Coal combustion products

**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