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

INTERNATIONAL JOURNAL OF CIVIL
ENGINEERING AND TECHNOLOGY (IJCIET)

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)
www.jifactor.com

©IAEME

SOME STUDIES ON MODE-II FRACTURE OF ARTIFICIAL LIGHT
WEIGHT SILICA FUME PELLETIZED AGGREGATE CONCRETE
1

Dr. V. BHASKAR DESAI,

2

A. SATHYAM,

3

S. RAMESHREDDY

1

Professor, Dept. of Civil Engineering, JNTUA College of Engineering,
Anantapuram – 515002, A.P.
2
Conservation Assistant Gr-I, Archaeological Survey of India, Anantapuram Sub Circle,
Anantapuram & Research Scholar, JNTUA College of Engineering, Anantapuram – 515002, A.P.
3
M.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
33


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
34


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.

35


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.

36


Square steel bar
Supports at bottom

(a) Loading and support arrangement

(b) Bottom view while testing

Top loaded area

(c) Top view while testing

in elevation while testing

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.

37


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

489 min
4%

Normal consistency

33.50 %

Specific Gravity

2.60

Fineness modulus

4.10

Specific Gravity

2.68

Fineness modulus

4.23

Bulk density compacted

1620 Kg/m3

Specific Gravity

1.14

Fineness modulus

4.20

Bulk density compacted

4

60 min

Fineness
Fine Aggregate passing 4.75mm
sieve

3.07

Final Setting time

3

Specific Gravity
Initial setting time

2

OPC – 53 Grade

1035 Kg/m3

Coarse Aggregate passing
20 – 10 mm

Silica fume pelletized
Aggregate passing 20 – 10 mm

The constituent materials are presented from plates 2 to 5.

PLATE 2. CEMENT

PLATE 3. FINE AGGREGATE

38


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.

Name
of the
Mix
SF- 0
SF- 25
SF- 50
SF- 75
SF- 100

TABLE: 2 DETAILS OF MIX DESIGNATION
Replacement of Coarse Aggregate by
No of specimens cast
Volume percentage
Natural
Pelletized Silica
DCN
Plain
Aggregate
fume Aggregate
specimens
specimens
100
0
24
6
75
25
24
6
50
50
24
6
25
75
24
6
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.
39


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
STATE

PLATE 7. DCN SPECIMENS IN GREEN
STATE

PLATE 8. CURING POND

40


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 =

ࡸ࢕ࢇࢊ
࡭࢘ࢋࢇ

in N/mm2

PLATE 9: TEST SETUP FOR CUBE
COMPRESSIVE STRENGTH TEST
BEFORE TESTING

PLATE 10: VIEW SHOWS THE CUBE
COMPRESSIVE STRENGTH TEST
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.
28 days curing period
scale
x-axis 1 unit = 25%
2
y-axis 1 unit = 5 N/mm

cube compressive strength in N/mm

2

50
45
40
35
30
25
20
15
10
5
0
0

25

50

75

100

percentage of pelletized silicafume aggregate replacing natural aggregate

Fig 3. Superimposed variation between cube compressive strength and percentage of pelletized
silica fume aggregate replacing natural aggregate

41


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.
a/w
a/w
a/w
a/w

scale
x-axis 1 unit = 25%
y-axis 1 unit = 10 KN

150
140
130
120

= 0.30
= 0.40
= 0.50
= 0.60

ultimate load in KN

110
100
90
80
70
60
50
40
30
20
10
0
0

25

50

75

100

Percentage of pelletized silica fume aggregate replacing natural aggregate

ultimate load in KN

Fig 4. Superimposed variation between ultimate load and percentage of pelletized silica fume
aggregate replacing natural aggregate
a/w
a/w
a/w
a/w

scale
x-axis 1 unit = 25%
y-axis 1 unit = 10 KN

200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
0

25

50

75

= 0.30
= 0.40
= 0.50
= 0.60

100


42

Ultimate load in KN

Scale
x-axis 1 Unit = 25%
y-axis 1 Unit = 10 KN

200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0

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

0

25

50

75

100



Scale
X-AXIS 1 UNIT = 25%
2
Y-AXIS 1 UNIT = 0.50 N/mm
Curing period = 28 Days

In-Plane shera streSS in N/mm

2

4.5
4.0

a/w = 0.30
a/w = 0.40
a/w = 0.50
a/w = 0.60

3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0

25

50

75

100


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

Scale
X-AXIS 1 UNIT = 25%
2
Y-AXIS 1 UNIT = 0.50 N/mm
Curing period = 90 Days

In-Plane shera streSS in N/mm

2

6.0
5.5

a/w = 0.30
a/w = 0.40
a/w = 0.50
a/w = 0.60

5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0

25

50

75

100



43

Scale
x-axis 1 Unit = 25%
2
y-axis 1 Unit = 0.50 N/mm

6.5
6.0
5.5

28 Days Curing
a/w = 0.30
a/w = 0.40
a/w = 0.50
a/w = 0.60

5.0

90 Days Curing
a/w = 0.30
a/w = 0.40
a/w = 0.50
a/w = 0.60

4.5

Y Axis Title

4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0

25

50

75

100

X Axis Title

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
44


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.

