bricks types and flyash bricks

                            Types of bricks 

There are literally thousands of different bricks, but they 
can be broken down into a handful of basic types. The vast 
majority are made from clay and are kiln-fired.  

Facing Bricks 

Quality, durable bricks with an attractive appearance for 
external use above ground


Wirecut 

The clay is continuously extruded to a 
required size and shaope and then cut into 
individual bricks by means of a wire, much 
like a cheese is cut by cheesewire. 
Thousands of variations in colour and 
texture. Usually the cheapest facings 
available as the manufacturing process is 
highly automated.  


Stock 

The clay is wetted to a so-called "soft mud" 
and then moulded to shape, before being 
allowed to dry prior to firing in the kiln. 
Much of the process is automated. Tend to 
be slightly irregular in shape. Usually a bit 
more expensive than wirecuts.  
Stock bricks  

Handmade 

Usually made on a bench, in a mould, much 
as described above for a stock brick. 
Because the clay isn't firmly compacted by 
machine, each brick normally has 
distinctive creasing known as a 'smile'. 
Very desirable, and the most expensive of 
the facings, but well worth it on prestige 
jobs.  


Fletton 

Also known as 'London Bricks'. A unique 
facing brick manufactured from the Lower 
Oxford clay found only in SE England. 

This clay contains coal traces, which burn during 
firing, reducing the amount of fuel needed 
for the kiln, which not only keeps down 
costs but also produces some interesting 
effects in the bricks themselves.  

What is fly ash?

Power plants fueled by coal produce more than half of the electricity we consume today. But in addition to electricity, these plants produce a material that is fast becoming a

vital ingredient for improving the performance of a wide range of concrete products.

That material is fly ash.

Fly ash is comprised of the non-combustible mineral portion of coal. When coal is consumed in a power plant, it is first ground to the fineness of powder. Blown into the power plant’s boiler, the carbon is consumed — leaving molten particles rich in silica, alumina and calcium. These particles solidify as microscopic, glassy spheres that are collected from the power plant’s exhaust before they can “fly” away — hence the product’s name: Fly Ash.

Chemically, fly ash is a pozzolan. When mixed with lime (calcium hydroxide), pozzolans combine to form cementitious compounds. Concrete containing fly ash becomes stronger, more durable, and more resistant to chemical attack.

Mechanically, fly ash also pays dividends for concrete production. Because fly ash particles are small, they effectively fill voids. Because fly ash particles are hard and round, they have a “ball bearing” effect that allows concrete to be produced using less water. Both characteristics contribute to enhanced concrete workability and durability.

Finally, fly ash use creates significant benefits for our environment. Fly ash use conserves natural resources and avoids landfill disposal of ash products. By making concrete more durable, life cycle costs of roads and structures are reduced. Furthermore, fly ash use partially displaces production of other concrete ingredients, resulting in significant energy savings and reductions in greenhouse gas emissions

Flyash bricks can be divided into the following types

 
Clay Flyash Bricks.

Manufacturing process of clay flyash bricks by manual or extrusion process involves mixing
of flyash (60 %) with clay of moderate plasticity. The green bricks are dried under ambient
atmospheric conditions or in shed to equilibrium moisture level of below 3 percent. Dried
bricks are fired in traditional brick kilns at 1000º ± 30º C with a soaking period of 5 – 7 hours
at maturing temperature. This technology has great potential to reduce not only precious top
soil and consumption of coal in making conventional clay bricks, but also requires minimum
charges in existing set up at kiln sites and not very much susceptible to quality of ash.

Flyash – Sand Lime Bricks.

In presence of moisture, fly ash reacts with lime at ordinary temperature and forms a
compound possessing cementitious properties. After reactions between lime and flyash,
calcium silicate hydrates are produced which are responsible for the high strength of the
compound.

This processes involves homogeneous mixing of raw materials (generally fly ash, sand and
lime), moulding of bricks and then curing of the green bricks. Some technologies call for
usage of chemical accelerator like gypsum. These processes are almost similar and vary
slightly from water curing to steam curing at low pressure or autoclaving at 10-14 kg/cm2.
Bricks made by mixing lime and flyash are, therefore, chemically bonded bricks. These
bricks are suitable for use in masonry just like common burnt clay bricks. These bricks posses
adequate crushing strength as a load-bearing member and are lighter in weight than ordinary
clay bricks.

Generally, dry fly ash available from power plants meets the properties specified in IS: 3812
and is suitable for manufacture of Fly Ash – lime bricks in accordance with the requirements
of IS: 12894.

