20320140502005 2-3-4

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),

ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 33-51 © IAEME

33

SOME STUDIES ON MODE-II FRACTURE OF ARTIFICIAL LIGHT

WEIGHT SILICA FUME PELLETIZED AGGREGATE CONCRETE

1Dr. V. BHASKAR DESAI,

2A. SATHYAM,

3S. RAMESHREDDY

1Professor, Dept. of Civil Engineering, JNTUA College of Engineering,

Anantapuram – 515002, A.P. 2Conservation Assistant Gr-I, Archaeological Survey of India, Anantapuram Sub Circle,

Anantapuram & Research Scholar, JNTUA College of Engineering, Anantapuram – 515002, A.P. 3M.Tech Student, JNTUA College of Engineering, Anantapuram – 515002, A.P.

ABSTRACT

The recent advancements in the construction industry necessitate the development of new

materials which have high performance than the ordinary conventional concrete. In the present

scenario light weight aggregate has been the subject of extensive research which affects the shear

strength properties of cement concrete. The adaptation of certain class of light weight concrete gives

an outlet for industrial waste which would otherwise create problem for disposal. An attempt has

been made to prepare artificial light weight aggregate concrete by using pelletized silica fume

aggregate.

Shear strength is a property of major significance for wide range of civil engineering

materials and structures. Shear and punching shear failures particularly in deep beams in corbels and

in concrete flat slabs are considered to be more critical and catastrophic than other types of failures.

This area has received greater attention in recent years due to various attempts which have been

made to develop Mode-II (sliding shear) test specimen geometries for investigating the shear type of

failures in cementitous materials. In this area number of test specimen geometries is proposed for

Mode-II fracture of cementitous materials. Out of these the best suited is suggested as Double

Centered Notched (DCN) specimen geometry proposed by Sri Prakash Desai and Sri Bhaskar Desai.

In this present experimental investigation an attempt is planned to study the Mode II fracture

properties of light weight aggregate concrete, with Silica Fume pellets is considered. The Silica

Fume pellets were prepared by mixing of 47% Silica fume, 47% lime, 6% cement and 12.50% of

water by overall weight of the sample, using pelletization machine. By varying the percentages of

Silica Fume pellets in concrete replacing the conventional granite aggregate in percentages of 0, 25,

50, 75, 100 by volume of concrete, the property of in plane shear strength is studied by casting and

INTERNATIONAL JOURNAL OF CIVIL

ENGINEERING AND TECHNOLOGY (IJCIET)

ISSN 0976 – 6308 (Print)

ISSN 0976 – 6316(Online)

Volume 5, Issue 2, February (2014), pp. 33-51

© IAEME: www.iaeme.com/ijciet.asp

Journal Impact Factor (2014): 3.7120 (Calculated by GISI)

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IJCIET

©IAEME



34

testing around 50x3 samples consisting of 120 notched specimens of size 150mm x150mm x 150mm

with different notch depth ratios and 30 no of plain cubes of size 150 x 150 x 150mm for testing after

28 days and 90 days curing.

Key words: Light Weight Aggregate, Mode II Fracture, Shear Strength, Silica Fume Pellets.

INTRODUCTION

Due to continuous usage of naturally available aggregates within short length of time these

natural resources get depleted and it will be left nothing for future generations. Hence there is a

necessity for preparing artificial aggregates making use of waste materials from agricultural produce

and industrial wastes. From the earlier studies it appears that much less attention has been made

towards the study of using artificial coarse aggregate. An attempt has been made to use silica fume as

the basic ingredient in preparing artificial coarse aggregate which is also light in nature.

LIGHTWEIGHT AGGREGATE

Structural lightweight aggregate concrete are considered as alternative to concrete made with

dense natural aggregate, because of the relatively high strength to unit weight ratio that can be

achieved. Other reasons for choosing lightweight concrete as a construction material is more

attention is being paid to energy conservation and to the usage of waste materials to replace the

exhaustible natural sources.

One of the disadvantage of conventional concrete is the high self weight of concrete. Density

of the normal concrete is in the order of 2200 to 2600Kg/m³. This heavy self weight will make it to

some extent an uneconomical structural material. Attempts have been made and lightweight

aggregate concrete have been introduced whose density varies from 300 to 1850 Kg/m³.

