Beautifully engraved Certificate from the Alpha Portland Cement Company
in 1925. This historic document was printed by the American Banknote Company and has an
ornate border around it with a vignette of two allegorical women standing beside a seal of the company. This item is hand signed by the company's officers and is
over 84 years old.
The company changed its name to Alpha Portland Industries in 1972.
Portland cement is a fine powder, gray or white in color, that consists of a mixture of
hydraulic cement materials comprising primarily calcium silicates, aluminates and aluminoferrites.
More than 30 raw materials are known to be used in the manufacture of portland cement, and these
materials can be divided into four distinct categories: calcareous, siliceous, argillaceous, and
ferrifrous. These materials are chemically combined through pyroprocessing and subjected to
subsequent mechanical processing operations to form gray and white portland cement. Gray portland
cement is used for structural applications and is the more common type of cement produced. White
portland cement has lower iron and manganese contents than gray portland cement and is used
primarily for decorative purposes. Portland cement manufacturing plants are part of hydraulic cement
manufacturing, which also includes natural, masonry, and pozzolanic cement.
Portland cement accounts for 95 percent of the hydraulic cement production in the United
States. The balance of domestic cement production is primarily masonry cement. Both of these
materials are produced in portland cement manufacturing plants.
The initial production step in portland cement manufacturing is raw materials acquisition.
Calcium, the element of highest concentration in portland cement, is obtained from a variety of
calcareous raw materials, including limestone, chalk, marl, sea shells, aragonite, and an impure
limestone known as "natural cement rock". Typically, these raw materials are obtained from open-face
quarries, but underground mines or dredging operations are also used. Raw materials vary from
facility to facility. Some quarries produce relatively pure limestone that requires the use of additional
raw materials to provide the correct chemical blend in the raw mix. In other quarries, all or part of
the noncalcarious constituents are found naturally in the limestone. Occasionally, pockets of pyrite,
which can significantly increase emissions of sulfur dioxide (SO2), are found in deposits of limestone,
clays, and shales used as raw materials for portland cement. Because a large fraction (approximately
one third) of the mass of this primary material is lost as carbon dioxide (CO2) in the kiln, portland
cement plants are located close to a calcareous raw material source whenever possible. Other elements
included in the raw mix are silicon, aluminum, and iron. These materials are obtained from ores and
minerals such as sand, shale, clay, and iron ore. Again, these materials are most commonly from
open-pit quarries or mines, but they may be dredged or excavated from underwater deposits.
Either gypsum or natural anhydrite, both of which are forms of calcium sulfate, is introduced
to the process during the finish grinding operations.
History from the EPA Website.