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Int. J. Environmental Technology and Management, Vol. 16, Nos.
1/2, 2013 129
Copyright 2013 Inderscience Enterprises Ltd.
Characterisation of LD slag of Bokaro Steel Plant and its
feasibility study of manufacturing commercial fly ashLD slag
bricks
Rajeev Singh Abhijeet Group, Ranchi 834001, Jharkhand, India
Email: [email protected]
A.K. Gorai* Environmental Science & Engineering Group, Birla
Institute of Technology, Mesra, Ranchi 835215, Jharkhand, India
Email: [email protected] *Corresponding author
R.G. Segaran Bokaro Steel Plant, SAIL, Bokaro Steel City 827001,
Jharkhand, India Email: [email protected]
Abstract: The aim of this study is to couple several analytical
techniques in order to carefully undertake physical, chemical and
mineralogical characterisations of LD steel slag to determine its
feasible utilisation in commercial brick manufacturing. The
characterisation results of LD slag showed that the pH and
electrical conductivity of the samples were very high indicating
high percentage of lime presence and presence of ionic form of
various salts, respectively. The specific gravity and bulk density
of LD slag samples were found to be high in comparison to fly ash
samples. The EDS X-ray micro analysis showed that major elemental
compositions of LD slag samples are O and Ca by weight. The XRF
analysis showed that the major components of the LD slag samples
are CaO, FeO and SiO2. The differential thermal analysis result
showed that an endothermic peak at 450.7C in the DTA curve was
found. The compressive strength of the brick samples type A (Fly
ash 35% + LD slag 30% + Gypsum 5% + Quarry dust 20% + Lime 9.75% +
CaCl2 0.25%) was found to be more than 100 kg/cm2 after 14 days of
curing which is sufficiently higher than that of the strength of a
normal red clay bricks (5070 kg/cm2) and may be its feasible
replacement for commercial purposes in civil jobs.
Keywords: LD slag; brick; fly ash; waste management;
characterisation.
Reference to this paper should be made as follows: Singh, R.,
Gorai, A.K. and Segaran, R.G. (2013) Characterisation of LD slag of
Bokaro steel plant and its feasibility study of manufacturing
commercial fly ashLD slag bricks, Int. J. Environmental Technology
and Management, Vol. 16, Nos. 1/2, pp.129145.
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130 R. Singh, A.K. Gorai and R.G. Segaran
Biographical notes: Rajeev Singh is Engineer (Environment) at
Abhijeet Group, Ranchi, India.
A.K. Gorai is Assistant Professor at Environmental Science &
Engineering Group of Birla Institute of Technology, Mesra, Ranchi,
India.
R.G. Segaran is AGM of ECD Bokaro Steel Plant of Steel Authority
of India Ltd. (SAIL) at Jharkhand, India.
1 Introduction
Steel is an indispensable part of our everyday lives. Integrated
steel plant utilises primarily raw materials like iron ore,
limestone, air, water, fuel and power to produce steel. During
production of steel, considerable amount of different types of
solid wastes (blast furnace slag, blast furnace flue dust, LD slag,
coke breeze, tar sludge, etc.) are generated. The composition of
these materials varies widely depending on the source of
generation, the quality of raw materials and the metallurgical
operations. The wastes produced in steel plants are generally
disposed by dumping in a haphazard method which causes many
environmental problems. Nowadays, environmental legislations and
economics force steel industry to minimise generation of wastes and
maximise its recycling or utilisation. Recycling or utilisation of
waste has become necessary today because of shortage of space, fast
depletion of natural resources, associated health hazards and for
economic advantages. Due to increasing awareness of the
environment, disposal, recycling or reuse of wastes without harming
the environment has became a prime concern for the industry.
