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Stone Cement: Many other combinations of mineral oxides would qualify as hydraulic cements but cannot compete for use in jrdinary construction because of their cost. Most hydraulic cement is used in the form of concrete, ivhich consists of cement, water, sand, and gravel )r crushed stone cement. The cement is the bonding igent, and the other rock materials, which are :alled aggregates, act as filler.
Three classes of cements have been developed ;ommercially: natural cements (including hy-Iraulic limes), aluminous cements, and portland :ements.
About 98% of the cement produced in the United States is Portland cement, which is not a brand name but a type of hydraulic cement. The name was given in 1824 by Joseph Aspdin, a bricklayer of Leeds, England, to a hydraulic lime that he patented, because when set with water and sand, it resembled a natural limestone cement quarried on the Isle of Portland in England.
At about the same time it was discovered that an excellent cement could be made by pulverizing the nodules, called grappiers, which occasionally became sintered (that is, formed into a non-porous solid without melting) when hydraulic lime was fired.
(5) Portland cement concrete. This is made by mix-ng Portland cement, sand, stone cement or gravel, and water. Portland cement is produced by mixing together argil-aceous and calcareous materials (such as clay or shale md limestone cement), heating them to a high temperature, and ;rinding the resulting clinker to a fine powder.
(6) Miscellaneous materials. These are blast furnace ilag, seashells, coral rock, caliche (in natural deposits), ind the residue of the spontaneous combustion of waste 'rom lignite coal mines. They are useful in road sur-acing because they do not soften when it rains or break eadily under wheel loads. |
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