 1 of IS 456 : 2000 (page34)2. Cases that lie below the bold line require additional measures necessary to reduce risk of spalling.


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C. CONCRETE MIX DESIGN

Different ingredients of concrete need to be mixed in appropriate proportions during the production of concrete. This can

be done either by volume or by weight, the latter being more precise and scientific. It is essential that concrete mixes bedesigned for a particular set of given ingredients to produce specific properties of concrete in the most economical

ways.

Rational proportioning of the ingredients of concrete, generally referred as mix proportioning or mix designing is aprocess by which one can arrive at the right combination of cement, aggregates, water and admixtures (if any) forproducing concrete to satisfy given specifications. The purpose of mix proportioning is to obtain a product that willperform to certain predetermined requirements.

The objective of mix design is to ensure that the concrete:

1. Complies with the compressive strength as laid down in the specifications2. Conforms to the specified durability requirements to resist the environment in which the structure will be

serviceable during its design life

3. has adequate workability4. is capable of being mixed, transported, laid down and compacted as efficiently as possible5. And last but not least, be as economical as possible.

To achieve an optimum mix proportion to fulfill the above parameters is a challenging task. The work of mix designing isa trial and error exercise, which need to be carried out by an experienced person in a laboratory.

The concrete mix needs to be designed to produce the grade of concrete having characteristic strength not less than the

appropriate values given in Table 20. The mix also needs to be designed for adequate workability so that it could bebeing mixed, transported, laid down and compacted as efficiently as possible. Depending upon the placing conditions,European Standard (DIN EN206) has recommended different range of workability and these are given in Table 25. Inaddition, the concrete has to satisfy the durability requirements. Some of these requirements, namely the minimumcement content, maximum water cement ratio and minimum grade of concrete, as specified by IS 456 are already given

in Table 17. It may be noted that the code has specified the minimum grade of concrete to be not less than M20 forreinforced concrete constructions.

a. Slump suitable for different placing conditions : Table 25(Ref: DIN EN 206)

USE OF CONCRETESLUMPCLASS

SLUMP RANGEin mm

Kerb laying S1 10 to 40

Floor and hand placed pavements S2 50 to 90

Mass concrete foundations, Normal reinforced concrete in

slabs, beams and columns and Pumped concreteS3 100 to 150

Trench filling, In situ piling S4 160 to 210

Self compacting concrete S5 >220


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I. Guidelines for concrete mix proportioning1. Data for Mix ProportioningThe following data are required for mix proportioning of a particular grade of concrete:

a. Grade designationb. Type of cementc. Maximum nominal size of aggregated. Minimum cement contente. Maximum water cement ratiof. Workabilityg. Exposure conditions as per Tables 4 and 5 of IS456h. Maximum temperature of concrete at the time of placingi. Method of transporting and placingj. Early age strength requirements, if requiredk. Type of aggregates,l. Maximum cement content andm. Whether an admixture shall or shall not be used and the type of admixture and the condition of use.

2. Target Strength for Mix proportioningIn order that not more than the specified proportion pf test results are likely to fall below the characteristics strength,the concrete mix has to be proportioned for somewhat higher target average compressive strength fck. The marginover characteristic strength is given by the following relation:

fck = fck+ 1.65 * Swhere

fck = target mean compressive strength at 28 days.

fck = characteristics compressive strength at 28 days, andS = Standard deviation

Standard Deviation

The standard deviation for each grade of concrete shall be calculated separately.

Standard deviation based on test strength of sample

1. Number of test results of samples: The total number of test strength of samples required to constitute anacceptable record for calculation of standard deviation shall be not less than 30. Attempts should be made toobtain the 30 samples (taken from site), as early as possible, when a mix is used for the first time.

2. In case of significant changes in concrete: When significant changes are made in the production of concretebatches (for example changes in the materials used, mix proportioning, equipment or technical control), thestandard deviation value shall be separately calculated for such batches of concrete.

3. Standard deviation to be brought up to date: The calculation of the standard deviation shall be brought upto date after every change of mix proportioning.


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Assumed Standard deviation

Where sufficient test results for a particular grade of concrete are not available, the value of standard deviationgiven in table 26 may be assumed for the proportioning of mix in the first instance. As soon as the results of

samples are available, actual calculated standard deviation shall be used and the mix proportioned properly.However, when adequate past records for a similar grade exist and justify to the designer a value of standarddeviation different from that shown in table 26, it shall be permissible to use that value.