ARTIFICIAL LEIGHT WEIGHT AGGREGATE

The production of concrete requires aggregate as inert filler to provide bulk volume as well as

stiffness. Crushed aggregate are normally used in concrete which can be depleting the natural

resources and necessitates an alternate building material. This led to widespread research on using a

viable waste material as aggregate. Silica Fume is one promising material which can be used as both

cementitous materials as well as to produce light weight aggregate. The use of cost effective

construction materials has accelerated in recent times due to the increase in demand of light weight

concrete for mass applications. This necessitates the complete replacement or partial replacement of

concrete constituents to bring down the escalating construction costs. In recent times, the addition of

artificial aggregate has shown a reasonable cut down in the construction costs and had gained good

attention due to quality on par with conventional aggregate. Despite of its lower compressive

strength and lower modulus elasticity, Silica Fume concrete can be potentially used in many kinds of

structural elements.

PELLETIZING PROCESS

The desired grain size distribution of an artificial light weight aggregate is by means of

agglomeration process. The Pelletization process is used to manufacture light weight Coarse

aggregate. Some of the parameters need to be considered for the efficiency of the production of

pellets such as speed of revolution of pelletizer disc, moisture content, angle of pelletizer disc and

duration of Pelletization (HariKrishnan and RamaMurthy, 2006)1. The different types of pelletizer



35

machine were used to make the pellets such as disc or pan type, drum type, cone type and mixer

type. With mixer type pelletizer small grains are formed initially and are subsequently increased. In

the cold bonded method increase of strength of pellets is by increase the Silica Fume/ lime & cement

ratio by weight. Moisture content and angle of drum parameter influence the size growth of pellets

(HariKrishnan and RamaMurthy, 2006)2. The dosage of binding agent is more important for making

the Silica Fume balls. Initially some percentage of water is added in the binder and remaining water

is sprayed during the rotation Period because while rotating without water in the drum the Silica

Fume and binders (Lime & Cement) tends to form lumps and does not increase the distribution of

particle size. The pellets are formed approximately in duration of 6 to 7 minutes. The cold bonded

pellets are hardened by normal water curing method. The setup of machine for manufacture of Silica

fume aggregate is as shown in plate 1.

PLATE 1. PELLETIZATION MACHINE

MODES OF CRACKING

A crack in a structural component can be stressed in three different modes, which are as

shown in Fig.1.

Mode – I: Opening Mode –II: In-plane shear Mode – III: Out of plane shear

Fig.1: Different modes of cracking

Normal stresses give rise to the “Opening mode” denoted as Mode-I in which the

displacements of the crack surfaces are perpendicular to the plane of the crack.



36

In-plane shear results in Mode-II or “Sliding mode”, in which the displacement of the crack

surfaces is in the plane of the crack and perpendicular to the leading edge of the crack (crack front).

The “Tearing mode” or Mode-III is caused by out-of-plane shear: in which the crack surface

displacements are in the plane of the crack and parallel to the leading edge of the crack.

With the inter disciplinary research and development in material science and

engineering have lead to the development of several important composite construction

materials such as concrete made with partial replacement of conventional aggregate by light

weight aggregate such as pumice.

In this present experimental investigation an attempt is planned to be made to study the

Mode-II fracture properties of light weight aggregate concrete, such as Silica Fume aggregate

concrete since in recent years an attempt has been made only on normal aggregate and on partial

replacement of normal concrete with heavy weight aggregate.

If a structural element is considered in which crack has developed due to bad workmanship,

due to the application of repeated loads or combination of loads and aggressive environmental

conditions, this crack will grow with time. The longer the crack, the higher the stress concentration

induced by it. This indicates that the rate of crack propagation will increase with time. The total

useful life of the structural component depends on the time necessary to initiate a crack and to

propagate the crack from subcritical dimensions to the critical size due to cyclic stresses.

Due to the presence of the crack, the strength of the structure will decrease, which will be

lower than the original design strength.

REVIEW OF LITERATURE

In this chapter brief review of the available studies related to the present Mode-II fracture

of cementitious materials are presented.

Aggarwal and Giare (3) investigated that critical strain energy release rate in Mode-II is

less than half of that Mode-I or Mode-III indicating that in the case of fibrous composites, the

fracture toughness tests in Mode-II may be more important than the tests in mode-I and Mode-III.

Symmetrically notched “Four point shear test specimen was used by Bazant and Pfeiffer

(4,6) to study the shear strength of concrete and mortar beams and they concluded that the

ratio of fracture energy for Mode II to Mode I is about 24 times for concrete and 25 times

for mortar.

Watekins and Liu (5) conducted the finite element analysis technique simulating in-plane

shear mode, fracture mechanics has been used to analyse fracture behaviour in a short shear beam

specimen in plain concrete and fracture toughness, KIIc values are determined.

