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Fly ash brick (FAB) is a building material, specifically masonry units, containing class C or class F fly ash and water. Compressed at 28 MPa (272 atm) and cured for 24 hours in a 66 °C steam bath, then toughened with an air entrainment agent, the bricks can last for more than 100 freeze-thaw cycles.
Photomicrograph made with a scanning electron microscope and back-scatter detector: cross section of fly ash particles. Fly ash, flue ash, coal ash, or pulverised fuel ash (in the UK)—plurale tantum: coal combustion residuals (CCRs)—is a coal combustion product that is composed of the particulates that are driven out of coal-fired boilers together with the flue gases.
In 2017, 38.2 million short tons (34.7 × 10 ^ 6 t) of fly ash, and 9.7 million short tons (8.8 × 10 ^ 6 t) of bottom ash, were generated. [3] Coal contains trace levels of arsenic , barium , beryllium , boron , cadmium , chromium , thallium , selenium , molybdenum , and mercury , many of which are highly toxic to humans and other life.
A version known as fly ash bricks, manufactured using fly ash, lime, and gypsum (known as the FaL-G process) are common in South Asia. Calcium-silicate bricks are also manufactured in Canada and the United States, and meet the criteria set forth in ASTM C73 – 10 Standard Specification for Calcium Silicate Brick (Sand-Lime Brick).
In addition, when coal ash is recycled, costs related to coal ash disposal sites are avoided. [5] [15] There are two forms of coal ash recycling: “encapsulated” and “unencapsulated." [5] [15] When coal ash is bound to other materials it is encapsulated. [5] For example, coal ash can be reused in making concrete, bricks and wallboards. [15]
Aluminum powder is used at a rate of 0.05%–0.08% by volume (depending on the pre-specified density). In some countries, like India and China, fly ash generated from coal-fired power plants, and having 50–65% silica content, is used as an aggregate. [citation needed]
Standard shapes are usually bricks that have a standard dimension of 9 in × 4.5 in × 2.5 in (229 mm × 114 mm × 64 mm) and this dimension is called a "one brick equivalent". "Brick equivalents" are used in estimating how many refractory bricks it takes to make an installation into an industrial furnace.
In the lime industry, limestone is a general term for rocks that contain 80% or more of calcium or magnesium carbonate, including marble, chalk, oolite, and marl.Further classification is done by composition as high calcium, argillaceous (clayey), silicious, conglomerate, magnesian, dolomite, and other limestones. [5]