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New ALTERNATIVE WALLING MATERIAL.
1. INTRODUCTION
About 80 million tones of fly ash is being produced
and thrown out as a waste, from about 60 Thermal Power stations
functioning in our country. This fine material not only creates pollution
but also poses serious disposal problem. One of the best ways of
utilizing this hazardous pollutant is to convert it into a building material
like brick. Brick is considered to be the most common walling material,
used by the man from pre-Vedic period. The conventional burnt clay
brick has been causing severe depletion of fertile land, directly affecting
the countrys green revolution campaign. Production of fly ash sand
lime bricks can, to a certain extent, help to solve the above mentioned
problems.
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2. MATERIALS
Fly ash is a siliceous material with association of
amorphous/Glassy mass. The constituent particles of fly ash react with
lime at elevated temperature and pressure of steam to form calcium
silicate hydrate and calcium aluminates hydrate. The nature and extent
of formation of calcium silicate hydrate depends upon many factors like
physics-chemical and mineralogical characteristics of raw materials,
molar ratio of calcium oxide and silica, and proportioning and curing
conditions. In the present study, three fly ash samples containing un
burnt carbon 0.5, 4.3, 7.9 percent have been taken. Different mixes
having Fly ash, sand and lime in 70: 20: 10, 60: 30: 10, 50: 40: 10 by
weight were prepared for producing Bricks.
TABLE 1
Raw materials Requirement
(a) Fly Ash
(b) Sand
(c) Lime
(d) Ordinary Portland cement
(e) Gypsum
Accelerator
CBRI
50-60%
30-40%
8-10%
--
0.5-2.0%
NIL
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3. PROCESS DETAILS
The CBRI has developed four technological options to
produce fly ash sand lime bricks are as under:
i) Shaping of bricks at high pressure and steam curing at high
pressure known as Autoclaved Fly ash sand lime bricks.
ii) Shaping of bricks at high pressure and steam curing at atmospheric
pressure.
iii) Shaping by vibro-compaction and steam curing at high pressure.
iv) Shaping by vibro-compaction and steam curing at atmospheric
pressure called C Bricks.
Option No.1:-
Shaping of bricks at high pressure and steam curing at
high pressure.
This option involves four major operations namely
proportioning of raw materials using screw feeds or box feeder, dry and
wet mixing by means of pair of double shaft mixer, shaping by suitable
press, enabling to impart a pressure of 200-240 Kg/Cm2 and steam curing
at 10 14 Kg/cm2 in autoclaves.
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1. Proportioning Unit
2. Bucket Elevator
3. Double Shaft Mixer
4. Water Spraying
5. Double Shaft Mixer
6. Belt Conveyor
7. Hydraulic Press
8. Off- Take Belt Conveyor
9. Trolley with Bricks
10. Autoclave
SCHEMATIC DIAGRAM FOR PRODUCTION OF BRICKS BY HIGH PRESSURE
SHAPING AND HIGH PRESSURE STEAM CURING
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VARIATION OF COMPRESSIVE STRENGTH WITH LOSS ON
IGNITION
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Inference:
This option has a potential handle a fly ash with
unburnt carbon as high as 8% to produce bricks of compressive strength
more than 100 Kg/Cm2. In other words with this option even pond ash
can directly be used for brick production.
Brief Project Profile :
Capacity of plant : 40,000 bricks per day in 3 shifts
Total capital investment : Rs. 350 lacks.
Cost of Purchased Equipment : Rs 200 lacks.
Man power requirement : 100 persons.
Land Required : 0.6 Hectares
Installed power : 300 KW
Estimated cost of Production : Rs 1400 per 1000 bricks.
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Option No 2:
Shaping of bricks at high pressure and steam curing at
atmospheric pressure
In this option proportioning and shaping operations are done exactly as
in option no.(1). The steam curing of green bricks is done in ordinary
chambers at 1 Kg/Cm2 pressure instead of autoclaves.
Inference:
This option has a potential to handle a fly ash having
unburnt carbon upto 5% to produce bricks of compressive strength more
than 80 Kg/Cm2.
Brief Project Profile.
Capacity of Plant : 40,000 bricks per day in shifts.
Total capital investment : Rs.300 lacs.
Cost of purchased equipment : Rs. 130 lacs.
Manpower Requirement : 100 persons.
Land Requirement : 0.6 Hecters.
Installed Power : 300 K W.
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1. Proportioning Unit
2. Bucket Elevator
3. Double Shaft Mixer
4. Water Spraying
5. Double Shaft Mixer
6. Belt Conveyor
7. Hydraulic Press
8. Off- Take Belt Conveyor
9. Trolley with Bricks
10. Steam curing chamber
SCHEMATIC DIAGRAM FOR PRODUCTION OF BRICKS BY HIGH
PRESSURE SHAPING AND ATMOSPHERIC PRESSURE STEAM CURING
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VARIATION OF COMPRESSIVE STRENGHT WITH LOSS ON
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Option No 3:-Shaping by Vibro-compaction and steam curing at high
pressure.
