Fly ash (one of several coal combustion products, or CCPs) is the finely divided mineral residue resulting from the combustion of coal in electric generating plants. Fly ash consists of inorganic, incombustible matter present in the coal that has been fused during combustion into a glassy, amorphous structure. Coal combustion products (CCPs) are categorized in four groups, each based on physical and chemical forms derived from coal combustion methods and emission controls: Fly ash is most commonly used as a high-performance substitute for portland cement or as clinker for portland cement production. ... For other uses, see Mineral (disambiguation). ... A combustion reaction taking place in a igniting match Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. ... Coal Coal (IPA: ) is a fossil fuel formed in swamp ecosystems where plant remains were saved by water and mud from oxidization and biodegradation. ... For other uses, see Power station (disambiguation). ... Inorganic chemistry is the branch of chemistry concerned with the properties and reactions of inorganic compounds. ... This article is about the material. ...

Chemical composition and classification

Fly ash material solidifies while suspended in the exhaust gases and is collected by electrostatic precipitators or filter bags. Since the particles solidify while suspended in the exhaust gases, fly ash particles are generally spherical in shape and range in size from 0.5 µm to 100 µm. They consist mostly of silicon dioxide (SiO₂), aluminium oxide (Al₂O₃) and iron oxide (Fe₂O₃), and are hence a suitable source of aluminum and silicon for geopolymers. They are also pozzolanic in nature and react with calcium hydroxide and alkali to form calcium silicate hydrates (cementitious compounds). Bituminous coal Bituminous coal is a relatively hard coal containing a tar-like substance called bitumen. ... Sub-bituminous coal is a coal whose properties range from those of lignite to those of bituminous coal and are used primarily as fuel for steam-electric power generation. ... Coal Coal is a fossil fuel extracted from the ground by mining. ... Calcium oxide (CaO), commonly known as lime, quicklime or burnt lime, is a widely used chemical compound. ... Loss on Ignition is a test used in inorganic analytical chemistry, particularly in the analysis of minerals. ... An electrostatic precipitator (ESP), or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. ... A sphere is a symmetrical geometrical object. ... R-phrases R42 R43 R49 S-phrases S22 S36 S37 S45 S53 Flash point non-flammable Supplementary data page Structure and properties n, εr, etc. ... Aluminium oxide is an amphoteric oxide of aluminium with the chemical formula Al2O3. ... Iron oxide pigment There are a number of iron oxides: Iron oxides Iron(II) oxide or ferrous oxide (FeO) The black-coloured powder in particular can cause explosions as it readily ignites. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... Not to be confused with Silicone. ... Pozzolana is a fine sandy volcanic ash, originally discovered and dug at Pozzuoli in the region around Vesuvius, but later at a number of other sites. ... It has been suggested that Portlandite be merged into this article or section. ... In chemistry, an alkali (from Arabic: al-qalyالقلوي, القالي ) is a basic, ionic salt of an alkali metal or alkali earth metal element. ... Calcium silicate, otherwise known as slag, has a low bulk density and high physical water absorption. ... This article is about the construction material. ...

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. Engineering properties and development of strength over time are different depending on the chemical composition of the fly 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). Anthracite coal Anthracite (Greek Ανθρακίτης, literally a form of coal, from Anthrax [Άνθραξ], coal) is a hard, compact variety of mineral coal that has a high luster. ... Bituminous coal Bituminous coal is a relatively hard coal containing a tar-like substance called bitumen. ... Coal Coal is a fossil fuel extracted from the ground by mining. ...

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 standards have been established in the United States. Three-fourths 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 needs to be under 6%. The particle size distribution of raw fly ash is very often fluctuating constantly, due to changing performance of the coal mills and the boiler performance. This makes it necessary that fly ash used in concrete needs to be processed using separation equipment like mechanical air classifiers. Especially important is the ongoing quality verification. This is mainly expressed by quality control seals like the Indian ISI mark or the DCL mark of the Dubai Municipality. A typical Fly Ash processing plant with quality verification is the DIRK India plant in Nashik/Maharashtra, India. The fineness of a precious metal refers to the ratio of the primary metal to any additives or impurities. ... For other uses, see Carbon (disambiguation). ...

