Project Report OnMix Design of Concrete And Analysis of

Effect Of Reinforcement On Flexural Strength Of Concrete

Submitted as a part of short term trainingat

Raja Ramanna Centre for Advanced Technology,Department of Atomic Energy, Indore 452013

Under the guidance ofMr. GOVIND PARCHANI

ByMs. Saloni Bhand

Sushila Devi Bansal College Of Engineering

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A.B. Road, Umaria, Rau, Indore, M.P. - 453331

Government of IndiaDepartment of Atomic Energy

Raja Ramanna Centre for Advanced Technology

CERTIFICATE(To Whomsoever It may Concern)

This is to certify that Ms. Saloni Bhand , student of Sushila Devi Bansal College of Engineering has successfully completed project entitled “ Mix Design Of Concrete and Analysis of Effect of Reinforcement on Flexural Strength of Concrete“ from 15th May , 2013 to 31st July , 2013 at Civil Section , RRCAT, Indore.I wish to add that she is very sincere and hardworking and wish her all the best in his future endeavour.

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Date: Project Guide:

Mr. Govind Parchani. Suptd. Engineer (GP),

Scientific Officer (H)

Government of IndiaDepartment of Atomic Energy

Raja Ramanna Centre for Advanced Technology

APPROVAL SHEET

This is to certify that the project entitled “Mix Design of Concrete and Analysis of Effect of Reinforcement on Flexural Strength of Concrete” has been carried out at the Civil Department, RRCAT, Indore by Ms.

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Saloni Bhand during a period of 45 days from 15thMay, 2013 to 31stJuly, 2013.

Date: Project Guide:

Mr.Govind Parchani. Suptd. Engineer (GP),

Scientific Officer (H)

ACKNOWLEDGEMENT

The project entitled “Mix Design Of Concrete

I would like to thank all of the persons who helped me in my project work.

I take this opportunity to convey my deepest sense of gratitude to my

project guide Mr. Govind Parchani for his constant support, motivation,

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valuable guidance and immense help during the entire course of this work.

Date:

By: Ms. Saloni Bhand

CONTENTS

Chapter Title Page

1.Introduction

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2.Properties of concrete

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3.Concrete mix design

155

4.Practical trial mix design of concrete for

compressive strength 20N/mm2 29

5.Flexural Strength of concrete

36

6.Flexural Strength test of concrete

37

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1. INTRODUCTION

1.1 Concrete:

Concrete is the most widely used man-made construction material in the world, and is second only to water as the most utilized substance on the planet. It is obtained by mixing cementing materials, water and aggregates, and sometimes admixtures, in required proportion.

Components Of Concrete

The mixture when placed in forms and allowed to cure, hardens into a rock like mass known as concrete.

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The hardening is caused by chemical reaction between water and cement and it continues for a long time, and consequently the concrete grows stronger with age.

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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 with smaller particles (Fine aggregates) and the voids of fine aggregates are filled with cement. In a concrete mix the cementing material and water form a paste called “cement-water” paste which in addition to filling the voids of fine aggregates, coats the surface of fine and coarse aggregates and binds them together as it cures, thereby cementing the particles of the aggregates together in a compact mass.

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After hardening, concrete gains its strength, durability and other properties.

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1.2 Requirements of Good Concrete:

A good concrete should:

Meet the strength requirements measured by compressive strength.

Full fill durability requirements to resist the environment in which the structure is expected to serve.

Can be mixed, transported and compacted as efficiently as possible.

Can be as economical as possible.

1.3 Making Good Concrete:

Making good concrete involves:

Good quality raw materials. Proportioning of materials. Mixing of concrete materials. Transporting of concrete. Placing of concrete. Compaction of concrete. Curing of concrete.

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1.4 IS CODE:

The Bureau of Indian Standards (BIS), the National Standards Body of India is involved in the development of technical standards (popularly known as Indian Standards), product quality and management system certifications and consumer affairs. It includes all matters concerning Standardization, Certification and Quality. They have given various codes for various purposes known as “IS Codes”.

