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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

    Temperature

    CHAPTER III

    EXPERIMENTAL DETAILS MATERIALS AND METHODS

    3.1 MATERIALS

    43 grade Ordinary Portland Cement (Ultra Tech) has been used. The fly ash

    collected from the silo of Raichur Thermal Power Plant, Raichur, Karnataka, Mettur

    Thermal Power Plant, Mettur, Tamil Nadu, Rayala Seema Thermal Power Plant, Rayala

    Seema, Andhra Pradesh have been used as supplementary cementitious material in the

    study. Standard sand (conforming to IS: 650-1991) and potable/ distilled water as per the

    requirement is used for preparation of the composition and all experiments. Hyper

    plasticizer SP 340 FOSROC Company was used to achieve the workability.

    3.2 CHARACTERIZATION OF RAW MATERIALS - TEST METHODS

    Characterization is the art of describing the distinctive characteristics or essential

    features of the material in question. It is an important activity undertaken to completely

    understand the related properties the materials with reference to particular application.

    Generally, materials are characterized for physical, chemical, mineralogical and

    morphological characteristics.

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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

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    3.2.1 FLY ASH

    3.2.1.1 ANALYSIS OF CHEMICAL PROPERTIES OF RAICHUR FLY ASH

    Table3.1: Chemical Properties of Fly ash Used

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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

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    3.2.1.2 ANALYSIS OF PHYSICAL PROPERTIES OF FLY ASH

    Table 3.2 Physical Properties of Fly Ash Used

    3.2.2 CEMENT

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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

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    An Ordinary Portland Cement OPC 43 Grade conforming to IS: 8112-1989samples

    were tested to obtain the following characteristics:

    3.2.2.1 SPECIFIC GRAVITY (IS: 1727-1967) [22]

    Specific gravity is defined as the ratio of density of the powder to the density of

    water.

    The density of the cement samples was determined by using standard specific

    gravity bottles. The specific gravity bottles used are generally, are of 50 ml or 100 ml

    capacities. The procedure for determination of specific gravity is as follows.

    (1) The weight of the empty specific gravity bottle was measured.

    (2) The weight of the specific gravity bottle filled with distilled water was measured.

    (3) The weight of the specific gravity bottle filled with kerosene was measured.

    (4) Nearly 2.5 g of sample was taken in the specific gravity bottle, filled with kerosene and

    closed with the lid. Care was taken to ensure that the specific gravity bottle with the sample

    is completely filled with kerosene.

    (5) The sample was allowed to settle for two minutes and tapped gently to release any

    entrapped air bubbles.

    (6) The weight of the specific gravity bottle filled with sample and kerosene was measured.

    (7) Specific gravity was calculated using the formula.

    W5 (W3-W1)

    Specific gravity = ---------------------------

    (W5+W3-W4)*(W2-W1)

    Where,

    W1 = Weight of the empty specific gravity bottle.

    W2 = Weight of the specific gravity bottle + distilled water.

    W3 = Weight of the specific gravity bottle + kerosene.

    W4 = Weight of the specific gravity bottle + kerosene + sample.

    W5 = Weight of the sample taken.

    Specific Gravity of Cement sample tested is 3.14

    3.2.2.2 CONSISTENCY AND SETTING TIMES

    The standard consistency test was conducted to determine the quantity of water

    required for producing a paste of standard consistency. The tests were conducted using

    Vicat Apparatus, conforming to IS: 5513-1976.The stiffening times of the cement paste

    were determined by the setting time viz., initial and final setting times. When the paste

    attains the stage of initial set, it can no longer be properly handled or placed. The final set

    corresponds to the stage at which the hardening of cement paste begins. The test block was

    prepared with paste of cement and pozzolan mixtures, prepared by gauging the cement

    pozzolana mixture with 0.85 times the water required to give a paste of standard

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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

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    consistency. The paste thus prepared was placed in the Vicat mould, resting on a non-

    porous glass plate. For determination of the initial setting times, the needle bearing C was

    fixed to the Vicat Apparatus and lowered to make contact with the top surface of the paste

    in the mould. The needle was gently released to pierce only the depth of 5 mm from the

    bottom of the mould was recorded as initial setting times of the paste. For determination of

    the final setting times, the initial setting time C was replaced with the needle bearing F

    (annular end needle). The time taken such that, the needle makes an impression on the

    paste, whereas the attachment makes no impression on the paste was deemed as the final

    setting time of the paste. The apparatus used for the determination of consistency and

    setting times (VICAT Apparatus) is shown in Fig 3.1.