Liu et al(7) examined the in-plane shear behavior of polypropylene and steel fiber reinforced

concrete and investigated that the fracture toughness results in shear (KIIc) are independent of the

fiber content of the mix and this is in contrast to KIc results for steel fiber reinforced concrete which

increases with the increasing fiber content.

Devies et al (8) conducted tests on mortar cubes subjected to shear loading, and both

analytical and experimental approaches are used in evaluating the fracture toughness of mortar.

Prakash Desayi, Raghu Prasad B.K, and Bhaskar Desai.V, (9, 10, 11, 12, 13, 14 and 15)

arrived at Double Central Notched specimen geometry which fails in predominant Mode-II failure,

They have also made finite element analysis to arrive at stress intensity factor. Using this DCN

geometry lot of experimental investigation using cement paste, mortar, plain concrete has been done.

Details of DCN test set up are presented in fig 2.



37

Fig 2. Details of DCN test specimen geometry

EXPERIMENTAL INVESTIGATION

Mix design has been conducted for M20 concrete making use of ISI method of mix design

using normal constituents of concrete. An experimental study has been conducted on concrete with

partial to complete replacement of conventional coarse aggregate i.e., Granite by light weight

aggregate i.e., Silica Fume Aggregate to know the shear strength Double Centered Notched (DCN)

specimens having different a/w ratios of 0.30, 0.40, 0.50 and 0.60. Analysis of the results has been

done to investigate the shear strength variation in Mode-II fracture with addition of different

percentages of Silica Fume Aggregate. Variations of various combinations have been studied. The

constituent materials are used in the present investigation are presented in table.1.

CONSTITUENT MATERIALS: The constituent materials used in the present investigation for

making artificial light weight aggregate are;

SILICA FUME: Silica fume is by product of the reduction of high purity quartz with coal in electric

furnaces in the production of Silicon and ferro silicon alloys. Before mid 1970’s nearly all silica

fume was discharged into the atmosphere. After environmental concerns necessitated the collection

and land filling of Silica fume, it became economically justified to use silica fume in various

applications. Silica Fume consists of very vitreous particles with a surface area ranging from 13,000

to 30,000 m2/Kg when measured by nitrogen absorption technique with particles approximately 100

to 150 times smaller than the cement particle. Silica fume is procured from Ferro silicon unit,

Kurnool. Because of its extreme fineness and high silica content, it is an effective pozzolanic

material and is used in concrete to improve its properties. It has been found that Silica Fume

improves compressive strength, bond strength, abrasion resistance and reduces permeability and

therefore helps in protecting reinforcing steel from Corrosion.

(a) Loading and support arrangement

in elevation while testing

(b) Bottom view while testing (c) Top view while testing

Square steel bar Supports at bottom

Top loaded area



38

CEMENT: Ordinary Portland cement of Ultra-tech 53 grade with specific gravity of 3.07 is used as

binder. Initial setting and final setting times are 60 minutes and 420 minutes respectively.

LIME: Locally available lime used is as another binder.

WATER: Locally available potable water which is free from concentration of acids and

organic substances has been used in this work for mixing and curing.

TABLE 1: PROPERTIES OF CONSTITUENT MATERIALS IN M20 GRADE CONCRETE

Sl.No Name of the material Properties of material

1 OPC – 53 Grade Specific Gravity 3.07

Initial setting time 60 min

Final Setting time 489 min

Fineness 4 %

Normal consistency 33.50 %

2 Fine Aggregate passing 4.75mm

sieve

Specific Gravity

2.60

Fineness modulus 4.10

3 Coarse Aggregate passing

20 – 10 mm

Specific Gravity

2.68


Bulk density compacted 1620 Kg/m3

4 Silica fume pelletized

Aggregate passing 20 – 10 mm

Specific Gravity

1.14


Bulk density compacted 1035 Kg/m3

The constituent materials are presented from plates 2 to 5.

PLATE 2. CEMENT PLATE 3. FINE AGGREGATE



39

PLATE 4. COARSE AGGREGATE PLATE 5. PELLETIZED COARSE

AGGREGATE

TEST PROGRAMME

In this present investigation it is aimed to study the Mode-II fracture properties of concrete by

modifying the conventional concrete with Silica fume aggregate which is replaced in percentages of

0%, 25%, 50%, 75% & 100%, by volume of natural aggregate in concrete and designated as mixes

SF-0, SF-25, SF-50, SF-75 & SF-100 respectively. Hence cement, fine aggregate, coarse aggregate,

i.e., Granite and Silica fume aggregate in required percentages were calculated. Then required

quantity of water is added to this and mixed thoroughly by hand mixing.

