Fly ash bricks are made from fly ash also known as pulverized fuel ash or flue ash, sand, stone dust, cement, gypsum, lime, and water. This fly ash is the residue that is produced during the combustion of coal to produce energy in thermal power stations.
The fly ash is in the form of fine particles that rise with the flue gases. It contains trace amounts of toxic metals like mercury, arsenic, chromium, antimony, selenium, lead, cadmium, etc. These metals can have harmful effects on human health, plants, and land.
As such, this fly ash is converted into fly ash bricks that can be used for the construction of buildings and structures. These bricks do not emit any mercury, in fact, they absorb a small amount of mercury from the air. This makes the ambient air slightly cleaner for people to breathe.
Advantages And Disadvantages Of Fly Ash Bricks
The disposal of fly ash from thermal power stations becomes quite a big issue if not utilized properly. Fly ash pollutes air and water and causes respiratory problems to humans if inhaled. If it gets decomposed in the soil the land becomes infertile.
As such, it becomes very important to utilize fly ash in an appropriate way to save land, flora, and fauna from its harmful effects. Making fly ash bricks is one such way, these bricks are not harmful to health and the environment and they are very useful as a construction material.
Let’s have a look at some of the main advantages and disadvantages of these bricks.
Advantages Of Fly Ash Bricks
In comparison to the normal burnt clay bricks, the fly ash bricks are very light in weight. This makes it easier to carry and transport from one place to another. It also greatly reduces the dead load on the building and the structures.
Fly ash bricks have very high fire resistance, as these bricks have fly ash as their major constituent. This fly ash is the unburned residue of the coal-fired in the thermal power plant, as such figuratively it cannot be burnt.
These bricks are very environment friendly as they help in reducing fly ash, which is a byproduct of thermal power stations, and if not utilized properly it may harm the environment. It also helps to save agricultural land which is used for manufacturing clay bricks.
These bricks are used in fewer numbers as compared to the normal burnt clay bricks as these bricks are available in regular full sizes. This helps to reduce wastage and unwanted expenditure.
Uniform Shape And Size
These bricks are uniform in shape and size in comparison to the clay bricks. This means they require less mortar in brickwork, masonry, and finishing. This results in cost-saving because of less consumption of cement mortar.
The fly ash bricks do not require soaking in water for 24 hours prior to use as the traditional red clay bricks. Even normal sprinkling of water before application of the fly ash bricks is enough, as such, it helps to save a lot of water.
As compared to the traditional clay bricks the fly ash bricks cost at least 20 percent less. As such they help to reduce the overall cost of materials and they also help to reduce labor cost as masonry is easier with these bricks.
These bricks are sound absorbent in nature and they help to restrict the sound transmission from outside to inside and vice versa. This helps in keeping the interiors pleasant with a lesser amount of noise from outside.
Disadvantages Of Fly Ash Bricks
Less Bonding Strength
The mechanical bonding strength of the fly ash bricks is weak as compared to the traditional red clay bricks. But one can improve this bonding strength by adding marble or stone dust and cementing materials.
The fly ash bricks are manufactured only in standard modular sizes, as such there is a limitation of size with these bricks. The large size fly ash bricks will result in more breakages.
No Heat Absorption
These bricks do not have the capacity to absorb heat, accordingly, they are only good for the places where the climate is warm most of the time. As they do not absorb heat they are not a good candidate for places that have a colder climate.
It is very important to use only high-quality fly ash brick for construction purposes. If it is made at a low-quality manufacturing unit the bricks may not be suitable for use in the construction of the building.
Making Process Of Fly Ash Bricks
The manufacturing of these bricks is done in standard quality manufacturing units. The raw materials used in the manufacturing process are fly ash, sand, stone dust, gypsum, cement or lime, water, etc.
Generally these raw materials are used in the following ratio –
- Fly Ash – 50% to 70%
- Sand or Stone Dust – 20% to 40%
- Cement or lime – 10% to 30%
- Gypsum – 2% to 15%
- Water – As Required
The proportion of these raw materials may change, depending upon the quality of raw materials to produce different strengths and different densities of the bricks. For making the bricks the fly ash, lime, sand, and gypsum are manually put into a pan mixer, where water is added in the required proportion for proper mixing.
One can use Ordinary Portland cement in place of hydrated lime and gypsum. The materials in the required proportion are mixed in a pan mixer, to have a semi-dry uniform mix. After mixing, the mixture goes on a belt conveyor to pass to the hydraulic or vibratory press machine which compacts the semi-dry mix to form the bricks.
These bricks then dry under normal sunlight for 24 to 48 hours. These newly molded bricks dry for one to two days in shade depending upon the weather conditions. And then water curing of these bricks takes place for about 14 to 21 days, and after that testing and sorting of bricks takes place before their final dispatch.
Cost Or Price Of Fly Ash Bricks
The cost of nine-inch by four-inch by three-inch fly ash brick is approximately Rs 5.00 per piece in the local market. The cost of fly ash brick will vary depending upon the location and quality of the brick. These bricks are normally available for a price of about 20% to 30% less than the traditional clay bricks in the same market.