CHAPTER 7 EXPERIMENTAL INVESTIGATION OF …shodhganga.inflibnet.ac.in/bitstream/10603/39791/10/10_chapter7.pdf · The test programme was designed to study the flexure response of

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CHAPTER 7

EXPERIMENTAL INVESTIGATION OF EFFECT OF FLY ASH ON FLEXURE

STRENGTH OF R. C. BEAMS IN AGGRESSIVE AND NORMAL CONDITION.

7.1 Introduction

Nowadays in the electric power generation become viable with coal-based thermal power

plants ,which producing a large volume of environmentally polluting fly ash with disposal

problem. Fly ash has a great virtue of being pozzolanic. This beneficial aspect of fly ash can be

advantageously used with cement. This leads to replacing cement with larger percentage of fly

ash. The content of fly ash incorporated in the blended cement, sold in market currently is of the

order of 20 to 30 %by weight of cement. The addition of such moderate percentage of fly ash

results in great benefits such as reduction in heat of hydration, minimisation of potential alkali-

aggregate reaction, significant reduction of steel corrosion, improvement of durability of

concrete, reduction in cost and the same time, this kind of substitution did not substantially affect

the early-age strength.

This experimental study is to investigate the flexure behavior of reinforced concrete

beams that were casted replacing upto 40 % cement by good quality of fly ash obtained from

thermal power plant at Sikka- Jamnagar Gujarat. The flexure behavior of beams casted with fly

ash were compared with that of control concrete beams, cured in normal condition (in potable

water) and cured in aggressive condition(sea water). The behavior in strength, deformation and

structural performance were compared in both curing conditions for both types of beams.

The test programme was designed to study the flexure response of conventional

reinforced concrete beams made of two different kinds of concrete, one of different percentage

of fly ash and the other control concrete for comparison. The percentage of reinforcement used

in the beams ranged from less than the minimum specified in the code to over reinforcement in

flexure members.

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7.2 Objective of the Experiment

The experimental work is undertaken to evaluate the effect of just replacing the cement

by fly ash used in concrete and to study the flexural strength of reinforced concrete beam under

varying percentage of fly ash, as well as to study, the effect of curing in normal and aggressive

environment with age of concrete. From varying percentage of replacement of cement by fly ash,

to determine optimum percentage of fly ash for maximum flexural strength of reinforced

concrete flexure element.

This information is needed for understanding the actual behavior of flexural member

when cement has been replaced by fly ash and to ascertain strength of the reinforced element,

which is one of the important criteria of the concrete. Also the effect of curing time period under

different conditions is to be evaluated. Also to study the flexural crack width developed and its

signification on influence on rebar corrosion rate in cracked reinforced concrete structure and

thus by adherence to the crack width, elimination of additional risk of rebar corrosion in

concrete. Effect of fly ash incorporation on durability of concrete, study the role of fly ash in

enhancing the service life of reinforced concrete flexure members. The effect of cover to the

reinforcement is also considered in the study. The extent of corrosion is checked with the width

of cracks and intersection of crack to rebar. Comparison of flexural response of concrete beam

casted with different percentage of fly ash with controlled concrete, in view of strength,

deformation and structural performance in normal condition and cured in aggressive condition.

The flexure member is subjected to certain portion for pure bending, to determine the

actual strength of beams in pure bending and theoretical ultimate moment of the element in

flexure as per IS 456 was determined and the comparison of experimental ultimate and

theoretical ultimate moment studied. The study of deflection, first crack development and crack

width progress for different beams also carried out with age of concrete in normal and aggressive

condition.

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7.3 Experimental Work

7.3.1 Materials

The constituents of concrete mix, Cement, fly ash, Fine Aggregate, Coarse Aggregate,

water and mid steel as a reinforcement are used in casting of flexure concrete elements. The

detailed descriptions and test properties of materials are as follows.

7.3.1.1 Cement

The cement used was ordinary Portland cement of 53 grade confirming to IS 12269-1987.

The net weight of each bag was 50 kg . In order to have more uniformity in the results of the

work, the cement used for the complete work was selected from the same lot. The cement was

stored in dry placed and cover with damp proof plastic cover. The physical properties of the

cement are given in table no. 7.1.

Table 7.1

PHYSICAL PROPERTIES OF CEMENT

Sr. No. Properties Values

01 Grade of cement 53 GRADE

02 Setting time Initial 88 Minutes

Final 217 Minutes

03 Compressive Strength 03 Days 28.0 MPa

07 Days 38.5 MPa

28 Days 54.3 Mpa

04 Soundness 1.0 mm

05 Fineness 4.8 %

06 Consistency 26.5 %

07 Specific Gravity 3.15

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7.3.1.2 Fly Ash

The volume collected in dry form of generated fly ash is more suitable for addition in

cement and concrete. Although large quantity of fly ash available, all the ashes cannot be

suitable for use in concrete. The carbon content, fineness, gradation, lime reactivity etc. of fly

ashes are important properties which have considerable bearing on the properties of concrete.

Fly ash is brought from the SICAA THERMAL POWER STATION near JAMNAGAR.

The physical and chemical analysis were carried out and the results are as shown in table no. 7.2

From the test results it is conclude that the fly ash belongs to grade-I as per IS-3812 and Class-F

according to ASTM classification.

Table 7.2

CHEMICAL AND PHISICAL PROPERTIES OF FLY ASH

Sr.

No.

Particular Requirement as per

IS:3812 in %

Test Results in %

Chemical Properties of Fly Ash

01 SiO2 35.0 Min. 60.21

02 Al2O3 Not Specified 26.08

03 Fe2O3 Not Specified 4.80

04 SiO2+Al2O3+Fe2O3 70.0 Min. 91.09

05 CaO Not Specified 1.00

06 MgO 5.0 Max. 0.25

07 Total alkali as Na2O 1.5 Max. 0.86

08 SO3 3.0 Max. 0.25

09 Cl 0.05 Max. 0.005

10 LOI(Loss in Ignition) 5.0 Max. 1.71

Physical Properties of Fly Ash

01 Lime Reactivity 4.5 Min. 6.10

02 Fineness (m2/Kg) 320 Min 330

03 Specific Gravity Not Specified 2.23

04 Residue on 0.045 mm sieve 34.0 Max. 34.0

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7.3.1.3 Fine Aggregate

Aggregates are the important constituents in concrete. They give body to the concrete,

reduce shrinkage and effect economy. The aggregate approximately occupy 70 -80 percent of the

volume of the concrete, their impact on various characteristics and properties of concrete is

considerable. The aggregate whose size is 4.75 mm and less is considered as fine aggregate.

Size, shape, texture and strength are important properties of aggregate, which effect the

properties of concrete.

Locally available sand brought from river Tarana-Morana was used as the fine aggregate.

It is hard durable and free from organic matters. The dust content varies from 1 % to 2 %. It is

stored in open place free from dust and water. The sieve analysis and physical properties of fine

aggregate are as shown in table no. 7.3.

Table 7.3

SIEVE ANALYSIS OF FINE AGGREGATE AND PHYSICAL PROPERTIES

Sr. No. Sieve Size Percentage passing

1 10.0 mm 100.0

2 4.75 mm 92.3

3 2.36 mm 86.5

4 1.18 mm 61.3

5 600 micron 31.8

6 300 micron 8.9

7 150 micron 1.3

8 Pan 0.0

Physical properties


2 Dry Bulk Loose Density 1572 Kg/m3

3 Silt and Clay Content 0.85

4 Fineness Modulus 3.18

5 Gradation Zone – I

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7.3.1.4 Coarse Aggregate

The size of aggregate bigger than 4.75 mm is considered as coarse aggregate. Mortar

contains aggregate of size 4.75 mm and concrete upto maximum size of 150 mm. The gradation,

shape and surface texture, has an important effect on the workability and finishing characteristics

of fresh concrete, consequently on the properties of hardened concrete. Well graded aggregate

containing minimum voids will require minimum paste to fill up the voids in the aggregates,

which increase the economy, higher strength, lower shrinkage and greater durability.