LD converter steel slags are industrial by-products resulting
from a steelmaking process in oxygen converters (LinzDonawitz
process). Their interesting mechanical properties made it possible
to use them as natural aggregates replacement in road construction
(Xue, 2006; Wu, 2007; Shen, 2009). This use is beneficial because
it helps save natural resources (Motz, 2001) and reduces the
tonnage of slag grains that are stocked every year. However, only a
small part of these slags can actually be used in road construction
because their hydraulic reactivity is not very efficient (Shi,
2000; Srinivasa, 2006; Kourounis, 2007; Mahieux, 2009).
According to previous studies, this instability is mainly due to
the presence of lime and magnesia in slag grains (Geiseler, 1996;
Auriol, 2004). These compounds, resulting from variable additions
of lime, dolostone and pure magnesia into oxygen converters during
LinzDonawitz process, are hydrated and carbonated with ageing
leading to dimensional damage. Nevertheless, there is no a clear
correlation between free lime and free magnesia contents of LD
steel slags and the swelling of the roads. It is then necessary to
improve the understanding of the mechanisms that lead to
dimensional damage.
The aim of this study covers characterisation of LD slag of
Bokaro Steel Plant and its feasible utilisation for commercial
brick manufacturing. There may be a good scope for production of
such bricks on commercial scale with sufficient load bearing
especially in those areas where good clay is not available for
manufacturing of burnt clay bricks. This would also help in
boosting the rural economy and rural housing.
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Characterisation of LD slag of Bokaro Steel Plant 131
2 Characterisation of LD slag
2.1 Physical properties
2.1.1 pH The instrument mainly used for pH measurement was a
glass electrode pH meter (DPM) with camel reference electrode
including salt bridge. The pH of the LD slag sample was observed to
be 11.35.
2.1.2 Electrical conductivity Ions are the carrier of
electricity, thus the electrical conductivity of the LD slag water
system rises according to the content of soluble salt in the LD
slag, giving rise to more ions or dissociation as it happens in
case of a dilute solution. The electrical conductivity of the LD
slag sample was observed to be 6.7.
2.1.3 Specific gravity Specific gravity is defined as the ratio
of the weight of a given volume of solids to the weight of an
equivalent volume of water at 4C. This test is done to determine
the specific gravity of LD slag sample by density bottle method as
per IS: 2720 (Part III/Sec 1) 1980. The LD slag sample (50 g)
initially passes through a 2 mm IS sieve for determining specific
gravity. The specific gravity of LD slag sample was found to be
3.099.
2.1.4 Bulk density Bulk density is the measurement of the weight
of the solid (such as soil) per unit volume (g/cc), usually given
on an oven-dry (110C) basis. The bulk density of the LD slag sample
was observed to be 1.89 gm/cc.
2.1.5 Particle size distribution analysis Particle size
distribution analysis of LD slag was carried out by the sieve
analysis. The gradation analysis was done in accordance with ASTM
422 standards. The percentage passing of sample vs. the sieve size
used to plot the graph is shown in Figure 1.
Figure 1 Particle size distribution from sieve analysis for LD
slag (see online version for colours)
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132 R. Singh, A.K. Gorai and R.G. Segaran
The uniformity of a sample is reflected by the grain size
distribution curve. For example a steep curve indicates a more or
less uniform size whereas an S-shaped curve represents a well
graded size. The uniformity coefficient (Cu = D60/D10) and
coefficient of gradation (Ck = D30/D60 D10) of the sample were 7.55
and 0.67, respectively. These values indicate that the LD slag
sample was a well graded sample.
2.2 Morphological and mineralogical study
2.2.1 SEM-EDX study In order to investigate the morphology of
the slag LD slag sample was examined by scanning electron
microscopy (Jeol, JSM-6390 LV, Japan) at Central Instrumentation
Facility, BIT Mesra. The accelerating voltage of the instrument was
fixed at 20 kV. The detector type of the SEM was secondary image
detector and it was working in high vacuum condition. LD slag which
was examined at the magnification of X1500, X5000 and X12,000.
The SEM study of the sample shown in Figures 24 reveals that LD
slag is rough textured, cubical and angular in external appearance.
