Fly ash utilization

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Contents
Abstract...............................................................................................3
INTRODUCTION....................................................................................6
COMPOSTION ......................................................................................8
CLASSIFICATION...................................................................................9
Class F fly ash...........................................................................9
Class C fly ash...........................................................................9
APPLICATIONOF FLY ASH ...................................................................11
RECYCLING AND REUSE.......................................................................11
AREAS OF APPLICATION......................................................................12
3.1 Advantages of using fly ash for road and embankment construction
..........................................................................................................13
3.2. Economy in use of fly ash.............................................................16
3.3. Environmental Impact of Fly ash use ............................................17
APPLICATION IN CONCRETE................................................................18
4.1. Features of fly ash concrete .........................................................18
4.2. Contribution to Workability..........................................................20

Optimization in FLY ASH PPC
Devendra Kumar Patel Page 2
4.3. Contribution to Strength..............................................................21
4.4. Environmental Impact..................................................................22
APPLICATIONIN BRICKS......................................................................23
5.1. Features of Fly ash bricks .............................................................24
5.2. Environmental Impacts ................................................................25
5.3. Economic Benefit.........................................................................26
INDIAN SCENARIO IN FLY ASH APPLICATIONS ......................................27
Ash Concrete......................................................................................28
Advantages and Disadvantages of Using Fly ash In Concrete................28
The disadvantages of using fly ash in concrete ....................................31
Chemical composition and classification .............................................32
Disposal and market sources ..............................................................36
Environmental problems ....................................................................38
Exposure concerns .............................................................................43
CONCLUSION .....................................................................................44
REFERENCES:......................................................................................47

Abstract
India has a vast coal reserve of 211 billion tones making
coal one of the most extensively used fossil fuel for
generating power. More than 175 million tones of fly ash
are expected to be generated in the country due to
combustion of coal by the year 2012. This would require
about 40000 hectares of land for the construction of ash
ponds for ash disposal.
Power plant ashes are generated as the finer pozzolanic
fly ash. Recognizing the reutilization of fly ash, the huge
pressures on land and water and the grave environmental
consequences, power plants are shifting to separating the
bottom ash and the fly ash and collecting ash to send it to
alternative users.
Fly ash utilization has great potential to lower green house
gas emissions by decreased mining activities and reducing
Carbon dioxide production during manufacture of
materials that can be substituted by fly ash. Fly ash holds
a potential to improve the physical health of the soil.
Owing to its pozzolanic properties, fly ash is used as a
replacement for some of the Portland cement content of
concrete .Use of fly ash as a partial replacement for
Portland cement is generally limited to Class F fly
ashes.Fly ash can substitute up to 66% of cement in the
construction of dams. It is also used as a pozzolanic

substitute for cement in Roller Compacted Concrete dams.
Fly ash from coal fired thermal power plants is an
excellent material for the manufacture of other
construction materials like fly ash bricks, mosaic tiles and
hollow blocks. The manufacture of conventional clay bricks
requires the consumption of large amounts of clay. This
depletes top soil and leads to degradation of land. Some
of the high volume applications of fly ash are for use in
paving, building embankments and mine fills. Utilizing fly
ash in bricks and roads saves top soil, avoids creation of
low lying areas, does not deprive the nation of the
productivity of top soil and reduces the demand of land for
fly ash disposal. It also finds use in stabilization of soil, in
flowable fills and mine reclamation.
Various experimental research activities have revealed
that use of fly ash contributes towards enhancing the
property of the material in which it is used. Their use
contributes towards higher durability, lower shrinkage,
reduced heat of hydration, higher long term strength and
decreased permeability. Due to the spherical shape of fly
ash particles, it increases the workability of cement while
reducing water demand.
The use of fly ash has really good impacts on the
environment. The replacement of Portland cement with fly
ash is considered by its promoters to reduce the
greenhouse gas "footprint" of concrete, as the production

of one ton of Portland cement produces approximately one
ton of carbon dioxide as compared to zero CO2 being
produced using existing fly ash. Utilization of fly ash not
only minimizes the disposal problem but also help in
utilizing land in a better way. The Indian Government has
taken a lot of initiatives and made certain stipulations to
encourage reuse of fly ash. Proper and efficient use of fly
ash results in saving of hundreds of crores of rupees
resulting in a positive impact on the economy.