Dried angular aggregates obtained from the crushing of the rocks with maximum size of

20 mm were used throughout the experimental program. It was free from any organic impurities.

The physical property and sieve analysis of the coarse aggregate are shown in table no. 7.4.

Table 7.4

SIEVE ANALYSIS OF COARSE AGGREGATE AND PHYSICAL PROPERTIES

Sr. No. Sieve Size in mm Percentage passing

1 40.0 100.0

2 25.0 89.3

3 20.0 79.1

4 12.5 9.3

5 10.0 1.8

6 4.75 0.0

Physical properties


2 Dry Bulk Loose Density 1393 Kg/m3

3 Impact value 10.9 %

4 Flakiness index 22.5

5 Elongation index 20.3

6 Crushing value 16.3 %

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7.3.1.5 Steel

Mild steel bars of different diameters are used in casting of specimens of different RC

flexural elements for testing. The physical test result of reinforced bars are shown in table no.

7.5, and table no. 7.6

Table 7.5

WEIGHT DIMENSION TEST OF REINFORCED STEEL

Sr.

No.

Diameter(mm) Length (mm) Weight(gms) Actual Dia. (mm)

01 6 1002 222.32 5.999

02 6 1005 222.00 5.997

03 6 998 221.29 6.001

04 8 1006 396.95 8.000

05 8 1002 394.09 7.987

06 8 1000 394.19 7.996

07 10 996 614.07 10.000

08 10 1001 616.78 9.997

09 10 1003 617.64 9.994

10 12 1004 891.22 11.999

11 12 1003 899.55 12.061

12 12 998 893.88 12.053

Table 7.6

PHYSICAL TEST RESULTS OF REINFORCED BARS IN TENSILE TEST

Sr.

No.

Dia.

Of bar

(mm)

Area of

bar

(sq. mm)

Ult.

Tensile

Str.(Mpa)

Ave.Ult

Ten. Str.

(MPa)

Elongation

(In %)

Yield

Stress

(Mpa)

Average

Yield

Stress

(MPa)

01 6 28.27 537.67

547.16

24.30 445.51

437.90 02 6 28.25 534.51 24.25 437.37

03 6 28.28 569.31 21.45 430.81

04 8 50.27 626.62

634.18

17.6 427.69

428.98 05 8 50.10 642.71 17.5 431.14

06 8 50.22 620.71 18.25 428.12

07 10 78.54 620.53

617.51

18.10 413.80

413.73 08 10 78.50 617.52 17.52 418.15

09 10 78.44 614.48 18.45 409.23

10 12 113.08 614.55

615.33

15.2 411.18

415.87 11 12 114.25 612.69 14.5 415.75

12 12 114.10 618.76 15.5 420.68

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7.3.1.6 Water

Clean potable tap water was used for mixing of the concrete and for normal condition

curing same water was used for curing. While to study the behavior of concrete in aggressive

environment the cube are cured for 7 days in potable water while those are kept in sea water. The

potable water used in casting of concrete and sea water are tested, the potable water is used

satisfied the requirement as per IS456-2000. The Physico-chemical analysis of potable and sea

water is shown in table no. 7.7.

Table 7.7

PHYSICO-CHEMICAL ANALYSIS OF POTABLE AND SEA WATER

Sr. No. Types of Solids Content in

Potable

Water

Content in

Sea Water

Max. Permissible

Limits(IS456-2000)

01 Organic 130 510 200

02 Inorganic 610 39500 3000

03 Sulphate 180 1174 400

04 Chlorides 380 27000 2000

05 Total Dissolved Solids 880 40010 2000

06 pH Value 7.2 8.0 <6.0

07 Total Hardness CaCO3 - 6760 -

08 Sodium(as Na+) 430 8705 -

09 Calcium(as Ca++) 80 496 -

All parameters are expressed in mg/lit. except pH value.

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7.3.2 Concrete Mix Design

In this research the fly ash concrete was produced by replacing cement with fly ash, the

replacement level varied from 10 percent to 40 percent. The replacement level of fly ash is

primarily based on the required compressive strength of concrete among all other things. In

current investigation, to arrive at the content of fly ash to be blended with cement. The question

for new materials is always on, for better efficiency, functional utility, easy availability,

environmental acceptability and finally lesser cost.

All the R. C. elements and cubes are casted with concrete Mix -20, the mix is design as

per IS method and the proportion of materials required per m3 are shown in table no. 7.8

Table 7.8

CONTENT PER m3 OF CONCRETE

Sr.

No.

Description Content per m3 of concrete

01 Coarse Agg. [kg] 1240.0 1240.0 1240.0 1240.0 1240.0

02 Fine Agg. [kg] 614.0 614.0 614.0 614.0 614.0

03 Water[lit.] 191.6 191.6 191.6 191.6 191.6

04 Fly Ash % replacement of

cement

0 10 20 30 40

05 Fly Ash [kg] 0.0 38.3 76.6 114.9 153.2

06 Cement[ kg ] 383.0 344.7 306.4 268.1 229.8

07 Water/Cementitious

material

0.5 0.5 0.5 0.5 0.5

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7.3.3 Instruments

To test the materials used in the casting of reinforced flexural concrete elements, i. e.

cement, fine aggregate, coarse aggregate, water and fly ash, some of the instruments used in

laboratory are already described in chapter 6 in para 6.3.3 and addition instruments used are as

follows.

1, Dial gauge: 0.01 mm x 25 mm travel.

Baker make high sensitive with dual dial

having least count 0.01 mm and travel of 25

mm

2, To cast the beam elements, beam moulds 150mm x 150 mm x 700 mm size made of cast iron

confirming to IS 10086 -1982 are used, as shown in figure no.7.1 .

Figure 7.1 Beam mould 700 mm x 150mm x 150 mm

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3, Universal Testing Machine : To test the tensile strength of reinforcement steel of different

diameter and flexural test on reinforced concrete beam in pure bending the universal testing

machine as shown in figure 7.2, with three measuring range of maximum capacity of 400 kN.

was used.

Figure 7.2 Universal Testing Machine

The machine has the facilities for flexure loading for pure bending and load stabilizer

device for the consistent load. Electrically operated with facility of to apply uniform rate of

loading, with following specification and standard accessories was used.

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Specifications of Universal Testing Machine

Model detail ENKAY ENTERPRISE

Load Dial Range I, 0 - 40 kN Least count 0.1 kN

II , 0 - 200 kN Least count 0.5 kN

III, 0 - 400 kN Least count 1 kN

Clearance for Tension test 0- 700mm

Clearance for compression test 0 - 700 mm

Clearance between column 500 mm

Ram stroke 200 mm

Straining/piston speed at no load 0 – 150 mm/min.

Standard Accessories:

For tension clamping jaws for round specimens 6 – 20 mm and 25 – 40 mm

Pair of compression plate of diameter 120 mm

For transverse test,

Table with adjustable rollers width of rollers

160 mm

Diameter of rollers 30 mm

Maximum clearance between supports 700 mm

Radius of punch tops 12 mm and 16 mm

Operation Hydraulic pressure

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7.4 Planning of Experiments

In this experimental investigation, about 40 concrete reinforced beams of 150mm x 150

mm cross section and 700 mm longitudinal length with 2 bars of 12 mm dia. at bottom and 10

mm dia. at top as reinforcement and 15 mm cover to bars, as shown in figure no. 7.4, were casted

and divided into two series, each series had 20 beams and tested, for study of the flexural

behavior of reinforced concrete elements in normal and aggressive conditions.

Beams are casted with varying percentage of fly ash (0, 10, 20, 30, and 40 percent) of

replacement by cement content and it is planned to test beam at 28, 56, 112, and 365 days for

normal condition and aggressive condition, to decide the optimum level of fly ash to replacement

for maximum flexure strength of reinforced concrete and to study the effect of fly ash in

aggressive condition as compare to normal condition. In normal condition the beams are placed

in to the curing tank for maximum of 28 days and then they are kept inside of laboratory. In case

of aggressive conditions the beams are kept in sea water till those are tested.