Internally, each particle was vesicular in nature with many
non-interconnected cells. The cellular structure was formed by the
gases entrapped in the hot slag at the time of cooling and
solidification. Since these cells did not form connecting passages,
the term cellular or vesicle was more applicable to steel slag than
that of the term porous.
Figure 2 SEM of LD slag: sample at magnification X1500
Figure 3 SEM of F LD slag: sample at magnification X5000
Figure 4 SEM of LD slag: sample at magnification X12,000
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Characterisation of LD slag of Bokaro Steel Plant 133
The electron image of LD slag sample in EDS X-ray micro analysis
is shown in Figure 5 and its corresponding graph showing the
elemental peaks is shown in Figure 6. Elemental composition of LD
slag sample analysed by EDS is shown in Table 1.
Spectrum label: Spectrum 1
Total spectrum counts: 194853
Acquisition geometry (degrees): Tilt = 0.0, Azimuth = 0.0,
Elevation = 33.0
Figure 5 EDS image of LD slag Sample A
Figure 6 EDS analysis of fresh LD slag Sample A
2.2.2 Chemical analysis by XRF study X-ray spectrometry is a
non-destructive technique used to determine the percent of element
in a substance. A beam of X-ray is directed on the sample causing
secondary X-ray to be emitted which contains characteristic
wavelength of each element present in the sample. This
characteristic radiation was analysed by crystal detector and was
processed in an electronic circuit and computer for determining the
concentration of element.
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134 R. Singh, A.K. Gorai and R.G. Segaran
The chemical composition of the LD slag samples generated at two
steel melting shops, namely SMS-I and SMS-II of Bokaro Steel Plant
is shown in Table 2. Table 1 Elemental composition of fresh LD slag
Sample A by EDS
Element Approximate Concentration Intensity
Correction Weight% Weight% Deviation Atomic%
C 4.93 0.6006 3.13 0.32 5.84
O 57.89 0.4491 49.15 0.56 68.84
Mg 1.64 0.6299 0.99 0.08 0.91
Al 1.85 0.7462 0.95 0.07 0.79
Si 10.91 0.8504 4.89 0.11 3.90
P 0.00 1.2039 0.00 0.10 0.00
S 0.30 0.8663 0.13 0.08 0.09
Ca 82.06 1.0052 31.13 0.37 17.40
Ti 0.22 0.7616 0.11 0.06 0.05
Fe 8.15 0.8225 3.78 0.14 1.52
Au 11.70 0.7777 5.74 0.44 0.65
Total 100.00
Table 2 Chemical composition of LD slag (%)
Components FeO SiO2 Al2O3 CaO MgO MnO P2O5 TiO2 S
Average 24.05 2.20
14.05 1.24
4.34 1.53
45.41 2.24
8.17 0.60
0.84 0.60
1.53 0.14
0.76 0.06
0.24 0.04
Based on the characterisation test of the samples by XRF, it was
observed that the main components of LD slag were CaO, FeO and
SiO2.
2.2.3 Thermal analysis of LD slag
Differential thermal analysis is a technique for recording the
difference in temperature between a substance and a reference
material against either time or temperature as the two specimens
are subjected to identical temperature regimes in an environment
heated or cooled at a controlled rate.
In order to investigate thermal stability of the slag LD slag
sample was examined by Thermo Gravimetric Analyser (Shimadzu,
Japan, DTG-60) at Central Instrumentation Facility, BIT Mesra. The
sample was performed under nitrogen atmosphere and in the
temperature range of ambient to 800C. The heating rate of sample
was 10C/min.
The result of TGA for Fresh LD slag sample A is shown in Figure
7. The weight loss percent of LD slag was analysed in four stages
in the temperature range of 30270C, 270430C, 430620C and 620685C,
respectively. The weight loss rates in four stages were found to be
1.3%, 2.44%, 2.36% and 1.09%, respectively.