Table 26: Assumed Standard Deviation(Ref: Table 1 of IS 10262:2007)

Grade of ConcreteAssumed standard deviation

N/mm2

M10

M153.5

M20

M254.0

M30

M35

M40

M45

M50

M55

5.0

a. Selection of Mix Proportions1. Selection of water cement ratioSince different cements, supplementary cementitious materials and aggregates of different maximum size,grading, surface texture, shape and other characteristics may produce concretes of different compressivestrength for the same free water cement ratio, the relationship between strength and free water cement ratio

should preferably be established for the materials actually to be used. In the absence of such data, thepreliminary free water cement ratio (by mass) corresponding to the target strength at 28 days may be selected

from the established relationship if available. Otherwise, the table 17 may be used as a starting point for selectionof water cement ratio for respective environment exposure conditions.

Note--- The supplementary cementitious materials that is , mineral admixtures shall also be considered inwater cement ratio calculations in accordance with table 17.

The free water cement ratio selected should be checked against the limiting water cement ratio for therequirements of durability and the lower of the two values adopted.


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Table 28: Volume of Coarse Aggregate per unit volume of concrete for Different Zones of FineAggregate (Ref: Table 3 of IS10262:2007)

Volume of Coarse Aggregate** per unit volume of concretefor different zones of Fine AggregateNominal maximum size

of Aggregate in mm

Zone IV Zone III Zone II Zone I

10 0.50 0.48 0.46 0.44

20 0.66 0.64 0.62 0.60

40 0.75 0.73 0.71 0.69

** Volumes are based on aggregates in saturated surface dry condition

For more workable concrete mixes which is sometimes required when placement is by pump or when theconcrete must be worked around congested reinforcing steel, it may be desirable to reduce the estimated coarseaggregate content determined using Table 28 up to 10 percent. However, caution shall be exercised to assurethat the resulting slump, water cement ratio and strength properties of concrete are consistent with the

recommendations of IS 456 and meet project specification requirement as applicable.

2. Estimation of Fine Aggregate ProportionWith the completion of above procedure, all the ingredients have been estimated except the coarse and fineaggregate content. These quantities are determined by finding out the absolute volume of cementitious material,water and the chemical admixture; by dividing their mass by their respective specific gravity, multiplying by1/1000 and subtracting the result of their summation from unit volume. The values so obtained are divided intocoarse and Fine Aggregate fractions by volume in accordance with coarse aggregate proportion alreadydetermined. The coarse and fine aggregate contents are then determined by multiplying with their respectivespecific gravities and multiplying by 1000.

3. Combination of Different Coarse Aggregate FractionsThe coarse aggregate used shall conform to IS 383. Coarse aggregates of different sizes shall be combined insuitable proportions so as to result in an overall grading conforming to Table 2 of IS 383 for particular nominalmaximum size of aggregate.

Determination of mass per m3 yield and cement factor of freshly mixed concrete shall be carried out as per IS1199.

c. Trial MixesThe calculated mix proportions shall be checked by means of trial batches.Workability of the trial mix no.1 shall be measured. The mix shall be carefully observed for freedom from segregation andbleeding and its finishing properties. If the measured workability of trial mix no.1 is different from the stipulated value,

the water and /or admixture content shall be adjusted suitably. With this adjustment, the mix proportion shall berecalculated keeping the free water cement ratio at the pre selected value, which will comprise trial mix no.2. In additiontwo mor trial mixes no.3 and 4 shall be made with the water content same as trial mix no.2 and varying the free watercement ratio by +/- 10 percent of the pre selected value.

Mix no.2 to 4 normally provides sufficient information, including the relationship between compressive strength and watercement ratio, from which the mix proportions for field trials may be arrived at. The concrete for field trials shall beproduced by methods of actual concrete production.


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D. An Illustrative example of concrete mix proportioning is given below.

DESIGN MIX

STIPULATIONS FOR PROPORTIONING

01. Grade designationM20

02. Type of CementOPC 53 grade

03. Maximum nominal size of aggregate20 mm

04. Minimum cement content300 kg/m3

05. Maximum water cement ratio0.55

06. Workability 130 mm (Slump)

07. Exposure ConditionMild

08. Method of concrete Placing Pumping

09. Degree of Supervision Good

10. Type of Fine AggregateNatural River Sand and

Crushed Rock fines

11. Type of Coarse AggregateCrushed Rock

12. Maximum cement content450 Kg/m3

13. Type of Chemical AdmixtureSuper plasticizer.

14. Brand of AdmixtureBASF Rheobuild 4839

TEST DATA FOR RAW MATERIALS

1. Cement used OPC 53grade conforming IS12269

2. Specific gravity of Cement 3.15

3. Specific gravity of coarse aggregate 2.65

4. Specific gravity of Fine aggregate 2.61

5. Water absorption of coarse aggregate 0.5 percent

6. Water absorption of Fine aggregate 1.0 percent


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7. Sieve analysis of Fine aggregate