MIXING, CASTING AND CURING

The mix adopted here is M20 designed mix concrete with the mix proportion of 1:1.55:3.04.

It means that 1 part of cement, 1.55 parts of fine aggregate and 3.04 parts of coarse aggregate

consisting of granite and Silica fume aggregate with required replacement are mixed with water

cement ratio of 0.5. Keeping the volume of concrete constant with saturated and surface dry Silica

fume aggregate was added to concrete in 5 different volumetric fractions to prepare five different

mixes which are designated as shown in table 2.

TABLE: 2 DETAILS OF MIX DESIGNATION

Name

of the

Mix

Replacement of Coarse Aggregate by

Volume percentage No of specimens cast

Natural

Aggregate

Pelletized Silica

fume Aggregate

DCN

specimens

Plain

specimens

SF- 0 100 0 24 6

SF- 25 75 25 24 6

SF- 50 50 50 24 6

SF- 75 25 75 24 6

SF- 100 0 100 24 6

Total 120 30

To proceed with the experimental program initially steel moulds of size 150x150x150 mm

with different a/w ratios of 0.3, 0.4 ,0.5, and 0.6 along with plain moulds each in 3 numbers were

taken and these moulds were cleaned without dust particles and were brushed with machine

oil on all inner faces to facilitate easy removal of specimens after 24 hours of casting.



40

To start with, all the materials were weighed in the ratio 1:1.55:3.04. First fine aggregate and

cement were added and mixed thoroughly and then coarse aggregate of granite and required

percentage of surface dry Silica Fume aggregate were mixed with them. All of these were mixed

thoroughly. No admixture i.e. super plasticizer was added as the slump of mix is around 2.5 cm to 5

cm and compaction factor is 0.92 to 0.93.

Each time 15 cube specimens, out of which 12 specimens with a/w ratios 0.3, 0.4, 0.5, and

0.6, 3 numbers of plain cubes were cast and casted specimens as shown in plate 6 and 7. For all test

specimens, moulds were kept on the vibrating table and the concrete was poured into the moulds in

three layers each layer being compacted thoroughly with tamping rod to avoid honey combing.

Finally all specimens were vibrated on the table vibrator after filling up the moulds up to the brim.

The vibration was effected for 7 seconds and it was maintained constant for all specimens and all

other castings. The steel plates forming notches were removed after 3 hours of casting carefully and

neatly finished.

However the specimens were de moulded after 24 hours of casting and were kept immersed in

a clean water tank for curing as shown in plate 8. After 28 and 90 days of curing the specimens were

taken out of water and were allowed to dry under shade for few hours.

PLATE 6. PLAIN CUBES IN GREEN PLATE 7. DCN SPECIMENS IN GREEN

STATE STATE

PLATE 8. CURING POND



41

TESTING OF SPECIMENS

COMPRESSION TEST ON PLAIN CUBES

Compression test is done as per IS: 516-1959. All the concrete specimens were tested in a

3000KN capacity automatic compression testing machine with 0.5KN/sec rate of loading until the

specimens are crushed. Concrete cubes of size 150mm x150mm x 150mm are tested for compressive

strength. The displacements were automatically recorded through 3000KN digital compression

testing machine. The maximum load applied to the specimens has been recorded and dividing the

failure load by the area of the specimen, the compressive strength has been calculated. The test set up

of 3000KN compression testing machine with specimens as shown in plate 9 and 10.

Compressive strength = ��

�� in N/mm

2

PLATE 9: TEST SETUP FOR CUBE PLATE 10: VIEW SHOWS THE CUBE

COMPRESSIVE STRENGTH TEST COMPRESSIVE STRENGTH TEST

BEFORE TESTING AFTER TESTING

Variations of cube compressive strength with various percentage replacements of silica fume

replacement of natural aggregate in concrete for 28 and 90 days curing has been calculated and

variations are recorded vide table 3, and graphically super imposed variations are represented for the

above periods vide fig 3.

Fig 3. Superimposed variation between cube compressive strength and percentage of pelletized

silica fume aggregate replacing natural aggregate

0 25 50 75 100

0

5

10

15

20

25

30

35

40

45

50

cube c

om

pre

ssiv

e s

trength

in N

/mm

2

percentage of pelletized silicafume aggregate replacing natural aggregate

28 days curing period


scale

x-axis 1 unit = 25%

y-axis 1 unit = 5 N/mm2



42

MODE-II FRACTURE TEST ON DCN SPECIMENS

The Mode-II fracture test on the double centered notched cubes was conducted in 3000KN

digital high arm compression testing machine. The rate of loading was applied at 0.5KN/sec. The

specimens after being removed from water were allowed to dry under shade for 24 hours and white

washed for easy identification of minute cracks, while testing.