Force

↓

Figure 7.3 Details of loading arrangement, the cross section, reinforcement and cover of test specimen

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Planning of Experiments

↓

7.5 Experimental Procedure

7.5.1 Designation

The concrete beams casted as per design mix are designated as under,

Sr.

No.

Designation Description

1 WFAW Without Fly Ash Normal Condition

2 WFAA Without Fly Ash Aggressive Condition

3 FA10W With Fly Ash 10 % Normal Condition

4 FA10A With Fly Ash 10 % Aggressive Condition







Total 40 beams casted

8 beams 0 %fly ash

8 beams 10 % fly ash


4 nos beams cured in normal

condition

4 nos of beams cured in

aggressive condition

1 beam tested at age of 28

days


days


days


days

8 beams30 % fly ash


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7.5.2 Moulds and Their Preparation

Utmost care was taken in selecting the moulds for the preparation of the test specimens.

The moulds were made so as to facilitate the removal of the molded specimen without any

damage. The moulds used for casting the concrete beams specimens were of the size 150mm ×

150mm × 700 mm. Each was inspected to prevent any leakage during compaction and that

dimension of the mould was accurate within the allowable limit. Before filling the concrete, the

inner face of the moulds was oiled to prevent sticking of the concrete to the sides of the moulds.

The care was taken to kept uniform cover to reinforcement with standard cement cover pieces.

Simultaneously concrete cubes are also casted for checking of characteristic compressive

strength and concrete cylinders are also casted for splitting tensile strength of concrete.

7.5.3 Preparation of the concrete mix

Dried materials were taken, as per weight batching system. First coarse aggregate

dumped in the hopper of concrete mixer, and fine aggregate, cement and fly ash are in sequence

pored in hoper. All materials are transferred in drum of mixer and then with help of gauged

container, water pored in the drum as per water /cemititious material ratio. Mixed materials until

the concrete appeared to be homogenous had a desired consistency.

7.5.4 Casting of the Specimens

In order to obtain a dense mix of the concrete, it was essential to compact it well.

Compaction of the concrete was achieved by using an electrically driven vibrating table. At a

time, three moulds were filled with wet concrete and were vibrated on the vibrating table.

Concrete was fully compacted by giving vibration on the vibrating table. Sufficient care was

taken to see that the wet concrete was properly filled in the corners and the edges of the mould

and proper cover to the reinforcement bars. As soon as air bubble stopped to rise to the top

surface, the mould was removed from the vibrating table and the surface was finished with

trowel. It was then carefully stored at a suitable space in laboratory.

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7.5.5 Vibrating Period

At a time, three specimens of beams were vibrated on table. The time of vibration to

properly compacted the concrete in the mould is variable depending on the grade of concrete and

water – cementitious materials ratio. It depends upon the type of coarse aggregate, proportion of

fine to coarse aggregate and water- cementitious materials ratio of the concrete mix. In short, it

depends on the workability of the concrete mix. Mixes prepared with crushed stone and greater

water cement ratio requires less time than that with lower water cement ratio. The time required

for compacting concrete by vibration in this experimental work is 1 minute. As such the exact

time of vibration on the table vibrator cannot be specified and is to be continued till a smooth top

surface is obtained. The air bubble must cease to rise to the top of the mould.

7.5.6 Demoulding and Numbering of the Specimens

After casting of the concrete beams, they were left undisturbed in the mould for the first

24 hours. Then the specimens were carefully removed from the moulds without damaging the

edges of the beams. The concrete beams are then placed carefully on the floor and numbered.

The date of casting and the designation of the mix were mentioned on two faces of the concrete

cubes with paint or marker. A table was prepared on each day, which could immediately identify

any specimen cast on that day and the method of curing used for those specimens.

7.5.7 Curing of the Specimens

After casting of the specimens, for water curing the beams are placed inside curing tank

and they are allowed for water curing maximum up to 28 days then they are kept inside the

laboratory. In case of curing in aggressive environment the cubes were kept in sea water for the

curing up to testing period. All the specimens were properly grouped according their different

mix designation so the removal of the specimen from place for testing work, could be

conveniently done in a proper sequence.

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7.6 Testing of Specimens for Flexure Strength, Deformation and Structural Behaviors

7.6.1 Testing Procedure

The test specimens were instrumented to obtain the measurement of transverse deflection

at mid span, crack width and flexural strength during the entire test. For pure bending the

transverse test assembly with two roller are adjusted for proper distance. Then suitable loading

range was adjusted. The concrete reinforced beam specimen was placed on flexural assembly

and load is applied on the specimen such that it produce pure bending. A dial gauge with a

magnetic base of maximum 25 mm capacity and 0.01 mm least count was used to measure the

deflections at mid span. The crack widths were measured with the help of a hand – held

microscope, the instrument was capable of measuring a maximum width of 10 mm and a

minimum width of 0.1 mm. By judgment, it was possible to measure 0.05 mm crack width. After

each load increment, a search was conducted for all cracks in the test zone to identify the widest

crack. A general view of test setup, in which the beam was supported on two pedestals on o span

of 600 mm with a pure moment zone of 100 mm, for flexural tests is shown in figure 7.5.

Figure 7.4 Beam loading arrangement in flexure

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Each beam was tested to failure by applying loads in a series of increments of 5 kN load.

It took one and one half minute for increasing the load to the specified limit. The holding period

for each increment varied from two to three minutes, during which load and deformation data

were noted and stored. The load was stabilized to a certain value with increment by help of load

stabilizer device attached with the machine.

7.6.2 Test Results

The testing of beam specimens of cross section 150 mm x 150 mm over the simply

supported span of 600 mm. The beam is supported on two pedestals and the load was applied to

the beam with help of flexure load assembly, to create the pure bending in a certain middle part

of the beam, which served as test zone. The beam has reinforcement at bottom 2 -12 mm dia.

and 2- 10 mm dia. at top, with effective cover of 15mm, tests were carried out as per testing

procedure, for the beams of control concrete and the beams having various percentage of fly ash.

The tests were carried out for two same groups of beams kept in normal condition and aggressive

condition.

The results were tabulated for the flexure load and respective central deflection and crack

width, for different load increment. For each beam the first crack load were observed and

beams was tested to the failure by applying loads in a series of increments.

Load – deflection curves for all the beams at the age of 28 days, 56 days 112 days and

365 days in normal condition are shown in figure 7.5 to 7.8 and similarly Load – deflection

curves for all the beams at the age of 28 days, 56 days 112 days and 365 days in aggressive

condition are shown in figure 7.9 to 7.12.

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7.6.2.1 Test Results for the Specimens Cured in Normal condition

The test results of the concrete beams in normal condition, at age of 28 days, 56 days,

112 days and 365 days are shown in table 7.9 to 7.12

Table 7.9

TEST RESULTS OF REINFORCED BEAM IN NORMAL CONDITION IN FLEXURE AT 28

DAYS AGE

Sr.

No

Load (kN)

↓

Central deflection in mm

↓

Percentage of fly ash

to replace cement→

0 10 20 30 40

01 5.00 0.05 0.08 0.10 0.13 0.15

02 10.00 0.20 0.24 0.25 0.28 0.34

03 15.00 0.27 0.29 0.32 0.36 0.41

04 20.00 0.36 0.39 0.42 0.46 0.51

05 25.00 0.41 0.45 0.50 0.54 0.60

06 30.00 0.49 0.54 0.62 0.68 0.75

07 35.00 0,56 0.64 0.69 0.73 0.81

08 40.00 0.68 0.72 0.78 fc 0.82 fc 0.88fc

09 45.00 0.76 0.80 0.92 0.94 0.92

10 50.00 0.89 0.94 fc 1.05 1.12 0.98

11 55.00 1.01 1.08 1.11 1.17 1.19

12 60.00 1.15fc 1.22 1.30 1.38 1.36

13 65.00 1.28 1.38 1.48 1.56 1.60

14 70.00 1.52 1.64 1.72 1.80 1.98

15 75.00 1.70 1.84 1.94 2.08 2.25

16 80.00 1.96 2.10 2.21 2.31 -

17 85.00 2.22 2.42 2.54 - -

18 90.00 2.70 2.85 2.98 -

19 95.00 3.15 - - - -

Ult. Load(kN) → 96.00 92.00 91.00 82.00 78.00

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Figure 7.5 Flexure behavior of beam at the age of 28 days with different % of fly ash in normal condition.