Cumulative Percentagepassing

IS SieveDesignation

River Sand Stone Sand

Cumulative % passingwhen river sand & stonedust are mixed in 70:30

Requirements forZone II as per

IS:383-1970(% Passing)

4.75 mm 98.5 100 98.95 90 100

2.36 mm 93.3 100 95.31 75 100

1.18 mm 66.3 77 69.51 55 90

600 microns 41.0 56 45.5 35 59

300 microns 14.3 33 19.91 8 30

150 microns 7.4 6 6.98 0 10

8. Sieve analysis of Coarse aggregate

IS SieveDesignation

Cumulative% Passing

20mm

Cumulative% Passing

12.5 mm

Cumulative % passingwhen 20mm&12.5mm

are mixed in 58:42 ratio

Requirements ofCum. % passing

for 20mm gradedagg . as perIS:383-1970

20 mm 98.25 100 98.98 95 100

16 mm 54.25 100 73.46 ---

12.5 mm 21.75 95.84 52.86 ---

10 mm 2.75 61.68 27.50 25 - 55

4.75 mm ---- 0.20 0.08 0 - 10

Design Mix calculation for M20 grade

Target Strength for Mix Proportioning

Fck= Fck+ 1.65 * S

WhereFck= target average compressive strength at 28 days.Fck= Characteristics compressive strength at 28 days.S = Standard deviation

From IS 10262:2007, Table 1, standard deviationS = 4 N/mm2

Therefore, Target Strength = 20 + 1.65*4 =26.66N/mm2


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Selection of Water-Cement Ratio

From IS 456:2000, Table 5, Maximum water cement ratio = 0.55Based on experience, adopt water cement ratio as 0.53

0.53 < 0.55, hence OK.

Selection of Water Content

From IS 10262:2007, Table 2, Maximum water content for 20 mm aggregate = 186 Kg (for 25 mm to 50mm slumprange)

Estimated water content for 100 mm slump =186 + 3/100 * 186 =192 Kg

As super plasticizer is used, the water content can be reduced up to 30 percent.

Based on trials with super plasticizer water content reduction of 17 percent has been achieved. Hence the arrivedwater content = 192 * 0.83 =159.36 Kg

Calculation of Cement content

Water cement ratio = 0.53Cement content =159/0.53 =300 Kg/m3

Check for exposure condition from IS 456, Table 5

Minimum cement content 300 Kg/m3Hence, OK.

Proportion of volume of coarse aggregate and Fine aggregate content

From Table 3, Volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate Zone II =0.62

For Pumpable concrete these values should be reduced by 10 percent

Therefore volume of coarse aggregate = 0.62*0.93 = 0.5766

Volume of fine aggregate content = 1 - 0.5766 = 0.4234

Mix Calculations

Volume of Concrete = 1 m3

Volume of cement = (Weight. of cement/Sp.gravity of cement) * (1/1000)= (300/3.15) * (1/1000)=0.0952 m3

Volume of Water = (Weight. of water/Sp.gravity of water) * (1/1000)= (159/1) * (1/1000)=0.159 m3


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Volume of chemical = (Weight. of Admixture/Sp.gravity of Admixture) * (1/1000)

Admixture = (1.8/1.19) * (1/1000)(@0.6% by mass of =0.0015m3

Cement)

Volume of all in = (1-(0.0952+0.159+0.0015))

Aggregate =0.7443 m3

Mass of Coarse =0.7443 * 0.5766 * Sp.gravity of C.A * 1000Aggregate =0.7443 * 0.5766 * 2.65 * 1000

=1137.28 say1130 Kg

Mass of Fine =0.7443 * 0.4234 * Sp.gravity of F.A * 1000Aggregate =0.7443 * 0.4234 * 2.61 * 1000

=822.50 say810 Kg

MATERIAL REQUIRED FOR M20 GRADE - ONE CUM OF CONCRETE

01. Cement 300 Kg

02. Free Water 159 Kg.

03. River Sand 570 Kg.

04. Crushed Rock Fines 240 Kg

05.

COARSE AGGREGATE

20 mm

12 mm

660 Kg

470 Kg

06. Admixture 1.80Kgs.

07. Water for Absorption (CA & FA ) 14.0 Kg

08. Total Water 173 Kg

Free Water Cement Ratio - 0.53

Note:1) Weight Batching correction for Surface Moisture in Aggregates Should be Carried out Regularly.


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E. Making Good Concrete

The following points pertaining to materials and workmanship are important.