For testing double centered notched (DCN) specimen of size 150x150x150mm, supports in the

form of square steel bar throughout the width were introduced at one third portion slightly away from

notches as shown in fig 2. Uniformly distributed load was applied over the central one third part

between the notches and square cross section steel supports were provided at bottom along the outer

edges of the that the central portion could get punched and sheared through along the notches

on the application of loading. The test set up is shown vide plate 12 and 13.

The notch depths provided were 45, 60, 75 and 90mm running throughout the width of the

specimen. Thus the values of a/w ratio were 0.3, 0.4, 0.5, and 0.6 where ‘a’ is the notch depth and ‘w’

is the specimen depth 150mm. The distance between the notches is kept constant at 50mm and width

of the notch was 2mm.

For Double centered notch specimens the ultimate loads are recorded through 3000KN high

arm digital compression testing machine. The test results were recorded vide table no 4 to 7 for

ultimate load in Mode-II for DCN samples with a/w ratios of 0.3, 0.40, 0.50 & 0.60. Superimposed

Variations for percentage of Silica fume aggregate replacing natural aggregate and ultimate load for

28 and 90 days are represented graphically vide fig 4 to 6. Also Superimposed Variations for

percentage of Silica fume aggregate replacing natural aggregate and in-plane shear stress for 28 and

90 days are represented graphically vide fig 7 to 9.

Fig 4. Superimposed variation between ultimate load and percentage of pelletized silica fume

aggregate replacing natural aggregate



0 25 50 75 100

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

scale

x-axis 1 unit = 25%

y-axis 1 unit = 10 KN


ultim

ate

load in K

N

Percentage of pelletized silica fume aggregate replacing natural aggregate

a/w = 0.30

a/w = 0.40

a/w = 0.50

a/w = 0.60

0 25 50 75 100

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

scale

x-axis 1 unit = 25%

y-axis 1 unit = 10 KN


ultim

ate

load in K

N


a/w = 0.30

a/w = 0.40

a/w = 0.50

a/w = 0.60



43



0 25 50 75 100

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Scale

X-AXIS 1 UNIT = 25%

Y-AXIS 1 UNIT = 0.50 N/mm2

Curing period = 28 Days

In-P

lan

e s

hera

str

eS

S i

n N

/mm

2


a/w = 0.30

a/w = 0.40

a/w = 0.50

a/w = 0.60

Fig 7. Superimposed variation between in-plane shear stress and percentage of pelletized silica

fume aggregate replacing natural aggregate

0 25 50 75 100

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

ScaleX-AXIS 1 UNIT = 25%

Y-AXIS 1 UNIT = 0.50 N/mm2

Curing period = 90 Days

In-P

lan

e s

hera

str

eS

S in

N/m

m2


a/w = 0.30

a/w = 0.40

a/w = 0.50

a/w = 0.60



0 25 50 75 100

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

Scale

x-axis 1 Unit = 25%

y-axis 1 Unit = 10 KN

Ult

imate

lo

ad

in

KN


28 Days Curing

a/w = 0.30

a/w = 0.40

a/w = 0.50

a/w = 0.60

90 Days Curing

a/w = 0.30

a/w = 0.40

a/w = 0.50

a/w = 0.60



44



DISCUSSION OF CRACK PATTERNS

The presence of cracks is a characteristic structural feature of most cement based materials.

Micro cracking may takes place first as a consequence of the partial segregation of the aggregates

and plastic shrinkage while the fresh concrete is setting. Temperature differences and drying

shrinkage promote further cracking of concrete. After the concrete hardens, various factors aggravate

the already existing micro cracks and cause the initiation of new ones. It is thought that cracks

whatever their origin is (mechanical, thermal, chemical etc) can act as major pathways for water or

aggressive chemical ions to penetrate into concrete, reducing its strength.

In case of cubes under compression initial cracks are developed at top and propagated to

bottom with increase in load and the cracks are widened at failure along the edge of the cube more

predominantly along the top side of casting.

In case of DCN specimens during testing, for most of the specimens with a/w= 0.3 initial

hair line cracks started at the top of one or both the notches, and as the load was increased further,

the cracks widened and propagated at an inclination and sometimes to the middle of the top loaded

zone. Simultaneously the cracks formed at the bottom of one or both the notches and propagated

downwards visible inclination. In some cases cracks branched into two either at the two edges of the

supporting square bar at bottom or at the edge of the loaded length at top or at both places.