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5 3 3.5

Load

in k

N


Flexure behavior of beam at age of 28 day with different % of fly ash

0 % fly ash

10 % fly ash

20 % fly ash

30% fly ash

40 % fly ash

- 142 -

Table 7.10

TEST RESULTS OF REINFORCED BEAM IN NORMAL CONDITION IN FLEXURE AT 56

DAYS AGE

Sr.

No

Load (kN)

↓


↓



0 10 20 30 40

01 5.00 0.15 0.18 0.20 0.22 0.30

02 10.00 0.19 0.22 0.25 0.27 0.32

03 15.00 0.26 0.29 0.32 0.34 0.39

04 20.00 0.33 0.34 0.40 0.42 0.47

05 25.00 0.38 0.42 0.49 0.51 0.58

06 30.00 0.43 0.51 0.58 0.60 0.70

07 35.00 0.53 0.62 0.65 0.71 0.78

08 40.00 0.63 0.70 0.72 fc 0.79 fc 0.86 fc

09 45.00 0.71 0.82 0.86 0.95 1.08

10 50.00 0.80 0.90 fc 1.00 1.10 1.24

11 55.00 0.88 1.02 1.10 1.21 1.28

12 60.00 1.00 fc 1.18 1.25 1.36 1.36

13 65.00 1.11 1.25 1.42 1.52 1.64

14 70.00 1.23 1.42 1.66 1.72 1.98

15 75.00 1.38 1.65 1.86 1.98 2.20

16 80.00 1.50 1.95 2.15 2.28 3.42

17 85.00 1.62 2.12 2.46 2.66 -

18 90.00 1.80 2.35 2.98 3.05 -

19 95.00 1.98 2.62 3.08 - -

20 100.00 2.22 2.98 3.22 - -

Ult. load (kN → 102.00 104.00 105.00 94.00 84.00

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0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5

Load

in k

N



0 % fly ash

10 % fly ash

20 % fly ash

30 %fly ash

40 % fly ash

- 144 -

Table 7.11

TEST RESULTS OF REINFORCED BEAM IN NORMAL CONDITION IN FLEXURE AT

112 DAYS AGE

Sr.

No

Load (kN)

↓


↓



0 10 20 30 40

01 5.00 0.05 0.08 0.11 0.13 0.13

02 10.00 0.12 0.22 0.24 0.26 0.27

03 15.00 0.18 0.27 0.29 0.31 0.39

04 20.00 0.28 0.34 0.38 0.41 0.46

05 25.00 0.34 0.41 0.46 0.48 0.54

06 30.00 0.39 0.50 0.56 0.59 0.67

07 35.00 0.46 0.62 0.63 0.68 0.73

08 40.00 0.57 0.68 0.70 0.76 fc 0.79 fc

09 45.00 0.63 0.75 0.82 0.88 0.88

10 50.00 0.72 0.88 0.98 fc 1.06 1.12

11 55.00 0.83 1.02 1.10 1.18 1.21

12 60.00 0.98 1.15fc 1.21 1.30 1.34

13 65.00 1.08 1.32 1.38 1.48 1.60

14 70.00 1.20 fc 1.60 1.62 1.70 1.92

15 75.00 1.36 1.64 1.84 1.92 2.08

16 80.00 1.45 1.70 2.10 2.25 2.28

17 85.00 1.62 1.96 2.34 2.55 2.80

18 90.00 1.81 2.32 2.56 3.05 -

19 95.00 1.86 2.44 2.72 3.25 -

10 100.00 1.93 2.95 3.00 - -

Ult. Load(kN) → 104.00 106.00 109.00 96.00 88.00

- 145 -

Figure 7.7 Flexure behavior of beam at the age of112 days with different % of fly ash in normal condition.

0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5

Load

in k

N



0 % fly ash

10 % fly ash

20 % fly ash

30 % fly ash

40 % fly ash

- 146 -

Table 7.12

TEST RESULTS OF REINFORCED BEAM IN NORMAL CONDITION IN FLEXURE AT

365 DAYS AGE

Sr.

No

Load (N)

↓


↓



0 10 20 30 40

01 5.00 0.04 0.07 0.08 0.11 0.12

02 10.00 0.12 0.18 0.20 0.24 0.24

03 15.00 0.18 0.24 0.27 0.30 0.33

04 20.00 0.26 0.33 0.36 0.40 0.46

05 25.00 0.30 0.38 0.41 0.45 0.52

06 30.00 0.35 0.45 0.52 0.56 0.62

07 35.00 0.43 0.52 0.60 0.64 0.71

08 40.00 0.55 0.62 0.70 0.76 0.79 fc

09 45.00 0.62 0.70 0.82 0.89 0.94

10 50.00 0.68 0.82 0.98fc 1.06fc 1.12

11 55.00 0.78 0.94 1.08 1.18 1.22

12 60.00 0.90 1.10fc 1.21 1.30 1.34

13 65.00 1.00 1.28 1.38 1.45 1.60

14 70.00 1.15 fc 1.55 1.62 1.70 1.92

15 75.00 1.27 1.59 1.69 1.95 2.35

16 80.00 1.40 1.65 1.78 2.25 2.95

17 85.00 1.55 1.90 2.02 2.64 3.40

18 90.00 1.75 2.25 2.36 3.05 3.90

19 95.00 1.80 2.56 2.64 3.40 -

20 100.00 1.88 2.95 3.00 - -

Ult. Load (kN) → 104.00 110.00 114.00 98.00 94.00

- 147 -


0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5

Load

in k

N



0 % fly ash

10 %fly ash

20 % fly ash

30 % fly ash

40 % fly ash

- 148 -

7.6.2.2 Test Results for the Specimens in Aggressive condition

The test results of the concrete beams specimens of cross section 150 mm x 150 mm over

the span of 500 mm, having reinforcement at bottom 2 -12 mm dia. and 2- 10 mm dia. at top,

with effective cover of 15mm, in aggressive condition, at 28 days, 56 days, 112 days and 365

days age of elements are shown in table 7.13 to 7.16

Table 7.13

TEST RESULTS OF REINFORCED BEAM IN AGGRESSIVE CONDITION IN FLEXURE

AT 28 DAYS AGE

Sr.

No

Load (kN)

↓


↓



0 10 20 30 40

01 5.00 0.05 0.06 0.07 0.11 0.12

02 10.00 0.15 0.18 0.21 0.24 0.28

03 15.00 0.21 0.24 0.27 0.29 0.36

04 20.00 0.32 0.34 0.39 0.40 0.46

05 25.00 0.38 0.42 0.46 0.50 0.56

06 30.00 0.48 0.53 0.58 0.61 0.69

07 35.00 0.57 0.61 0.66 0.69 0.78

08 40.00 0.68 0.72 0.73 0.76 0.85fc

09 45.00 0.71 0.77 0.84 0.89 0.94

10 50.00 0.78 0.82 1.00 fc 1.04fc 1.12

11 55.00 0.87 0.93 1.08 1.14 1.21

12 60.00 1.04fc 1.11fc 1.18 1.30 1.34

13 65.00 1.18 1.24 1.32 1.44 1.52

14 70.00 1.38 1.49 1.52 1.65 1.88

15 75.00 1.54 1.64 1.75 1.90 2.65

16 80.00 1.75 1.87 2.11 2.20 3.26

17 85.00 1.88 1.99 2.32 3.42 -

18 90.00 2.05 2.25 2.58 - -

19 95.00 3.21 - - - -

Ult. Load(kN) → 98.00 93.00 92.00 86.00 82.00

- 149 -

Figure 7.9 Flexure behavior of beam at the age of 28 days with different % of fly ash in aggressive condition.

