Portland cement is the most common type of cement and typically originates from limestone. It is the key ingredient in concrete, mortar and stucco and used throughout the world. When added to concrete, it is the paste that binds the aggregate (consisting of gravel and sand) with the water.
Defined as hydraulic cement (cement that not only hardens by reacting with water but also forms a water-resistant product), it is “produced by pulverizing clinkers consisting of essentially hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an inter ground addition.” The concrete mix’s strength depends on the reaction of the calcium silicates with the water.
The Portland Cement Association explains that, “Cement is manufactured through a closely controlled chemical combination of calcium, silicon, aluminum, iron and other ingredients.” To produce portland cement, raw materials such as limestone, shell, or chalk are combined with clay, silica sand, shale, bauxite, fly ash, slag and iron. This mixture is heated in huge cement kilns at temperatures as high as 2,700 degrees Fahrenheit. A dark grey nodular about the size of a marble called a clinker is produced from the extreme heat and is ground into a fine powder to make the cement. Once it has cooled, a small amount of gypsum may also be added to control the setting process.
Portland cement is thought to be the invention of Joseph Aspdin, a bricklayer from England, and named for its similarity to a common building stone found on the Isle of Portland in Dorset, England. Aspdin experiments were conducted in his kitchen stove where he fired ground limestone and clay together to create the first artificial cement. His new cement was a much stronger material than the standard unfired crushed limestone used during that period of time.
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Sources: en.wikipedia.org/wiki/Portland_cement, cement.org/cement-concrete-basics/how-cement-is-made