    Standard Consistency

    Standard consistency as per IS: 4031 Part 4 [23] of the cement sample was found tobe 29%.

    Initial Setting Time (IST)

    Initial setting time (IS: 4031 1968 Part 5) [24] = 32 minutes

    Final Setting Time (FST)

    Final setting time (IS: 4031 1968 Part 5) [24] = 240 minutes

    Figure 3.1 VICAT Apparatus

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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

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    3.2.2.3 FINENESS OF CEMENT

    Fineness of cement is a measure to the surface area and grain size of the cement.

    The development of shrinkage cracks also depends on fineness of the cement. As the

    fineness of cement increases the rate of development of shrinkage cracks also increases.

    Hence it is very much essential to determine the fineness of cement. (IS sieve of size 90

    sieve was used for fineness test)

    Fineness of the cement sample = 4%

    3.2.3 FINE AGGREGATE

    This experiment is conducted to determine the fineness modulus of the aggregates.

    This gives an idea about the fineness of the aggregates. In this experiment the known

    quantity of aggregate is sieved in IS standard sieves. The weights of aggregates retained

    and passed in each of the standard sieves is determined. Knowing these values the fineness

    modulus of the sample taken can be calculated.

    In the present investigation, the river sand, which was available in the construction site

    inside the campus, was used as fine aggregate and the following tests were carried out on

    sand as perIS : 2386-1968 (III) [25]

    Specific gravity of the tested fine aggregate sample was 2.58

    Sieve Analysis and Fineness Modulus

    Table 3.3 Results of Sieve Analysis on Fine Aggregates Used

    Sieve

    Size

    Weight

    Retained

    (gms)

    Weight

    Passing

    (gms)

    %

    Coarser

    %

    Finer

    Cumulative

    Weight

    Retained

    Cumulative

    % of

    Coarser

    4.75mm 0.0 1000 0.00 100.00 0.00 0.00

    2.36mm 10.0 990 1.00 99.00 10.00 1.00

    1.18mm 76.0 914 7.60 91.40 86.00 8.60

    600 194.0720 19.40

    72.00 280.00 28.00425 532.0 188 53.20 18.80 812.00 81.20

    150 174.0 14 17.40 1.40 986.00 98.60

    PAN 14.0 Nil 1.40 - 1000.00

    Total=1000.0 = 217.40

    Cumulative FA retained 217.40

    FM = -------------------------------- = ---------- = 2.17

    100 100

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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

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    Figure 3.2: Graphical representation Results of Sieve Analysis for fine Aggregates

    As seen from the sieve analysis curve for the aggregates the curve is giving S shape

    indicating uniformly graded aggregate.

    Water absorption = 2.0% (by mass)

    Free (surface) moisture = 0.94%

    3.2.4 COARSE AGGREGATE

    Specific Gravity of the tested coarse aggregate sample was 2.695 (IS : 2386-

    1968 Part 3) [25]

    Sieve Analysis (IS : 2386-1968 Part 3) [25]

    Table 3.4 Results of Sieve Analysis on Coarse Aggregates

    Sieve

    Size

    Weight

    Retained

    (gms)

    Weight

    Passing

    (gms)

    %

    Coarser

    %

    Finer

    Cumulative

    Weight

    Retained

    Cumulative

    % of

    Coarser

    40 0.0 5000 0.00 100.00 0.00 0.00

    20 356.0 4644.0 7.12 92.88 356.00 7.12

    10 4610.0 34.0 92.20 0.68 4966.00 99.32

    4.75 34.0 0.0 0.68 0.00 5000.00

    Total=1000.0 = 106.44

    Cumulative FA retained 106.44

    FM = -------------------------------- = ---------- = 1.06

    100 100

    GRADATION CURVE FOR FINE AGGREGATE

    0

    20

    40

    60

    80100

    120

    0.15 0.425 0.6 1.18 2.36 4.75

    SEIVE SIZE IN MICRO MM

    %OFFINER

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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

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    Figure 3.3: Graphical representation Results of Sieve Analysis for Coarse Aggregates

    For coarse aggregate it is giving destructed S curve with a sharp height b/n 10 & 20 mm

    sieve size.