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5 3

Load

in k

N



0 % fly ash

10 % fly ash

20 % fly ash

30 % fly ash

40 % fly ash

- 150 -

Table 7.14


AT 56 DAYS AGE

Sr.

No

Load (kN)

↓


↓

Percentage of fly ash to

replace cement→

0 10 20 30 40

01 5.00 0.05 0.06 0.08 0.08 0.11

02 10.00 0.13 0.17 0.19 0.20 0.24

03 15.00 0.18 0.21 0.25 0.27 0.28

04 20.00 0.27 0.28 0.32 0.35 0.41

05 25.00 0.34 0.36 0.39 0.42 0.49

06 30.00 0.42 0.43 0.46 0.52 0.62

07 35.00 0.48 0.51 0.55 0.60 0.68

08 40.00 0.56 0.62 0.68 0.71 fc 0.77 fc

09 45.00 0.61 0.70 0.74 0.80 0.89

10 50.00 0.70 0.82 fc 0.84fc 0.94 1.12

11 55.00 0.78 0.89 0.92 0.99 1.20

12 60.00 0.92fc 0.98 1.04 1.15 1.29

13 65.00 1.01 1.10 1.18 1.32 1.48

14 70.00 1.17 1.22 1.46 1.52 1.68

15 75.00 1.35 1.50 1.62 1.78 1.90

16 80.00 1.70 1.82 1.98 2.18 2.62

17 85.00 1.81 1.94 2.18 2.32 2.75

18 90.00 1.95 2.15 2.48 2.65 2.95

19 95.00 - 2.60 2.80 2.95 -

20 100.00 - 2.98 3.22 - -

Ult. load (kN → 93.00 103.00 108.00 96.00 91.00

- 151 -


0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5

Load

in k

N



0 %fly ash

10 % fly ash

20 % fly ash

30 % fly ash

40 % fly ash

- 152 -

Table 7.15


AT 112 DAYS AGE

Sr.

No

Load (kN)

↓


↓


replace cement→

0 10 20 30 40

01 5.00 0.04 0.05 0.08 0.10 0.10

02 10.00 0.10 0.15 0.18 0.21 0.23

03 15.00 0.15 0.19 0.22 0.27 0.31

04 20.00 0.22 0.25 0.29 0.35 0.41

05 25.00 0.26 0.29 0.33 0.40 0.46

06 30.00 0.32 0.34 0.38 0.48 0.54

07 35.00 0.38 0.40 0.46 0.55 0.60

08 40.00 0.46 0.49 0.56 0.64 0.68

09 45.00 0.52 0.54 0.64 0.74 0.83

10 50.00 0.60 0.72 0.76 0.86 1.04fc

11 55.00 0.68 0.79 0.85 0.99 1.11

12 60.00 0.80 0.90fc 1.02fc 1.15fc 1.22

13 65.00 0.88 1.02 1.16 1.27 1.39

14 70.00 1.00fc 1.20 1.32 1.45 1.58

15 75.00 1.12 1.30 1.44 1.61 1.77

16 80.00 1.30 1.42 1.61 1.85 2.08

17 85.00 1.42 1.66 1.88 2.25 2.65

18 90.00 1.60 1.92 2.16 2.85 3.25

19 95.00 1.71 2.16 2.40 2.96 3.68

20 100.00 1.85 2.45 2.84 3.15 3.95

Ult. Load(kN) → 112.00 114.00 122.00 106.00 102.00

- 153 -


0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5

Load

in k

N



0 % fly ash

10 % fly ash

20 % fly ash

30 % fly ash

40 % fly ash

- 154 -

Table 7.16


AT 365 DAYS AGE

Sr.

No

Load (N)

↓


↓


replace cement→

0 10 20 30 40

01 5.00 0.04 0.04 0.05 0.07 0.08

02 10.00 0.10 0.11 0.12 0.16 0.22

03 15.00 0.14 0.16 0.19 0.22 0.26

04 20.00 0.21 0.23 0.28 0.31 0.36

05 25.00 0.26 0.29 0.34 0.37 0.44

06 30.00 0.35 0.37 0.42 0.48 0.56

07 35.00 0.39 0.42 0.48 0.57 0.63

08 40.00 0.46 0.50 0.56 0.67 0.72

09 45.00 0.51 0.55 0.58 0.73 0.86

10 50.00 0.58 0.61 0.64fc 0.84fc 1.01fc

11 55.00 0.66 0.69 0.73 0.92 1.14

12 60.00 0.78 fc 0.79fc 0.88 1.12 1.30

13 65.00 0.87 0.96 1.05 1.29 1.48

14 70.00 1.00 1.24 1.32 1.54 1.68

15 75.00 1.11 1.29 1.38 1.74 1.98

16 80.00 1.25 1.35 1.48 2.02 2.52

17 85.00 1.38 1.44 1.62 2.25 2.71

18 90.00 1.50 1.55 1.76 2.65 2.95

19 95.00 1.82 1.90 2.06 2.84 3.24

20 100.00 2.25 2.45 2.50 3.10 -

Ult. Load (kN) → 115.00 124.00 128.00 102.00 98.00

- 155 -


0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5

Load

in k

N



0 % fly ash

10 % fly ash

20 % fly ash

30 % fly ash

40 % fly ash

- 156 -

7.6.2.3 Test Results of the Concrete Cubes for Characteristic Compressive Strengths

The concrete cubes of the same mix were casted during casting of beam specimens for

flexure. The results of characteristic compressive strength were tabulated for different percentage

of fly ash and control concrete for different conditions. The results are used to calculate the

flexure strength of beam theoretically and to compare with practical values. The characteristic

compressive strength tabulated in table 7.17 as follows.

Table 7.17

AVERAGE CHARACTERISTIC COMPRESSIVE STRENGTH OF CONCRETE MIX

Curing period

↓

Compressive Strength of Concrete in N/mm2

↓

Condition of

Environment

↓ Percentage of fly ash to

replace cement→

0 10 20 30 40

28 Days 29.33 28.89 26.22 24.44 20.44 Normal

32.44 32.44 32.00 28.00 26.67 Aggressive

56 Days 37.78 37.33 39.11 32.44 28.89 Normal

41.78 42.22 41.77 37.33 35.56 Aggressive

112 Days 42.22 44.88 45.78 37.33 30.67 Normal

45.33 46.67 46.22 39.11 36.00 Aggressive

365 Days 44.88 47.55 48.00 38.67 32.00 Normal

44.00 47.11 48.00 40.88 38.22 Aggressive

7.6.2.4 Calculation Of Theoretical Ultimate Moment Of The Beams

For flexural strength prediction, ultimate theory is used for the fly ash concrete beams

and for control concrete beams, Ultimate flexural moment is calculated as per IS 456-2000

clause 38.1 by using the value of respective characteristic compressive strength at respective age

as shown in table 7.17 and yield stress in steel 415.787 N/mm2

obtain as shown in table 7.6 are

tabulated in table 7.18.

- 157 -

For rectangular sections without compression reinforcement the moment of resistance

would be obtain as follows. (IS 456-2000 clause 38.1 ANNEX - G

The depth of neutral is determine as follows

---------------- (1)

The respective value of obtained by equation (1) are less than the limiting value

0.48 for steel grade 415 as per IS 456-2000 clause 38.1 page 70, hence ultimate moment of

resistance of the sections are calculated by using the following equation as per IS 456-2000

Clause 38.1 ANNEX – G page 96.

