Cement was first patented in 1824 by Joseph Aspdin, a British stonemason who first created it from clay and limestone in the kitchen of his home. The mixture, when combined with water, dried to resemble the stones quarried from the nearby Isle of Portland, so Aspdin named the building mixture "Portland Cement." Cement has grown to be the top medium for both commercial and residential construction in the United States and is rapidly expanding to new markets in the Far East and Africa.
Cement Content
Cement was traditionally made from raw materials that included limestone, shells or chalk, shale, clay, sand and iron ore. Today, cement is mixed using calcium, silicon, aluminum and iron, in addition to the quarried clay. Water is added to the mixture to create a hard building material.
Types of Cement
The American Society for Testing and Materials (ASTM) tests cement products manufactured in the United States. This group has identified eight types of Portland cement ranked by specifications for use of the cement product and the stress factor associated with the mix. The building industry also categorizes cement by the color of the product. White cement appears that color after the product has dried. Other names identify the process used to make the product (blended cement) and the properties of the type of cement (expansive cement).
Production Methods
Cement is produced in either a dry or wet process. The dry process takes quarried clay that is first crushed into 5-inch pieces and then crushed again into pieces 3/4 inch in size. The dry material is then crushed into a powder blend and dried in a kiln. The wet process applies water to the crushed clay mixture. This slurry is then dried in a rotating kiln that is used to fuse the mixture together. The hot solid is next cooled, mixed with gypsum and then ground. Most cement is currently created using the dry process due to the ease of production and the energy savings over cement produced using the wet process.
U.S. Production
The U.S. Portland Cement Association reports that in 2007, 116 cement plants operated in 36 states. These plants created over $11.9 billion worth of cement. The large number of cement companies does not accurately indicate individual participation, since the top five companies produce over 51 percent of all the cement produced in the United States, with the top producer responsible for over 12 percent of production in 2007. Foreign owners hold over 80 percent interest in U.S. cement companies.
World Production
The largest producer of cement is China, followed by India and the United States. China will dramatically increase production due to economic factors creating a building boom in the country. The United States cement production plants export less than one percent of the total production each year. American companies imported 22.7 metric tons of cement in 2007, according to the Portland Cement Association, with imports arriving from China, Canada, Columbia, Mexico and the Republic of Korea.
The Future of Cement
The 2008-2009 economic downturn had an immediate impact on cement production in the United States with reduced production schedules during the peak months of May through October--the height of the residential building season. The decline in new American housing starts reduced the amount of cement production for 2009.
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