    Water Absorption = 1.94 %

    Free (surface) moisture = NIL

    3.3 CONCRETE MIX DESIGN

    Mix design can be defined as the process of selecting suitable ingredients of

    concrete and determining their relative proportions with the object of producing concrete of

    certain minimum strength and durability as economical as possible. The purpose of

    designing as can be seen from the above definitions is two-fold. The first object is to

    achieve the stipulated minimum strength and durability. The second object is to make the

    concrete in the most economical manner. One of the ultimate aims of studying the various

    properties of the materials of concrete, plastic concrete and hardened concrete is to design a

    concrete mix for a particular strength and durability. Design of concrete mix needs not only

    the knowledge of material properties and properties of concrete in plastic condition, it also

    needs wider knowledge and experience of concreting, Even then the proportion of the

    materials of concrete found out at the laboratory requires modification and readjustments to

    suit the field conditions.

    Indian Standard Recommended Method of Concrete Mix Design (IS 10262-2009)

    The Bureau of Indian Standards recommended a set of procedure for design of

    concrete mix mainly based on the work done in national laboratories. The mix design

    GRADATION CURVE FOR COARSE AGGREGATE

    0

    20

    40

    60

    80

    100

    120

    0 5 10 15 20 25 30 35 40 45

    %FINER

    32

    40

    SEIVE SIZE IN MM

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    procedures are covered in IS 10262-2009. The methods given can be applied for both

    medium strength and high strength concrete.

    (a) Design stipulations

    (i) Characteristic Compressive Strength

    Required in the field at 28 days 30 MPa

    (ii) Maximum size of aggregate 20 mm (angular)

    (iii) Degree of workability 75 mm slump

    (iv) Degree of quality control Good

    (v) Type of Exposure Severe

    (b) Test data for materials

    (i) Specific gravity of cement 3.14

    (ii) Compressive Strength of cement at 7 daysSatisfies the requirement of IS: 269

    -1989

    (iii) 1. Specific gravity of coarse aggregates 2.695

    2. Specific gravity of fine aggregates 2.58

    (iv) Water absorption

    1. Coarse aggregate 1.94 %

    2. Fine aggregate 2.0 % (by mass)

    (v) Free (surface) moisture

    1. Coarse aggregate Nil

    2. Fine aggregate 0.94%

    (vi) Sieve analysis conducted indicates that the tested sample of fine aggregates

    falls under the Zone II. Coarse aggregates of 20 mm size are used for casting samples.

    (c) Target mean strength of concrete

    The target mean strength for specified characteristic cube strength is given by

    f'ck= fck+ 1.65 s= 30 + 1.65 x 5

    = 38.25 MPa = 38.25 N/mm2

    (d) Selection of water-cement ratio

    From Table 5 of IS: 456-2000, maximum free water cement ratio for M30 concrete

    exposed to severe condition =0.45Based on experience adopt water cement ratio as 0.40

    0.4 < 0.45, hence ok

    (e) Selection of water content

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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

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    From Table-2 of IS 10262:2009, maximum water content = 186 liters (for 25mm

    50mm slump range and for 20 mm aggregates)

    Estimated water content for 75 mm slump = 186 + 3/100 x186 = 191.58 192 liters

    (f) Determination of cement content

    Water/cement ratio = 0.40

    Cement = 192/ 0.40 = 480.0 Kg/m3

    From Table 5 of IS: 456, minimum cement content for severe exposure condition = 320

    kg/m3. Hence OK

    (g) Determination of coarse and fine aggregate contents

    From Table 3 of IS 10262 - 2009,

    Volume of coarse aggregate corresponding 20mm size aggregate and for Fine

    aggregate confirming to zone II for W/C ratio of 0.50 = 0.62

    Therefore, Volume of CA = 0.62 + (0.01 x 0.1/0.05) = 0.64 (at the rate of +0.01% for every

    0.05 decrease in W/C ratio) and

    Volume of CA = 1 0.64 = 0.36

    (h) Mix calculations

    I. Volume of Concrete = 1 m3

    II. Volume of Cement = (480 / 3.14) x (1 / 1000) = 0.1528 m3

    III. Volume of Water = (192 / 1) x (1 / 1000) = 0.192 m3

    IV. Volume of all in aggregates (e) = I ( II + III )

    = 1- (0.1528+0.192)

    = 0.6552 m3

    V. Mass of Coarse aggregate = 0.6552x0.64x2.695x1000

    = 1161.6 Kg

    VI. Mass of Coarse aggregate = 0.6552x0.36x2.58x1000

    = 608.50 Kg

    (i) Mix proportion for trail 1.

