Portland cement is the essential binding ingredient in concrete, made from finely ground materials including lime, iron, silica, and alumina. Lime is derived primarily from limestone, marble, marl, seashells, and clays, which also supply iron and alumina, while silica is sourced from sand, chalk, and bauxite. Contemporary manufacturing of Portland cement is a significant source of carbon dioxide emissions, prompting research into reducing its content in concrete through alternative supplementary materials, such as industrial by-products like iron furnace slag, fly ash, and silica fume.
The manufacturing process involves crushing these ingredients, followed by either a wet or dry method to prepare the cement. In the dry process, raw materials are ground into powder, mixed, and heated in a kiln, whereas the wet process involves mixing ground materials with water to form a slurry before heating. The high-temperature kiln, operating between 2600 to 3000°F, transforms the material into clinker, which is then cooled and ground with a small amount of gypsum to produce a fine powder. The added gypsum helps control the cement's setting time.
Portland cement is predominantly shipped in bulk by rail or large trailers and sold by the ton. Smaller quantities are packaged in bags that typically weigh 94 pounds and contain one cubic foot of cement.