-------------------------- (2)

The values calculate by the equation (2) for respective characteristic compressive strength of

concrete and yield stress of steel are tabulated in table 7.18

Table 7.18

THEORETICAL ULTIMATE MOMENT OF THE BEAMS

Curing period

↓

Theoretical Ultimate Moment (kNm)

↓

Condition of

Environment


replace cement→

0 10 20 30 40

28 Days 9.29 9.27 9.09 8.95 8.54 Normal

9.47 9.47 9.44 9.22 9.12 Aggressive

56 Days 9.69 9.67 9.74 9.47 9.27 Normal

9.82 9.83 9.82 9.67 9.60 Aggressive

112 Days 9.83 9.90 9.93 9.67 9.37 Normal

9.92 9.95 9.94 9.74 9.62 Aggressive

365 Days 9.90 9.95 9.98 9.72 9.44 Normal

9.98 9.97 9.98 9.79 9.71 Aggressive

- 158 -

7.6.2.5 Calculation Of Experimental Ultimate Moment Of The Beams

The beam specimen of 150 mm x 150 mm x 700 mm is supported as shown in figure 7.5 over the

span of 600 mm with pure bending arrangement by applying load through two point load, in pure

bending are tested and the ultimate moment of the beams calculated and are tabulated as shown

in table 7.19

Table 7.19

EXPERIMENTAL ULTIMATE MOMENT OF THE BEAMS

Curing period

↓

Experimental Ultimate Moment (kNm)

↓

Condition of

Environment


replace cement→

0 10 20 30 40

28 Days 12.00 11.50 11.38 10.25 9.75 Normal

12.25 11.62 11.50 10.75 10.25 Aggressive

56 Days 12.75 13.00 13.12 11.75 10.50 Normal

11.62 12.88 13.50 12.00 11.38 Aggressive

112 Days 13.00 13.25 13.62 12.00 11.00 Normal

14.00 14.25 15.25 13.25 12.75 Aggressive

365 Days 13.00 13.75 14.25 12.25 11.75 Normal

14.38 15.50 16.00 12.75 12.25 Aggressive

7.6.2.6 Theoretical Calculation of Crack Width

Cracking of concrete should not adversely affect of the appearance or durability of the

structure, the acceptable limits of cracking would vary with the type of structure and

environment. Where specific attention is required to limit the designed crack width to a

particular value.

If the strain in the tension reinforcement is not more than 0.8fy/Es, the crack width

calculated by the following equation as per IS 456 -2000 ANNEX – F with reference of clause

35.3.2 and 43.1.

- 159 -

Design surface crack width

Wcr = --------- (3)

Where acr = distance from the point considered to the surface of the nearest

longitudinal bar,

Cmin = minimum cover to the longitudinal bar,

Em = average steel strain at the level considered,

h = overall depth of the member, and

x = depth of the neutral axis

The average steel strain Em may be calculated on the basis of the following assumption;

The concrete and the steel are both considered to be fully elastic in tension and in

compression.

The elastic modulus of the steel may be taken as 200 kN/mm2 and the elastic modulus of

the concrete is as derived from the equation Ec = 5000 √fck both in compression and in tension.

The assumptions are illustrated in below figure

STRESS IN CONCRETE

1 N/Sq.mm.IN SHORT TERM

0.55 N/Sq.mm IN LONG TERM.

fSfS/ES

h

As

x

fc

SECTION CRACKED STRAIN STRESS

fS/EC

Where h = overall depth of the section ,

x = the depth from the compression face to the neutral axis,

fc = the maximum compressive stress in the concrete,

fs = the tensile stress in the reinforcement, and

Es = the modulus of elasticity of the reinforcement.

Alternatively, as an approximation, it will normally be satisfactory to calculate the steel stress on

the basis of the cracked section and then reduce this by an amount equal to the tensile force

generated by the triangular distributions, having the value of zero at the neutral axis and a value

- 160 -

at the centroid of the tension steel of 1 N/mm2 instantaneously, reducing to 0.55 N/mm

2 in the

long-term, acting over the tension zone divided by the steel area. For a rectangular tension zone

this gives

Єm = Єl – --------------- (4)

Where As = area of tension reinforcement,

b = width of the section at the centroid of the tension steel,

Єl = strain at the level considered, calculated ignoring the stiffening

of the concrete in the tension zone,

a = distance from the compression face to the point at which the

crack width is being calculated, and

d = effective depth.

The value of the crack width for the control concrete specimen at the age of 28 days cured in

normal condition, having ultimate moment 12 kNm for the section of 150mm x 150 mm with

reinforcement of 2 bars of 12 mm dia. is calculated as per IS 456-2000 by using the above

equation (3) and (4) as follows,

Using equation (1) and (2) to determine the actual fy,

→0.48 = --------- (A)

and

→ 12X 10 6

= ------ (B)

From (A) and (B) the values of

31.70 N/mm2 and fy = 563.64 N/mm

2

Єl = fy/Es

= 2.818 X 10-3

therefore

Єm = 2.818 X 10-3

–

Єm = 2.715 X 10-3

Hence crack width is given by

Wcr = = 0.122 mm

- 161 -

The practical objective of calculating crack width is merely to give guidance to the designer in

making appropriate structural arrangements and in avoiding gross errors in design, which might

result in concentration and excessive width of flexural crack.

The surface width of the cracks should not, in general, exceed 0.3 mm in members where

cracking is not harmful and does not have any serious adverse effects upon the preservation of

reinforcing steel nor upon the durability of the structures. In members where cracking in the

tensile zone is harmful either because they are exposed to the effects of the weather or

continuously exposed to moisture or in contact soil or ground water, an upper limit of 0.2 mm is

suggested for the maximum width of the cracks. For particularly aggressive environment, such as

the severe category as per IS 456-2000 clause 8.2.2.1, the assessed surface width of cracks

should not in general, exceed 0.1 mm. The cracks width of the control concrete and the concrete

with fly ash with normal and aggressive condition at ultimate load and at service load are

calculated as per the above equations and tabulated in table 7.20

Table 7.20

THEORETICAL CALCULATION OF CRACK WIDTH AT SERVICE LOAD AND

ULTIMATE LOAD

Curing

period

↓

CRACK WIDTH AT SERVICE LOAD AND ULTIMATE LOAD

(In mm)

↓

Condition

of Envin

↓

→

% of fly

ash

0 10 20 30 40

At

servi load

At

ult. load

At

servi load

At

ult. load

At

servi Load

At

ult. Load

At

servi Load

At

ult. load

At

servi load

At

ult. Load

28 Days 0.080 0.122 0.076 0.117 0.076 0.116 0.068 0.104 0.064 0.098 Normal

0.082 0.125 0.077 0.118 0.076 0.117 0.071 0.109 0.068 0.104 Aggressive

56 Days 0.085 0.130 0.087 0.133 0.088 0.156 0.078 0.120 0.069 0.106 Normal

0.077 0.118 0.086 0.134 0.090 0.138 0.080 0.122 0.076 0.116 Aggressive

112 Days 0.082 0.133 0.089 0.135 0.o91 0.139 0.080 0.122 0.073 0.112 Normal

0.094 0.143 0.096 0.146 0.103 0.156 0.089 0.135 0.085 0.130 Aggressive

365 Days 0.082 0.133 0.092 0.141 0.096 0.146 0.082 0.125 0.078 0.120 Normal

0.097 0.147 0.104 0.159 0.103 0.164 0.082 0.125 0.082 0.125 Aggressive

- 162 -

7.7 Comparison of Test results

The deformations of beam specimens containing different percentage of fly ash concrete

are compared with those of the companion control concrete beams for both curing condition, this

is done at service load and ultimate load. Normally serviceability criteria are checked at

theoretical service load in design. In the present investigation, essentially the performance of fly

ash concrete was checked with the control concrete in bending experimentally. Hence

experimental service load is taken for comparison purpose. Load- deflection curves of all the

beams are shown in figure 7.5 to 7.8 in normal condition and 7.9 to 7.12 in aggressive condition.

Principal test results containing experimental deformations of beams at cracking, at

service load and at ultimate loads are shown in below tables at different age.

Principal test results containing experimental deformations of beams at first crack, at service

load and at ultimate loads are shown in below table at 28 days age for normal and aggressive

condition shown in table 7.21.

Table 7.21

EXPERIMENTAL DEFORMATION OF BEAMS IN PURE BENDING AT 28 DAYS AGE

Beam

No.

% of

Fly

Ash

Curing

Condition

Cube

comp. Str.

at 28 days

N/mm2

Moment

at first

crack

kNm

Ult.

moment

kNm

Deflection (mm) Crack

Width at

ultimate

load

(mm)

At first

crack

At ult.

