india - research paper - santosh - 021106

STUDY ON THE PROPERTIES OF CONCRETE CONTAINING RICE HUSK ASH AS AN ADMIXTURE

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Dept. of CIVIL Engg. Basaveshwar Engineering College, Bagalkot

CHAPTER 5 EXPERIMENTAL PROGRAMME

5.1 Introduction:

The objective of this programme was to obtain experimental data of effect on

1. Workability

2. Compressive strength

3. Flexural strength

4. Split tensile strength

5. Modulus of elasticity

6. Poison’s ratio

The size of the specimen considered for comparative strength test was

(150x150x150) mm, for flexure strength - (100x100x500) mm, for modulus of

elasticity and poison’s ratio tests- cylinders of 150mm dia and 300mm height

moulds. The cement was replaced by RHA by 5%, 10%, 15%, 20% by volume

of cement taken.

Table 5.1 Materials used for the tests:

Material Source

1. Cement Ultra -Tech Cement ( Grasim Industries )

2. Aggregate Bijapur Local quarry ( Trap )

3. Sand Bhima river Bed Bijapur Dist. )

4. Rice Husk Ash N.K. Enterprises, Jhurusguda ( Orissa )


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5.2 EXPERIMENTAL DETAILS:

5.2.1 Mix design details

To compare the changes in the properties of concrete and to study the

performance of Rice husk ash, the following design mixes and percentages of

rice husk ash have been considered.

% of RHA by weight of cement – 10 , 15, 20, 25 %

Table 5.2 Mix Design Details:

Mixes Proportions W/C ratio

Cement

(Kg/ m3)

Sand

(Kg/m3) Aggregate (Kg/m3)

I 1:1.47:2.77 0.45 412 628.92 (36%) 1141.24

II 1:1.25:2.58 0.4 463.5 582.87(34%) 1198.12

III 1:1.06:2.62 0.35 480 510.17(30%) 1257.79

Superplasticizer used – Conplast SP430 – 1 % by weight of Cement.

5.2.2 Aggregate properties

The aggregates of size 20 mm and below are used for the tests. The

properties are as follows.

Water absorption - 0.42 %

Specific gravity – 2.8


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Table 5.3 Grading of aggregates confirming to IS: 383 – 1970

IS Designation mm % Passing for graded aggregate of nominal % Selected

80 --

63 -- --

40 100 100

20 95-100 95

16 -- --

12.5 -- --

10 25-55 40

4.75 0-10 05

2.36 -- --

5.2.3 Cement properties Cement used for the test – Ultra tech cement

Table 5.4 Properties of Cement:

S.No Characteristics test results IS-8112-1989 specifications

1 Fineness 6.9 < 10

2 Specific Gravity 3.1 --

3 Standard consistency (%) 32 --

4 Initial Setting time (min) 47 > 30

5 Final Setting time (min) 110 < 600

6 Compressive strength (MPa)

3 days 24.5 > 23

7 days 38.45 > 33


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5.2.4 Sand properties

The sand used for the test confirms to Grade – III of Is: 383 – 1970

Specific Gravity of sand – 2.65

Table 5.5 The grading of aggregate:

IS Sieve (mm) % Passing of sand taken % Passing for Grade - III

10 100 100

4.75 100 90 -100

2.36 100 85 - 100

1.18 86 75 - 100

0.6 61 60 - 79

0.3 27 12. - 40

0.15 5.5 0 - 10

5.2.5 RHA specifications.

Table 5.6 Minimum Guaranteed Specifications for Rice Husk Ash

SiO2 - Silica 85 % minimum

Humidity 2 % maximum

Particle size 25 microns average

Colour Grey

Loss on ignition at 800°C 4 % maximum

Ph value 8

5.2.6 Superplasticizer details

superplasticizer – Conplast SP430 ( FOSROC Chemicals)

Description: Conplast SP430 is based on sulphonated Napthalene Polymers

and supplied as a brown liquid instantly dispersible in water. Conplast SP430


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has been specially formulated to give high water reductions up to 25% without

loss of workability or to produce high quality concrete of reduced permeability.

Standard compliance: Conplast SP430 complies with IS:9103:1999 and

BS:5075 part 3. Conplast SP430 conforms to ASTM-C-494 Type F and Type

A depending on the dosage used.