1. Cement:Select the appropriate type of cement. Use fresh cement of approved quality. Store it properly toprevent deterioration.

2. Aggregates:use well graded aggregates, free from silt, organic matter and other undesirable impurities. Storeaggregates properly and dont allow different fractions to mix together.

3. Water:Use potable quality of water. It should be free from impurities and harmful ingredients. It should bewithin the tolerable limits specified by BIS.

4. Chemical Admixtures:Use appropriate type of admixtures in correct dosages, as recommended by themanufacturer, and or confirmed by laboratory tests. Ensure that the admixtures are compatible with the cementand other ingredients. Trial mixes should be mad, if necessary. Ensure that there is no batch to batch variation inquality.

5. Durability:Ensure that the durability requirements like minimum cement content, maximum water cement ratio,grade of concrete, cover to reinforcement, etc as specified in IS 456:2000 are satisfied for the given ExposureConditions.

6. Mix Design:Use of properly designed concrete mix is essential for large jobs. BIS permits use of nominal mixesfor works using concrete grades of M 20 and below.

7. Batching:Batching materials by weight is preferable and the BIS emphasize its use. If batched on volume basis,use measurement boxes in units of 35 liters, which is the capacity of one 50 kg bag of cement. The cementshould, in any case, be batched only by weight and preferably by whole bags. Allowance for water on account ofbulking of sand and surface water carried by coarse aggregates is essential.

8. Quantity of mixing water:Use the minimum quantity of mixing water, consistent with the degree ofworkability required to enable easy placing and compaction of concrete.

9. Mixing:Use a mixing machine. There should be uniform distribution of the material until the mass is uniform incolour and consistency. Avoid hand mixing.

10.Transportation:Avoid drying out, segregation, setting, loss of any ingredients, and ingress of foreign matter orwater during transportation.

11.Placing:Place concrete in its final position before setting starts: avoid segregation of materials and disturbanceof the forms: lay concrete in suitable layers without any break of continuity; maximum free-fall of concrete shouldnot exceed 1.5m.

12.Compaction:Ensure thorough compaction, particularly around the reinforcement and embedded fixtures andinto the corners of the formworks. Use internal/external form vibrators: avoid under and over vibration.

13.Finishing:Finish after a little stiffening.14.Curing:Keep concrete continuously moist, preferably for a period of 7 to 14 days.15.Formwork:Use formwork which is rigid and closely fitted, with sufficient strength to support the wet concrete

and to prevent loss of slurry. The face of the form work should be treated with form release agents.

16.Reinforcement:Make sure that the reinforcement used is free from loose rust, oil, paint, mud, etc. Thereinforcement shall be placed and maintained in position by providing proper cover blocks, spacers, supportingbars, etc. Reinforcement shall be placed and tied such that concrete placement is possible without segregation,and compaction possible by an immersion vibrator.


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F. A Laboratory Manual for Quality Control of Concrete

I. List of Laboratory Testing for Quality concrete

a. Cement

1 Specific gravity of Cement

2 Fineness of Cement

3 Standard Consistency and Setting Time

4 Compressive strength of Cement

b. Aggregates

1 Specific gravity and Water absorption of Fine Aggregate

2 Specific gravity and Absorption of Coarse Aggregate

3 Unit Mass and Voids of concrete Aggregates

4 Moisture content of Concrete Aggregates

5 Fineness modulus and Grain size distribution

6 Silt Content

7 Bulking of Sand

8 Flakiness and Elongation Indices of Coarse Aggregate

C. Concrete

1 Slump Test

2 Strength of Cement concrete


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a. CEMENT:1. Specific Gravity of Cement

Object

To determine the specific gravity of cement.

Apparatus

Weighing balance, specific gravity bottle, kerosene free from water, etc.

Theory

Specific gravity is normally defined as the ratio between the mass of a given volume of material and massof an equal volume of water. One of the methods of determining the specific gravity of cement is by the useof liquid such as water free kerosene which does not react with cement.

Procedure

1. Weigh the specific gravity bottle dry. Let the mass of empty bottle be W1.2. Fill the bottle with distilled water and weigh the bottle filled with water. Let the mass be W2.3. Wipe dry the specific gravity bottle and fill it with kerosene and weigh. Let this mass be W3.4. Pour some of the kerosene out and introduce a weighed quantity of cement (about 50 grams) into

the bottle. Roll the bottle gently in inclined position until no further air bubbles rise to surface. Fill thebottle to the top with kerosene and weigh it. Let this mass be W4.