Load

01 00 Normal 29.33 6.00 9.60 1.15 2.70 0.50

02 00 Aggressive 32.44 6.00 9.80 1.04 2.05 1.10

03 10 Normal 28.89 5.00 9.20 0.94 2.85 0.55

04 10 Aggressive 32.44 6.00 9.30 1.11 2.25 1.15

05 20 Normal 26.22 4.00 9.10 0.78 2.98 0.55

06 20 Aggressive 32.00 5.00 9.20 1.00 2.58 1.20

07 30 Normal 24.44 4.00 8.20 0.82 2.31 0.65

08 30 Aggressive 28.00 5.0 8.60 1.04 2.20 1.40

09 40 Normal 20.44 4.00 7.80 0.88 1.98 0.65

10 40 Aggressive 26.67 4.00 8.20 0.85 1.88 1.45

- 163 -

Principal test results containing experimental deformations of beams at first crack, at

service load and at ultimate loads are shown in below tables at 56 days age for normal and

aggressive condition shown in table 7.22.

Table 7.22


Beam

No.

% of

Fly

Ash

Curing

Condition

Cube

comp. Str.

at 28 days

N/mm2

Moment

at first

crack

kNm

Ult.

moment

kNm


Width at

ultimate

load

(mm)

At first

crack

At ult.

Load

01 00 Normal 37.78 6.00 10.2 1.00 2.22 0.45

02 00 Aggressive 41.78 6.00 9.30 0.70 3.00 1.30

03 10 Normal 37.33 5.00 10.40 0.90 2.98 0.40

04 10 Aggressive 42.22 5.00 10.3 0.82 2.98 1.35

05 20 Normal 39.11 4.00 10.5 0.72 3.22 0.55

06 20 Aggressive 41.77 5.00 10.8 0.84 3.22 1.35

07 30 Normal 32.44 4.00 9.40 0.79 3.05 0.60

08 30 Aggressive 37.33 4.00 9.60 0.71 2.65 1.45

09 40 Normal 28.89 4.00 8.40 0.86 1.98 0.85

10 40 Aggressive 35.56 4.00 9.10 0.77 2.95 1.60



aggressive condition shown in table 7.23

- 164 -

Table 7.23


Beam

No.

% of

Fly

Ash

Curing

Condition

Cube

comp. Str.

at 28 days

N/mm2

Moment

at first

crack

kNm

Ult.

moment

kNm


Width at

ultimate

load

(mm)

At first

crack

At ult.

Load

01 00 Normal 42.22 7.00 10.40 1.2 1.83 0.35

02 00 Aggressive 45.33 7.00 11.20 1.00 1.85 0.85

03 10 Normal 44.88 6.00 10.60 1.15 2.95 0.35

04 10 Aggressive 46.67 6.00 11.40 0.72 2.45 0.95

05 20 Normal 45.78 6.00 10.9 0.98 3.00 0.55

06 20 Aggressive 46.22 6.00 11.02 12.20 2.84 1.10

07 30 Normal 37.33 4.00 9.60 0.78 3.07 0.60

08 30 Aggressive 39.11 6.00 10.60 1.15 3.15 1.25

09 40 Normal 30.67 4.00 8.80 0.79 2.28 0.60

10 40 Aggressive 36.00 5.00 10.20 0.68 3.25 1.30



aggressive condition shown in table 7.24

Table 7.24


Beam

No.

% of

Fly

Ash

Curing

Condition

Cube

comp. Str.

at 28 days

N/mm2

Moment

at first

crack

kNm

Ult.

moment

kNm


Width at

ultimate

load

(mm)

At first

crack

At ult.

Load

01 00 Normal 44.88 7.00 10.40 1.15 1.88 0.35

02 00 Aggressive 44.00 6.00 11.50 0.78 2.25 0.75

03 10 Normal 47.55 6.00 11.00 1.10 2.95 0.40

04 10 Aggressive 47.11 6.00 12.40 0.79 2.45 0.95

05 20 Normal 48.00 5.00 11.40 0.98 3.00 0.55

06 20 Aggressive 48.00 5.00 12.80 0.84 2.50 1.25

07 30 Normal 38.67 5.00 9.80 1.06 3.05 0.65

08 30 Aggressive 40.88 5.00 10.2 0.84 3.10 1.45

09 40 Normal 32.00 4.00 9.40 0.79 2.95 0.85

10 40 Aggressive 38.22 5.00 9.80 1.01 2.95 1.60

- 165 -

7.8 Discussion of Test Results

The fly ash concrete beams contain 10 percent fly ash to replace cement exhibited, 4.34

percent, 20 percent fly ash concrete exhibited 5.5 percent, 30 percent fly ash concrete exhibited

17 percent and 40 percent fly ash concrete exhibited 23 percent lower strength than the control

concrete at 28 days age in normal condition.

The fly ash concrete beams contain 10 percent fly ash to replace cement exhibited, 2

percent, 20 percent fly ash concrete exhibited 3 percent, higher strength and 30 percent fly ash

concrete exhibited 8.5 percent and 40 percent fly ash concrete exhibited 18 percent lower

strength than the control concrete at 56 days age in normal condition.



concrete exhibited 8 percent and 40 percent fly ash concrete exhibited 18 percent lower strength

than the control concrete at 112 days age in normal condition.

While the fly ash concrete beams contain 10 percent fly ash to replace cement exhibited,

6 percent, 20 percent fly ash concrete exhibited 9 percent, higher strength and 30 percent fly ash


than the control concrete at 365 days age in normal condition.


percent, 20 percent fly ash concrete exhibited 6.5 percent, 30 percent fly ash concrete exhibited

14 percent and 40 percent fly ash concrete exhibited 19 percent lower strength than the control

concrete at 28 days age in aggressive condition.


percent, 20 percent fly ash concrete exhibited 16 percent, 30 percent fly ash concrete exhibited 3

percent higher strength and 40 percent fly ash concrete exhibited 2 percent lower strength than

the control concrete at 56 days age in aggressive condition.

- 166 -




than the control concrete at 112 days age in aggressive condition.

While the fly ash concrete beams contain 10 percent fly ash to replace cement exhibited,

8 percent, 20 percent fly ash concrete exhibited 11 percent, higher strength and 30 percent fly

ash concrete exhibited 12 percent and 40 percent fly ash concrete exhibited 17 percent lower

strength than the control concrete at 365 days age in aggressive condition.

The companion beam of control concrete and fly ash contain identical beams cured in

aggressive condition and cured in normal condition the strength of elements exhibited more in

most cases 4 to 6 percent, for beam contain 10 and 20 percent fly ash while the beam containing

30 and 40 percent fly ash exhibited nearly same at 28 days age and 56 days age and at 112 days

age and 365 days age, exhibited 5 percent lower strength.

The fly ash concrete beams contain 10 percent fly ash to replace cement the first crack

started at 54 percent load of ultimate load and exhibited deflection was 0.94mm, and 20 percent

fly ash concrete beam exhibited first crack at 44 percent of ultimate load with deflection of 0.78

mm, 30 percent fly ash concrete exhibited first at 49 percent of ultimate load, with deflection of

0.82mm and 40 percent fly ash concrete exhibited first crack at 51 percent of ultimate load with

deflection of 0.88 mm which are lower strength than the control concrete beam exhibited first

crack at 62.5 percent load of ultimate load with deflection of 1.15 mm at 28 days age in normal

condition. Similar results are obtain in other specimens tested at the age of 56 days age, 112 days

age and 365 days age in normal condition.

The fly ash concrete beams contain 10 percent fly ash to replace cement the first crack

started at 64 percent load of ultimate load and exhibited deflection was 1.11mm, and 20 percent

fly ash concrete beam exhibited first crack at 54 percent of ultimate load with deflection of 1.00

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mm, 30 percent fly ash concrete exhibited first at 58 percent of ultimate load, with deflection of

1.04 mm and 40 percent fly ash concrete exhibited first crack at 49 percent of ultimate load with

deflection of 0.85 mm which are lower strength than the control concrete beam exhibited first

crack at 61 percent load of ultimate load with deflection of 1.04 mm at 28 days age in aggressive

condition. Similar results are obtain in other specimens tested at the age of 56 days age, 112 days

age and 365 days age in aggressive condition.