Project Member
INTRODUCTION

Fly ash is one of the residues generated in combustion,
and comprises of fine particles that rise with the flue
gases. In an industrial context, fly ash usually refers to
ash produced during combustion of coal. Fly ash is
produced through the combustion of coal used to generate
electricity. After coal is pulverized, it enters a boiler where
flame temperatures reach up to 1500 degrees Celsius.
Upon cooling, the inorganic matter transforms from a
vapour state to a liquid and solid state. During this
process individual, spherical particles are formed. This is
fly ash. It is then collected by either using electrostatic
precipitators, bag houses or a combination of both. Fly
ash from these systems is collected in hoppers and then
transferred to storage silos. Fly ash is tested for physical
properties such as fineness, loss on ignition, and
moisture, before it is allowed to be shipped to its end
user.

COMPOSTION
They consist mostly of silicon dioxide (SiO2 ), aluminium
oxide (Al2O3) and iron oxide (Fe2O3). The chemical
properties of the fly ash are largely influenced by the
chemical content of the coal burned (i.e., anthracite,
bituminous, and lignite).
Fly ash also contains environmental toxins in significant
amounts, including arsenic (43.4 ppm); barium (806
ppm); beryllium (5 ppm); boron (311 ppm); cadmium
(3.4 ppm); chromium (136 ppm); chromium VI (90 ppm);
cobalt (35.9 ppm); copper (112 ppm); fluorine (29 ppm);
lead (56 ppm); manganese (250 ppm); nickel (77.6
ppm); selenium (7.7 ppm); strontium (775 ppm);
thallium (9 ppm); vanadium (252 ppm); and zinc (178
ppm).
Fly ashes are generally highly heterogeneous, consisting
of a mixture of glassy particles with various identifiable
crystalline phases such as quartz, mullite, and various iron
oxides.

CLASSIFICATION
Two classes of fly ash are defined by ASTM C618:
1.Class F fly ash
2.Class C fly ash
The chief difference between these classes is the amount
of calcium, silica, alumina, and iron content in the ash.
Class F fly ash
Class F fly ash is produced by the burning of harder, older
anthracite and bituminous coal. This fly ash is pozzolanic
in nature, and contains less than 20% lime (CaO).
Possessing pozzolanic properties, the glassy silica and
alumina of Class F fly ash requires a cementing agent,
such as Portland cement, quicklime, or hydrated lime,
with the presence of water in order to react and produce
cementitious compounds.
Class C fly ash
Class C fly ash is produced from the burning of younger
lignite or sub-bituminous coal, in addition to having
pozzolanic properties, also has some self-cementing
properties. In the presence of water, Class C fly ash will
harden and gain strength over time. Class C fly ash
generally contains more than 20% lime (CaO). Unlike
Class F, self-cementing Class C fly ash does not require an

activator. Alkali and sulfate (SO4) contents are generally
higher in Class C fly ashes. Class C will generate more
heat of hydration than Class F. Class C ash will generate
more strength at early ages than Class F.

APPLICATION OF FLY ASH
RECYCLING AND REUSE
The recycling of fly ash has become an increasing
concern in recent years due to increasing landfill costs
and current interest in sustainable development.
Recognizing the reutilization of fly ash, the huge
pressures on land and water and the grave
environmental consequences, power plants are shifting
to separating the bottom ash and the fly ash and
collecting ash to send it to alternative users
The reuse of fly ash as an engineering material
primarily stems from its –
1)Spherical shape:
 Less water is needed which ultimately makes the
concrete stronger and reduces particle segregation
while the concrete sets and improves workability while
the concrete is being finished.
 Pumping properties are improved as the round
particles essentially act as a lubricant.
 Cohesion between the cement paste and aggregate is
also improved since the particles are so fine.
2) Pozzolanic properties
3) Relative uniformity

AREAS OF APPLICATION
 Portland cement
 Embankments and structural fill
 Waste stabilization and solidification
 Raw feed for cement clinkers.
 Mine reclamation
 Stabilization of soils
 Road sub-base
 Agriculture related applications
 Aggregate
 Flowable fill
 Mineral filler in Asphaltic concrete

APPLICATION OF FLY ASH IN ROADS
AND EMBANKMENTS
3.1 Advantages of using fly ash
for road and embankment
construction
 Fly ash is a lightweight material, as compared to
commonly used fill material i.e. local soils, therefore,
causes lesser settlements. It is especially attractive for
embankment construction over weak sub grade such as
alluvial clay or silt where excessive weight could cause
failure.