5. Let the Mass of cement be W5.6. From these data calculate the specific gravity of the cement.

Observations and calculations

1 Mass of empty bottle W1, gm

2 Mass of bottle + water W2, gm

3 Mass of bottle + Kerosene W3, gm

4 Mass of cement W5, gm

5 Mass of bottle + cement + kerosene W4, gm

6 Sp. gr. of kerosene, s = ( W3-W1)/(W2-W1)

7 Sp. Gr. of cement, S = W5(W3-W1)/(W5+W3-W4)(W2-W1)


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2. Fineness of cementObject

To determine the fineness of a cement sample by sieving through a 90 micron IS Sieve.

Theory

The degree of fineness of cement is a measure of the mean size of the grains in cement. The rate of hydrationand hydrolysis and consequent development of strength in cement mortar depends upon the fineness of cement. To

have same rate of hardening in different brands of cement, the fineness has been standardized. The finer cement hasquicker action with water and gains early strength though its ultimate strength remains unaffected. However, theshrinkage and cracking of cement will increase with the fineness of cement.

Apparatus

90 micron IS sieve, rice plate, weighing balance, bristle brush (25 or 40 mm brush with 250mm handle).The sieve has mesh openings of 0.087 mm.

Procedure

1. Weigh accurately 100 gm of cement in a plate and transfer it to a clean dry IS test sieve and break down anyair set lumps.

2. While holding the sieve and pan in both hands, sieve with gentle wrist motion until most of the fine materialhas passed through and the residue looks fairly clean. This usually requires three to four minutes.

3. Place the cover on the sieve and remove the pan. With sieve and cover held firmly in one hand, the otherside of the sieve is tapped with the handle of the brush which is used for cleaning the sieve. Sweep clean theunderside 0f the sieve.

4. Empty the pan and wipe it clean with a cloth. Replace the sieve in the pan and remove the cover carefully.Return any coarse material that had been caught in the cover during tapping the sieve.

5. The sieving is continued as described above for 15 minutes, rotating the sieve continuously throughout thesieving operation, involving no danger of spilling the cement.

6. Weigh the residue.Observations and calculations

1 Mass of cement taken on IS sieve Gm 100 100

2 Mass of residue after sieving, Gm

3 Fineness = mass of residue in gms / 100 percent

Result

Residue of cement is _________ percent.

Precautions

a. Any air set lump in the sample should be broken down with fingers, but do not rub on the sieve.b. The sieve must be cleaned thoroughly before starting the experiment.c. The care should be taken to ensure that no cement is spilled. After sieving all residues must be taken out

carefully and weighed.

References

1. IS 4031 (part 1):1996 --- Procedure for conducting the test


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90 micron IS sieve with Pan and Lid


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3. Standard Consistency and Setting TimeObject

To determine1. Standard consistency and2. Initial and Final setting times of a given cement sample by vicat apparatus.

Theory and scope

1. Standard ConsistencyThe object of conducting this test is to find out the amount of water to be added to the cement to get a paste ofnormal consistency, i.e., the paste of a certain standard solidity, which is used to fix the quantity of water to bemixed in cement and before performing tests for setting time, soundness and compressive strength.

2. Setting TimeIn order that the concrete may be placed in position conveniently, it is necessary that the initial setting time of

cement is not too quick and after it has been laid, hardening should be rapid so that the structure can be madeuse of as early as possible. The initial set is a stage in the process of hardening after which any crack that mayappear will not re-unite. The concrete is said to be finally set when it has obtained sufficient strength andhardness.

Apparatus

Vicat apparatus with vicat plunger, vicat needles and vicat mould, gauging trowel, measuring jar (100 to 200mlcapacity), weighing balance, stop watch, rice plates, rubber gloves and glass plates.

The Vicat apparatus consists of a frame bearing a movable rod with a cap at one end and detachable needle orplunger at the other end. The movable rod carries an indicator which moves over a graduated scale having

graduations in mm from zero to 40 on either direction to measure the vertical movement of the plunger. Thescale is attached to the frame. The movable part with all attachments, i.e., the cap and rod with needle or

plunger, weighs 300gm.

The Plunger required for determining the consistency, is of polished brass 10mm in diameter and 50 mm longwith the lower end flat and small projection at upper end for insertion into movable rod.

The Needle A, required for determining the initial setting time, is 1mm square or 1.13 mm in diameter with thelower end being flat.

The Needle B, required for determining the final setting time, is the same as needle A but with a metal

attachment hollowed out so as to leave a circular cutting edge 5mm in diameter, the end of the needle projectsby 0.50 mm.

The vicat mould for cement paste consists of a split ring 80mm in diameter and 40mm in height and rests on a

non-porous plate.