Various IS codes used in mix design of concrete are:

IS 456:2000 IS 10262:2009 IS 516:1959 SP 43:1987

1.5 Reinforcement in Concrete

A reinforcer is the stimulus that strengthens the behaviour and reinforcement is a strengthening of a specific behaviour. Reinforcement is done in concrete to improve its tensile behaviour. As concrete is weak in tension strength the concrete elements subjected to tensile stresses must be reinforced with materials that are strong in tension.

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Reinforcement in concrete

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The reinforcement is often steel, rebar (mesh, spiral, bars and other forms).The amount of primary and secondary reinforcing in concrete structures contributes to a reduction in the amount of shrinkage, creep and cracking of concrete.

1.6 Flexural strength of concrete:

Flexural strength of concrete is that strength property of concrete by virtue of which it resists rupture. The flexural strength is expressed as “Modulus Of Rupture” (MR) in MPa. Flexural strength is also known as “bend strength” or “fracture strength”.

Designers of pavements use a theory based on flexural strength. Therefore, laboratory mix design based on flexural strength tests may be required, or a cementitious material content may be selected from past experience to obtain the needed design Modulus of Rupture. Some also use Modulus of Rupture for field control and acceptance of pavements. Very few use flexural testing for structural concrete.

Relation between Flexural strength of concrete and Compressive strength of Concrete:

f f=0.723√ f ck

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2. PROPERTIES OF CONCRETE

2.1 Strength :

Concrete has relatively high compressive strength, but significantly lower tensile strength.

a) Compressive strength:

The compressive strength is the capacity of a material or structure to withstand loads tending to reduce size. It can be measured by plotting applied force against deformation in a testing machine. Some material fracture at their compressive strength limit; others deform irreversibly, so a given amount of deformation may be considered as the limit for compressive load. Compressive strength is a key value for design of structures. Compressive strength is often measured on a universal testing machine. In SI system its unit is N/mm2.

The ultimate strength of concrete is influenced by the water-cementitious ratio (w/cm), the design constituents, and the mixing, placement and curing methods employed. All things being equal, concrete

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with a lower water-cement (cementitious) ratio makes a stronger concrete than that with a higher ratio.

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b) Tensile Strength:

Tensile strength is the maximum stress that a material can withstand while being stretched or pulled before failing or breaking. Tensile strength is the opposite of compressive strength and the values can be quite different.

The tensile strength is usually found by performing a tensile test and recording the stress versus strain; the highest point of the stress-strain curve is the ultimate Tensile Strength. It is an intensive property; therefore its value does not depend on the size of the test specimen. However, it is dependent on other factors, such as the preparation of the specimen, the presence or otherwise of surface defects, and the temperature of the test environment and material.

Tensile strengths are rarely used in the design of ductile members, but they are important in brittle members. Tensile strength is defined as a stress, which is measured as force per unit area. For some non-homogeneous materials (or for assembled components) it can be reported just as a force or as a force per unit width. In the SI system, its unit is the Pascal (Pa).

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2.2 Density:

The density of a material is its mass per unit volume. Also, density is loosely defined as its weight per unit volume. The density of concrete varies, but is around 2,400 kg/m³.

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2.3 Elasticity:

The modulus of elasticity of concrete is a function of the modulus of elasticity of the aggregates and the cement matrix and their relative proportions. The modulus of elasticity of concrete is relatively constant at low stress levels but starts decreasing at higher stress levels as matrix cracking develops. The elastic modulus of the hardened paste may be in the order of 10-30 GPa and aggregates about 45 to 85 GPa. The concrete composite is then in the range of 30 to 50 GPa.

2.4 Thermal expansion and shrinkage:

Concrete has a very low coefficient of thermal expansion. However, if no provision is made for expansion, very large forces can be created, causing cracks in parts of the structure not capable of withstanding the force or the repeated cycles of expansion and contraction.