Under this option, mixing of raw materials is done in
a pan mixer and shaping is done in a vibro-compaction machine which
produces a low moulding pressure. The green bricks are dried before
subjecting to steam curing at high pressure in autoclaves.
Inference
The fly ash having higher unburnt carbon can be used
for producing bricks of adequate strength by adopting this option i.e.
vibro-compaction moulding and high pressure steam curing.
Brief Project profile :
Capacity of Plant : 3000 bricks per shift.
Total capital investment : Rs. 8 lacs.
Cost of purchased equipment : Rs. 6 lacs.
Man Power Requirement : 14 persons.
Land requirement : 800 Sq. metres.
Installed power : 10 KW.
Estimated cost of production : Rs.1100/- per 1000 bricks.
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1. Flyash2. Sand
3. Lime
4. Pan Mill
5. Shaping Machine6. Autoclave
7. Ready Bricks
SCHEMATIC DIAGRAM FOR PRODUCTION OF BRICKS BY VIBRO-
COMPACTION SHAPING AND HIGH PRESSURE STEAM CURING
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VARIATION OF COMPRESSIVE STRENGTH WITH LOSS
ON IGNITION
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Option No 4
Shaping by vibro-compaction and steam curing at
atmospheric pressure. Under this option, proportioning, mixing and
shaping operations are done exactly as in option No 3 excepts for the
steam curing of green bricks at 1 Kg/Cm2 in ordinary chambers.
It is worth while to mention here that if cement is added as binder in this
option wet curing of 28 days can replace the steam curing.
Inference : In this option, fly ash with higher percentage of unburnt
carbon is not found to be suitable for producing good quality of bricks.
Therefore, it is necessary to go in for a fly ash with lower percentage of unburnt
carbon, obviously hopper ash can directly be used. With such fly ash being light
in colour, use of an appropriate pigment can also be made to produce
red/chocolate coloured bricks.
Brief Project Profiles:
Capacity of plant : 3000 bricks per shift.
Total capital investment : Rs. 3 lacks.
Cost of purchased equipment : Rs.1.25 lacks.
Manpower : 10 persons.
Installed power : 10 KW
Estimated cost of production : Rs. 1000/- per 1000 bricks.
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1. Fly ash2. Sand
3. Lime
4. Pan Mill
5. Shaping Machine
6. Chamber
7. Ready Bricks
SCHIMATIC DIAGRAM FOR PRODUCTION OF BRICKS BY VIBRO-
CPOMECTION SHAPING AND ATMOSPHERIC PRESSURE STEAM
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VARIATION OF COMPRESSIVE STRENGTH WITH
LOSS ON IGNITION
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4. PROPERTIES
A) ENGINEERING PROPERTIES :
i) Shrinkage : Depending on the characteristics properties of raw
materials and the process adopted for production, these bricks
show a drying shrinkage of the order of 0.02 to 0.04 %.
ii) Absorption Properties : The saturation coefficient tends to one,
indicating openness in the pore structure. This facilitated easier
evaporation of the water absorbed by the external face in wet
season. The initial rate of absorption ranges between25 to 35,
which is comparable to conventional bricks thus imparting similar
bonding characteristics.
iii) Prism strength : Masonry prisms with different mortars and having
a height to base ratio of 2 were tested in compression to assess
masonry strength. Observed prism strengths with 1: 1: 6, 1:1:9
(cement: Lime : Sand ) and 1:6 (Cements : Sand) mortars were
between 0.40 to 0.43 to the unit strength. This value is certainly
better than that of conventional bricks, which ranges between 0.3to
0.35.
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B) PHYSICAL PROPERTIES :
i) Compressive strength - 40 80(Wet comp. Strength) Kg/Cm2
ii) Water absorption - 15 20 %
iii) Durability - Good
iv) Efflorescence - Free from Efflorescence.
v) Bulk Density - 1400 1600
Kg/Cm2
vi) Shape - Uniform
vii) Finish - Smooth
5. ADVANTAGES
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In presence of moisture, fly ash reacts with lime at
ordinary temperature and forms a compound possessing cementations
properties. After reactions between lime and fly ash, calcium silicate
hydrates are produced which are responsible for the high strength of the
compound. Bricks made by mixing lime and fly ash are, therefore,
chemically bonded bricks. These bricks are suitable for use in masonry
just like common burnt clay bricks. These bricks have the following
advantages over the clay bricks.
1) Possess crushing strength more than that of good quality clay bricks
and can therefore be used as a load bearing member.
2) Have cement colour in appearance, are uniform in shape and smooth
in finish and require no plastering for building work.
3) Are lighter in weight than ordinary clay bricks. Are less porous than
the ordinary clay bricks.
4) Have more Durability than the ordinary clay bricks.
6. CONCLUSION
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Good quality building bricks can be produced from fly
ash by adopting an appropriate technology from the four technological
options described above. One can pick up the best suitable option in the
given set of conditions governed by characteristic properties of available
raw materials, desired Engineering properties of the end product and
financial investments.
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