    Water Cement Fine aggregate Coarse aggregate

    192 480.0 Kg 608.5 Kg 1161.6 Kg

    0.40 1 1.26 2.42

    Quantity required per bag of Cement

    Water Cement Fine aggregate Coarse aggregate

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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

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    20.0 50.0 63.0 121.0

    j) Correction for water content

    Extra quantity of water to be added for absorption in case of CA at 1.94% by mass

    for 50 kg of cement = 0.97 lit.

    Extra quantity of water to be added for absorption in case of FA at 2.0% by mass

    for 50 kg of cement = 1.0 lit.

    Quantity of water to be deducted for free moisture present in FA at 0.94% for 50 kg

    of cement i.e., for 1 bag cement = 0.47 lit.

    i) Actual quantities required after correction:

    Actual quantity of water required to be added for 1 bag of cement

    = 20.0+0.97+1.0-0.47 =21.63 lit.

    Actual quantity of sand required = 63.0 + 0.34 allowing for mass of free moisture

    = 63.34 Kg for 1 bag cement

    Actual quantity of coarse aggregate = 121.0 Kg for 1 bag of cement.

    Final quantity required per bag of Cement

    Water Cement Fine aggregate Coarse aggregate

    21.63 50.0 63.34 121.0

    0.42 1 1.27 2.42

    k) Quantity of each material required for 6 moulds

    Volume of 1 mould = 0.495x0.10x0.10

    = 0.00495 m3.

    Therefore, volume of 6 moulds = 0.00495x 6

    = 0.0297 m3

    .Therefore, weight of concrete = 0.0297 x 2400

    = 71.28 Kg

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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

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    Table 3.5 Quantity of each material required for 6 moulds at different replacement level of

    fly ash

    Sl.No%

    Replacement

    Cement

    (Kg)

    Fly

    Ash

    ( Kg)

    Fine

    Aggregates

    ( Kg)

    Coarse

    Aggregates

    ( Kg)

    Water

    ( Liter )

    1 0 15.20 - 19.30 36.78 6.38

    2 10 13.68 1.52 19.30 36.78 5.75

    3 12 12.16 3.04 19.30 36.78 5.11

    4 30 10.64 4.56 19.30 36.78 4.47

    5 35 9.88 5.32 19.30 36.78 4.15

    6 40 9.12 6.08 19.30 36.78 3.83

    3.6 FLEXURAL STRENGTH ANALYSIS

    The following steps of procedureare followed while producing the concrete mixes.

    The materials were introduced into the mixing tray, so that coarse aggregates and fine

    aggregates are added first and mixed well. The surfaces of aggregates are made wet by

    adding 10 percent of total water. Fly ash is added followed by the cement and mixed till a

    uniform mixture is obtained. Further, mixing was made by adding the 65 percent of the

    total water. Then 0.5 percent of weight of cement of super plasticizer (SP 340, supplied by

    M/s Fosroc chemicals (India) Pvt. Ltd.) was added to the remaining 25 percent of total

    water and stirred well. Finally, this solution is spread over the mixture of aggregates,

    cement and fly ash in the tray. And the mixing was continued till a uniform paste of

    concrete is obtained. The obtained fly ash concrete was then transferred to the moulds of

    495 mm x 100 mm x 100 mm in three layers. Then the compaction was done in the table

    vibrator till the slurry is seen at the top. Demoulding of the specimens was carried out after

    24 hours and above, depending upon their final set. Then, the specimens were placed

    immediately in the moist curing for 28 days of curing. The similar procedure was adopted

    for mixing different replacement percentages (10, 20, 30, 35 and 40) of cement with fly

    ash.

    The concrete prisms were taken out after the curing period and kept for drying for

    few hours. When the surface of the cubes are dry, the samples were kept in the oven for

    heating to 100oC, 200C and 300C for durations of 1, 2 and 3 hours respectively. The

    samples were taken out of the oven and waited till the temperature of the specimen reachedback to room temperature.

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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

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    Figure 3.4: Heating of specimens in oven up to 300C

    Two specimens were prepared for each duration and the flexural test was conducted

    in the Universal Testing Machine. The flexural load in KN was noted for the specimen. The

    average of the two loads was taken as the mean load of specimen.

    Figure 3.5: The Specimen being tested in the Universal Testing Machine

    The Flexural Strength of the specimen was determined by the following formula.

    Flexural Strength, R = PL/BD2

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    Flexural Strength Properties of Fly Ash Composite Concrete Sustained at Elevated

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    Where,

    R = Flexural strength in N/mm2 or MPa

    P = Mean load of Failure in N

    L = Length of Specimen in mm

    B = Width of Specimen in mm

    D = Depth of Specimen in mm

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