 Fly ash embankments can be compacted over a wide
range of moisture content, and therefore, results in less
variation in density with changes in moisture content.
 Easy to handle and compact because the material is
light and there are no large lumps to be broken down.
Compaction can be done using either vibratory or static
rollers.
 High permeability ensures free and efficient drainage.
After rainfall, water gets drained out freely ensuring
better workability than soil. Work on fly ash fills/
embankments can be restarted within a few hours after
rainfall, while in case of soil it takes much longer.
 Fly ash has considerably low compressibility resulting in
negligible subsequent settlement within the fill.
 Use of fly ash helps in conserving good earth, which is
precious topsoil, thereby protecting the environment.

 It has higher value of California Bearing Ratio as
compared to soil thus, providing for a more efficient
design of road pavement.
 Pozzolanic hardening property imparts additional
strength to the road pavements/ embankments and
decreases the post construction horizontal pressure on
retaining walls.
 Fly ash is amenable to stabilisation with lime and
cement.
 It can replace a part of cement and sand in concrete
pavements thus making them more economical than
roads constructed using conventional materials.
 Fly ash admixed concrete can be prepared with zero
slump making it amenable for use as roller compacted
concrete.
Considering all these advantages, it is extremely
essential to promote use of fly ash for construction of
roads and embankments.

3.2. Economy in use of fly ash
Use of fly ash in road works results in reduction in
construction cost by about 10 to 20 per cent. Typically
cost of borrow soil varies from about Rs.100 to 200 per
cubic metre. Fly ash is available free of cost at the power
plant and hence only transportation cost, laying and
rolling cost are there in case of fly ash. Hence, when fly
ash is used as a fill material, the economy achieved is
directly related to transportation cost of fly ash. If the
lead distance is less, considerable savings in construction
cost can be achieved. Similarly, the use of fly ash in
pavement construction results in significant savings due to
savings in cost of road aggregates. If environmental
degradation costs due to use of precious top soil and
aggregates from borrow areas quarry sources and loss of
fertile agricultural land due to ash deposition etc. the
actual savings achieved will be much higher.

3.3. Environmental Impact of
Fly ash use
 Utilization of fly ash not only minimizes the disposal
problem but also help in utilizing land in a better way.
 Construction of road embankments using fly ash
involves encapsulation of fly ash in earthen core or with
RCC facing panels. Since there is no seepage of rain
water into the fly ash core, leaching of heavy metals is
also prevented. When fly ash is used in concrete, it
chemically reacts with cement and reduces any leaching
effect.
 In stabilization work, a similar chemical reaction takes
place which binds fly ash particles.
Hence chances of pollution due to use of fly ash in road
works are negligible

APPLICATION IN CONCRETE
4.1. Features of fly ash concrete
 Higher durability
It is more resistant to attack by sulfate, mild acid,
soft water and sea water.
 Similar abrasion resistance to as that of normal
concrete

 Relatively lower drying shrinkage
The lubricating action of fly ash reduces the water
content and thus drying shrinkage.
 Reduced heat of hydration
The pozzolanic reaction between fly ash and lime
generates less heat, resulting in reduced thermal
cracking when fly ash is used to reduce Portland
cement
 Reduced sulphate attack and reduced
efflorescence.
Fly ash ties up free lime that can create efflorescence
and also combine with sulfates to create destructive
expansion.
 High strength
Fly ash continues to combine with free lime,
increasing compressive strength over time.
 Decreased permeability
Increased density and long term pozzolanic action of
fly ash, which ties up free lime, results in fewer bleed
channels and decreases permeability.
 Higher setting time
This is beneficial in hot weather as it allows more
time for transporting and placing concrete. In cold
weather, excessive set retardation can be avoided by
raising the temperature or using set accelerating
admixtures.