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 10% 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. A pozzolan is a material which, when combined with calcium hydroxide, exhibits cementitious properties. ... This article or section does not adequately cite its references or sources. ...

Class C fly ash

Fly ash produced from the burning of younger lignite or subbituminous 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. In inorganic chemistry, a sulfate (IUPAC-recommended spelling; also sulphate in British English) is a salt of sulfuric acid. ...

Disposal and market sources

In the past, fly ash produced from coal combustion was simply taken up by flue gases and dispersed into the atmosphere. This created environmental and health concerns that prompted laws which 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. In India alone, fly ash landfill covers an area of 40,000 acres (160 km²). Flue gas is gas that exits to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. ... Look up landfill in Wiktionary, the free dictionary. ...

The recycling of fly ash has become an increasing concern in recent years due to increasing landfill costs and current interest in sustainable development. In 2005, U.S. coal-fired power plants reported producing 71.1 million tons of fly ash, of which 29.1 million tons was reused in various applications.^[1] If the nearly 42 million tons of unused fly ash had been recycled, it would have reduced the need for approximately 27,500 acre-feet of landfill space.^[1][2] Other environmental benefits to recycling fly ash includes reducing the demand for virgin materials that would need quarrying and substituting for materials that may be energy-intensive to create (such as Portland cement). anyone doing this homework. ... For other uses, see Quarry (disambiguation). ... Sampling fast set Portland cement Portland cement is the most common type of cement in general usage, as it is a basic ingredient of concrete, mortar and plaster. ...

Fly ash reuse

The reuse of fly ash as an engineering material primarily stems from its pozzolanic nature, spherical shape, and relative uniformity. Fly ash recycling, in descending frequency, includes usage in:

• Portland cement and grout;
• Embankments and structural fill;
• Waste stabilization and solidifaction;
• Raw feed for cement clinkers;
• Mine reclamation;
• Stabilization of soft soils;
• Road subbase;
• Aggregate;
• Flowable fill;
• Mineral filler in asphaltic concrete;
• Other applications include cellular concrete, roofing tiles, paints, metal castings, and filler in wood and plastic products.^[2][3]

Grout is a construction material used to embed rebars in masonry walls, connect sections of pre-cast concrete, fill voids, and seal joints (like those between tiles). ... In order to keep a road or rail line straight and/or flat, and where the comparative cost or practicality of alternate solutions (such as diversion) is too prohibitive, the land over which the road or rail line will travel is built up to form an embankment. ... Cement clinker, in the manufacture of Portland cement, is the product of the kiln. ... Mine reclamation is the process of creating useful landscapes that meet a variety of goals, typically creating productive ecosystems (or sometimes industrial or municipal land) from mined land. ... For other uses, see Clay (disambiguation). ... Base course refers to the sub-base layer of an asphalt roadway. ... Aggregate is the component of a composite material used to resist compressive stress. ... The use of flowable fill as a highway construction material is becoming more widespread throughout the United States. ... Asphalt As shown in this cross-section, many older roadways are smoothed by applying a thin layer of asphalt concrete to the existing portland cement concrete. ... This article does not cite any references or sources. ... This article is about the manufacturing process. ...

Portland cement

Owing to its pozzolan properties, fly ash is used as a replacement of Portland cement in concrete.^[4] The use of fly ash as a pozzolanic ingredient was recognized as early as 1914, although the earliest noteworthy study of its use was in 1937.^[5] Before its use was lost to the Dark Ages, Roman structures such as aqueducts or the Pantheon in Rome used volcanic ash (which possesses similar properties to fly ash) as pozzolan in their concrete.^[6] As pozzolan greatly improves the strength and durability of concrete, the use of ash is a key factor in their preservation. A pozzolan is a material which, when combined with calcium hydroxide, exhibits cementitious properties. ... Sampling fast set Portland cement Portland cement is the most common type of cement in general usage, as it is a basic ingredient of concrete, mortar and plaster. ... This article is about the construction material. ... For other uses, see Aqueduct (disambiguation). ... Facade of the Pantheon The Pantheon (Latin Pantheon[1], from Greek Πάνθεον Pantheon, meaning Temple of all the gods) is a building in Rome which was originally built as a temple to the seven deities of the seven planets in the state religion of Ancient Rome. ...