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Characterisation of LD slag of Bokaro Steel Plant 135
Figure 7 TGA curve of LD slag (see online version for
colours)
0.00 200.00 400.00 600.00 800.00Temp [C]
80.00
90.00
100.00
%TGA
30.00 CStart
270.00 CEnd
-0.105 mg
-1.300 %
Weight Loss
270.00 CStart
430.00 CEnd
-0.197 mg
-2.440 %
Weight Loss
430.00 CStart
480.00 CEnd
-0.191 mg
-2.366 %
Weight Loss
620.00 CStart
685.00 CEnd
-0.088 mg
-1.090 %
Weight Loss
30.00 CStart
800.00 CEnd
-0.700 mg
-8.670 %
Weight Loss
Thermal Analysis ResultA.tad TGA
The differential thermal analysis result is shown in Figure 8.
From the graph, it is evident that an endothermic peak at 450.7C in
the DTA curve was observed.
Figure 8 DTA curve of LD slag (see online version for
colours)
0.00 200.00 400.00 600.00 800.00Temp [C]
-100.00
-50.00
0.00
uVDTA
422.52 COnset
469.03 CEndset
450.78 CPeak
-74.66 J
-9.25 kJ/g
Heat
Thermal Analysis ResultA.tad DTA
3 Feasibility study of commercial LD slagfly ash brick
manufacturing
3.1 Materials and methodology
The raw materials required for the bricks were fly ash, LD slag,
quarry dust, lime, gypsum and calcium chloride. The characteristics
of lime, gypsum and calcium chloride are given below.
Lime: Lime is a very important ingredient for manufacturing
bricks, and hence it should satisfy the following minimum
requirements:
Lime, while slaking should not attain less than 60C temperatures
and slaking time should not be more than 15 min.
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136 R. Singh, A.K. Gorai and R.G. Segaran
CaO content in lime should be minimum 60%. MgO content should be
maximum 5%. Gypsum: It is added to the mixture in order to
accelerate hardening process and acquiring the early strength. It
should have minimum 35% of purity.
Calcium chloride: Calcium chloride plays the role of an
activator in the mixture and it particularly activates LD slag as
well as helps in silicate formation after drying.
3.2 Brick sample preparation
The samples were prepared with five different composition of LD
slag (Sample type A, Sample type B, Sample type C, Sample type D
and Sample type E) in brick manufacturing for the study. All types
of samples are prepared with the different compositions of fly ash,
LD slag, gypsum, quarry dust, lime and calcium chloride. The
percentage compositions of different raw materials in different
types of samples are shown in Table 3. Table 3 Composition of
different samples of fly ashLD slag brick
Material (in %) S. No. Sample Type
Fly ash LD slag Gypsum Quarry dust Lime CaCl2 1 A 35 30 5 20
9.75 0.25 2 B 40 50 5 5 3 C 30 40 5 15 10 4 D 30 50 5 10 5 5 E 20
60 5 10 5
3.3 Sample preparation
The pan mixture of brick making machine can hold 200 kg of
mixture of raw material for sample preparation.
Sample type A: The calcium chloride was mixed in water while the
appropriate amounts of other raw materials were added in pan
mixture. After few minutes the water containing calcium chloride
solution was poured in the pan mixture with regular intervals.
Hence, 70 kg of fly ash, 60 kg of LD slag, 10 kg of gypsum, 40 kg
of quarry dust, 19.50 kg of lime and 0.5 kg of calcium chloride
were weighted for the preparation of Sample type A. The consumption
of LD slag in the sample type A was 30%.
Sample type B: Similarly, Sample B was prepared with 80 kg of
fly ash, 100 kg of LD slag, 10 kg of gypsum and10 kg of quarry
dust.
Sample type C: Sample C was prepared with 60 kg of fly ash, 80
kg of LD slag, 10 kg of gypsum, 30 kg of quarry dust and 20 kg of
lime.
Sample type D: Sample D was prepared with 60 kg of fly ash, 100
kg of LD slag, 10 kg of gypsum and 20 kg of quarry dust and 10 kg
of lime.