The companion beam of control concrete and fly ash contain identical beams cured in

aggressive condition first crack develops early as compared to cured in normal condition. But the

deflection of specimens cured in aggressive are nearly 10 percent less than cured in normal

condition. For beam contain 10 and 20 percent fly ash show similar results, while the beam

containing 30 and 40 percent fly ash exhibited deflections are more or nearly same cured in

aggressive condition as compare to cured in normal condition.

The fly ash concrete beams contain 10 percent fly ash to replace cement exhibited,

0.55mm crack width, which is 10 percent more than control concrete beam. Similarly 20 percent

fly ash concrete shows 0.55 mm crack width, 30 percent fly ash concrete shows 0.65 mm crack

width and 40 percent fly ash concrete beam shows 0.65 mm crack width at ultimate load which

are 10 to 13 percent more as compare to control concrete beam specimen at 28 days age in

normal condition.


mm crack width, which is 5 percent more than control concrete beam. Similarly 20 percent fly

ash concrete shows 1.20 mm crack width, 30 percent fly ash concrete shows 1.40 mm crack

width and 40 percent fly ash concrete beam shows 1.45 mm crack width at ultimate load which

are 09 to 30 percent more as compare to control concrete beam specimen at 28 days age in

aggressive condition.

The crack width at 56 days age of concrete for similar specimen in normal condition

curing the width is 10 to 40 more in fly ash containing specimens as compared to control

concrete specimen, at 112 days age this value varies between10 percent to 55 percent while at

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365 days age of concrete the values varies from 10 percent to twice width cured in normal

condition.

The crack width at 56 days age of concrete for similar specimen in aggressive condition

curing the width is 4 percent to 23 percent more in fly ash containing specimens as compared to

control concrete specimen, at 112 days age this value varies between 6 percent to 50 percent

while at 365 days age of concrete the values varies from 13 percent to twice width cured in

normal condition.

The crack width of same age companion specimen cured in normal condition were 50

percent of the specimens cured in aggressive condition for control concrete as well as for the

concrete containing fly ash of similar percentage.

For flexural strength prediction, same ultimate theory as per IS 456-2000 used for control

and fly ash containing specimens cured in normal condition and in aggressive condition. The

ratio of Mu expt and Mu theory are 1.29 for control concrete, 1.24 for 10 percent fly ash concrete

specimen, 1.25 for 20 percent fly ash concrete, 1.14 for 30 percent fly ash concrete and 1.14 for

the specimens containing 40 fly ash at the age of 28 days in normal curing condition. In

aggressive condition the ratio of Mu expt and Mu theory at the age of 28 days are 1.29 for control

concrete, 1.22 for 10 percent fly ash concrete specimen, 1.22 for 20 percent fly ash concrete,

1.16 for 30 percent fly ash concrete and 1.12 for the specimens containing 40 fly ash.

The ratio of Mu expt and Mu theory are 1.32 for control concrete, 1.34 for 10 percent fly ash

concrete specimen, 1.34 for 20 percent fly ash concrete, 1.21 for 30 percent fly ash concrete and

1.13 for the specimens containing 40 fly ash at the age of 56 days in normal curing condition. In



1.24 for 30 percent fly ash concrete and 1.18 for the specimens containing 40 % fly ash.



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1.17 for the specimens containing 40 fly ash at the age of 112 days in normal curing condition. In






1.24 for the specimens containing 40 % fly ash at the age of 365 days in normal curing condition.

In aggressive condition the ratio of Mu expt and Mu theory at the age of 365 days are 1.44 for control



The ratio of Mu expt and Mu theory at the age of 28 days of concrete for control concrete and

concrete having fly ash 10 percent and 20 percent are nearly same or 4 to 5 percent less in

normal condition and in aggressive condition, while it less 10 to 14 percent in case of specimens

contain 30 and 40 percent fly ash in both conditions. But at 56 days age of concrete the

specimens having 10 and 20 percent fly ash shows same or slightly more values than control

concrete specimens and for 30 percent and 40 percent fly ash the value are less. At the of age

112 days and 365 days this ratio is 5 to 10 percent more in cases of specimen containing 10 and

20 percent fly ash, while it is shows lower values 10 to 15 percent than control concrete in

normal as well as aggressive curing condition.

These companion beams of control concrete and fly ash concrete shows nearly same

strength and deformation characteristics cured in respective condition having fly ash 10 and 20

percent, while fly ash contains are 30 and 40 percent the strength is less with excessive

deformation also in normal condition and aggressive condition also.

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7.9 Conclusions

The following conclusions are drawn from the study of flexural behavior of beams on

conventionally reinforced concrete using fly ash concrete beams over the control concrete

beams.

The experimental work undertaken here, produced fly ash concrete replacing 10 percent,

20 percent, 30 percent and 40 percent of cement with STPS fly ash.

At the early age the characteristic compressive strength of concrete with fly ash is less

than control concrete, but at the age of 56 days, the concrete having 10 percent and 20

percent fly ash have same and 3 % more strength respectively in normal condition and in


At the age of 112 days, the concrete having 10 percent and 20 percent fly ash have 3 %

and 9 % more strength respectively in normal condition and near to same value in


At the age of 365 days, the concrete having 10 percent and 20 percent fly ash have 6 %

and 9 % more strength respectively in normal condition and near to same value in


The beams with the reinforcement less than the minimum specified in the code, the

cracking strength was 62 % to 67 % of ultimate strength for control concrete, while it is

42 % to 54% for concrete having fly ash 10 % to 40 % in normal condition. For

aggressive condition the cracking strength was 52 % to 62 % for control concrete while it

is near to 50 % for concrete having fly ash

The concrete contain fly ash cured in aggressive condition shows same or slightly less

ultimate strength than the companion control beams. While it is more in normal

condition.

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The theoretical strength prediction of beam in flexure as per IS 456-2000 shows the

average value of 28 days, 56 days, 112 days and 365days of Mu expt / Mu theory was 1.31

for control concrete and 1.32 for 10 percent fly ash, 1.35 for 20 percent fly ash, 1.22 for

30 percent fly ash and 1.17 for 40 percent fly ash concrete in normal condition.

The theoretical strength prediction of beam in flexure as per IS 456-2000 shows the

average value of 28 days, 56 days, 112 days and 365days of Mu expt / Mu theory was 1.34

for control concrete and 1.38 for 10 percent fly ash, 1.44 for 20 percent fly ash, 1.26 for

30 percent fly ash and 1.22 for 40 percent fly ash concrete in aggressive condition.

The ratio of Mu expt in aggressive condition and in normal condition of the companion

beams are near to 1.01 to1.05 at the age of 28 days.







Generally, the fly ash concrete beams with 10 % and 20 % fly ash recorded slightly

higher transverse deflections at service load as compare to control concrete. But the beam

having 30 % and 40 % fly ash have more deflection.

At service load the crack width varying from 0.082 to 1.25 mm for all the beams. The

control shows equal or 4 to 5 % more crack width than the companion fly ash concrete

beams. The crack width in aggressive condition, at service load as well as at ultimate load

was higher than the normal condition for all the companion beams.

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The experimental investigation clearly demonstrated that there was no difference in

strength, deformations and structural performance between the control and the having 10

percent fly ash and 20 percent fly ash.

As for design, the theory applied for strength prediction of control beams is equally valid

for that of fly ash concrete beams.

20 percent fly ash concrete beam shows higher strength, permissible deformations and

superior structural performance as compare to control concrete after 56 days age of

concrete. control concrete one cubic meter needs 383 Kg cement and 20 percent replaced

cement by fly ash needs 306 Kg cement which is clear saving of cement of 77 Kg per

cubic meter of concrete.

Documents

CHAPTER 7 EXPERIMENTAL INVESTIGATION OF …shodhganga.inflibnet.ac.in/bitstream/10603/39791/10/10_chapter7.pdf · The test programme was designed to study the flexure response of