4.2. Contribution to Workability
 Light weight concrete
Easier to pump as pumping requires less energy
 Improved finishing:
This results in creamier texture and sharp, clearer
architectural definition is easier to achieve
 Reduced segregation and bug holes
Improved cohesiveness of fly ash reduces
segregation.
 Reduced Bleeding
Fewer bleed channels decrease permeability and
chemical attack. Bleeding
of HVFAC ranges from negligible values to low
values due to its very low
water content.
 Less sand needed in the mix to produce required
workability.

4.3. Contribution to Strength
Cement normally gains majority of its strength within 28
days. So the specifications normally require the 28-day
strength as standard. Typically concrete made with fly ash
will be slightly lower in strength than straight cement
concrete upto 28 days, almost equal strength at 28 days
and substantially higher strength within a year’s time.
Conversely in cement concrete, this lime would remain
intact and over time it would be susceptible to the effects
of weathering and loss of strength and durability

4.4. Environmental Impact
Studies show that one ton of Portland cement production
discharges 0.87 tonnes of Carbon dioxide in the
Environment. Another Japanese study indicates that every
year barren land approximately 1.5 times of the Indian
Territory need to be afforested to compensate for the total
global accumulation of Carbon Dioxide discharged into the
atmosphere because of total global cement production.
The replacement of Portland cement with fly ash is
considered by its promoters to reduce the green house
gas "footprint" of concrete, as the production of one ton of
Portland cement produces approximately one ton of
carbon dioxide as compared to zero CO2 being produced
using existing fly ash. Utilization of fly ash in cement
concrete minimizes the Carbon dioxide emission problem
to the extent of its proportion in cement.

APPLICATION IN BRICKS
Bricks made of lime and sand, popularly known as calcium
silicate bricks are hardened by high pressure steam
curing. The process requires finely ground sand. Fly ash,
which is already fine, replaces ground sand partially or
totally, thus conserving on grinding costs. Being a
pozzolan, fly ash also reacts with lime resulting in bricks
of superior quality.

5.1. Features of Fly ash bricks
 Good earthquake resistance features
 Fire resistant
 Easy handling and faster construction
 Excellent acoustic barriers
 Reduction in plastering almost by 50% due to even
walls
 Due to high strength, practically no breakage during
transport & use
 No soaking in water required for 24 hours. Only
sprinkling of water before use.
 Good freeze-thaw resistance.

5.2. Environmental Impacts
The Various environmental concerns regarding fly ash
bricks are
 Potential for radon and mercury vapor emission
 Potential for leaching pollutants (heavy metals)
 Potential for polluting landfills when building is
demolished and broken fly ash products enter
landfills.
But the bricks made out of fly ash have been found to
be environmentally safe .
 Fly ash bricks made from class C fly ash do not emit
mercury into air. On contrary they adsorb mercury
from air, making ambient air cleaner .
 They emit radon but only 50% of what is emitted by
concrete. So safe to use.
 Leaching of pollutants from fly ash bricks caused by
rain is negligible
 They are non-hazardous for land fills.

5.3. Economic Benefit
180 billion tonnes of clay brick production per year
consumes 540 million tonnes of clay, makes 65000
acres of land barren, and consumes 30 million tonnes of
coal equivalent, generates26 million tonnes of Carbon
Dioxide. A 10% switchover to fly ash bricks will use 30
million tonnes of fly ash every year, save environment
and coal and yield a benefit of 300 crores by way of
reduction in brick cost production

INDIAN SCENARIO IN FLY ASH
APPLICATIONS
The Fly-ash mission was commissioned in 1994 with
the Department of Science and Technology as the
nodal agency and the Technology Information and
Assessment Council (TIFAC) as the implementing
agency. The Ministry of Environment and Forests, Govt.
of India, Ministry of Power, Thermal Power stations,
R&D Institutions and Industry together have launched
a Technology Project in Mission Mode (TPMM). Their
focus is on the demonstration of coal ash related
technologies for infusing confidence and thus ensuring
large scale adoption
The Government of India has withdrawn the 8% excise
duty imposed earlier on fly ash products. Now no
excise duty is levied on manufacture of goods in which
a minimum of 25% w/w fly ash is used.
Government of Orissa has exempted fly ash bricks and
other products from sales tax.
Financial support, in many forms, is being extended to
promote industrial units for production of building
materials based on fly ash products.
Ministry of Environment and Forests (MOEF) and
Ministry of Power stipulations are made for 20% Fly