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Characterisation of LD slag of Bokaro Steel Plant 137
Sample type E: Sample E was prepared with 40 kg of fly ash, 120
kg of LD slag, 10 kg of gypsum and 20 kg of quarry dust and 10 kg
of lime.
The fly ashLD slag brick samples for different sample types are
shown in Figures 9ae.
Figure 9 Fly ash: (a) LD slag Sample A; (b) LD slag Sample B;
(c) LD slag Sample C; (d) LD slag Sample D and (e) LD slag Sample E
(see online version for colours)
(a) (b)
(c) (d)
(e)
3.3 Manufacturing process
The process of manufacturing fly ashLD slag brick is based on
the reaction of CaO present in LD slag as well as lime with silica
of fly ash and quarry dust or sand. The quality of bricks obtained
is highly dependent on the quality of raw materials. The
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138 R. Singh, A.K. Gorai and R.G. Segaran
manufacturing process of bricks broadly consists of three
operations viz. mixing the ingredients, pressing the mixture in
machine and curing the bricks for stipulated period. The
manufacturing system of bricks in site is shown in Figure 10.
Figure 10 Brick manufacturing system (see online version for
colours)
3.3.1 Mixing the ingredients in pan mixture Gypsum was added to
the pan mixture and the grinding process was started. Secondly,
lime was added into the mixture then LD slag was added for
grinding. Thirdly, the quarry dust was fed into the mixture for
grinding. Finally, the fly ash was added in the pan for mixing. The
mixtures were then mixed in pan mixer for 3 min and meanwhile the
water was poured in the mixture for proper mixing. In case, we want
to add calcium chloride in the sample, it has to be mixed with
water to be poured into the pan mixture. The water should be
optimum so that the mixture could bind properly.
3.3.2 Pressing the mixture in brick manufacturing machine After
mixing the raw materials in the pan mixture, it will discharge the
materials into the hopper. Conveyor belt was situated below the
hopper having capacity to transport the material of two times of
pan mixture capacity. The material was then discharged from the
hopper into belt conveyor which transported the raw material
mixture up to the brick manufacturing machine and was discharged
into it. The raw materials mixture was compressed in brick
manufacturing with 40 tonne pressure operated hydraulically. Now
the moulded bricks came out from the machines brick sized framed
plates automatically. The moulded bricks were then lifted manually
and kept on pallet. The technical specification of brick
manufacturing machine and its operating principles are given
below.
Technical specifications
1 Type of the press:Low-stroke.
2 Capacity: 30 tonne.
3 Day light gap: 350 mm.
4 Mode of operation: Auto.
5 Production speed: 6 bricks per cycle.
6 Production capacity: 1000 bricks per hour.
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Characterisation of LD slag of Bokaro Steel Plant 139
3.3.3 Operating principle Brick making machine is hydraulically
operated, fully automatic system and controlled by Programmable
Logic Control (PLC). This machine produces 1000 bricks per hour.
Newly designed component of hydraulic system develops the
compressive force of 40 tonnes so that the material would be
compressed fully and good quality of bricks is maintained.
Adjusting the relief valve system can vary force.
3.3.4 Method of curing The moulded bricks were hauled from the
hydraulic trolley in the drying yards. After drying for 48 h it was
cured by adding water for 1421 days.
4 Results and discussion
4.1 Uni-axial compressive strength
It is the strength of the brick that can sustain without
failure, when the load applied in one direction (parallel to the
axis) only. Compressive strength is a vital parameter to judge the
durability/stability of the brick.
2kg cmFA
where, F = load applied in kg and A = area in cm2.