Properties: Specific Gravity 1.220 to 1.225 at 30 degrees

Chloride contents Nil to IS: 456

Air entrainment Approx 1% additional air is entrained

Compatibility: can be used with all types of cement except high alumina

cement. Conplast SP430 is compatible with other types of Fosroc admixtures

when added separately to the mix. Site trials should be carried out to optimize

dosage.

Workability: can be used to produce flowing concrete that requires no

compaction. Some minor adjustment may be required to produce high

workable mix without segregation.

Cohesion: Cohesion is improved due to dispersion of cement particles thus

minimizing segregation and improving surface finish.

Compressive strength: Early strength is increased up to 20% if water

reduction is taken advantage of. Generally, there is improvement in strength

up to 20% depending upon W/C ratio and other mix parameters.

Durability: Reduction in W/C ratio enables increase in density and

impermeability thus enhancing durability of concrete.

Dosage: The rate of addition is generally in the range of 0.5-2.0 litres/100 Kg

of cement.

Uses: To produce pumpable concrete, to produce high strength, high grade


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concrete M30 and above by substantial reduction in water resulting in low

permeability and high early strength and to produce high workability concrete

requiring little or no vibration during placing.

Procedure for Specimen Preparation.

The different ingredients of Concrete Viz. Cement, sand & aggregates

were weighed according to the proportions. All these ingredients were

thoroughly dry mixed in the drum mixture. To this dry mix RHA was added

and dry mixed. To this dry mix the calculated amount of water was added and

thoroughly mixed at this stage superplasticizer was also added at slow rate.

This homogeneous concrete mix was filled into the concrete moulds, which

wee then kept on the vibrating table for vibration. After vibration the

specimens were smoothly finished. After 24 hours the specimens were

removed and transferred to the curing tank, where in they wee allowed to cure

for 3, 7 and 28 days. Then specimens were tested for their respective

strength.

5.3 COMPRESSIVE STRENGTH TEST: ( IS: 516 )

The specimen shall be cubical in shape of size 15 x 15 x 15 cm, if the

largest nominal size of the aggregate does not exceed 20 mm.

Procedure:

1. Sampling of material

2. Preparation of material

3. Proportioning of material

4. Weighing

5. Mixing of concrete


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6. Compacting – Compacting has been done by mechanical vibrator

7. Curing-

8. Testing - testing machine – compression testing machine

9. Age of test – tests shall be made at recognized ages of the test

specimens

10. Number of specimens – at least 3 specimens required.

11. Placing of specimen in the testing machine – In the case of cubes, the

specimen shall be placed in the machine in such a manner that the

load shall be applied to opposite sides of the cubes as cast, i.e. not to

the top and bottom.

12. Calculation: the measured compressive strength of the concrete

specimen shall be calculated by dividing the maximum load applied to

the specimen during the test by cross sectional area, calculated from

the mean dimension of the section and shall be expressed to the

nearest N/mm2.

Maximum Load applied

Compressive strength =

Cross sectional area

5.4 SPLIT TENSILE STRENGTH OF CONCRETE. ( IS – 5816-1999 )

The cylinder specimen shall have diameter not less than four times the

maximum size of coarse aggregate and not less than 150mm. For routine

testing specimen shall be cylinder 150mm in diameter and 300 mm long.

Procedure:

1. Sampling of material


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2. Preparation of material

3. Proportioning of material

4. Weighing

5. Mixing of concrete

6. Compacting – Compacting has been done by mechanical vibrator

7. Curing-

8. Testing - testing machine – compression testing machine

9. Age of test – tests shall be made at recognized ages of the test

specimens

10. Number of specimens – at least 3 specimens required.

11. Placing of specimen in the testing machine- the test specimen shall be

placed in the centering jig with packing strip carefully positioning along

the top and bottom of the plane of loading of the specimen. The jig

shall then be placed in the machine so that the specimen is located

centrally.

12. Calculation – the measured splitting tensile strength of the specimen

shall be calculated to the nearest 0.05 n/mm2 using the following

formula

fct = 2 p / π ld

where,

p = maximum load in Newton

l = length of the specimen

d = cross sectional dimension

5.5 COMPACTION FACTOR TEST:

It is more precise and sensitive than the slump test and is particularly


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useful for concrete mixes of very low workability as are normally used when

concrete is to be compacted by vibration. This test works on the principle of

determining the degree of compaction achieved by a standard amount of work

done by allowing concrete to fall through a standard height.