Cold Bonded Lightweight Flyash Bricks, Blocks and Tiles

The material can be produced in a variety of building blocks, bricks and tiles, depending on
local markets and regulations. Keraton consists of cheap and ubiquitous raw materials such as
fly ash and / or other waste materials. These materials are mixed and a cold bonding agent is
added. The mixed raw material is cast in moulds, after which the moulds are processed in a
microwave oven for transportation to the building site.

The products can be applied as a lightweight material in the house building industry and utility building, such as stables, barns, garages, etc. A surface treatment or coating for coloring is possible. Strong points are the
ability to use fly ash, the insulation properties and the production flexibility.

Flux Bonded Flyash Bricks Blocks and Tiles

The process is similar to the one in the conventional tile industry: fly ash is mixed with less
than 10 % plastic clay and a few additives and tiles, bricks or blocks are pressed. These
shapes are fired in the range of 900ºC to 1000ºC to make the final product. More than 85% of
flyash is used in the process.

The process is based on the formation of low melting fluxes at
the firing temperature, which partly react with the fly ash and form a high temperature
reactive glass binder phase. The bricks, tiles and blocks are brick red in colour, but changing
the initial composition can make a variety of colours.

 Difference between Flyash brick and Clay bricks

Flyash brick Uniform pleasing colour like cement	Normal clay brick Varying colour as per soil
Uniform in shape and smooth in finish	Uneven shape as hand made
Dense composition	Lightly bonded
No plastering required	Plastering required
Lighter in weight	Heavier in weight
Compressive strength is around 100 Kg/cm2	Compressive strength is around 35 Kg/cm2
Less porous	More porous
Thermal conductivity 0.90-1.05 W/m2 ºC	Thermal conductivity 1.25 – 1.35 W/m2 ºC
Water absorption 6-12%	Water absorption 20-25%

For manufacturing flyash bricks , most of the machine manufacturers suggest the following TWO mixing ratio, YOU CAN CHOOSE PROFITABLE MIXING RATIO TO SURVIVE IN THE MARKET if you are facing lowavailability of Flyash .

At the same time you should maintain the quality too.

---

NORMAL METHOD

Process of Manufacture: 
Fly ash, Hydrated lime, Quarry dust and gypsum are manually fed into a pan mixer where water is added in the required proportion for intimate mixing. The proportion of the raw material is generally in the ratio

62%	fly ash
8%	lime
5%	Gypsum
25%	sand or Quarry Dust

 depending upon the quality of raw materials. 
After mixing, the mixture is shifted to the hydraulic Brick Making machines. The bricks are carried on wooden pellets to the open area where they are dried and water cured for 14 days. The bricks are tested and sorted before dispatch.

---

PROFITABLE METHOD

20%	fly ash
15%	lime
5%	Gypsum
60%	sand or Quarry Dust

Cement bricks or concrete hollow bricks

   Cement concrete hollow blocks have an important place in modern building 
industry. They are cost effective and better  alternative to burnt clay bricks by 
virtue of their good durability, fire  resistance, partial resistance to sound, 
thermal insulation, small dead load and high speed of construction. Concrete 
hollow blocks being usually larger in size than the normal clay building bricks 
and less mortar is required, faster of construction is achieved.
Also building construction with cement concrete hollow blocks provides facility 
for concealing electrical conduit, water and sewer pipes wherever so desired and 
requires less plastering.

RAW MATERIALS
Concrete is a mixture of ordinary Portland cement, mineral aggregate (sand and 
stone chips) and water. The water used in preparing the concrete serves two 
purposes:
(1)It combines with the cement to form a hardened paste
(2)It lubricates the aggregates to form a plastic and workable mass
The water that combines with the cement varies from about 22 to 28% of the 
total amount of mixing water in concrete.
Mineral aggregates (sand and stone chips) are normally divided into two 
fractions based on their particle size. Aggregate particles passing through the 
No.4 or 4.7 mm Indian Standard sieve are known as fine aggregate. The 
particles retained on this sieve are designated as coarse aggregate. Natural sand 
is often used as fine aggregate in cement concrete mixture. Coarse aggregate are 
crushed stone chips.  Crushed stone  chips  broken into particle sizes passing 
through the 4.7 mm sieve may also be used as fine aggregate. The maximum 
size of the coarse aggregate that may be used in cement concrete hollow blocks 
is 12.5 mm. However, the particle size of the coarse aggregate should not 
exceed one third thickness of the thinnest web of the hollow blocks.
Ordinary Portland cement is  the cementing material used in cement concrete 
hollow blocks. Cement is  the highest priced material per unit weight of the 
concrete. Hence, the fine and coarse aggregates are combined in such 
proportions that the resulting concrete is workable and has minimum cement 
content for the desired quality.