The uni-axial compression tests were conducted for different
composition of the fly ashLD slag brick samples on 7th day, 14th
day, 21st day and 28th day from the date of manufacturing. The
brick sample was prepared on 12 February 2010, and hence the tests
were conducted on 19 February 2010, 26 February 2010, 05 March 2010
and 12 March 2010. The compressive strength tests of the samples
were carried out as per standard practices. The results of
compressive strength of various samples are given in Table 4. The
trends of compressive strength of different sample A, B and C are
shown in Figure 11, Figure 12 and Figure 13, respectively. The
sample types D and E were not tested as cracks were developed
within 7 day from the date of manufacturing.
Figure 11 Compressive strength of fly ashLD slag brick Sample
type A (see online version for colours)
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140 R. Singh, A.K. Gorai and R.G. Segaran
Figure 12 Compressive strength of fly ashLD slag brick Sample
type B (see online version for colours)
Figure 13 Compressive strength of fly ashLD slag brick Sample
type C (see online version for colours)
Table 4 Compressive strength of fly ashLD slag brick samples
Compressive strength (Kg/cm2) 7th day 14th day 21st day 28th day
S. No. Sample type Sample CODE 19/2/10 26/2/10 5/3/10 12/3/10
A1 65.1 109.7 133.2 134.4 A2 58.9 107.8 127.4 129.6 A3 52.7
105.4 125.3 128.1
1 A
Average S.D 58.9 6.2 107.6 2.1 128 4.0 130.7 3.2 B1 42.7 96
107.8 92.5 B2 48.6 101.9 119.5 107 B3 38.3 91 102.7 87.9
2 B
Average S.D 43.2 5.1 96.4 5.3 110 8.6 95.8 9.9
C1 39.2 88.2 117.6 103.8
C2 41.3 90.1 111.7 103.8 C3 43.2 92.3 119.9 108.8
3 C
Average S.D 41.2 2.0 90.2 2.0 118.4 4.2 105.4 2.8
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Characterisation of LD slag of Bokaro Steel Plant 141
Figure 11 shows the changing behaviour of compressive strength
with passage of days for Sample type A. The average values of
compressive strength of Sample type A was found to be 58.9 kg/cm2,
107.6 kg/cm2, 128 kg/cm2 and 130.7 kg/cm2 after 7th day, 14th day,
21st day and 28th day from the date of manufacturing, respectively.
It is evident from Figure 11 that the compressive strength of the
sample increases rapidly up to 21st day and then it is more or less
stabilised with a constant value.
Figure 12 shows the changing behaviour of compressive strength
with passage of days for Sample type B. The average values of
compressive strength of Sample type B was found to be 43.2 kg/cm2,
96.4 kg/cm2, 110 kg/cm2 and 95.8 kg/cm2 after 7th day, 14th day,
21st day and 28th day from the date of manufacturing, respectively.
It is evident from Figure 12 that the compressive strength of the
sample increases up to 21st day and then it starts declining. From
the trend of the compressive strength, it can be inferred that the
samples of this composition type will not sustain or provide good
results in long run. The reason may be that the higher percentage
of LD slag (consists of high percentage of lime) in the sample
leads to internal cracks formation in the brick during drying.
Figure 13 shows the changing behaviour of compressive strength
with passage of days for Sample type C. The average values of
compressive strength of Sample type C was found to be 41.2 kg/cm2,
90.2 kg/cm2, 118.4 kg/cm2 and 105.4 kg/cm2 after 7th day, 14th day,
21st day and 28th day from the date of manufacturing, respectively.
It is evident from Figure 13 that the compressive strength of the
sample increases up to 21st day and then it starts declining. From
the trend of the compressive strength, it can be inferred that the
samples of this composition type will not sustain or provide good
results in long run. The reason may be that the higher percentage
of LD slag (consists of high percentage of lime) in the sample
leads to cracks formation in the brick during drying.
The comparative trends for compressive strength of three
different types of samples A, B and C for their average value are
shown in Figure 14. From the above graph, it is evident that the
compressive strength is continuously increasing for Sample type A
whereas the compressive strength for Sample type B and C are of
decreasing trend after 21st days. This may be due to the lower
percentage of LD slag in sample type A.
