Seminar Report on
FLY ASH UTILIZATION - Creating Wealth Out Of Waste
Submitted By: SHARBANEE PRUSTY ROLL NO: 107CE026 Department of Civil Engineering
FLY ASH UTILIZATION: CREATING WEALTH OUT OF WASTE 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. 2
CONTENT 1. Introduction 1.1.
Composition……………………………………………..4
1.2.
Classification ……………………………………………4
2. Application of Fly ash 2.1 Recycling and reuse………………………………………..6 2.2 Areas of Application……………………………………….7 3. Application of Fly ash is roads and embankments 3.1 Advantages…………………………………………………..8 3.2 Economy in Use……………………………………………..9 3.3. Environmental Impact………………………………………9 4. Application in Concrete 4.1. Features of Fly ash concrete…………………………….....10 4.2. Contribution to workability………………………………..10 4.3. Contribution to Strength……………………………………11 4.4. Environmental Impact………………………………………11 5. Application in Bricks. 5.1. Features of fly ash bricks…………………………………...13 5.2. Environmental Impacts……………………………………...12 5.3. Economic Benefits………………………………………….12 6. Indian Scenario in Fly ash application……………………………....13 7. Conclusion……………………………………………………………13 8. References…………………………………………………………….15
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1. 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. 1.1.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. 1.2. 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. 4
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.
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2. APPLICATION OF FLY ASH 2.1.
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
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2.2.
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
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3. 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.
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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
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4. 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. 10
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.
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5. 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
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6. 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% utilization of fly ash within one year of commissioning of the plants with progressive 10% utilization increases for the next 7 years reaching to 100% utilization within 9 years .
7. 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.
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8. 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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