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Vicat Apparatus with Mould, Plunger and needle A & B

Procedure

Standard Consistency

The standard consistency of a cement paste ( the amount of water expressed as percentage by mass of

the dry cement) which permits the Vicat plunger to penetrate to a height 5 to 7mm from the bottom of the vicatmould when the cement paste is tested as described below.

1. For preparing one mould take 400gm of cement passing 850-micron IS sieve and prepare a paste of cement witha weighed quantity of water (100ml) taking care that the time of gauging is between 3 to 5 minutes. The gauging

time is counted from the time of adding water to the dry cement until commencing to fill the mould.2. Fill the vicat mould resting upon non-porous plate with this paste. After completely filling the mould, smooth off

the surface of the paste by single movement of palm making it level with the top of the mould. The mould maybe slightly shaken to expel air.

3. Place the test block in mould with the non porous resting plate under the rod attached with the plunger. Lowerthe plungers gently to touch the surface of the test block and release it quickly, allowing it to sink into the paste.

4. Prepare the trial paste with varying percentage of water(firstly at an interval of 4%, that is of 24%,28%, and32% and then at an interval of 1% and 0.25% between the percentage range determined by the previous test)

and test as described above until the amount of water necessary for the standard consistency as defined isobtained.

Setting Time of Cement

1. Prepare a neat cement paste by gauging the cement with 0.85 P water, where P = standard consistency as foundbefore. The gauging time is again kept between 3 to 5 minutes. Start the stop watch at the instant when thewater is added to the cement.

2. Fill the Vicat mould and smooth off the surface of the paste making it level with the top of the mould. Thecement block thus prepared is known as test block.

3. For the determination of initial setting time, place the test block confined in the mould and resting on non-porousplates under the rod attached with the needle A, lower the needle gently in contact with the surface of the testblock and release quickly, allowing it to penetrate into the test block.

4. Repeat this procedure until the needle fails to pierce the block for about 5mm measured from the bottom of themould. The period elapsed between the time when water is added to the cement and the time at which theneedle fails to pierce the test block by about 5 mm is the initial setting time.

5. For the determination of Final setting time replace the needle A of the vicat apparatus by the needle with anannular attachment B. The cement is considered finally set when, upon applying the needle B gently to thesurface of the test block, the needle makes an impression thereon, while the attachment fails to do so. In theevent of scum forming on the surface of the test block, use the underside of the block for the determination offinal setting time.


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Observations and Calculations

For Standard Consistency

Mass of cement taken for one mould = 400 gm.

1 Percentage of water

2 Initial reading

3 Final reading

4 Height not penetrated, mm

Note: Initial reading is the indicator reading when the lower end of plunger touches the bottom of non poroussurface of the mould.

For Setting Time

Mass of cement taken = 400 gm

Mass of water taken = 0.85 * P * 400 gm.

1 Time in Minutes

2 Initial reading

3 Final reading

4 Height not penetrated, mm

Results

1. Standard Consistency of cement = __________ percent2. Initial setting time of cement =_______________ percent3. Final setting time of cement =________________ percent

Precautions

1. The experiment should be conducted at a room temperature of 27 +- 20C and at a relative humidity of 90percent.

2. After a half minute from the instant of adding water, it should be thoroughly mixed with fingers for at leastone minute. A ball of this paste is prepared and then it is pressed into the test mould, mounted on the non-

porous plate.3. The plunger should be released quickly without pressure or jerk, after the rod is brought down to touch the

surface of the test block.

4. For each repetition of the experiment fresh cement is to be taken.5. Plunger should be cleaned during every repetition and make sure that it moves freely and that there are no

vibrations.

References

1. IS 4031 (part 4): 1988 --- Procedure for conducting Standard Consistency2. IS4031 (part 4): 1988 --- Procedure for conducting Initial and Final setting Time3. IS 5513:1996 --- Specification for Vicat Apparatus

4. IS 10086:1982 --- Specification for Gauging Trowel


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4. Compressive Strength of CementObject

To determine the compressive strength of 1: 3 cement-sand mortar cubes after 3 days, 7 days and 28 dayscuring.

Scope

The compressive strength of cement mortar is determined in order to verify whether the cement conforms to IS

specification (IS 12269 & IS 8112) for 53 & 43 grades respectively) and whether it will be able to develop therequired compressive strength of concrete. According to IS, the ultimate compressive strength of cubes of cementsand mortar of the ratio 1 : 3, containing ((P/4)+3) percent of water should be as follows:

Sl No. Age in days For 53 grade For 43 grade

1 After 3 days Not less than 27 Mpa Not less than 23 Mpa



Apparatus

Compressive testing machine, cube moulds, vibrating machine, crucible for mixing cement and sand, measuringcylinder, trowels, non-porous plate and weigh balance.

