Arizona Concrete :: essays research papers fc

Arizona Concrete According to the Mine Faculty at the University of Arizona, cement is manufactured primarily from suitable limestone and shale rocks. Arizona had two dry-process cement plants in 1969, namely the Arizona Portland Cement Company plant in Pima County, near Tucson, and the American Cement Corporation plant at Clarkdale, in Yavapai County (52-53). The use of cementing materials goes back to the ancient Egyptians and Romans, but the invention of modern portland cement is usually attributed to Joseph Aspdin, a builder in Leeds, England, who obtained a patent for it in 1824. Currently, the annual world production of portland cement is around 700 million metric tons (Danbury). Many people use the words concrete and cement interchangeably, but they're not. Concrete is to cement as a cake is to flour. Concrete is a mixture of ingredients that includes cement but contains other ingredients also (Day 6- 7). Portland cement is produced by pulverizing clinker consisting essentially of hydraulic calcium silicates along with some calcium aluminates and calcium aluminoferrites and usually containing one or more forms of calcium sulfate (gypsum) as an interground addition. Materials used in the manufacture of portland cement must contain appropriate proportions of calcium oxide, silica, alumina, and iron oxide components. During manufacture, analyses of all materials are made frequently to ensure a uniformly high quality cement. Selected raw materials are crushed, milled, and proportioned in such a way that the resulting mixture has the desired chemical composition. The raw materials are generally a mixture of calcareous (calcium oxide) material, such as limestone, chalk or shells, and an argillaceous (silica and alumina) material such as clay, shale, or blast-furnace slag. Either a dry or a wet process is used. In the dry process, grinding and blending operations are done with dry materials. In the wet process, the grinding and blending are done with the materials in slurry form. In other respects, the dry and wet processes are very much alike. After blending, the ground raw material is fed into the upper end of a kiln. The raw mix passes through the kiln at a rate controlled by the slope and rotational speed of the kiln. Burning fuel (powdered coal, oil, or gas) is forced into the lower end of the kiln where temperatures of 2600Â °F to 3000Â °F change the raw material chemically into cement clinker, grayish-black pellets about the size of 1/2-in.-diameter marbles. The clinker is cooled and then pulverized. During this operation a small amount of gypsum is added to regulate the setting time of the cement. The clinker is ground so fine that nearly all of it passes through a No.