The sample of concrete to be tested is placed in the upper hopper up

to brim. The trap door is opened so that the concrete falls into the lower

hopper. The trap door of the lower hopper is opened and the concrete is

allowed to fall into the cylinder. The excess concrete remaining above the top

level of the cylinder is then cut off with the help of plane blades. The concrete

is filled up exactly up to the top level of the cylinder. I is weighed to the

nearest 10 gms. The cylinder is emptied and then refilled with concrete from

the same sample in layers approximately 5 cm deep. The layers are heavily

rammed or vibrated so as to obtain full compaction. The top surface is struck

off and is weighed.

Then,

Weight of partially compacted concrete

Compaction Factor =

Weight of fully compacted concrete

5.6 LATERAL EXTENSOMETER: ( IS: 516 )

Introduction:

The equipment is designed to measure the lateral extension of 15 cm dia x 30

cm high concrete cylinder specimen tested for compression. The deformation

of the diameter ( lateral extension) is indicated on a dial gauge 0.002 x 12

mm. the dial gauge reading are 2.5 times the actual extension in the


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specimen and hence the observed readings are to be divided by 2.5 to get the

actual extension.

Description:

It consists of 2 semicircular dial gauge frames, which are pivoted at the

fulcrum screw. 4 no of hardened and tapered end screws are fitted

diametrically opposite for holding the extensometer on to the specimen. The

ratio of the distance from the center if the frame to the center of the fulcrum

and distance between the centers of the dial gauge spindle and the center of

the fulcrum is 1:2.5 thus the dial gauge shows the reading 2.5 times the actual

extension.

A spacer strip is provided to fix the extensometer to the specimen and

to initially set the dial gauge. the spacer strip is kept in position with the help

of thumb screws. a spring is provided to keep the tip of the dial gauge in

contact with anvil. the tension of the spring can be adjusted with the help of

the spring adjustment nut.

Setting up of and Test procedure:

Keep the spacer strip in a position with the help of the thumbscrews. Adjust

the spring adjustment nut so that there is very little spring tension. Place the

concrete cylinder 15 x 30 cm and keep the extensometer midway of the

concrete cylinder along its height. Tighten the screws in a way that the

specimen is held by the extensometer diametrically with the axis of the

extensometer. Lock the screws in position with the help of the locking nuts.

Keep the specimen in the compression-testing machine. Adjust anvil so

that the dial gauge spindle is in the upper most position. Lock the anvil and

take the dial gauge reading. Remove the spacer strip by unscrewing the


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thumbscrews. See that the dial gauge is not disturbed. if it is disturbed, initial

reading should be taken again.

Start applying compression load across the two faces of the cylinder.

Record the dial gauge reading at different loads until the specimen fails.

Calculate lateral extensometer of the specimen by dividing the dial

gauge reading by 2.5.

5.7 LONGITUDINAL COMPRESSOMETER:

The equipment has been fabricated for determination of the strain and

deformation characteristics of cement concrete cylinder of 15cm dia x 30 cm

long. a dial gauge of 0.002 x 12 mm is fixed. Due to the pivot, the

compression readings are magnified twice and to get the actual deformation

of the specimen, the observed readings of the dial gauge are to be divided by

two.

Description:

The compressometer consists of two frames for clamping to the

concrete specimen by means of five tightening screws having hardened and

tapered ends. The bottom frame is tightened to the specimen with three

tightening screws placed at 120 degrees. The top frame has two tightening

screws placed diametrically opposite. The two frames are held in position by

means of two spacers. Spacer screws are provided to fix the spacers to the

frame. The center distance of the tightening screws of the bottom and top

frame is 20 cm. a pivot rod rests on pivot screws. The pivot rod can be

adjusted, to get the proper friction between the rod and its supports, by

adjusting and locking the pivot screws. a spring provided so that the pivot rod


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is always in contact with the pivot screws. Ball chain is provided to adjust the

tension of the spring. the spring loading clips are fixed to the top and bottom

frames. A dial gauge of 0.002 x 10mm is fixed to a bracket fitted to the top

frame. The dial gauge spindle rests on an adjustable anvil. the distances from

the center of the frame to the center of the pivot rod and center of the dial

gauge spindle are equal. So the dial gauge will be showing twice the actual

deformation.