Ash Concrete
Advantages and Disadvantages
of Using Fly ash In Concrete
Fly ash is the residue that is left from burning coal, and
this is formed when the gaseous releases of the coal is
efficiently cooled. It is somewhat like a glass powder
that is fine in nature. However, the chemical
constituents of this residue might vary from one other.
Fly ash has several industrial applications and is widely
found in power plant chimneys. The material is also
used as substitute cement by mixing it with lime and
water. The material is embedded with myriad beneficial
features and so is being utilized as a significant building
material for the construction purposes. This type of
concrete is much dense and smooth. Below listed are
few of the advantages and disadvantages of fly ash
concrete.
The Pros and Cons of Using Fly ash
Fly ash is used in many countries because of its
advantages. There are also some disadvantages of using
fly ash in concrete. These pros and cons are described
in brief below.
The significant benefits of using fly ash in concrete

The advantages of using fly ash in concrete
includes the followings.
 Fly ash in the concrete mix efficiently replaces
Portland cement that in turn can aid in making big
savings in concrete material prices.
 It is also an environmentally-friendly solution, which
meets the performance specifications. It can also
contribute to LEED points.
 It improves the strength over time and thus, it offers
greater strength to the building.
 Increased density and also the long-term
strengthening action of flash that ties up with free
lime and thus, results in lower bleed channels and
also decreases the permeability.
 The reduced permeability of concrete by using fly
ash, also aids to keep aggressive composites on the
surface where the damaging action is reduced. It is
also highly resistant to attack by mild acid, water
and sulfate.
 It effectively combines with alkalis from cement,
which thereby prevents the destructive expansion.
 It is also helpful in reducing the heat of hydration.
The pozzolanic reaction in between lime and fly ash

will significantly generate less heat and thus,
prevents thermal cracking.
 It chemically and effectively binds salts and free
lime, which can create efflorescence. The lower
permeability of fly ash concrete can efficiently reduce
the effects of efflorescence.

The disadvantages of using fly
ash in concrete
There are also some disadvantages of using fly ash that
should be considered.
The quality of fly ash to be utilized is very vital. Poor
quality often has a negative impact on the concrete.
The poor quality can increase the permeability and thus
damaging the building.
Some fly ash, those are produced in power plant is
usually compatible with concrete, while some other
needs to be beneficiated, and few other types cannot
actually be improved for using in concrete. Thus, it is
very much vital to use only high quality fly ash to
prevent negative effects on the structure of the building.
The aforesaid is few advantages and disadvantages of
fly ash concrete. This type of concrete offers many
advantages and as mentioned above it also has some
disadvantages. There are various other advantages of
utilizing fly ash concrete such as it is much easier to
place with reduced effort and it is also able to have
improved finishing to the structure with such type of
concrete. Fly ash concrete can certainly add greater
strength to the building.

Chemical composition and
classification
ComponentBituminous Subbituminous Lignite
SiO2 (%) 20-60 40-60 15-45
Al2O3 (%) 5-35 20-30 20-25
Fe2O3 (%) 10-40 4-10 4-15
CaO (%) 1-12 5-30 15-40
LOI (%)0-15 0-3 0-5
Fly ash material solidifies while suspended in the
exhaust gases and is collected by electrostatic
precipitators or filter bags. Since the particles solidify
rapidly while suspended in the exhaust gases, fly ash
particles are generally spherical in shape and range in
size from 0.5 µm to 300 µm. The major consequence of
the rapid cooling is that few minerals have time to
crystallize, and that mainly amorphous, quenched glass
remains. Nevertheless, some refractory phases in the
pulverized coal do not melt (entirely), and remain
crystalline. In consequence, fly ash is a heterogeneous
material. SiO2, Al2O3, Fe2O3 and occasionally CaO are
the main chemical components present in fly ashes. The
mineralogy of fly ashes is very diverse. The main phases
encountered are a glass phase, together with quartz,

