fly ash as a construction material
TRANSCRIPT
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Submitted By:-GOURAV AGARWAL
APresentation
on FLY ASH
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It is one of the residues generated in combustion of coal.
Comprises of fine particles which rise with the flue gases.
1. Introduction:
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One of the major pollutants which originate from combustion.
Due to recent mandate of using pollution control equipments, these are now collected using electrostatic precipitators and other particle filters.
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It is a heterogeneous material containing SiO2, Al2O3 and Fe2O3 as major constituents with CaO occasionally being the minor constituent.
Exact composition varies according to the parent coal bed makeup.
Also has Arsenic, Beryllium, Cadmium, Chromium, Cobalt, Mercury, Molybdenum, Selenium, Strontium, etc (in the order of hundred ppm).
2. Chemical Composition:
Component (%)
Bituminous Sub-Bituminous
Lignite
SiO2 20-60 40-60 15-45Al2O3 5-35 20-30 20-25Fe2O3 10-40 4-10 4-15CaO 1-12 5-30 15-40
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Based upon differences in quantities of major constituents, it is divided in two classes : Class C and Class F.
Class F: Produced by burning of anthracite and bituminous coal. It is pozzolanic in nature and contains less than 20% lime.
Class C: Produced by burning young lignite or sub-bituminous coal. It is both pozzolanic and self-cementing in nature. Contains more than 20% lime.
3. Classification:
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4. Production/Segregation Process:
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Admixture for Portland CementSoil StabilizationFlyash Bricks Asphalt ConcreteEmbankmentsGeopolymersAs a catalystWaste Treatment
5. Uses:
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% Usage of flyash by different sectors across the globe.
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Fly ash, being primarily pozzolanic, can actually replace a percentage of the Portland cement, to produce an even stronger, more durable and more environment friendly concrete.
The initial compressive strength is low but as days pass, flyash concrete gains more strength and eventually has a lot more strength as compared to normal Portland cement.
Significantly reduces the release of CO2 into the atmosphere.
Can be used for construction of structures on/under water.
a) Portland Cement:
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0 30 45 550
0.5
1
1.5
2
2.5
Ratio of 28/7 days strengthRatio of 90/7 days strengthRatio of 365/7 days strength
Cement Replacement by Fly ash(%)
Com
pres
sive
Str
engt
h R
atio
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3 7 28 56 90 1800
10
20
30
40
50
60
Plain Cement Concrete
Flyash Concrete
Age (Days)
Com
pres
sive
Str
engt
h (M
Pa)
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Soil stabilization is the alteration of soil properties to improve the engineering performance of soils.
Modification of soil properties is the temporary enhancement of sub-grade stability to speedup construction.
Stabilization can increase the shear strength of a soil and/or control the shrink-swell properties of a soil, thus improving the load-bearing capacity of a sub-grade to support pavements and foundations.
Stabilization can be used to treat a wide range of sub-grade materials from expansive clays to granular materials.
b) Soil Stabilization and Modification:
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• Fly ash possesses both ceramic as well as pozzolanic properties and therefore can be utilized in a unique way for manufacturing bricks.
• This proves to be very useful for building construction.
• These bricks produced by the new process are superior in quality as they offer higher cold crushing strength and smooth, uniform size.
c) Fly Ash Bricks:
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S.NO
FEATURES NORMAL CLAY
BRICKS
FLY ASH BRICKS
1 BINDING LIGHT DENSE
2 COLOUR VARY UNIFORM
3 SHAPE IRREGULAR UNIFORM
4 WEIGHT MORE LESS
5 COMPRESSIVE
STRENGTH
35 KGS/SQ.CM
100 KGS/SQ.CM
6 WATER ABSORPTION
20-25% 6-12%
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Asphalt concrete is a composite material consisting of an asphalt binder and mineral aggregate.
Both Class F and Class C fly ash can typically be used as a mineral filler to fill the voids.