Description of the Apparatus

Vibrating Machine

Vibrating machine (12000+/- 400 rpm, amplitude of vibration 0.055 mm, and 3phase motor with automatic cut-off).

It consists of a heavy frame, on one side of which is fixed an electric motor and on the other side there is a set offour springs. Above these springs is fixed a mould on another frame and this mould is removable. With the framecarrying mould, a pulley is attached and the belt runs on the pulley and the motor. The mould is fitted with adetachable hopper at the top. Through the hopper mortar or concrete can be put into the mould without any loss ofsample. A weight is attached to the frame to keep the mould in balance. When motor is started, the belt moves the

pulley and gives vibrations to the mould at the rate of 12000 +/- 400 cycles per minute. These vibrations are simpleharmonic at 90o out of phase. The normal running speed of electric motor is 12000 +/- 400 rpm. Due to the loadattached to the frame, the C.G. of machine falls near the weight.

Cube Moulds

The moulds are of special shape and dimensions. The cube mould for compression test has 70.5 mm side (5000 mm2

face). It is constructed in such a way that it can be split up in parts in order to take out the cube without anydamage. The base plate is non-porous and of such a size that there should be no leakage of water from the bottom.

The side of the cube mould is 70.5 +/- 1.27mm and angle between adjacent interfaces should be 90 +/- 0.5 degrees.


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Vibrating Machine and Cube moulds of size 7.05 cm

Three Types of Standard Sand

Procedure

1. Calculate the material required. The material for each cube shall be mixed separately and the quantities ofcement and standard sand shall be as follows:

Cement = 200 gmStandard sand = 600 gmWater = ((P/4) + 3) percent of total mass

Where P is percentage of water for standard consistency.

2. Place the mixture of cement and standard sand in the proportions of 1:3 by mass on a non-porous plate or chinadish and mix it dry with a trowel for one minute and then with water until the mixture is of uniform colour. The

percentage of water to be used shall be ((p/4) +3). The time of mixing (gauging) in any event shall not be lessthan 3 minutes and if the time taken to obtain a uniform colour exceeds 4 minutes, the mixture shall be rejectedand the operation is repeated with a fresh quantity of cement, sand and water.

3. Place the assembled mould on the table of the vibrating machine and firmly hold it in position by means ofsuitable clamps. Securely attach the hopper at the top of the mould to facilitate filling and this hopper shall notbe removed until completion of the vibration period.

4. Immediately after mixing the mortar as explained above, fill the entire quantity of mortar in the hopper of thecube mould and compact by vibration. The period of vibration shall be 2 minutes at the specified speed of 12000+/- 400 cycles per minute.


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5. Remove the mould from the machine and keep it at a temperature of 27 +/- 2 0C in an atmosphere of at least 90percent relative humidity for 24 hours after completion of vibrations.

6. At the end of this period, remove the cube from the mould and immediately sub merge it in clean and fresh wateand keep there until taken out just prior to breaking. The water in which the cubes are submerged shall berenewed after every 7 days and be maintained at a temperature of 27 +/- 2 0C. Keep the cubes wet till they areplaced in machine for testing.

7. Test the specimens at the required periods.Observations and calculations

Sl No.Grade ofcement

Age indays

Weightof cube

(Kg)

Failure Load(KN)

Compressivestrength N/mm2

Avg. Comp.StrengthN/mm2

1 3

2 3

3 3

4 7

5 7

6 7

7 28

8 28

9 28

Precautions

1. The mortar shall not be compressed into the moulds with hand.2. Neglect the results which fall outside by 15 percent of the average results on either side.3. The cubes should be tested on their sides and not on their faces.4. The inside of the cube mould should be oiled to prevent the mortar from adhering to the sides of the mould.5. The size of sand particles should be such that not more than 10 percent by mass shall pass a 60 micron IS

sieve and shall completely pass through an 85 micron IS sieve.

6. The time of wet mixing shall not be less than 3 minutes. If the time of mixing exceeds 4 minutes to bring auniform colour, the mixture shall be rejected and fresh mortar should be prepared.

References

1. IS 4031 (part 6)-1988 ---- Procedure for conducting the test2. IS 10080 :1982 ---- Specification for vibration Machine3. IS 10086 :1982 ---- Specification for moulds & gauging Trowel4. IS 650:1991 ---- Specification for Standard Sand


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b.AGGREGATE1. Specific Gravity and Water Absorption of Fine AggregateObject

Determination of specific gravity and water absorption of Fine aggregate.

Theory and Scope

The specific gravity of an aggregate is defined as the ratio of the mass of a given volume of sample to the massof an equal volume of water at the same temperature.