5.7.1 SETTING UP AND TEST PROCEDURE:

Assemble the top and bottom frame by keeping the spacers in position. Keep

the pivot rod on the screws. Adjust the screws and lock them in position. Keep

the tightening screws of the bottom and top frame unscrewed (but not

completely)

Keep the specimen on a level surface. Keep the compressometer

centrally on the specimen so that the tightening screws of the bottom and top

frame are at an equal distance from the two ends. Screw the tightening

screws so that the compressometer is held on the specimen. Remove the

spacers by unscrewing the spacer screws.

Keep the specimen with compressometer centrally on the lower platen

of the compression-testing machine. Set the dial gauge and take the initial

readings. start applying load at a uniform rate. go on noting the dial gauge

readings at different loads until the specimen fails.

Actual deformation = observed reading / 2

5.8 TEST FOR FLEXURAL STRENGTH OF CONCRETE ( IS: 516 )

Size of the specimen: (10 x 10 x 50) cm


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Apparatus: Beam mould: beam mould confirming to IS: 10086 - 1982 ,

vibrator, Universal Testing Machine

Procedure: Test specimens stored in water at a temperature of 24 - 36o C

shall be tested immediately on removal from the water while they are still in

wet condition. The dimension of the specimen shall be noted. no preparation

of the surface is required.

Placing the specimen in the testing machine: the bearing surfaces of

the supporting and loading rollers shall be wiped clean and any loose sand or

other material removed from the surfaces of the specimen where they are to

make contact with rollers. The specimen shall be then spaced in the machine

in such a manner such that the load shall be applied to the upper most

surface as cast in the mould along two lines spaced at 13.33 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 fiber stress increases

at approximately 180 kg/min. the load shall be increased until the specimen

fails and the max load applied to the specimen during the test shall be

recorded. the appearance of the fractured faces of the concrete and many

unusual features in the type of the failure shall be noted.

Calculation:

The flexural strength of the specimen shall be expressed as the modulus of

rupture fb, which, if 'a' equals the distance between the line of fracture and the

nearer support, measured on the centerline of the tensile side of the

specimen, in cm, shall be calculated to the near 0.5 Kg/ cm2 as follows


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fb = (p x l) / ( b x d2)

when a is greater than 13.3 cm for 10 cm specimen

fb = (3 xp x a) / ( b x d2)

when a is less than 13.33 cm but grater than 11 cm for 10 cm specimen

where b = measured width in cm of the specimen

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

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

p = max load in Kg applied to the specimen

if a is less than 11 cm for 10 cm specimen the results of the test shall be

discarded.

5.9 POISON’S RATIO Poison’s ratio = lateral strain / longitudinal strain

5.10 MODULUS OF ELASTICITY

Modulus of Elasticity = longitudinal stress / strain


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CHAPTER 6

TEST RESULTS AND DISCUSSION The following table shows the different test results of concrete containing Rice

Husk Ash as an admixture.

6.1 COMPACTION FACTOR

Compaction factors of MIX – II

MIX – II Proportion - 1:1.25:2.58

W / C ratio – 0.4

Superplasticizer – Conplast SP 430 – 1 % by weight of cement

Table 6.1 Compaction factors:

S. No % of RHA Compaction Factor

1 0 0.91

2 5 0.86

3 10 0.81

4 15 0.77

5 20 0.73 Workability was checked by compaction factor test the results of the

same are represented in Table 6.1 which range from 0.91 – 0.73. Compaction

factor goes on reducing as addition of RHA increases. Workability reduces

with addition of R.H.A. This is mainly due to the large surface area of RHA

which is in the range of 50 – 100 m2/ gm. Large addition would produce dry or

unworkable mix unless water reducing admixture or superplasticizers are

used. Due to absorptive character of cellular RHA particles, concrete

containing RHA require more water for a given consistency. [ 5 ] by addition of

25% of RHA it is difficult to get any workability, hence superplasticizer is must

whenever we replace cement by RHA as an mineral admixture. G.Roddiguez


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De Sensale reported that at all the replacement levels the RHA concrete

require more superplasticizers compared to controlled concrete to obtain

desired slump which is due to high specific area of RHA [12].