In a few cases, initial cracks started at the bottom of the one or both notches. As the load was

increased propagation of theses cracks at an inclination was observed along with the formation of

cracks at top of the notches. These cracks finally propagated toward the middle of the top loaded

zone leading to failure of the specimen. Hence failure of the specimens with a/w = 0.3, could be

attributed to the flexure cum shear type of failure.

For most of the specimens with a/w = 0.4, 0.5, 0.6, as the load was applied formation of

initial hair line cracks at the top of one or both the notches was observed. With the increase of load

propagation of these cracks in more or less vertical direction along with the formation of new cracks

at the bottom of one or both the notches was observed. Finally the specimens failed by shearing

along the notches. In most of the cases the cracks branched into two to join either the two edges of

the supporting square bars at bottom or at the edge of the loaded length at top or at both places. In

this case also, in a few specimens, initial cracks started at the bottom of one or both the notches. As

the load was increased propagation of these cracks in more or less vertical direction along with

formation of new cracks at top of the one or both the notches was observed leading to final collapse

of the specimens along the notches.

Thus except for some of the specimens of lower notch-depth ratio i.e., 0.3, the specimens

of other higher a/w ratios of cement concrete failed all along the notches in more or less vertical

0 25 50 75 100

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

Scale

x-axis 1 Unit = 25%

y-axis 1 Unit = 0.50 N/mm2

28 Days Curing

a/w = 0.30

a/w = 0.40

a/w = 0.50

a/w = 0.60

90 Days Curing

a/w = 0.30

a/w = 0.40

a/w = 0.50

a/w = 0.60

Y A

xis

Title

X Axis Title



45

fashion. The breaking sound of aggregate is more for 100% replacement of natural aggregate by

Silica fume aggregate. Natural aggregate does not have any sound while crushing. In general the

crack widths are more in light weight aggregate than in normal aggregate concrete. Plate 11 and 14

shows the DCN specimens before and after testing respectively.

PLATE 11. DCN SPECIMENS BEFORE TESTING

PLATE 12. TEST SET UP OF DCN CUBES PLATE 13. DCN SPECIMENS AFTER

TESTING

a/w= 0

a/w=0.60

a/w= 0.50

a/w = 0.40

a/w=0.3



46

PLATE 14. CRACK PATTERN AFTER TESTING

DISCUSSION OF TEST RESULTS

INFLUENCE OF PELLETIZED SILICA FUME AGGREGATE ON CUBE

COMPRESSIVE STRENGTH

In the present study Silica fume aggregate has been replaced by natural aggregate in

volumetric percentages of 0, 25%, 50%, 75% and 100%. The variation of compressive strength

versus percentage replacement of Silica fume aggregate with natural aggregate is presented in table 3

and superimposed graphical variation for the two periods of curing are represented in fig 3. From this

figure and table, it is observed that the decrease in compressive strength of concrete with 100 %

replacement of Silica fume aggregate with natural aggregate is 65.60 % at 28 days and 43.07% at 90

days of curing. The cube compressive strength is found to increase drastically from 28 days to 90

days of curing.

The target mean strength of M20 grade of concrete i.e., 26.6 N/mm² has been found to be

achieved when the natural aggregate is replaced even with 100% of Silica fume aggregate after 90

days of curing as tabulated in table 3. However the target mean strength of M20 grade of concrete

i.e. 26.60 N/mm2 at 28 days has not been achieved with any percentage of replacement of silica fume

aggregate with natural aggregate.

INFLUENCE OF PELLETIZED SILICA FUME AGGREGATE ON ULTIMATE LOAD

All the DCN specimens with different a/w ratios i.e., 0.3, 0.4, 0.5 and 0.6 and with

different percentages of Silica fume aggregates i.e., 0%, 25%, 50%, 75%, 100%, were tested with

load in Mode-II (in-plane shear). The variations of ultimate loads versus percentage of Silica fume

aggregate replacement of natural aggregate in concrete are presented in the tables 4 to 7.

Super imposed variation of percentage decrease in ultimate load verses percentage of Silica

fume aggregate replacement of natural aggregate in concrete are represented vide fig 4 to 6 for

different a/w ratios (i.e., 0.3, 0.4, 0.5, 0.6). From the above figs, it may be observed that

a/w= 0

a/w=0.60

a/w= 0.50

a/w = 0.40

a/w=0.3



47

with the addition of Silica fume aggregate the ultimate load in in-plane shear of the specimens

decreases continuously up to 100% replacement of natural aggregate by Silica fume aggregates and

increases with age i.e. from 28 days to 90 days curing.

