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 …showed first 75 words of 1309 total…

…showed last 75 words of 1309 total…