mullite and the iron oxides hematite, magnetite and/or
maghemite. Other phases often identified are
cristobalite, anhydrite, free lime, periclase, calcite,
sylvite, halite, portlandite, rutile and anatase. The Ca-
bearing minerals anorthite, gehlenite, akermanite and
various calcium silicates and calcium aluminates
identical to those found in Portland cement can be
identified in Ca-rich fly ashes.[5] The mercury content
can reach 1 ppm,[6] but is generally included in the
range 0.01 - 1 ppm for bituminous coal. The
concentrations of other trace elements vary as well
according to the kind of coal combusted to form it. In
fact, in the case of bituminous coal, with the notable
exception of boron, trace element concentrations are
generally similar to trace element concentrations in
unpolluted soils.
Two classes of fly ash are defined by ASTM C618: Class
F fly ash and Class C fly ash. The chief difference
between these classes is the amount of calcium, silica,
alumina, and iron content in the ash. The chemical
properties of the fly ash are largely influenced by the
chemical content of the coal burned (i.e., anthracite,
bituminous, and lignite).[8]
Not all fly ashes meet ASTM C618 requirements,
although depending on the application, this may not be
necessary. Ash used as a cement replacement must

meet strict construction standards, but no standard
environmental regulations have been established in the
United States. 75% of the ash must have a fineness of
45 µm or less, and have a carbon content, measured by
the loss on ignition (LOI), of less than 4%. In the U.S.,
LOI must be under 6%. The particle size distribution of
raw fly ash tends to fluctuate constantly, due to
changing performance of the coal mills and the boiler
performance. This makes it necessary that, if fly ash is
used in an optimal way to replace cement in concrete
production, it must be processed using beneficiation
methods like mechanical air classification. But if fly ash
is used also as a filler to replace sand in concrete
production, unbeneficiated fly ash with higher LOI can
be also used. Especially important is the ongoing quality
verification. This is mainly expressed by quality control
seals like the Bureau of Indian Standards mark or the
DCL mark of the Dubai Municipality.
Class F fly ash
The burning of harder, older anthracite and bituminous
coal typically produces Class F fly ash. This fly ash is
pozzolanic in nature, and contains less than 7% lime
(CaO). Possessing pozzolanic properties, the glassy
silica and alumina of Class F fly ash requires a
cementing agent, such as Portland cement, quicklime,
or hydrated lime—mixed with water to react and

produce cementitious compounds. Alternatively, adding
a chemical activator such as sodium silicate (water
glass) to a Class F ash can form a geopolymer.
Class C fly ash[edit]
Fly ash produced from the burning of younger lignite or
sub-bituminous coal, in addition to having pozzolanic
properties, also has some self-cementing properties. In
the presence of water, Class C fly ash hardens and gets
stronger over time. Class C fly ash generally contains
more than 20% lime (CaO). Unlike Class F, self-
cementing Class C fly ash does not require an activator.
Alkali and sulfate (SO
4) contents are generally higher in Class C fly ashes.
At least one US manufacturer has announced a fly ash
brick containing up to 50% Class C fly ash. Testing
shows the bricks meet or exceed the performance
standards listed in ASTM C 216 for conventional clay
brick. It is also within the allowable shrinkage limits for
concrete brick in ASTM C 55, Standard Specification for
Concrete Building Brick. It is estimated that the
production method used in fly ash bricks will reduce the
embodied energy of masonry construction by up to
90%.[9] Bricks and pavers were expected to be
available in commercial quantities before the end of
2009.[10]

Disposal and market sources
In the past, fly ash produced from coal combustion was
simply entrained in flue gases and dispersed into the
atmosphere. This created environmental and health
concerns that prompted laws that have reduced fly ash
emissions to less than 1% of ash produced. Worldwide,
more than 65% of fly ash produced from coal power
stations is disposed of in landfills and ash ponds,
although companies such as Duke Energy are starting
initiatives to excavate coal ash basins due to the
negative environmental impact involved.
The recycling of fly ash has become an increasing
concern in recent years due to increasing landfill costs
and current interest in sustainable development. As of
2005, U.S. coal-fired power plants reported producing
71.1 million tons of fly ash, of which 29.1 million tons
were reused in various applications.[11] If the nearly 42
million tons of unused fly ash had been recycled, it
would have reduced the need for approximately 27,500
acre·ft (33,900,000 m3) of landfill space.[11][12] Other
environmental benefits to recycling fly ash includes
reducing the demand for virgin materials that would
need quarrying and cheap substitution for materials
such as Portland cement.

