**Coal Combustion Products:** – Fly Ash: – Comprises 60% of coal combustion waste – Used as substitute for Portland cement – Common in building materials like grouts and roofing tiles – Found in asphaltic concrete pavements – Utilized in geotechnical applications like soil stabilization – Flue-Gas Desulfurization (FGD) Materials: – Produced by chemical scrubber emission control systems – Comprise 24% of coal combustion waste – Common types include FGD gypsum and spray dryer absorbents – Used in gypsum panel products and agricultural applications – Applied in mining and land reclamation activities – Bottom Ash and Boiler Slag: – Used as raw feed for manufacturing Portland cement clinker – Comprise 12% and 4% of coal combustion waste respectively – Suitable for geotechnical applications like structural fills – Used in concrete masonry products – Boiler slag also used for roofing granules and blasting grit **Fly Ash Composition and Characteristics:** – Contains silicon dioxide, aluminum oxide, and calcium oxide – Can include trace elements like arsenic, lead, and mercury – Used as lightweight aggregate with economic and environmental benefits – Stored at coal power plants or in landfills – Classified into Class F and Class C fly ash by ASTM – Solidifies in exhaust gases and collected by filters – Spherical particles ranging from 0.5 µm to 300 µm – Contains SiO2, Al2O3, Fe2O3, and CaO – Diverse mineralogy including glass phase, quartz, and iron oxides – Mercury content can reach 1 ppm, varies based on coal type **Types and Benefits of Fly Ash:** – Types of Fly Ash: – Class F: from burning older anthracite and bituminous coals – Class C: from burning younger lignite or sub-bituminous coal – Class C fly ash hardens and strengthens with water – Class C contains over 20% lime (CaO) – Class C does not need an activator – Benefits of Fly Ash Bricks: – Bricks meet ASTM standards – Estimated 90% reduction in masonry construction energy – Commercial availability expected by end of 2009 – Fly ash brick can contain up to 50% Class C fly ash – Bricks meet shrinkage limits for concrete brick **Disposal and Environmental Impact:** – Disposal and Market Sources: – Over 65% of fly ash is disposed in landfills and ash ponds – Environmental concerns led to laws reducing fly ash emissions – Stored ash can leach toxins into water aquifers – Debate focuses on creating lined landfills for safe disposal – Coal plants often located near metropolitan areas and water sources – Environmental Impact: – Fly ash previously dispersed into the atmosphere – Laws in industrialized countries reduced fly ash emissions – Unlined fly ash basins pose risks of spills and flooding – Fly ash stored outdoors can leach toxic compounds – Current focus on preventing chemical leaching into groundwater **Future Trends and Innovations:** – Fly ash used in geopolymer production – Expected increase in fly ash brick production – Growing interest in sustainable construction materials – Research on enhancing fly ash properties for construction – Regulations driving innovation in fly ash disposal technologieshttps://en.wikipedia.org/wiki/Fly_ash