The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

86 ECONOMIC GEOLOGY This group includes plaster of Paris and the lime cements, In the second group the setting is due to new compounds being formed at a high temperature or by mixing materials that are chemically unstable. This group includes hydraulic limes, Portland cement, and cements with amorphous or glassy silica. The simplest kind of cement is prepared by burning lime- stone, from which at the temperature of 1400° to 1650° F., the carbon dioxide is driven off and lime left. When lime is mixed with water it slakes to the hydrate or slaked lime (CaO 4+ H,0 = CaH,0,), which when mixed with sand forms mortar and sets firmly on drying. No chemical reaction takes place between the lime and sand, which prevents excessive shrinkage, and hardens the material. The lime absorbs carbon dioxide from the air, and is reconverted to carbonate. Pure limestone yields ‘ fat lime,” in contradistinction to “lean lime,” which is impure and earthy. Many of the older limestones have too much silica or clay to form fat lime, and the impurities fuse in the kiln into useless slag. Hyprauric anp PortraND CEMENTS—The best known of the cements which set under water is’ Portland cement, which was discovered by Aspdin of Leeds in 1824, and named from its resemblance to Portland stone. He began its manufacture in 1825, and attention was called to its value by its use by Brunell in 1828 in the Thames Tunnel. Two years later experiments at Chatham proved that the same type of cement could be prepared by burning an appropriate mixture of chalk and mud from the Medway. The same materials are abundant along the Thames, which became for a time the chief seat of the Portland cement industry. The cements which can be used under water include three groups which are not sharply defined. Hydraulic cements are made from clayey limestones containing from 13 to 33 per cent. of earthy material, usually silica, silicate of alumina, and iron oxide. The material is burnt in a kiln; at from 1400° to 1500° F. the carbon dioxide is given off ; at about 1650° F. the lime begins to combine with the alumina as calcic aluminates; between 2000° F. and 2350° F. the silica combines with the lime as calcic silicate, but sufficient lime cemains to slake on the addition of water. In the South-east of England hydraulic cement was made

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