LD Slag Flyash Bricks Intl Journal

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.

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.

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)


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


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.


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.


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.


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.


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


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.


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)


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


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)


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.


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


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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LD Slag Flyash Bricks Intl Journal

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