INFLUENCE OF PELLETIZED SILICA FUME AGGREGATE ON IN-PLANE SHEAR

STRESS

The In-plane shear stress at ultimate load for different percentage replacements of Silica fume

aggregate (0- 100%) and for different notch depth ratios for 28 and 90 days are presented in tables 8

to 11. Also the super imposed variations of in-plane shear stress versus percentage replacement of

Silica fume aggregate with a/w ratios of 0.3, 0.40, 0.50 and 0.60 are presented vide fig 7 to fig 9 for

28 and 90 days curing.

It is observed that In-plane shear stress is decreasing continuously with the increase in

percentage replacement of conventional granite aggregate by Silica fume aggregate (i.e., 0%, 25%,

50%, 75%, 100%) and increasing with age from 28 to 90 days of curing for notch depth ratios of

0.30, 0.40, 0.50 and 0.60.

TABLE 3: CUBE COMPRESSIVE STRENGTH

Sl.

No

Name of

the mix

Percentage volume

replacement of coarse

aggregate (%)

Compressive

strength N/mm2

Percentage of decrease

in compressive strength

Natural

aggregate

Pelletized

Silica

Fume

Aggregate

28

Days

90

days

28

days

90

days

1 SF-0 100 0 41.08 47.39 0.00 0.00

2 SF-25 75 25 16.00 40.83 -61.05 -13.84

3 SF-50 50 50 14.65 34.68 -64.34 -26.82

4 SF-75 25 75 14.39 30.62 -64.97 -35.39

5 SF-100 0 100 14.13 26.98 -65.60 -43.07

TABLE 4: ULTIMATE LOAD AND PERCENTAGE OF INCREASE OR DECREASE IN

ULTIMATE LOAD IN MODE-II OF DCN SPECIMENS WITH a/w= 0.3

Sl.

No

Name

of the

mix

Percentage volume


aggregate (%)

Ultimate load in KN

Percentage of increase

or decrease in

Ultimate load of N.A.

Natural

aggregate

Pelletized

Silica Fume

Aggregate

28 days 90 days 28 days 90 days

1 SF-0 100 0 144.00 194.67 0.00 0.00

2 SF-25 75 25 100.00 115.00 -30.56 -40.93

3 SF-50 50 50 93.00 105.67 -35.42 -45.72

4 SF-75 25 75 89.67 101.33 -37.73 -47.95

5 SF100 0 100 86.33 88.33 -40.05 -54.63



48

TABLE 5: ULTIMATE LOAD AND PERCENTAGE OF INCREASE OR DECREASE IN

ULTIMATE LOAD IN MODE-II OF DCN SPECIMENS WITH a/w=0.4

Sl.

No

Name

of the

mix

Percentage volume


aggregate (%)

Ultimate load in KN


or decrease in


Natural

aggregate

Pelletized

Silica Fume

Aggregate


1 SF-0 100 0 105.00 138.00 0.00 0.00

2 SF-25 75 25 97.33 112.33 -7.30 -18.60

3 SF-50 50 50 89.33 103.00 -14.92 -25.36

4 SF-75 25 75 88.33 100.33 -15.88 -27.30

5 SF100 0 100 83.00 87.33 -20.95 -36.72

TABLE 6: PERCENTAGE OF INCREASE OR DECREASE IN ULTIMATE LOAD IN

MODE-II OF DCN SPECIMENS WITH a/w= 0.5

S.N

o

Name

of the

mix

Percentage volume


aggregate (%)

Ultimate load in KN


or decrease in


Natural

aggregate

Pelletized

Silica Fume

Aggregate


1 SF-0 100 0 95.00 124.67 0.00 0.00

2 SF-25 75 25 90.67 98.33 -4.56 -21.13

3 SF-50 50 50 86.33 93.67 -9.13 -24.87

4 SF-75 25 75 85.33 89.33 -10.18 -28.35

5 SF-100 0 100 60.67 73.00 -36.14 -41.45

TABLE 7: PERCENTAGE OF INCREASE OR DECREASE IN ULTIMATE LOAD IN

MODE-II OF DCN SPECIMENS WITH a/w= 0.6

Sl.

No

Name

of the

mix

Percentage volume


aggregate (%)

Ultimate load in KN


or decrease in


Natural

aggregate

Pelletized

Silica Fume

Aggregate


1 SF-0 100 0 90.33 95.67 0.00 0.00

2 SF-25 75 25 86.00 94.33 -4.79 -1.40

3 SF-50 50 50 82.67 92.33 -8.48 -3.49

4 SF-75 25 75 74.33 86.00 -17.71 -10.11

5 SF100 0 100 57.33 64.33 -36.53 -32.76



49

TABLE 8: IN-PLANE SHEAR STRESS (MODE-II) FOR DCN SPECIMENS WITH a/w=

0.30 WITH PERCENTAGE DECREASE

Sl.