As concrete matures it continues to shrink, due to the on-going reaction taking place in the material, although the rate of shrinkage falls relatively quickly and keeps reducing over time (for all practical purposes concrete is usually considered to not shrink due to hydration any further after 30 years).

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Because concrete is continuously shrinking for years after it is initially placed, it is generally accepted that under thermal loading it will never expand to its originally placed volume.

Due to its low thermal conductivity, a layer of concrete is frequently used for fireproofing of steel structures.

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2.5 Creep:

Creep is the permanent movement or deformation of a material in order to relieve stresses within the material. Concrete that is subjected to long-duration forces is prone to creep. Short-duration forces (such as wind or earthquakes) do not cause creep. Creep can sometimes reduce the amount of cracking that occurs in a concrete structure or element, but it also must be controlled.

2.6 Durability:

“Durability of concrete is the ability of concrete to withstand the harmful effects of environment to which it will be subjected to, during its service life, without undergoing into deterioration beyond acceptable limits”.

Durability can be assured keeping in view the environment exposure of structure, certain minimum cement binder content, max limit on w/c ratio and a

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certain minimum grade of concrete for that particular exposure.

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3. CONCRETE MIX DESIGN

3.1 Definition

Concrete mix design is defined as the appropriate selection and proportioning of constituents to produce a concrete withpre-defined characteristics in the fresh and hardened states.

3.2 Types of Mix Concrete

Generally, there are two kinds of “Concrete Mix” . They are:

1. Nominal Mix Concrete.2. Design Mix Concrete.

1. Nominal Mix ConcreteWhen the proportions of cement, aggregate and water are adopted based on arbitrary standard the concrete produced is termed as “Nominal Mix Concrete”.

Nominal mix concrete is used in works where the quality control requirements for design mixes are difficult to be implemented. Nominal mix concrete can be produced by taking cement, fine aggregate and coarse aggregate in the ratio of 1:n:2n for normal work.

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Nominal mix of concrete according to their “Grade”:

Here, M-25 means “Mix of concrete having compressive strength 25N/mm2at 28th day when cured at 27+2OC temperature.

2. Mix Design of Concrete

When the task of deciding the proportion of constituents of concrete is accomplished by use of certain established relationships (which are based on interferences drawn from large number of experiments) the concrete thus produced is termed as Mix Design of Concrete.

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Nominal Mix Concrete (1:n:2n)

Grade of Concrete

1:5:10 M-51:4:8 M-7.51:3:6 M-101:2:4 M-15

1:1.5:3 M-201:1:2 M-25

3.3 Methods Of Mix Design Of concrete

1. American Concrete Institute (ACI) Method.2. British DOE Method of Concrete Mix Design.3. Road Note No. 4 Method.4. Indian Standard Concrete Mix Proportioning.5. Rapid Method for Mix Design.

3.4 Main aspects to be considered Mix Design of Concrete

According to “Indian Standard Mix Proportioning Guidelines”-

In general, concrete mixes are designed in order to achieve a defined:

Workability. Strength. Durability.

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Mix Design

Workability

MSA

Consistency

Strength

Target mean Strength

Compressive strength

Characteristic strength

durability

Exposure class

a) Workability:

Workability is that property of freshly mixed concrete or mortar which determines the ease and homogeneity with which it can be mixed, placed, compacted and finished. Workability depend upon water-cement ratio of concrete.

Facts in connection with workability:

1. If more water is added to attain the required degree of workmanship, it results into concrete of low strength and poor durability.

2. It is also affected by the “Maximum Size of Coarse Aggregate”(MSA) to be used in mixture.

To test workability Slump test is commonly used in fields.

Workability of concrete

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b) Maximum Size Of Aggregate:

Size of concrete aggregates depends on the dimension of the place where concrete has to be used.

The maximum size of aggregate (MSA) depends upon the size of the member and the spacing of reinforcement.

