Fly ash is a byproduct of coal combustion in power plants that is collected from plant exhaust gases. It is composed mainly of silica and is spherical in shape. When mixed with water, fly ash reacts with calcium hydroxide to produce cementitious compounds, improving the strength and durability of concrete over time. The document discusses the various applications and advantages of using fly ash in concrete production, as well as information on packaging, shipping, and contact details for the company that produces and supplies fly ash.