This application is used in conjunction with, or as a replacement for, other binders (such as Portland cement or hydrated lime).
The hydrophobic nature of fly ash gives pavements better resistance to deterioration caused by water.
Fly ash has also been shown to increase the stiffness of the asphalt matrix, improving rutting resistance and increasing mix durability.
d) Asphalt Concrete:
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• Fly ash can be used for construction of road and embankment. This utilization has many advantages over conventional methods.
• Saves top soil which otherwise is conventionally used.• Avoids creation of low lying areas (by excavation of
soil to be used for construction of embankments) .• Avoids recurring expenditure on excavation of soil
from one place for construction and filling up of low lying areas thus created
e) Embankment:
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Does not deprive the nation of the agricultural produce that would be grown on the top soil which otherwise would have been used for embankment construction.
Reduces the demand of land for disposal/deposition of fly ash that otherwise would not have been used for construction of embankment. Good Compaction .
Free draining ( Less interruption due to raining ).
Light in weight ( can be used in weak sub – grade )
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More recently, fly ash has been used as a component in Geopolymers, where the reactivity of the fly ash glasses generates a binder comparable to a hydrated Portland Cement in appearance and properties, but with possibly reduced CO2 emissions.
f) Geopolymers:
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Fly ash, mainly class C, may be used in the stabilization/solidification process of hazardous wastes and contaminated soils. For example, the Rhenipal process uses fly ash as an admixture to stabilize sewage sludge and other toxic sludge.
g) As a Catalyst:
h) Waste Treatment: Fly ash, in view of its alkalinity and water
absorption capacity, may be used in combination with other alkaline materials to transform sewage sludge into organic fertilizer or biofuel.
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As seen above, there are a large number of sectors where flyash can be put into use. There are many reasons for the same like:
a) In terms of usability in Concrete and Cement:
Higher Ultimate StrengthIncreased Durability Improved WorkabilityReduced BleedingIncreased Resistance to Sulfate Attack Reduced ShrinkageAlmost zero emission of greenhouse gases.
6. Advantages:
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b) In terms of usage as flyash bricks:Reduces excavation of clay.Low cost of brick as compared to clay brick of same
quality.Number of bricks required per unit volume of
construction is less as dimensional accuracy is maintained.Lesser consumption of mortar.Better resistance to water damage.
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Reduces soil erosion by replacing top soil as ingredients for most construction mixes.
Reduces pollution measure by re-use of wastes.
Reduces the amount of greenhouse gases being added to the atmosphere.
Hydrophobic nature helps in proper draining off of water from roads and structures.
Production of crude oil from polyethylene.Also used in sewage treatment and
generation of biofuel as an alternate source of energy resource.
c) Other benefits of using flyash:
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Groundwater contamination due to runoffs carrying ill-treated flyash.
Cannot be used for structures requiring shorter setting time, a demand which is expected by most of the engineers and builders.
Air content control plays a vital role and can prove crucial for the quality of flyash concrete. Too much reduction in air content can be disastrous.
It is very difficult to use in winter season due to further increase in already longer setting time.
Difficult to control colour of cement containing flyash. Hence, a bit problematic to use where cosmetic quality plays a significant role.
7. Disadvantages:
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8. Scenario in India:Year Flyash produced in
million tonnesFlyash used n million tonnes
2006-07 116 24.82007-08 123 27.12008-09 130 29.72009-10 138 32.22010-11 145 34.72011-12 154 38.02012-13 163 42.5Projected Flyash production Flyash utilisation2013-14 173 48.0
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2006
-07
2008
-09
2010
-11
2012
-1305
1015202530
% use of flyash
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Flyash can be proclaimed as one of the most advantageous waste material.
Using it as a construction material will not only help in its disposal but will also add strength and durablity of structures.
Since, the current usage of flyash in India is still around 25% and below 45% even in the developed countries like United States, there is a huge scope for flyash in upcoming years.
So let us harness a billion dollar resource that has been wasted so far.
9. Conclusion:
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