The maximum size of the coarse aggregate is important because it affects the free water content and percentage of fine aggregate needed for a given level of workability.

Generally if the maximum size is increased, the free water content and the percentage of fine aggregate required for a given level of workability are reduced.

c) Consistency:

Factors Influencing Consistency (Slump):

The consistency of fresh concrete depends on many factors, the main ones being:

Water Content (kg/m3) W/c Ratio Fineness Modulus of the Aggregate

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MSA< 1/4th of the size of the member.

Use of Water Reducers (Plasticizers / Super plasticizers)

Type and shape of Aggregate Entrained Air Content

There are other secondary factors too, such as:

Mix temperature, aggregates, dust, cement type, additions (silica fume, fly-ash, slag, fibers), etc.

d) Strength:

Factors affecting Strength:The strength of hardened concrete depends on many factors, the main ones being:

W/C Ratio Strength of the Cement Type and shape of Aggregate Entrained Air Content

There are other secondary factors too, such as:

Mix temperature, etc.

e) DurabilityDurability can be assured keeping in view theenvironment exposure of structure, certainminimum cement binder content, max limit onw/c ratio and a certain minimum grade ofconcrete for that particular exposure.

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I. Making Durable Concrete:

Lowering the porosity and permeability ofconcrete is only way to reduce environmentalattacks on concrete,

Dense and compact concrete that prevents theingress of harmful elements is the key to“DURABLE CONCRETE”.

II. Durability Constraints:

Usually, durability requirements end in some constraints to the maximum W/C ratio and/or to the minimum cement content of the mix.

Very often these requirements are more stringent than those demanded by the strength requirements, which usually ends in concretes which are overdesigned in strength.

III. Durability Criteria as per IS 456- 2000

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Exposure

MildModerate

SeverVery Sever

Extreme

Plain Concr

eteMin.

Cement

220 kg/m3

240 kg/m3

250 kg/m3

Max. w/c

Ratio

.60.60

.50.45

.40

Min. Grade

--M 15

M 20

REinforced

Concrete

Min. Cement

300 kg/m3

300 kg/m3

320 kg/m3

Max. w/c

Ratio

.55.50

.45.45

.40

Min. Grade

M 20M 25

M 30

IV. Adjustments to minimum cement content for aggregates other than 20 mm nominal maximum size aggregates as per IS 456: 2000.

f) The Selection and Proportioning of Materials Depend on:

The structural requirements of the concrete. The environment to which the structure will be

exposed. The job site conditions, especially the methods of

concreteproduction, transport, placement, compaction and finishing.

The characteristics of the available raw materials.

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10 mm20 mm40 mm

+40 kg/cum

0-30 kg/cum

3.5 Mix Design Of Concrete According to IS Method:

According to IS 10262:2009, IS 456:2000, etc.Steps involved in mix design of concrete is represented below.

Step1:Grade of Concrete is specified, i.e. Minimum strength (fck) is specified.

Step2:Target mean strength for the mix to be designed is obtained depending upon quality control, by formula-

Where,

fm= Target mean strength of the concrete mix.

fck= Minimum compressive strength.

kσ= Characteristic strength.

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fm = fck+ kσ

k = Tolerance factor (i.e. 1.65 per 5% of concrete

cube can be tolerated below minimum strength)

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σ = Standard deviation can be known from table depends upon degree of Quality Control, as shown below:

Grade of Concrete Assumed Standard Deviation N/sq.mm

M 10M 15 3.5M 20M 25 4.0M 30M 35M 40M 45M 50M 55M 60

5.0

Step3:Water cement ratio is obtained from the standard curve, shown below:

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Water – cement Ratio is obtained for durability consideration, as shown in following table.

Select the lower value.