As of 2006, about 125 million tons of coal-combustion
byproducts, including fly ash, were produced in the U.S.
each year, with about 43% of that amount used in
commercial applications, according to the American Coal
Ash Association Web site. As of early 2008, the United
States Environmental Protection Agency hoped that
figure would increase to 50% as of 2011.[13]

Environmental problems
Present production rate of fly ash
In the United States about 131 million tons of fly ash
are produced annually by 460 coal-fired power plants. A
2008 industry survey estimated that 43% of this ash is
re-used.

Groundwater contamination
Since coal contains trace levels of trace elements (like
e.g. arsenic, barium, beryllium, boron, cadmium,
chromium, thallium, selenium, molybdenum and
mercury), fly ash obtained after combustion of this coal
contains enhanced concentrations of these elements,
and therefore the potential of the ash to cause
groundwater pollution needs to be evaluated. In the
USA there are documented cases of groundwater
pollution which followed ash disposal or utilization
without the necessary protection means.
In 2014, residents living near the Buck Steam Station in
Dukeville, North Carolina, were told that "coal ash pits
near their homes could be leaching dangerous materials
into groundwater."
Spills of bulk storage
Tennessee Valley Authority Fly Ash containment failure
on 23 December 2008 in Kingston, Tennessee
Where fly ash is stored in bulk, it is usually stored wet
rather than dry to minimize fugitive dust. The resulting
impoundments (ponds) are typically large and stable for
long periods, but any breach of their dams or bunding is
rapid and on a massive scale.

In December 2008, the collapse of an embankment at
an impoundment for wet storage of fly ash at the
Tennessee Valley Authority's Kingston Fossil Plant
caused a major release of 5.4 million cubic yards of coal
fly ash, damaging 3 homes and flowing into the Emory
River. Cleanup costs may exceed $1.2 billion. This spill
was followed a few weeks later by a smaller TVA-plant
spill in Alabama, which contaminated Widows Creek and
the Tennessee River.
In 2014, tens of thousands of tons of ash and 27 million
gallons (100,000 cubic meters) of contaminated water
spilled into the Dan River near Eden, NC from a closed
North Carolina coal-fired power plant that is owned by
Duke Energy. It is currently the third worst coal ash spill
ever to happen in the United States.[40][41] A 48-inch
(120 cm) pipe spilled arsenic and other heavy metals
into the river for a week, but was successfully plugged
by Duke Energy. The U.S. federal government plans to
investigate, and people along the river have been
warned to stay away from the water. Fish have yet to
be tested, but health officials say not to eat them.[42]
New regulations published in the Federal Register on
December 19, 2015 stipulate a comprehensive set of
rules and guidelines for safe disposal and storage.[43]
Designed to prevent pond failures and protect
groundwater, enhanced inspection, record keeping and

monitoring is specified. Procedures for closure are also
included and include capping, liners, and dewatering.
Contaminants
Fly ash contains trace concentrations of heavy metals
and other substances that are known to be detrimental
to health in sufficient quantities. Potentially toxic trace
elements in coal include arsenic, beryllium, cadmium,
barium, chromium, copper, lead, mercury,
molybdenum, nickel, radium, selenium, thorium,
uranium, vanadium, and zinc.[45][46] Approximately
10% of the mass of coals burned in the United States
consists of unburnable mineral material that becomes
ash, so the concentration of most trace elements in coal
ash is approximately 10 times the concentration in the
original coal.[47] A 1997 analysis by the U.S. Geological
Survey (USGS) found that fly ash typically contained 10
to 30 ppm of uranium, comparable to the levels found in
some granitic rocks, phosphate rock, and black
shale.[47]
In 2000, the United States Environmental Protection
Agency (EPA) said that coal fly ash did not need to be
regulated as a hazardous waste.[48] Studies by the U.S.
Geological Survey and others of radioactive elements in
coal ash have concluded that fly ash compares with
common soils or rocks and should not be the source of

alarm.[47] However, community and environmental
organizations have documented numerous
environmental contamination and damage
concerns.[49][50][51]
A revised risk assessment approach may change the
way coal combustion wastes (CCW) are regulated,
according to an August 2007 EPA notice in the Federal
Register.[52] In June 2008, the U.S. House of
Representatives held an oversight hearing on the
Federal government's role in addressing health and
environmental risks of fly ash.

