Fly Ash Bricks and Comparison with Clay Bricks – Composition, Manufacture

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Fly ash bricks are hi-tech well-improved quality bricks used for construction of brick masonry structures. They are used as replacement for normal clay bricks and has better properties than it. Fly ash bricks competitive in comparison to the conventional clay bricks and provide enormous indirect benefits. The utilization of fly ash bricks results in conservation of natural resources as well as protection of environment.

Composition of Fly Ash Bricks

The important compositions of fly ash bricks are:

• Fly ash
• Cement
• Sand
• Water

Sources of Fly Ash

72% of India's power plants are coal based. These power stations generate nearly 40 million tones of fly ash annually. Fly ash contains Co₂ emitted from Thermal power plants, industries using coal as a fuel emits unwanted ash and smoke from which fly ash is produced. In all the power plants and industries, they separate the fly ash by using the cyclone converter. This fly ash is then used as a raw material for manufacture of bricks.

Nature of Pollution Caused by Fly Ash

Fly ash causes severe pollution of air and water, and its disposal gobbles up large tracts of land. Well-planned programs for proper management of fly ash are therefore being undertaken to enhance the use of fly ash in various applications, so that our already perilously imbalanced environment can be protected

Manufacture of Fly Ash Bricks

The fly ash brick is nothing but a slow setting pozzalona cement mix. The process is same as making cement in cement factories whereas the clay and limestone are burnt with coal and gypsum. And it is mixed and ground to cement. In fly ash mix also the fly ash, which is burnt clay particles (oxides of clay) obtained from burning coal, which contains clay from the mines. When hydrated lime powder, gypsum are mixed and ground in a pan, the mixture gives a slow setting pozzalona cement. While the mix is pressed at low pressure at low moisture content in hydraulic machine, which is specially designed to give high pressure load at a slow rate, in the order of 350kg/square inch. At this of rate of pressure and with holding the pressure for a desired time gives ultimate strength to fly ash bricks.

Flowchart Showing the Manufacture of Fly Ash Bricks

Benefits of Fly Ash Bricks for Environment

The increase in greenhouse gases, out of which CO₂ is one of the major constituents, increases the global warming year after year, causing drought and floods. The total CO₂ Emissions globally account for 24,960 million tons at 1990 levels. Cement and building materials industry is one of the major contributors. The CO₂ emission is about ninety million tons out of cement and forty nine million tons out of clay bricks production in India. As per the ongoing practices in India, each million clay bricks consume about 200 tons of coal (or any other fuel with equal quantity of thermal values) and emit around 270 tons of CO₂. Fly ash bricks production in energy-free route saves the emissions totally, befitting the project to qualify under Clean Development Mechanism (CDM), as envisaged by Kyoto Protocol towards the welfare of Mother Earth.

Comparison of Clay Bricks and Fly Ash Bricks

Properties	Red Bricks/Clay Bricks	Fly Ash Bricks	Remarks
Density	1600-1750 kg/m3	1700-1850 kg/m3	Higher load bearing
Compressive strength	30-35 kg/cm2	90-100 kg/cm2	Higher load bearing
Absorption	15-25%	10-14%	Less dampness
Dimensional stability	Very low tolerance	High tolerance	Saving in mortar up to 25%
Wastage during transit	Up to 10%	Less than 2%	Saving in cost up to 8%
Plastering	Thickness vary on the both sides of wall	Even on both sides	Saving in plaster up to 15%.

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