The specific gravity of fine aggregate is generally required for calculations in connection with concrete mixdesign, for determination of moisture content and for the calculations of volume yield of concrete. The specificgravity also gives information on the quality and properties of aggregate. Departure of specific gravity from its

standard value indicates change in shape and grading.

AbsorptionIt influences the behavior of aggregate in concrete in several important aspects. A highly

absorptive aggregate, if used in dry condition, will reduce effective water cement ratio to an appreciable extentand may even make the concrete unworkable unless a suitable allowance is made. Hence determination ofabsorption of aggregate is necessary to determine net water cement ratio.

Apparatus

Pycnometer bottle or flask, weigh balance, conical mould, metal tray and drying oven to operate between 100-1100C

Pycnometer Bottle

Procedure

1. Calibrate the flask by weighing it empty and fill with water at room temperature. Roll and agitate theflask gently in an inclined position, to eliminate air.

2. Take a sample of fine aggregate and soak it in water and keep it for 24 +/- 0.5 hours. The temperatureshould be 27 +/- 50C.

3. Take out and spread the sample (approximately 1.5 kg) on a clean flat surface exposed to gently movingcurrent of warm air until the material just reaches free running condition ( flowing freely).

4. Place the sand loosely in conical mould and tamp it on surface 25 times. Lift the mould vertically. If thesand retains its shape, it means free surface moisture is present. Continue the drying with constantstirring until the cone of sand slumps on the removal of the mould. This indicates that sand has reached

a surface dry condition.5. Immediately weigh 500 gm of saturated surface dry sand in the flask.


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6. Fill the flask with water to the top of the cone. Roll the flask in an inclined position to eliminate all airbubbles and replace with water by means of fountain pen filler.

7. Wipe the flask dry and weigh it accurately.8. Calculate the specific gravity.

Absorption Test

1. Weigh the remaining 1000 gm of saturated surface dry sand in the tray of known weight.2. Dry the sample in an oven at 100-1100C for 24 hours3. Weigh the dry sand with tray.4. Calculate the absorption capacity as the percentage of oven dry Mass.

Bulk specific gravity = W2/ (W2-(W3-W1)

Percentage absorption = (W4-W5)*100/W5

Observations and Calculations

Mass of empty dry flask, W gm

Mass of flask + water, W1 gm

Mass of saturated surface dry sample, W2 gm

Mass of flask + sample + water, W3 gm

Mass of empty tray, We gm

Mass of tray + saturated surface dry sample, Ws gm

Mass of saturated surface dry sample, (We Ws) = W4 gm

Mass of tray + oven dry sample, Wo gm

Mass of oven dry sample, (Wo We) = W5 gm

Bulk specific gravity

Absorption percentage

Precautions

1. The entire sample should be frequently stirred to secure uniform drying.2. The air trapped in the aggregate should be brought to surface by rolling the flask in inclined position.3.

All weighing should be accurate to the nearest gm.4. Sand should not be allowed to stick to the sides of the jar or flask.

5. The results of different repetitions should not differ more than 0.02 for specific gravity and 0.005 percentfor absorption.

References:

1. IS 2386 part III 1963 ----- Methods of Test for Aggregates for Concrete


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2. Specific gravity and Absorption of Coarse AggregateObject

Determination of specific gravity and absorption of coarse aggregate

Scope

For design of concrete mix, information should be available about the specific gravity of the aggregates. Specificgravity of an aggregate gives valuable information on its quality and properties. If the specific gravity is above orbelow that normally assigned to a particular type of aggregate, it may indicate that shape and grading ofaggregate has altered.

Apparatus

Weigh balance, Wire basket 200 mm in diameter and 200 mm height of 4.75mm IS sieve net, water tub forimmersing the wire basket in water, suitable arrangement for suspending the wire basket from centre of scalepan of balance and absorbent cloth for surface drying of the sample.

Procedure

1. Take about 5 kg of aggregate by method of quartering; rejecting all material passing a 10 mm IS sieve.2. Wash thoroughly to remove the dust etc. from the surface of particles. Dry to constant mass at a

temperature of 105 +/- 50C.3. Immerse the sample in water at 22 to 320C for a period of 24 hours.4. Remove the aggregate from water and roll the same in a large piece of an absorbent cloth until all visible

films of water are removed, although the surface of particles will still appear to be damp.5. Now, weigh 3 kg of this sample in the saturated surface dry condition and note down the mass as W1 gm.6. Place the weighed aggregate immediately in the wire basket and dip it in water. Weight this basket with

aggregate, while keeping it in water, with the help of the b

Documents

Concrete Annexure