INTRODUCTION
Fly ash is a type of waste ash from the thermal power generation industry. It is a residue that is
collected from thermal power stations' flue gases after they have passed through the ESP (or
the electrostatic precipitator) and before they reach the chimneys. The composition of fly ash
will vary based on the type of coal burned and the type of burner employed. In addition to trace
elements such as mercury, arsenic, antimony, chromium, selenium, lead, cadmium, nickel, and
zinc, fly ash contains these additional elements as well.
The product's name is Fly Ash because these microscopic glass spheres, which solidify in the
power plant's exhaust before they can leave, are gathered from the power plant before they can
fly away. Underneath the layer of fly ash, there is a pozzolan. Cementitious compounds are
formed when pozzolans are mixed with lime (calcium hydroxide).
Growth in the industrial sectors is contributing to a rapidly rising power demand in the country.
Because the majority of the country's power is generated using thermal power, the amount of
ash produced will also increase. On the average, Indian coal has 30% to 40% Ash, and this is
one of the major reasons for increasing ash production and hence, problems in ash utilisation.
Fly ash is a major pollutant in the air, water, and soil, disrupting ecosystems. Additionally, there
are trace amounts of toxic metals present in the ash, which could negatively affect human health
and the ecosystem where the fly ash decomposed.
Waste disposal is a critical environmental issue for the environment and the ecosystem. A safe
and profitable use of this material has been a long-standing question in research.
Fly ash utilisation provides these advantages:
● space for waste disposal and resources conservation
● protection of the environment, as well as conserving energy
The ash use options include ash-based products, which are in the process of development.
In the presence of moisture, fly ash reacts with lime at room temperature to form a cementitious
compound. Calcium silicate hydrates (C-S-H) are formed during the reaction of lime and fly ash.
These hydrates are responsible for the compound's high strength.
This process entails homogeneous mixing of raw materials (generally fly ash, sand, and lime),
brick moulding, and finally curing the green bricks. Certain technologies require the use of a
chemical accelerator such as gypsum. These processes are nearly identical and differ slightly in
their application from water curing to steam curing at low pressure or autoclaving at a pressure
of 10-14 kg/cm2.
Chemically bonded bricks are those made by combining lime and fly ash. These bricks, like
standard burnt clay bricks, are suitable for use in masonry. These bricks have an adequate
crushing strength for use as a load-bearing member and are significantly lighter in weight than
conventional clay bricks.
Generally, dry fly ash obtained from power plants satisfies the requirements of IS: 3812 and is
suitable for the manufacture of Fly Ash – Lime Bricks in accordance with the IS: 12894
requirements
Fly ash, lime, gypsum, and sand are used to make fly ash bricks. Similar to conventional burnt
clay bricks, these can be employed in a variety of building construction tasks. Fly ash bricks are
lighter in weight and more durable than traditional clay bricks. Because fly ash is accumulating
as a waste material in large quantities near thermal power plants, posing serious environmental
pollution issues, its use as a primary raw material in the production of bricks will not only provide
ample opportunities for its proper and useful disposal, but will also aid in environmental pollution
control to a greater extent in the power plant's surrounding areas. The demand for Fly Ash
Bricks has increased as a result of its excellent quality, eco-friendly nature, and government
assistance
MANUFACTURING OF FLY ASH BRICKS:
● Hydraulic or vibratory presses are used to produce fly ash bricks.
● The raw materials required include fly ash (60-65 percent), bottom ash (less than 12
percent
loss on ignition when evaluated according to IS 1727), lime (class C hydrated
lime of IS 712 (8-12 percent), gypsum (5 percent), locally accessible sand/stone dust
(18-27 percent), and water.
● In addition to hydrated lime and gypsum, ordinary Portland Cement can be used.
● The raw components are mixed in the pan mixer in the proper proportions to produce a
semi-dry homogenous mix.
● The semi-dry mix is poured into the hydraulic/vibro press moulds.
For testing Fly Ash bricks, two BIS standards
(IS 3495 and IS 10077) are available.
-Compressive strength test IS 3495(part-1)
-Drying shrinkage test IS 4135
-Efflorescence test IS 3495(part-3)
-Water absorption test IS 3495(part-2)
Fly ash-Sand-Lime bricks have the following characteristics:
1. Bricks are uniform in size and shape.
2. They have a high compressive strength when wet.
3. They have a low shrinkage during the drying process.
4. They are efflorescent-free
5. It is determined that the quality of fly ash sand lime brick is superior to In some respects, such
as water absorption, conventional burnt clay bricks
crushing strength, and so forth.
6. Additionally, the bricks are lighter than burnt clay bricks.
COMPARITION OF RED BRICKS AND FLY
ASH BRICKS:
RED BRICKS/CLAY BRICKS: (in table or paragraph format)
• compressive strength - 30-35kg/m3
• Absorption. - 15-25%
• dimensional stability. - Very low
tolerance
• wastage during transit - up 10%
• density - 1600-1750kg/m
FLY ASH BRICKS:
•compressive strength. - 90-100kg/m3
•absorption. - 10-14%
•dimensional stability. - High tolerance
•wastage during transit. - Less than 2%
• density. - 1700-1850kg/m3
Advantages of fly ash bricks
Appearance
These bricks have a pleasing cement-like colour, are uniform in shape, and have a smooth
finish; additionally, they do not require plastering during construction. The bricks are densely
packed, uniform in shape with or without a frog, and free of visible cracks, warp-age, organic
matter, pebbles, and free lime nodules. They are lighter in weight and less porous than standard
clay bricks. The colour of fly ash bricks can be changed by adding admixtures during the brick
making process. They come in a variety of sizes, but are generally comparable to clay bricks.
Structural capability
These bricks have the advantage of being available in a variety of load-bearing grades,
requiring less mortar plastering, and producing attractive brickwork. The high compressive
strength eliminates breakages/wastages during transport and handling, and the cracking of
plaster is reduced due to the thinner joints and plaster, as well as the more compatible basic
material of the bricks. Due to the bricks' comparable density, they do not add any additional load
to the structure's design and provide superior resistance to earthquake loads due to panel
action with high strength bricks.
Thermal properties
Thermal conductivity ranges between 0.90 and 1.05 W/m2 oC (20-30% less than that of
concrete blocks). These bricks do not absorb heat; instead, they reflect it, providing the
maximum amount of light reflection without glare.
Sound insulation
It provides a level of sound insulation that is acceptable.
Durability and Moisture Resistance
These blocks are extremely durable; with proper joint pointing, the bricks can be painted directly
with dry distemper and cement paints without the need for a backing coat of plaster.
Rectangular in shape with pointed corners, solid, compact, and uniform in size Water absorption
is 6-12 percent, compared to 20-25 percent for handmade clay bricks, which reduces wall
dampness.
Fire and vermin resistance
The fire rating of fly ash bricks is excellent. It is free of vermin infestation or vermin attacks.
Building availability amd cost
The block's easy workability and high compressive strength prevent breakage/wastage during
handling, resulting in a neat finish with reduced joint and plaster thickness. The construction
technique is identical to that of standard bricks, ensuring material changes are simple and do
not require additional training for masons.