a/w= 0

a/w=0.60

a/w= 0.50

a/w = 0.40

a/w=0.3

PLATE 11. DCN SPECIMENS BEFORE TESTING

PLATE 12. TEST SET UP OF DCN CUBES

PLATE 13. DCN SPECIMENS AFTER
TESTING

45


a/w= 0

a/w=0.3

a/w = 0.40

a/w= 0.50

a/w=0.60

PLATE 14. CRACK PATTERN AFTER TESTING
DISCUSSION OF TEST RESULTS
INFLUENCE OF PELLETIZED
COMPRESSIVE STRENGTH

SILICA

FUME

AGGREGATE

ON

CUBE

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
46


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 (%)
Natural
aggregate

1
2
3
4
5

SF-0
SF-25
SF-50
SF-75
SF-100

100
75
50
25
0

Compressive
strength N/mm2

Pelletized
Silica
Fume
Aggregate
0
25
50
75
100

Percentage of decrease
in compressive strength

28
Days

90
days

28
days

90
days

41.08
16.00
14.65
14.39
14.13

47.39
40.83
34.68
30.62
26.98

0.00
-61.05
-64.34
-64.97
-65.60

0.00
-13.84
-26.82
-35.39
-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

1
2
3
4
5

Name
of the
mix

SF-0
SF-25
SF-50
SF-75
SF100

Percentage volume
aggregate (%)
Natural
aggregate
100
75
50
25
0

Pelletized
Silica Fume
Aggregate
0
25
50
75
100

Ultimate load in KN

Percentage of increase
or decrease in
Ultimate load of N.A.

28 days

90 days

28 days

90 days

144.00
100.00
93.00
89.67
86.33

194.67
115.00
105.67
101.33
88.33

0.00
-30.56
-35.42
-37.73
-40.05

0.00
-40.93
-45.72
-47.95
-54.63

47


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

1
2
3
4
5

Name
of the
mix

SF-0
SF-25
SF-50
SF-75
SF100

Percentage volume
aggregate (%)
Natural
aggregate
100
75
50
25
0

Pelletized
Silica Fume
Aggregate
0
25
50
75
100

Ultimate load in KN

or decrease in

28 days

90 days

28 days

90 days

105.00
97.33
89.33
88.33
83.00

138.00
112.33
103.00
100.33
87.33

0.00
-7.30
-14.92
-15.88
-20.95

0.00
-18.60
-25.36
-27.30
-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

1
2
3
4
5

Name
of the
mix

SF-0
SF-25
SF-50
SF-75
SF-100

Percentage volume
aggregate (%)
Natural
aggregate
100
75
50
25
0

Pelletized
Silica Fume
Aggregate
0
25
50
75
100

Ultimate load in KN

or decrease in

28 days

90 days

28 days

90 days

95.00
90.67
86.33
85.33
60.67

124.67
98.33
93.67
89.33
73.00

0.00
-4.56
-9.13
-10.18
-36.14

0.00
-21.13
-24.87
-28.35
-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 (%)

1
2
3
4

SF-0
SF-25
SF-50
SF-75

100
75
50
25

Pelletized
Silica Fume
Aggregate
0
25
50
75

5

SF100

0

100

Natural
aggregate

Ultimate load in KN

or decrease in

28 days

90 days

28 days

90 days

90.33
86.00
82.67
74.33

95.67
94.33
92.33
86.00

0.00
-4.79
-8.48
-17.71

0.00
-1.40
-3.49
-10.11

57.33

64.33

-36.53

-32.76

48


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 (%)
Natural
aggregate

1
2
3
4
5

SF-0
SF-25
SF-50
SF-75
SF-100

100
75
50
25
0

Pelletized
Silica Fume
Aggregate
0
25
50
75
100

In-plane shear stress
in N/mm2

or decrease in Ultimate
load with N.A.

28 days

90 days

28 days

90 days

4.57
3.17
2.95
2.85
2.74

6.18
3.65
3.35
3.22
2.80

0.00
-30.63
-35.45
-37.64
-40.04

0.00
-40.94
-45.79
-47.90
-54.69


Sl.
No

Name of
the mix

Percentage volume
aggregate (%)
Natural
aggregate

1
2
3
4
5

SF-0
SF-25
SF-50
SF-75
SF-100

100
75
50
25
0

Pelletized
Silica Fume
Aggregate
0
25
50
75
100

in N/Sq.mm

or decrease in Ultimate
load with N.A.

28 days

90 days

28 days

90 days

3.89
3.60
3.31
3.27
3.07

5.11
4.16
3.81
3.72
3.23

0.00
-7.46
-14.91
-15.94
-21.08

0.00
-18.59
-25.44
-27.20
-36.79

Percentage volume
or decrease in
in N/Sq.mm
Ultimate load with
aggregate (%)
Sl. Name of
N.A.
No the mix
Pelletized
Natural
Silica Fume
28 days
90 days
28 days
90 days
aggregate
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
49


Percentage volume
or decrease in
in N/Sq.mm
Ultimate load with
aggregate (%)
Sl. Name of
N.A.
No the mix
Pelletized
Natural
Silica Fume
28 days
90 days
28 days
90 days
aggregate
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.

50


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51

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