6.2 COMPRESSIVE STRENGTH Table 6.2 COMPRESSIVE STRENGTH: MIX I

COMPRESSIVE STRENGTH (N/mm2) RHA (%) 3 Days 7 days 28 Days

0 18.95 23.18 36.55 5 21.99 23.86 40.29

10 20.92 26.32 38.43 15 18.37 23.18 37.81 20 18.70 21.85 37.20

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20% of RHA

Com

pres

sive

stre

ngth

( N

/mm

2)

3 days7 days28 days

Fig 6.1 Compressive strength V/S % of RHA - MIX I


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Table 6.3 COMPRESSIVE STRENGTH: MIX II

COMPRESSIVE STRENGTH (N/mm2)

RHA (%) 3 Days 7 days 28 Days

0 20.73 26.33 40.35

5 25.62 27.77 45.95

10 24.52 29.37 44.66

15 20.66 27.25 42.85

20 20.26 24.88 41.07

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20% of RHA

Com

pres

sive

Str

engt

h (N

/mm

2)

3 days7 days28 days

Fig 6.2 Compressive strength V/S % of RHA – MIX II


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Table 6.4 COMPRESSIVE STRENGTH: MIX III

COMPRESSIVE STRENGTH (N/mm2)


0 23.8 30.58 46.81

5 28.59 32.41 57.37

10 26.36 34.13 54.78

15 23.92 31.7 50.72

20 22.94 30.51 48.27

0

10

20

30

40

50

60

70

0 5 10 15 20% of RHA

Com

pres

sive

Str

engt

h ( N

/mm

2)

3 days7 days28 days

Fig 6.3 Compressive strength V/S % of RHA – MIX III


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The cube specimens of Mix I, mix II and mix III were tested for

compressive strength as per IS:516, the results obtained are represented in

Table 6.2, 6.3 and 6.4 respectively. For addition of 5% of RHA there is an

increase in the compressive strength of concrete when compared to the

controlled concrete. The same has been produced below

Table 6.5 Percentage increase in compressive Strength

% Increase in compressive strength Mix No

3 days 7 days 28 days

I 16.04 11.54 20.15

II 13.55 11.54 10.41

III 10.23 13.87 22.55

The compressive strength test results shows that there is increase in

compressive strength for 5% replacement of cement by RHA. The increase in

strength is up to 22% in comparison with controlled concrete. Further, any

increase in RHA shows decreasing trend in compressive strength. From the

present study and literature reported it can be observed that there is an early

increase in strength of concrete containing RHA due to early pozzolanic

action, and also later strength (90 days). Because clinkering temperature of

RHA is 1500oC, polymorphism of silica such as quartz, tridymite and

cristobalite with open structured SiO2 in RHA is produced which can promote

pozzolanic action. There is no significant increase in 7 days strength. So we

can generalize that 5% addition of RHA can bring good results in compressive

strength.

The study carried out by Dr. P. K. Mehta reveals the same trend [5]

that compressive strength increases for addition of 5% RHA and reduces for

further increase in RHA.


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The addition of RHA results in reduction in porosity of cement paste

and causes refinement in the pore structure. RHA absorbs large amount of

water due to its high specific area. This reduces bleeding of water. It improves

the weakest transition zone under the aggregate, however adding the correct

amount of RHA is important for achieving high strength [5]. The study

undertaken by other researchers like A.A.F shaheen [8], Mohan prasad

Aryal[7], Mr. Nehdi, J. Duquette, A. E. Damatty [10] has also indicated same

results. G, Rodriguez De Sensale and D.C.C Dal Molin have shown that

higher compressive strength can be obtained with lower W/C ratio with

addition of RHA.

6.2 SPLIT TENSILE STRENGTH

Table 6.6 SPLIT TENSILE STRENGTH: MIX I

SPLIT TENSILE STRENGTH ( N/mm2)


0 1.69 1.93 2.73

5 1.81 2.04 3.02

10 1.49 2.08 3.09

15 1.24 2.14 3.32

20 1.23 1.88 2.96


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0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 5 10 15 20% of RHA

Tens

ile S

tren

gth

(N/m

m2)

3 days7 days28 days

Fig 6.4 Split Tensile strength V/S % of RHA – MIX I

Table 6.7 SPLIT TENSILE STRENGTH: MIX II



0 2.03 2.66 3.11

5 2.22 2.73 3.31

10 1.96 2.85 3.61

15 1.74 3.01 3.89

20 1.30 2.76 3.30


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0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

