<P> 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 in the Coplay Cement Company Kilns under the direction of David O. Saylor in Coplay, Pennsylvania . By the early 20th century, American - made Portland cement had displaced most of the imported Portland cement . </P> <P> ASTM C150 defines Portland cement as' hydraulic cement (cement that not only hardens by reacting with water but also forms a water - resistant product) produced by pulverizing clinkers which consist essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an inter ground addition' . The European Standard EN 197 - 1 uses the following definition: </P> <P> Portland cement clinker is a hydraulic material which shall consist of at least two - thirds by mass of calcium silicates, (3 CaO SiO, and 2 CaO SiO), the remainder consisting of aluminium - and iron - containing clinker phases and other compounds . The ratio of CaO to SiO shall not be less than 2.0 . The magnesium oxide content (MgO) shall not exceed 5.0% by mass . </P> <P> (The last two requirements were already set out in the German Standard, issued in 1909). </P>

What are the raw materials of portland cement
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