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Portland cement is the most common type of cement in general use around the world, used as a basic ingredient of concrete, mortar, stucco, and most non-speciality grout. It was developed from other types of hydraulic lime in England in the mid 19th century and usually originates from limestone. It is a fine powder produced by heating materials in a kiln to form what is called clinker, grinding the clinker, and adding small amounts of other materials. Several types of Portland cement are available with the most common being called ordinary Portland cement (OPC) which is grey in color, but a white Portland cement is also available. Portland cement is caustic, so it can cause chemical burns, the powder can cause irritation or with severe exposure lung cancer, and can contain some hazardous components such as crystalline silica and hexavalent chromium. Environmental concerns are the high energy consumption required to mine, manufacture, and transport the cement and the related air pollution including the release of greenhouse gases (e.g., carbon dioxide), dioxin, NOx, SO2, and particulates. The low cost and widespread availability of the limestone, shales, and other naturally occurring materials used in Portland cement make it one of the lowest-cost materials widely used over the last century throughout the world. Concrete produced from Portland cement is one of the most versatile construction materials available in the world. ==History== Portland cement was developed from natural cements made in Britain beginning in the middle of the 18th century. Its name is derived from its similarity to Portland stone, a type of building stone quarried on the Isle of Portland in Dorset, England. The development of modern Portland cement (sometimes called ordinary or normal Portland cement) began in 1756 when John Smeaton experimented with combinations of different limestones and additives including trass and pozzolanas relating to the planned construction of a lighthouse〔Robert G. Blezard, "The History of Calcareous Cements" in Hewlett, Peter C., ed.. ''Leaʼs chemistry of cement and concrete''. 4. ed. Amsterdam: Elsevier Butterworth-Heinemann, 2004. 1–24. Print.〕 now known as Smeaton's Tower. In the late 18th century, Roman cement was developed and patented in 1796 by James Parker;〔Saikia, Mimi Das. Bhargab Mohan Das, Madan Mohan Das. ''Elements of Civil Engineering''. New Delhie: PHI Learning Private Limited. 2010. 30. Print.〕 Roman cement quickly became popular, but was largely replaced by Portland cement in the 1850s.〔 In 1811 James Frost produced a cement he called British cement.〔 James Frost is reported to have erected a manufactory for making of an artificial cement in 1826. In 1843, Aspdin's son William improved their cement, which was initially called "Patent Portland cement", although he had no patent. In 1818, French engineer Louis Vicat invented an artificial hydraulic lime considered the "principal forerunner"〔 of Portland cement and "... Edgar Dobbs of Southwark patented a cement of this kind in 1811."〔 Portland cement was used by Joseph Aspdin in his cement patent in 1824〔 because of the cements' resemblance to Portland stone. The name "Portland cement" is also recorded in a directory published in 1823 being associated with a William Lockwood, Dave Stewart, and possibly others. However, Aspdins' cement was nothing like modern Portland cement, but was a first step in the development of modern Portland cement, called a 'proto-Portland cement'.〔 William Aspdin had left his fathers company and in his cement manufacturing apparently accidentally produced calcium silicates in the 1840s, a middle step in the development of Portland cement. In 1848, William Aspdin further improved his cement; in 1853, he moved to Germany, where he was involved in cement making.〔 William Aspdin made what could be called 'meso-Portland cement' (a mix of Portland cement and hydraulic lime). Isaac Charles Johnson further refined the production of 'meso-Portland cement' (middle stage of development) and claimed to be the real father of Portland cement.〔Hahn, Thomas F., and Emory Leland Kemp. ''Cement mills along the Potomac River''. Morgantown, WV: West Virginia University Press, 1994. 16. Print.〕 John Grant of the Metropolitan Board of Works in 1859 set out requirements for cement to be used in the London sewer project. This became a specification for Portland cement. The next development with the manufacture of Portland cement was the introduction of the rotary kiln patented by German Friedrich Hoffmann called a Hoffmann kiln for brick making in 1858 and then Frederick Ransome in 1885 (U.K.) and 1886 (U.S.) which allowed a stronger, more homogeneous mixture and a continuous manufacturing process.〔 The Hoffman "endless" kiln which gave "perfect control over combustion" was tested in 1860 and showed the process produced a better grade of cement. This cement was made at the Portland Cementfabrik Stern at Stettin, which was the first to use a Hoffman kiln. It is thought that the first modern Portland cement was made there. The Association of German Cement Manufacturers issued a standard on Portland cement in 1878.〔(【引用サイトリンク】title=125 Years of Research for Quality and Progress )〕 Portland cement had been imported into the United States from Germany and England and in the 1870s and 1880s it was being produced by Eagle Portland cement near Kalamazoo, Michigan, and in 1875, the first Portland cement was produced by Coplay Cement Company under the direction of David O. Saylor in Coplay, Pennsylvania.〔Meade, Richard Kidder. ''Portland cement: its composition, raw materials, manufacture, testing and analysis''. Easton, PA: 1906. The Chemical Publishing Co. 4–14. Print.〕 By the early 20th century American made Portland cement had displaced most of the imported Portland cement. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Portland cement」の詳細全文を読む スポンサード リンク
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