Use of fly ash as a partial replacement for Portland cement is generally limited to Class F fly ashes. It can replace up to 30% by mass of Portland cement, and can add to the concrete’s final strength and increase its chemical resistance and durability. Recently concrete mix design for partial cement replacement with High Volume Fly Ash (50 % cement replacement) has been developed. For Roller Compacted Concrete (RCC)[used in dam construction] replacement values of 70% have been achieved with POZZOCRETE (processed fly ash) at the Ghatghar Dam project in Maharashtra, India. Due to fly ash’s spherical shape, it can also increase workability of cement while reducing water demand.^[7] The replacement of Portland cement with fly ash also reduces the greenhouse gas signature of concrete, as the production of one ton of Portland cement produces one ton of CO₂. Since the worldwide production of Portland cement is expected to reach nearly 2 billion tons by 2010, its replacement by fly ash could dramatically reduce global emissions of carbon Top: Increasing atmospheric CO2 levels as measured in the atmosphere and ice cores. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ...

Embankment

Fly ash properties are somewhat unique as an engineering material. Unlike typical soils used for embankment construction, fly ash has a large uniformity coefficient consisting of silt-sized particles. Engineering properties that will affect fly ash’s use in embankments include grain size distribution, compaction characteristics, shear strength, compressibility, permeability, and frost susceptibility.^[7] Nearly all fly ash used in embankments are Class F fly ashes. Silt is soil or rock derived granular material of a specific grain size. ... The Proctor compaction test, and the related Modified Proctor compaction test, are tests to determine the maximum practically-achievable density of soils and aggregates, and are frequently used in geotechnical engineering. ... Shear strength in engineering is a term used to describe the strength of a material or component against the type of yield or structural failure where the material or component fails in shear. ... Fluid Dynamics Compressibility (physics) is a measure of the relative volume change of fluid or solid as a response to a pressure (or mean stress) change: . For a gas the magnitude of the compressibility depends strongly on whether the process is adiabatic or isothermal, while this difference is small in... Permeability has several meanings: In electromagnetism, permeability is the degree of magnetisation of a material in response to a magnetic field. ... Frost heaving (or frost heave) occurs when soil expands upward or outward and contracts due to freezing and thawing. ...

Soil stabilization

Soil stabilization involves the addition of fly ash to improve the engineering performance of a soil. This is typically used for a soft, clayey subgrade beneath a road that will experience many repeated loadings. Improvement can be done with both Class C and Class F fly ashes. If using a Class F fly ash, an additive (such as lime or cement) is needed whereas the self-cementing nature of Class C fly ash allows it to be used alone.

Flowable fill

Fly ash is also used as a component in the production of flowable fill (also called controlled low strength material, or CLSM), which is used as self-leveling, self-compacting backfill material in lieu of compacted earth or granular fill. The strength of flowable fill mixes can range from 200 to 1,200 lbf/in² (1.4 to 8.3 MPa), depending on the design requirements of the project in question. Flowable fill includes mixtures of Portland cement and filler material, and can contain mineral admixtures. Fly ash can replace fine aggregate (in most cases, river sand) as a filler material. High fly ash content mixes contain nearly all fly ash, with a small percentage of Portland cement and enough water to make the mix flowable. Low fly ash content mixes contain a high percentage of filler material, and a low percentage of fly ash, Portland cement, and water. Class F fly ash is best suited for high fly ash content mixes, whereas Class C fly ash is almost always used in low fly ash content mixes.^[7][8] The use of flowable fill as a highway construction material is becoming more widespread throughout the United States. ... A pressure gauge reading in PSI (red scale) and kPa (black scale) The pound-force per square inch (symbol: lbf/in²) is a non-SI unit of pressure based on avoirdupois units. ... The megapascal, symbol MPa is an SI unit of pressure. ...

Asphalt concrete

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 and provide contact points between larger aggregate particles in asphalt concrete mixes. This application is used in conjunction, or as a replacement for, other binders (such as Portland cement or hydrated lime). For use in apshalt pavement, the fly ash must meet mineral filler specifications outlined in ASTM D242. The hydrophobic nature of fly ash gives pavements better resistance to stripping. Fly ash has also been shown to increase the stiffness of the asphalt matrix, improving rutting resistance and increasing mix durability.^[7][9]

Polymers

More recently, fly ash has been used as a component in geopolymers mixtures. Geopolymer is a term covering a class of synthetic aluminosilicate materials with potential use in a number of areas, but predominantly as a replacement for Portland-based cements. ...