Exposure concerns
Crystalline silica and lime along with toxic chemicals are
among the exposure concerns. Although industry has
claimed that fly ash is "neither toxic nor poisonous," this
is disputed. Exposure to fly ash through skin contact,
inhalation of fine particle dust and drinking water may
well present health risks. The National Academy of
Sciences noted in 2007 that "the presence of high
contaminant levels in many CCR (coal combustion
residue) leachates may create human health and
ecological concerns".[1]
Exposure to crystalline silica like that in fly ash is known
to cause lung disease, in particular silicosis.
Another fly ash component of some concern is lime
(CaO). This chemical reacts with water (H2O) to form
calcium hydroxide [Ca(OH)2], giving fly ash a pH
somewhere between 10 and 12, a medium to strong
base. This can also cause lung damage if present in
sufficient quantities.

CONCLUSION
Fly ash utilization has great potential to lower green house
gas emissions by decreased mining activities and reducing
carbon dioxide production during manufacture of materials
that can be substituted by fly ash. Utilization of fly ash is
beneficial not only from environmental considerations, but
also to avoid land usage for fly ash dumping. Though
there has been a steady progress in fly ash utilization
from 1990, we have a long way to go to reach the target
of 100 per cent fly ash utilization. Fly ash can become a
wealth generator by making use of it for producing ‘green
building’ materials, roads, agriculture etc. Full utilization
of the generating stock will provide employment potential
for three hundred thousand people and result in a
business volume of over Rs.4,000 crores.

RESULT
PropertiesofFly ash Bricks Comparedto ClayBricks
Common Load Bearing Clay Load BearingFly ash Bricks
Bricks
Factory location On site of raw materials Anywhere,preferablyonsite
of coal powerstation
Factory location Must change whenmaterial No change needed
depletes
Excavation needed required None
Raw materialsqualities Variesdaily consistent
Raw material neededper 4-5 tonnesof clayand shale 2.75 tonnesof flyash
1000 bricks
Raw materialswastage per 1.7-2 tonnesof clayand shale None
1000 bricks
Grindingof rocks required None to grind
Mixingdry materials required None
Additive (subjectto None Required@0.2L/100 kg
provisional confidentiality)
Drying greenunits 7 days 3 days
Temperature of firingthe 1000o
C- 1300o
C 1000o
C- 1300o
C
units (1832 F-2372 F) (1832 F-2372 F)
Length of firingtime 1day-7 days Few hours(subjectto
provisional confidentiality)

Brick Type
Compressive
Strength
Modulusof
Rupture
Absorptio
n(IRA)
Absorpti
on
Capacity
Aver
age
Dens
ity
ClayBricks
Typical isfrom12 to 40
MPa. (1740 psi – 5800
5800psi)
From lessthan1
MPa (145 psi)to
greaterthan 2 Pa
MP 290 psi).
Default
value is0.8
MPa
(116 psi)
Typical range
between0.2
and 5
kg/m2
/min.
(5.9-147.5
lb/in2
/min)
5-20%
1800-2000
kg/m3
(112-125
lb/ft3
)
FlashBricks
43 MPa 10.3 MPa 4.5 kg/m2
/min 10%
(6235 psi) (1494 psi) (133 lb/in2
/min)
10.3 MPa
(1494 psi)
4.5 kg/m2
/min
(133 lb/in2
/min)
10%
1450 kg/m3
(91 lb/ft3
)
Samplesof the
bestclay bricks
34.8 MPa
(5046 psi)
3.6 MPa
(522 psi)
5.9
kg/m2
/min
(174 lb/in2
/min)
6%
2000 kg/m3
(125 lb/ft3
)

REFERENCES:
 Eco-friendly Techniques developed at Central Road
Research Institute ,India
 Headwaters resources, “Fly ash for concrete”
 N.Bhanumathidas and N.Kalidas, “ Fly ash: The
resource for construction industry”, Indian Concrete
Journal ,April 2003
 Sciencedirect.com
 Wikipedia
 wealthywaste.com

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