0 5 10 15 20% of RHA

TEns

ile S

tren

gth

(N/m

m2)

3 days7 days28 days

Fig 6.5 Split Tensile strength V/S % of RHA – MIX II

Table 6.8 SPLIT TENSILE STRENGTH: MIX III



0 2.10 3.18 3.25

5 2.29 3.32 3.65

10 1.74 3.4 3.82

15 1.63 3.61 3.92

20 1.48 3.23 3.43


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0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

0 5 10 15 20% of RHA

tens

ile S

tren

gth

(N/m

m2)

3 Days7 days28 Days

Fig 6.6 Split Tensile strength V/S % of RHA – MIX III

The cube specimens of Mix I, mix II and mix III were tested for split

tensile strength as per IS: 5816, the results obtained are represented in Table

6.6, 6.7 and 6.8 respectively. The increase in tensile strength compared to

controlled concrete is summarized below

Table 6.9 Percentage increase in tensile Strength

% Increase in tensile strength Mix No 3 days (5%) 7 days (15%) 28 days (15%)

I 8.7 10.88 21.61

II 9.35 13.11 25.08

III 9.04 13.52 20.62


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From the present study it can be observed that there is an increase in

tensile strength in concrete containing RHA as an admixture. The increase in

tensile strength is up to 25% for addition of 15% of RHA. There is an early

increase in strength for addition of 5 % of HA. The 7 and 28 days strength is

increased considerably fore addition of 15% of RHA. This character may be

due to pore refinement of transition zone by the filler action of fine RHA, which

improves the weakest one under the aggregate. Another point is to be

observed that compressive strength has increased for 5% addition of RHA,

but tensile strength increased for 15% addition of RHA.

Study carried out by A.A.F. Shaheen shows that for addition of 10%

RHA tensile strength increased up to 44%. G. Rodrguez de Sensale and

D.C.C Dal Molins results shows that there is an increase in tensile strength for

20% replacement of RHA by weight [12]. Study carried out by Mr. Mohan

Prasad Aryal shows that there is increase in tensile strength of concrete for

addition of 15% of RHA.

6.4 FLEXURAL STRENGTH

Table 6.10 FLEXURAL STRENGTH: MIX I

FLEXURAL STRENGTH ( N/mm2) RHA (%) 3 Days 7 days 28 Days

0 2.65 3.27 4.12 5 2.99 3.53 4.14 10 2.9 3.57 4.18 15 2.65 3.67 4.38 20 2.6 3.32 3.93


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0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 5 10 15 20% of RHA

Flex

ure

Stre

ngth

(N/m

m2)

3 Days7 days28 days

Fig 6.7 Flexural strength V/S % of RHA – MIX I

Table 6.11 FLEXURAL STRENGTH: MIX II

FLEXURAL STRENGTH ( N/mm2)

RHA (%) 3 Days 7 Days 28 Days

0 2.80 2.9 4.41

5 3.16 2.94 4.40

10 3.06 3.27 4.46

15 3.02 3.39 4.74

20 2.89 2.90 4.28


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0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 5 10 15 20% of RHA

Flex

ure

Stre

ngth

(N/m

m2)

RHA3 Days7 Days28 Days

Fig 6.8 Flexural strength V/S % of RHA – MIX II

Table 6.12 FLEXURAL STRENGTH: MIX III

FLEXURAL STRENGTH ( N/mm2)

RHA (%) 3 Days 7 Days 28 Days

0 3.08 3.56 4.89

5 3.56 3.55 4.90 10 3.18 3.6 4.92 15 2.9 3.22 5.16 20 2.88 2.93 4.8


- 27 –


0

1

2

3

4

5

6

0 5 10 15 20% of RHA

Flex

ural

Stre

ngth

( N

/mm

2)

3 days7 days28 days

Fi6.9 Flexural strength V/S % of RHA – MIX III

The cube specimens of Mix I, mix II and mix III were tested for Flexural

strength as per IS:516, the results obtained are represented in Table 6.10,

6.11 and 6.12 respectively The increase in flexure strength of concrete with

RHA compared to controlled concrete is summarized below.