Roller compacted concrete

Another new application is using fly ash in roller compacted concrete dams. This has been demonstrated in the Ghatghar Dam Project in India. Roller-Compacted Concrete (RCC) is a special blend of concrete that has the same ingredients as conventional concrete. ...

Bricks

Ash bricks have been used in house construction in Windhoek, Namibia since the 1970's. There is, however, a problem with the bricks in that they tend to fail or produce unsightly pop-outs. This happens when the bricks come into contact with moisture and a chemical reaction occurs causing the bricks to expand. --193. ...

In May 2007, Henry Liu, a retired 70-year old American civil engineer, announced that he had invented a new, environmentally sound building brick composed of fly ash and water. Compressed at 4,000 psi and cured for 24 hours in a 150°F (66°C) steam bath , then toughened with an air entrainment agent, the bricks last for more than 100 freeze-thaw cycles. Owing to the high concentration of calcium oxide in class C fly ash, the brick can be described as "self-cementing". The manufacturing method is said to save energy, reduce mercury pollution, and costs 20% less than traditional clay brick manufacturing. Liu intends to license his technology to manufacturers in 2008. ^[10][11] Henry Liu may refer to: Henry Liu (1932 - 1984), Taiwanese-American writer who wrote under the pen-name Chiang Nan Henry Liu (civil engineer), American civil engineer Henry C.K. Liu, Chinese-American commentator on economics and geopolitics Category: ... A civil engineer is a person who practices civil engineering. ... For other uses, see Brick (disambiguation). ... Psi has multiple meanings: Psi (letter) (Ψ, ψ) of the Greek alphabet Psi (Cyrillic) (Ñ°, ѱ), letter of the early Cyrillic alphabet, adopted from Greek Psi (parapsychology) Psi (instant messaging client), a popular Jabber client program J/ψ particle, a subatomic particle Wavefunction in Quantum Mechanics, ψ In mathematics, Ψ is used to denote the angle between... Air entrainment is the intentional creation of tiny air bubbles in concrete. ... Calcium oxide (CaO), commonly known as lime, quicklime or burnt lime, is a widely used chemical compound. ... General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery Standard atomic weight 200. ...

Waste management

Using a proprietary methodology, the US company N-Viro International Corporation uses the alkaline properties of fly ash to process human waste sludge into fertilizer.^[12] Similar the RHENIPAL process owned by DIRK Group utilizes fly ash mixtures for the stabilization of sewage sludge and other toxic sludges. This process was used to stabilize large amounts of Chromium 6 contaminated leather sludges in Portugal (Alcanena) Sewage treatment is the process that removes the majority of the contaminants from waste-water or sewage and produces both a liquid effluent suitable for disposal to the natural environment and a sludge. ...

Environmental problems

Fly ash, like soil, contains trace concentrations of many heavy metals that are known to be detrimental to health in sufficient quantities. These include nickel, vanadium, arsenic, beryllium, cadmium, barium, chromium, copper, molybdenum, zinc, lead, selenium, uranium, thorium, and radium. Though these elements are found in extremely low concentrations in fly ash, their mere presence has prompted some to sound alarm. A heavy metal is any of a number of higher atomic weight elements, which has the properties of a metallic substance at room temperature. ... For other uses, see Nickel (disambiguation). ... General Name, symbol, number vanadium, V, 23 Chemical series transition metals Group, period, block 5, 4, d Appearance silver-grey metal Standard atomic weight 50. ... General Name, Symbol, Number arsenic, As, 33 Chemical series metalloids Group, Period, Block 15, 4, p Appearance metallic gray Standard atomic weight 74. ... General Name, symbol, number beryllium, Be, 4 Chemical series alkaline earth metals Group, period, block 2, 2, s Appearance white-gray metallic Standard atomic weight 9. ... General Name, Symbol, Number cadmium, Cd, 48 Chemical series transition metals Group, Period, Block 12, 5, d Appearance silvery gray metallic Standard atomic weight 112. ... For other uses, see Barium (disambiguation). ... General Name, symbol, number chromium, Cr, 24 Chemical series transition metals Group, period, block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ... For other uses, see Copper (disambiguation). ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Standard atomic weight 95. ... General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... For Pb as an abbreviation, see PB. General Name, Symbol, Number lead, Pb, 82 Chemical series Post-transition metals or poor metals Group, Period, Block 14, 6, p Appearance bluish gray Standard atomic weight 207. ... For other uses, see Selenium (disambiguation). ... General Name, symbol, number uranium, U, 92 Chemical series actinides Group, period, block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Standard atomic weight 238. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Standard atomic weight 232. ... General Name, Symbol, Number radium, Ra, 88 Chemical series alkaline earth metals Group, Period, Block 2, 7, s Appearance silvery white metallic Standard atomic weight (226) g·mol−1 Electron configuration [Rn] 7s2 Electrons per shell 2, 8, 18, 32, 18, 8, 2 Physical properties Phase solid Density (near r. ...