No

Name of

the mix

Percentage volume


aggregate (%)

In-plane shear stress

in N/mm2


or decrease in Ultimate

load with N.A.

Natural

aggregate

Pelletized

Silica Fume

Aggregate


1 SF-0 100 0 4.57 6.18 0.00 0.00

2 SF-25 75 25 3.17 3.65 -30.63 -40.94

3 SF-50 50 50 2.95 3.35 -35.45 -45.79

4 SF-75 25 75 2.85 3.22 -37.64 -47.90

5 SF-100 0 100 2.74 2.80 -40.04 -54.69



Sl.

No

Name of

the mix

Percentage volume


aggregate (%)


in N/Sq.mm


or decrease in Ultimate

load with N.A.

Natural

aggregate

Pelletized

Silica Fume

Aggregate


1 SF-0 100 0 3.89 5.11 0.00 0.00

2 SF-25 75 25 3.60 4.16 -7.46 -18.59

3 SF-50 50 50 3.31 3.81 -14.91 -25.44

4 SF-75 25 75 3.27 3.72 -15.94 -27.20

5 SF-100 0 100 3.07 3.23 -21.08 -36.79



Sl.

No

Name of

the mix

Percentage volume


aggregate (%)


in N/Sq.mm


or decrease in

Ultimate load with

N.A.

Natural

aggregate

Pelletized

Silica Fume

Aggregate


1 SF-0 100 0 3.69 5.54 0.00 0.00

2 SF-25 75 25 3.53 4.37 -4.34 -21.12

3 SF-50 50 50 3.44 4.16 -6.78 -24.91

4 SF-75 25 75 3.29 3.97 -10.84 -28.34

5 SF-100 0 100 2.70 3.24 -26.83 -41.52



50



Sl.

No

Name of

the mix

Percentage volume


aggregate (%)


in N/Sq.mm


or decrease in

Ultimate load with

N.A.

Natural

aggregate

Pelletized

Silica Fume

Aggregate


1 SF-0 100 0 3.45 5.31 0.00 0.00

2 SF-25 75 25 3.28 5.24 -4.93 -1.32

3 SF-50 50 50 3.19 5.13 -7.54 -3.39

4 SF-75 25 75 3.13 4.78 -9.28 -9.98

5 SF100 0 100 2.19 3.57 -36.52 -32.77

CONCLUSIONS

From the limited experimental study the following conclusions are seem to be valid:

� From the study it may be concluded that the cube compressive strength has decreased

continuously with the increase in percentage of Silica fume aggregate. The target mean

compressive strength of M20 concrete i.e., 26.6 N/mm² has been achieved when the natural

aggregate is replaced even with 100% of Silica Fume aggregate after 90 days of curing. But the

cube compressive strength is found increase from 14.13 N/mm2

to 26.93 N/mm2

for 100%

replacement of Silica fume aggregate from 28 days to 90 days of curing.

� From the study it may be observed that the percentage of decrease in compressive strength is

increased with the percentage of increase in silica fume aggregate (0- 100%) and with 25%

replacement the percentage decrease is 61.05 and with 100% replacement it is 65.60% and it is

observed that the effect of percentage replacement of natural aggregate with silica fume

aggregate is almost same at 28 days.

� It is also observed that the compressive strength increases with age and the increase is around

15.36% for natural aggregate (28 to 90 days) and for 100% silica fume aggregate it is 90.94%

after 90 days over the 28 days strength.

� Ultimate loads in Mode-II fracture are found to decrease continuously with the percentage

increase in silica fume aggregate content

� Ultimate loads in Mode-II fracture are found to decrease continuously with the increase in a/w

ratio.

� It may be observed that In-plane shear stress at ultimate load decreases continuously with the

percentage increase in silica fume aggregate content and the In plane shear stress increases from

2.80 N/mm2

to 3.57 N/mm2

for 100% replacement of Silica fume aggregate for 90 days of curing

period with increase in a/w ratio i.e., from 0.3 to 0.60 and the in-plane shear stress increases with

age for all a/w ratios from 28 days to 90 days of curing.

� Based on the experimental investigations it is concluded that cold bonded artificial aggregate

manufactured from industrial waste i.e., Silica fume aggregate is in no way inferior to naturally

available light weight aggregate.



51

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pp. 193 - 201, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

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