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(Keywords: Fly Ash, fly ash uses, fly ash in construction, fly ash bricks, fly ash as a building material, fly ash concrete, fly ash concrete.)
Fly ash is finely divided resulting from the combustion of powered coal and transported by the flue gases and collected by Electrostatic Precipitator. It is the most extensively used Pozzolanic fabric material all around the world. Comprises of fine debris and particulate matters which rise upward with the flue gases via. Flue (A pipe or a channel for conveying exhaust gases from a fireplace). It is one of the major pollutants which originate from combustion and gets raised into the atmosphere through flue gases. Due to recent mandate of using pollution control equipment, these are now collected using Electrostatic Precipitators and other particles filters installed along with the chimneys.
Chemical composition: It is a heterogeneous material containing SiO(2), Al(2)O(3) and Fe(2)O(3) as major constituents with 'CaO' occasionally being the minor constituent.
Types of Fly ash
Class F: Fly ash normally produced by burning anthracite or bituminous coal, usually has less than 5% CaO. Class F Fly ash has pozzolanic properties only.
Class C: Fly ash normally produced by burning lignite or sub- bituminous coal. Some class C fly ash may have CaO content in excess of 10%. In addition to Pozzolanic properties which have a little to no cementitious value but will, in finely divided form and in the presence of moisture, surprisingly, class C fly ash also possesses cementitious properties more like a cement used for building construction.
Uses of fly ash are as follows:
1. Admixture for Portland cement:
Fly ash, being primarily pozzolanic, can actually replace a percentage of the Portland cement, to produce an even more durable and which has a higher compressive strength concrete than a normal one and more environmentally friendly concrete which reduces carbon footprint.
The initial compressive strength is low but with passing days, fly-ash concrete eventually gains more strength as compared to normal Portland cement.
Use of fly-ash can drastically reduces the release of carbon-dioxide into the atmosphere compared to a normal Portland cement.
It can be used for construction of structures on/under water.
2. Soil Stabilization and modification:
Soil Stabilization is the alteration of soil properties to improve the engineering performance of soils.
Use of fly-ash can significantly increase the Stability of the shear strength of a soil and/or control the shrink-swell properties of a soil due to the freezing and thawing action of climatic conditions, thus improving the load-bearing capacity of a sub-grade to support pavements and foundations.
3. Fly-ash Bricks:
Fly ash possesses both ceramic as well as pozzolanic properties and therefore can be utilized in a unique way for manufacturing bricks proving it to be very useful for building construction purposes.
These bricks produced by the new process are superior in quality as they offer higher cold crushing strength and smooth, uniform size.
4. Asphalt concrete:
Asphalt concrete is a composite material mostly made up of an asphalt binder and mineral aggregate.
The hydrophobic nature of fly ash gives pavements better resistance to deterioration caused by exposures to water.
Fly ash has also been shown to increase the stiffness of the asphalt matrix, improving rooting resistance and increasing mix durability.
5. Embankments:
Fly ash has been used for construction of road and embankment.
It is a good alternatives for backfilling and embankment creation in the construction industry due to its light weight and reduces tonnes of pressure as compared to commonly used materials like locally available soils.
6. Geo-polymers:
Fly ash has been used as a component in geo-polymers, where the reactive of the fly-ash glasses generates a binder comparable to a hydrate Portland cement in appearance and properties, but with possibly reduces CO(2) emissions.
7. As a catalyst:
Fly ash, in view of its alkalinity and water absorption capacity, may be used in combination with other alkaline materials to transform the sewage sludge into organic fertilizer or bio-fuel which is indeed a renewable energy.
Advantages
As seen above, there are a large number of sectors where fly-ash can be put into use. There are many reasons for the same like:
a) In terms of usability in concrete and cement:
Higher Ultimate Strength
Increased Durability
Improved Workability
Reduced Bleeding
Increase Resistance to sulphate Attack
Reduced Shrinkage
Almost Zero emission of greenhouse gases.
b) In terms of usage as fly-ash bricks:
Reduces excavation of clay.
Cost of the fly-ash bricks is lower as compared to clay-brick of same quality.
Number of bricks required per unit volume of construction is lesser as compared to the clay-bricks as dimensional accuracy is maintained throughout the construction process (more precise cutting).
Consumption of mortar is lesser as compared to clay-bricks in laying process.
Better resistance to water damage as the fly-ash has a hydrophobic property.
c) Other benefits of using fly-ash:
Reduces soil erosion by replacing top soil as ingredients for most construction mixes.
Reduces pollution measure by re-use of waters.
Using of fly-ash products can reduces the production of greenhouse gases.
Water repulsive property of the fly-ash products helps in proper draining off of water from roads and infrastructural areas.
Disadvantages
It can cause ground water contamination due to runoffs carrying ill-treated fly-ash.
It cannot be used for structures requiring shorter setting time of concrete.
It is difficult to control color of cement containing fly-ash in the production process.
Conclusion
Fly-ash can be proclaimed as one of the most advantageous waste material.
Using it as construction material will not only help in its disposal but will also add strength and durability of structures.
The current percentage of demand in India is only around 25% and much below 45% even in the developed countries like U.S, so there is a huge future prospect for fly-ash in coming years.
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