Figure 14 Comparison of compressive strength of different fly
ashLD slag brick samples (see online version for colours)
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142 R. Singh, A.K. Gorai and R.G. Segaran
4.2 Water absorption
The amount of water absorbed by a composite material when
immersed in water for a stipulated period of time is defined as
water absorption capacity. As per IS, water absorption capacity for
lime bricks should be within 20%. It is the ratio of the weight of
water absorbed by a material to the weight of the dry
materials.
The water absorption capacity of the tested brick samples are
given in Table 5. From Table 5 it can be observed that the water
absorption capacity was found to be less than 25% which showed that
the fly ashLD slag brick had less water absorption capacity than
the conventional red clay brick. The fly ashLD slag brick Sample
type A had average water absorption of 20.35%. Similarly, Sample
type B had average water absorption of 21.75% and Sample type C had
water absorption of 22.5%. Hence among the three samples which were
taken for water absorption, the Sample Type A had less water
absorption of 20.35% which is good for the civil work. Table 5
Water absorption (%) of fly ashLD slag brick
Water absorption (%) 7th day 14th day 21st day 28th day S. No.
Sample type
19/2/10 26/2/10 5/3/10 12/3/10 1 A 20.2 20.6 20.7 19.9 2 B 21.7
22.8 21.8 20.7 3 C 21.1 19.5 25 24.4
4.3 Bulk density
The bulk density is defined as the weight of material present in
a sample per unit volume.
Bulk density (gm/cm3) = Weight of material/Volume of
material
The bulk density of fly ashLD slag brick which is placed for
water absorption test was given in Table 6 and it was found in the
range of 1.471.79 gm/cm3. Table 6 Bulk density of fly ashLD slag
brick
Bulk density (gm/cm3) 7th day 14th day 21st day 28th day S. No.
Sample type
19/2/10 25/2/10 4/3/10 15/3/10 1 A 1.67 1.60 1.64 1.66 2 B 1.61
1.56 1.78 1.79 3 C 1.58 1.67 1.47 1.49
4.4 Fly ashLD slag brick dimensions
The average length, breadth and height of the bricks were 23.11,
11.06 and 7.53, respectively. Table 7 shows that the dimensions of
the tested sample of fly ashLD slag brick. The dimensions of the
brick samples were uniform which is very good for civil work.
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Characterisation of LD slag of Bokaro Steel Plant 143
Table 7 Dimension of fly ashLD slag brick
S. No. Sample code Length (cm) Breath (cm) Height (cm) Volume
(cm3)
1 A1 23.2 11.0 7.5 1914
2 A2 23.1 11.0 7.5 1905.7
3 A3 23.2 11.1 7.6 1939.5
4 B1 23.0 11.1 7.5 1897.5
5 B2 23.2 11.0 7.5 1914
6 B3 23.1 11.0 7.5 1905.7
7 C1 23.1 11.1 7.6 1948.7
8 C2 23.0 11.2 7.6 1922.8
9 C3 23.0 11.0 7.5 1914
4.5 Comparative study of fly ash-LD slag bricks with other types
of bricks
The comparative characteristics values of fly ashLD slag bricks,
fly ashlime-sand brick and normal red clay bricks are reported in
Table 8. The comparative strength of fly ashLD slag bricks is
higher than that of the fly ashlime-sand brick and normal red clay
bricks. The water absorption capacity of fly ashLD slag bricks is
within the range of 20% and higher than that of the fly
ashlime-sand bricks but lower than that of the normal red clay
bricks. Table 8 Comparative characteristics of various types of
bricks
Items Normal red clay bricks Fly ashlime-sand
brick
Fly ashLD slag bricks (Sample type A after 28 days of
curing)
Compressive strength around 35 Kg/cm2 around 100 kg/cm2 130.7
3.2 kg/cm2
Thermal conductivity 1.251.35 W/m2 C 0.901.05 W/m2 C Not
studied
Water absorption 2025% 612% 19.9%
Bulk density Higher than fly ash bricks Lower than normal
clay bricks 1.66
Source:
http://flyashbricksinfo.com/fly-ash-brick-vs-normal-clay-bricks.html#
The bulk density of fly ashlime-sand bricks is lower than that
of the normal red clay bricks. The bulk density of fly ash bricks
as in the range of 1.1721.223 gm/cm3 (Kumar, 2002) and thus from
Table 8 it can be observed that the bulk density of fly
ashlime-sand bricks is lower than that of the fly ashLD slag
bricks.