Step4:38

ExposureM ildM oderate

SeverV er y Sev er

Pla in Concrete

M in. Cem ent

220 kg/m 3

2 4 0 kg/m 3

M ax. w /c Rati o

.60.6 0

M in. G rade

--M 1 5

M 20

REinforced Concrete

M in. Cem ent

300 kg/m 3

3 0 0 kg/m 3

M ax. w /c Rati o

.55.5 0

M in. G rade

M 20M 2 5

M 30

Amount of water content and proportion ( % of sand ) of total aggregate for given set of condition are read. From following table:

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Step5:

Volume of coarse aggregate can be obtained by following table:

S.no.

Nominal Maximum Size of Aggregate

(mm)

Volume of Coarse Aggregate per Unit Volume of Total Aggregate for Different Zones of Fine Aggregate

Zone

IV

Zone

III

Zone

II

Zone

I1 10 .50 .48 .46 .442 20 .66 .64 .62 .603 40 .75 .73 .71 .69

Following adjustments are made according to the conditions:

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Step6:

Cement content is determined. As, from above steps we have values of w/c ratio and water content thus, cement content can be easily calculated with help of water-cement ratio relationship.

Step7:

Now amount of aggregates can be calculated with the help of “Absolute Volume Method” represented as follows:

For Fine Aggregate:

For Coarse Aggregate :

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w/c = Water content/Cement content

Where,

V= Absolute volume of wet Mix = 1 m3

Also, V= Absolute volume – air content entrapped

The value of air content entrapped can be obtained by following table:

W= water content in Kg.

C= Cement content in Kg.

F.A. = Content of fine aggregate in Kg.

C.A. = Content of Coarse Aggregate in Kg.

Sc = Specific gravity of cement.

SF.A. = Specific gravity of fine aggregate.

SC.A. = Specific gravity of coarse aggregate.

p = ∆p = correct fine aggregate per cent.42

1-∆p = Correct coarse aggregate per cent.

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4. PRACTICAL TRIAL MIX DESIGN OF CONCRETE FOR

COMPRESSIVESTRENGTH OF 20 N /mm2

a) Design stipulations:

Characteristic compressive strength required

in the field at 28th day = 20N/mm2

Maximum size of aggregate = 20mm

Shape of aggregates = angular/crushed

Degree of workability = medium; slum =

75mm

Degree of quality control= good

Exposure condition=mild

Type of cement= JK (PPC)

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b) Material tests data:

Specific gravity of cement = 3.15

Compressive strength of cement at 28 day =

54N/mm2

Specific gravity of fine aggregates (SF.A.)=2.671

Specific gravity of course aggregates

(SC.A.)=2.889

Fineness modulus of fine aggregates (FM)=2.68

Silt content of sand=1.81%

Impact value of course aggregates=14.46%

Flakiness & elongation index of coarse

aggregates=28.54%

Moisture content of fine aggregates = 1.32%

Maximum Size of Aggregates = 20mm

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c) Designing:

1. Target mean compressive strength:

fm = fck+ kσ (from table 1 IS 456:2000)fm= 20 + 1.65*4

fm= 26.6 N/mm2

fm≈27N/mm2 (say)

2. W/C Ratio = .54 ( By standard Curve)

Maximum w/c ratio for mild exposure = .55 (From Table 5 IS 456:2000 shown above)

Hence, it isO.K.47

3. Water Quantity required for 1m3 of concrete = 178 Kg.

Percentage of sand ∆p = 40% w/c ratio = .54 Slump = 75mm Fineness Modulus of fine aggregate = 2.68

4. Adjustment:

Quantity of water = 178kg + 8kg

=186Kg

Percentage of sand ∆p = 40 + .04×1 0.05

+0.50.1

×.08

∆p = 40+ 0.8 + 0.4

∆p = 41.2%

∆p ≈ 41% (say)

Corresponding increase in sand as 84% sand is passing through 4.75mm sieve= +4.27÷5%

=+.85%

Corresponding reduction in sand due to presence of silt component in sand = -1.81 x 2.5 x .5

= -2.28%

Corrected sand % ∆p = 41 + .85 – 2.28

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∆p = 39.5%≈ 39% (say).