Table 6.13 Percentage increase in Flexural Strength

% Increase in flexural strength Mix No

3 days (5%) 7 days (15%) 28 days (15%)

I 12.80 12.2 6.3

II 2.80 16.89 7.5

III 6.30 7.40 5.5


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By results it can be summarized that as in tensile strength results there

is an early increase in the flexural strength of concrete with 5% addition of

RHA this may be due to high pozzolanic action of RHA in early stages. But

later on the flexural strength increases up to 15% compared to controlled

concrete for 10 % addition of RHA. As silica is held in RHA in a non crystalline

state & micro porous structure the pozzolanic activity will be high. A.A.F.

Shaheen showed that there is an increase in flexural strength of 31% for 10 %

addition of RHA

6.5 LONGITUDINAL STRAIN Table 6.14 LONGITUDINAL STRAIN IN CYLINDRICAL SPECIMEN: MIX I

% RHA Strain in mm

0 0.00175

5 0.00185

10 0.0018

15 0.0018

20 0.0018


- 29 –


1.7E-03

1.7E-03

1.7E-03

1.8E-03

1.8E-03

1.8E-03

1.8E-03

1.8E-03

1.9E-03

0 5 10 15 20% OF RHA

STR

IN IN

Series1

Fig. 6.10 Longitudinal Strain V/S % of RHA – MIX I

Table 6.15 LONGITUDINAL STRAIN IN CYLINDRICAL SPECIMEN: MIX II

% RHA Strain in mm

0 0.00188

5 0.002

10 0.002

15 0.0021

20 0.00235


- 30 –


0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

0 5 10 15 20% OF RHA

STR

IN IN

Series1

Fig. 6.11 Longitudinal Strain V/S % of RHA – MIX II

Table 6.16 LONGITUDINAL STRAIN IN CYLINDRICAL SPECIMEN: MIX III

% RHA Strain in mm

0 0.00193

5 0.002

10 0.0023

15 0.00235

20 0.00238


- 31 –


0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03

0 5 10 15 20% OF RHA

STR

AIN

IN

Series1

Fig. 6.12 Longitudinal Strain V/S % of RHA – MIX III

6.6 MODULUS OF ELASTICITY Table 6.17 MODULUS OF ELASTICITY OF CONCRETE SPECIMENS

Modulus of Elasticity (GPa)

% of RHA Mix I Mix II Mix III

0 34.53 42.86 43.55

05 34.17 43.32 44.06

10 39.91 43.63 41.49

15 35.65 41.59 47.63

20 40.09 40.69 44.65


- 32 –


Fig 6.13 Stress-Strain curve Mix I

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

0.0000 0.0003 0.0006 0.0010 0.0012 0.0016 0.0019 0.0039 0.0063

strain

stre

ss (M

Pa)

Series1


- 33 –


Fig. 6.14 Stress-Strain curve Mix II

0.00

10.00

20.00

30.00

40.00

50.00

60.00

0.0000 0.0002 0.0006 0.0009 0.0012 0.0015 0.0019 0.0021 0.0023

srtain

stre

ss (M

Pa)

Series1


- 34 –


Fig. 6.15 Stress-Strain curve Mix III

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

0.0000 0.0002 0.0005 0.0007 0.0009 0.0011 0.0012 0.0013 0.0015 0.0017 0.0019 0.0020 0.0021 0.0023

strain

stre

ss( M

Pa)

Series1


- 35 –


The cylindrical concrete specimens of Mix I, Mix II and mix III were

tested to study the stress strain relationship. The stress-Strain curves are

presented in Fig.6.12- Fig 6.15.

Many researchers agree that high strength/performance concrete is

more brittle than normal strength concrete, such concrete develops a smaller

amount of cracking than normal strength concrete during all stages of loading,

in consequences, the ascending part of the stress strain curve is steeper and

linear up to a very high proportion of the ultimate strength. The descending

part of the curve is also very steep so that high strength concrete is more

brittle than ordinary concrete and explosive and sudden type of failure in

compression has often being encountered.

The stress- strain ratio at which micro-cracks begin to form continuous

crack pattern is higher for higher strength concrete, therefore the stress- strain

ratio at which stress- strain curve to curve more sharply to the horizontal is

higher for higher strength concrete. At maximum stress of 47.53, 48.67 and

62.25 N/mm2 of Mix I, Mix II and Mix III the corresponding strains are 0.0019,

0.0019 and 0.0018 respectively. It follows that the high strength concrete has

a higher modulus of Elasticity. According to IS 516 in the normal concrete the

cracks normally initiate at 30% of max or failure load. But in the present study

cracks initiated at 45% of the failure load. The failure occurred by the

mechanism of chipping of surfaces and vertical splitting of specimens parallel

to the loading direction. The stress strain curve showed linearity up to 45—55

% of the peak load.