5 Conclusion
The characterisation results of LD slag showed that the pH and
electrical conductivity of the samples were very high indicating
high percentage of lime presence and presence of
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144 R. Singh, A.K. Gorai and R.G. Segaran
ionic form of various salts, respectively. The specific gravity
and bulk density of sample was found to be high in comparison to
fly ash and due to these characteristics the LD slag bricks are
heavier than that of the fly-ash brick.
Uniformity Coefficient (Cu) and Coefficient of gradation (Ck)
values in particle size analysis indicate that the LD slag sample
used for the brick manufacturing was a well graded sample.
The SEM study of LD slag results showed that the sample was
rough textured, cubical and angular in external appearance.
Internally, each particle was vesicular in nature with many
non-interconnected cells. The cellular structure was formed by the
gases entrapped in the hot slag at the time of cooling and
solidification. Since these cells did not form connecting passages,
the term cellular or vesicle was more applicable to steel slag than
that of the term porous.
The EDS X-ray micro analysis of LD slag sample showed that the
elemental compositions of the sample are C, O, Mg, Al, Si, P, S,
Ca, Ti, Fe and Au. Among the above elements, O and Ca share the
major percentage by weight in the LD slag sample.
The XRF analysis showed that the major components of the LD slag
samples are CaO, FeO and SiO2.
Thermal Gravimetric Analysis (TGA) of LD slag Sample A showed
that the weight loss rates in four stages (in the temperature range
of 30270C, 270430C, 430620C and 620685C) were found to be 1.3%,
2.44%, 2.36% and 1.09%, respectively. The differential thermal
analysis result showed that an endothermic peak at 450.7C in the
DTA curve was observed.
Five different composition of fly ashLD slag samples were
prepared and tested for uni-axial compressive strength test and
water absorption. The average values of compressive strength of
Sample type A were found to be 58.9 kg/cm2, 107.6 kg/cm2, 128
kg/cm2 and 130.7 kg/cm2 after 7th day, 14th day, 21st day and 28th
day from the date of manufacturing, respectively. The compressive
strength of the sample increases up to 21st day and then it was
more or less stable. But the other samples were not sustained or
provide good results in long run. The reason may be that the higher
percentage of LD slag (consists of high percentage of lime) in the
sample leads to cracks development in the brick during drying.
The cost of fly ashLD slag brick depends upon the electricity
cost, water cost, maintenance cost, labour cost and the cost of raw
material used in brick making. The cost of raw material depends
upon the market value and the transportation cost of the material.
While other additional expenditure for brick making were
electricity cost, water cost, maintenance cost and labour cost
which is Rs.0.61/brick. Considering all the above costs, the
manufacturing cost of fly ashLD slag brick was estimated to be of
Rs.2.72/brick. The above cost is little bit higher than that of the
cost of conventional red clay bricks (approximately Rs.2.50). But
some indirect benefit (environmental) can be achieved with the
manufacturing of fly ashLD slag brick.
The compressive strength of the fly ashLD slag brick Sample type
A (above 100 kg/cm2) was sufficiently higher than that of the
normal red clay bricks (5070 kg/cm2) and can be a feasible
replacement for the commercial purposes in civil jobs. This will
not only solve the industrys waste disposal problem but also
protects environment and save energy (capacity of coal saving 37
t/lakhs of bricks).
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Characterisation of LD slag of Bokaro Steel Plant 145
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