Types of fly ash bricks

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

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.