Sudden and explosive type of failure is the indicative of the brittleness

of the material. The observed grater brittleness of high strength concrete to


- 36 –


that of normal strength concrete as reflected by its lesser amount of micro

cracking at all stress levels and smaller inelastic deformation is due mainly to

its greater homogeneity and there fore lesser stress concentrations. At low

and moderate stresses its smaller amount of bond cracking and therefore its

higher proportionality limit compared to normal strength concrete is due to

various reasons, namely, the smaller difference between the elastic modulie

of mortars and aggregate phases and higher bond strength of the aggregate

mortar interface, and the smaller total amount of interfacial areas that are

sensitive to local tensile or shear stresses [15].

6.6 POISON’S RATIO OF CONCRETE: Table 6.18 Poison’s Ratio of Mix – I

MIX I

% of RHA Poison's Ratio

0 0.200

5 0.163

10 0.176

15 0.170

20 0.196


- 37 –


Table 6.19 POISON’S RATIO OF CONCRETE SPECIMENS : MIX II

MIX II


0 0.150

5 0.200

10 0.156

15 0.170

20 0.170

Table 6.20 POISON’S RATIO OF CONCRETE SPECIMENS : MIX III

MIX III


0 0.155

5 0.172

10 0.195

15 0.180

20 0.175

The Values of Poison’s Ratio range from 0.15 to 0.20


- 38 –


CHAPTER 7 CONCLUSIONS

Based on the experimental studies carried out the following conclusions are

drawn:

1. The workability goes on reducing for every percentage increase of RHA

as an admixture and at 25% of addition of RHA, workability is difficult to

achieve even with the superplasticizer.

2. The compressive strength can be increased up to 22% by addition of 5% of

RHA when compared with controlled concrete. So addition of 5 % RHA can

give good results.

3. The compressive strength goes on reducing by adding more than 5% of

RHA but will not reduce beyond the strength for which controlled concrete is

designed.

4. It can be observed form the results that the increase in compressive

strength compared to normal concrete is 10.23, 13.87 and 22.55 % for W/C

ratio of 0.45, 0.4 and 0.35 respectively. So we can increase the strength by

reducing the W/C ratio i.e. we obtain better results for dense mix concrete.

5. Due to early pozzolanic reaction of RHA there is increase in 20.15% in

compressive strength when compared to controlled concrete at 3

days.

6. There is an increase in tensile strength up to 25% when compared

with controlled concrete


- 39 –


7. From the results it can be observed that there is 25% increase in tensile

strength for addition of 15% of RHA. Due to early pozzolanic reaction there is

increase of 10% in tensile strength at 3 days.

8. From the results it can be observed that there is only7% increase

in flexural strength when compared to controlled concrete.

9. As in tensile strength, the flexural strength increases for addition of 15% of

RHA. Due to early pozzolanic reaction there is an increase of 12% in the

flexural strength for addition of 5% of RHA.

10. From the results it can concluded that the modulus of Elasticity increases

with increase in characteristic strength of concrete. The modulus of elasticity

of Mix I, Mix II and Mix III are 40.13, 43.63 and 47.63 GPa respectively.

11. The proportionality limit of Stress-Strain curve obtained from the results

ranges from 50-60 % which is more than 40%, mentioned in the IS code.

12. The Poison’s Ratio obtained from the results for Mix I, Mix II and Mix III

varies from 0.15 to 0.20


- 40 –


CHAPTER 8 SCOPE FOR FUTURE INVESTIGATION

• The durability aspect of concrete with RHA as an admixture is to be

studied.

• The strength of concrete with RHA beyond 28 days can be studied

• Optimum percentage of RHA and superplasticizer can be done using

optimization techniques.

• The heat of hydration in concrete with RHA needs to be studied.

• The effect of setting time of concrete by addition of RHA can be

studied.

• The performance of RHA in concrete beyond M60 can be studied.

• The chloride penetration of concrete with RHA can be studied


- 41 –


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india - research paper - santosh - 021106

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