5. Weight of cement required for 1m3 of concrete:

w/c= WaterContentCementCon tent

.54 = 186CementContent

Cement Content =344.44Kg

Cement Content≈345Kg. (say)

Since, Cement Content 345Kg/m3> 300Kg/m3

i.e. Minimum cement content (Kg/m3) required as per IS 456:2000. Hence, it is O.K.

6. Aggregate Content by absolute volume method:

(i) Fine Aggregates:

Here,

V= Absolute volume-Air entrapped

Air entrapped = .2% = 0.02

Thus, V = 1-0.02 = .98

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Hence,.98 =[186+ 345

3.15+ 1

.39×F . A .2.671 ]× 1

1000

F.A. = 713 Kg

(ii) Coarse Aggregate:

.98=[186+ 3453.15

+ 11−.39

×C . A .2.889 ]× 1

1000

C.A. = 1122 Kg

7. Therefore, the Mix proportions are as follows:

Water Cement Sand Coarse Aggregate

186 345 713 112227 50 103 163

8. Adjustment in Quantity of water:

Moisture Content of fine aggregate = 1.32%

Thus,

Deduction of surface water = −(103×1.32100 )

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And, Actual water content = 27 −(103×1.32100 )

= 27– 1.36

= 25.64 Kg

≈ 25 Lt.

9. Coarse Aggregate distribution:

As 40% of total coarse aggregate is of size 20mm and 60% of total coarse aggregate is of size 10mm. Therefore,

a) Amount of aggregate size 10mm (M1) = .60 x 163

M1 = 97.80 Kg

M1 ≈ 98 Kg (say)

And,

b) Amount of aggregate size 20mm (M2) = .40 x163

M2 = 65.20 Kg

M2 ≈ 65 Kg (say)

10. Finally, the proportion is:

Water (lit) Cement (Kg) Sand (Kg) Coarse Aggregate (Kg)

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25 50 103 163

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5. FLEXURAL STRENGTH OF CONCRETE:

Flexural strength is one measure of the tensile strength of concrete. It is a measure of concrete structure to resist failure in bending. It is determined by standard test methods ASTM C 78 (third-point loading) or ASTM C 293 (centre point loading). As shown in fig below:

Flexural Modulus of rupture is about 10 to 20 % of compressive strength depending on the type, size

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and volume of coarse aggregate used. However, the best correlation for specific materials is obtained by laboratory tests for given materials and mix design.

The Modulus of Rupturedetermined by third-point loading is lower than the Modulus of Rupture determined by center-point loading, sometimes by as much as 15%.

6. FLEXURAL STRENGTH TEST

6.1 TEST:

Object:Determination of the flexural strength of concrete specimen.

Apparatus:

a) Standard moulds of size 15 x 15 x70 cm for preparing the specimen.

b) Tamping bar.

c) Testing Machine.

The permissible errors shall be not greater than ± 0.5% of the applied load where a high degree of

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accuracy is requiredand not greater than ± 1.5 % of the applied load for commercial type of use.

The bed of the testing machine shall be provided with two steel rollers, 38 mm in diameter, on which the specimen is to be supported, and these rollers shall be so mounted that the distance from centre to centre is 60 cm for 15.0 cm specimens or 40 cm for 10.0 cm specimens.

The load shall be applied through two similar rollers mounted at thethird points of the supporting span, that is, spaced at 20 or 13.3 cm centre to centre.

The load shall be divided equally between the two loading rollers, and all rollers shall be mounted in such a manner that the load is applied axially and without subjecting the specimen to anytorsional stresses or restraints. One suitable arrangement whichcomplies with these requirements is indicated in Fig.

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Procedure:

Test specimens stored in water at a temperatureof 24° to 30°C for 48 hours before testing,shall be tested immediately on removal from the water whilst they are still in a wet condition.

The dimensions of each specimen shall be noted before testing. No preparation of the surfaces is required.