The U.S. EPA confirms that coal fly ash does not need to be regulated as a hazardous waste. ^[13] The EPA's headquarters building in Washington, D.C. is constructed with concrete containing fly ash. Studies by the U.S. Geological Survey and others conclude that fly ash compares with common soils or rocks and should not be the source of alarm.^[14] EPA redirects here. ... For other uses, see Washington, D.C. (disambiguation). ... The United States Geological Survey (USGS) is a scientific agency of the United States government. ...

References

1. ^ ^{a b} American Coal Ash Association. "CCP Production and Use Survey".
2. ^ ^{a b} U.S. Environmental Protection Agency. "Using Coal Ash in Highway Construction - A Guide to Benefits and Impacts".
3. ^ U.S. Federal Highway Administration. Fly Ash.
4. ^ Scott, Allan N .; Thomas, Michael D. A. (Jan/Feb 2007). "Evaluation of Fly Ash From Co-Combustion of Coal and Petroleum Coke for Use in Concrete". ACI Materials Journal 104 (1): 62-70. Retrieved on 2007-02-23. 
5. ^ Halstead, W. (October 1986), "Use of Fly Ash in Concrete", National Cooperative Highway Research Project 127
6. ^ Moore, David. The Roman Pantheon: The Triumph of Concrete. 
7. ^ ^{a b c d} U.S. Federal Highway Administration. Fly Ash Facts for Highway Engineers.
8. ^ Hennis, K. W. & C. W. Frishette (1993), "A New Era in Control Density Fill", Proceedings of the Tenth International Ash Utilization Symposium
9. ^ Zimmer, F. V. (1970), "Fly Ash as a Bituminous Filler", Proceedings of the Second Ash Utilization Symposium
10. ^ Popular Science Magazine, INVENTION AWARDS : A Green Brick, May 2007
11. ^ National Science Foundation, Press Release 07-058, "Follow the 'Green' Brick Road?", May 22, 2007
12. ^ [1] N-Viro International
13. ^ Federal Register. “Notice of Regulatory Determination on Wastes From the Combustion of Fossil Fuels”.
14. ^ U.S. Geological Survey. "Radioactive Elements in Coal and Fly Ash: Abundance, Forms, and Environmental Significance".

EPA redirects here. ... The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 54th day of the year in the Gregorian calendar. ... Pantheon may refer to: Buildings: Pantheon, Rome, a temple built in 125 AD to all Roman gods, now a Christian church. ... The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. ... The Federal Register contains most routine publications and public notices of United States government agencies. ... The United States Geological Survey (USGS) is a scientific agency of the United States government. ...

External links

• American Coal Ash Association Established in 1969, the American Coal Ash Association is considered the "Voice of the Coal Combustion Products Industry"
• EcoSmart Concrete : A site dedicated to the use of Fly ash and other supplementary cementing materials in concrete.
• Fly Ash Information Center : Site explaining the history and uses of fly ash.
• United States Geological Survey - Radioactive Elements in Coal and Fly Ash (document)
• High Volume Fly Ash Concrete
• UK Quality Ash Association : A site promoting the many uses of fly ash in the UK