Placing the specimen in the testing machine:

The bearingsurfaces of the supporting and loading rollers shall be wiped clean, and any loose sand or other material removed from the surfaces of the

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specimen where they are to make contact with the rollers.

The specimen shall then be placed in the machine in such a manner that the load shall be applied to the uppermost surface as cast in the mould, along two lines spaced 20.0 or 13.3 cm apart. The axis of the specimen shall be carefully aligned with the axis of the loading device.

No packing shall be used between the bearing surfaces of the specimen and the rollers.

The load shall be applied without shock and increasing continuously at a rate such that the extreme fibre stress increases at approximately 7 kg/sqcm/min, that is, at a rate of loading of 400 kg/min for the 15.0 cm specimens and at a rate of 180 kg/min for the 10.0 cm specimens.

The load shall be increased until the specimen fails, and the maximum load applied to the specimen during the test shall be recorded.

The appearance of the fractured faces of concrete and any unusual features in the type of failure shall be noted.

Calculations:

The flexural strength of the specimen shall beexpressed as the modulus of rupture f b, which, if ' a '

equals the distance between the line of fracture and 57

the nearer support, measured on the centre line of the tensile side of the specimen, in cm, shall be calculated to the nearest 0.5 kg/sq cm as follows:

When ‘a’ is greater than 20.0 cm for 15.0 cm specimen, or greater than 13.3 cm for a 10.0 cm specimen,

f b=p× l

b×d2

Or,

When ‘a’ is less than 20.0 cm but greater than 17.0 cm for 15.0 cm specimen, or less than 13.3 cm but greater than 11.0 cm for a 10.0 cm specimen

f b=3 p×a

b×d2

Where,

b = measured width in cm of the specimen,

d = measured depth in cm of the specimen at the point of failure,

l = length in cm of the span on which the specimen was supported,

p = maximum load in kg applied to the specimen.

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If ‘a’ is less than 17.0 cm for a 15.0 cm specimen, or less than 11.0 cm fora 10.0 cm specimen, the results of the test shall be discarded.

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6.2 Specifications of specimens to be tested:

Two specimens are to betested under the flexural test machine whose specifications are as follows:

1. A beam of cement concrete.2. A reinforced beam of cement concrete.

Drawing and reinforcement details are given below:

Elevation of reinforced cement concrete beam:

Plan of reinforced cement concrete beam:

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Section of reinforced cement concrete beam:

Specifications of specimen shown above:

1. Size of specimens(both):

a) Length = 700mmb) Breadth = 150mmc) Depth =150mm

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2. Reinforcement detail:

a) Diameter of bars = 3mmb) 2 bars of 280mm length @ 80mm c/cc) 3 bars of 480mm length @60mm c/cd) 4 bars of 670mm length @ 40mm c/ce) Bottom cover = 10mmf) Side cover = 15mm

6.3 Results of test:-

The result of flexural strength test carried out on the beams as specified above by Third-Point-Loading Method comes out as follows:

1) The Beam of Cement-Concrete:

The beam of cement concrete fails at load of 21kN

Thus, Modulus of Rupture of beam = p×lb×d2

= 21× .600

.150× ( .150 )3

= 24888.88 kN/m2

= 24.88 N/mm2

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2) The Reinforced Cement Concrete Beam:

This beam of reinforced cement concrete fails at load of 70.510kN

Thus, Modulus of Rupture of beam = p×lb×d2

= 70.510× .600

.150×1503

= 83567.40 kN/m2

= 83.56 N/mm2

7. CONCLUSION

If a cement concrete beam is reinforced in above manner its flexural strength will be increasedby 3 times of unreinforced cement concrete beam. i.e. Modulus of Rupture of reinforced cement concrete beam = 83.56 N/mm2

= 3 x 24.88 N/mm2

= 3 x Modulus of Rupture of plain cement concrete beam.

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Modulus of Rupture of reinforced cement concrete beam = 3 x Modulus of Rupture of plain cement concrete