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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Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

CHAPTER XV THE GEOLOGY OF CEMENTS Derinrrion anD Groups oF CEMENTS — * Cements,” says Desch (Chemistry and Testing of Cement, 1911, p. 1), * may be defined as adhesive substances capable of uniting fragments or masses of solid matter to a compact whole.” The cements, excluding the organic such as glue, are mostly calcareous materials which have the property of ‘ setting hard. The name comes from the Latin caedimentum, or “ chipped broken stone,” and was given to a mixture of broken stone or tiles with lime; this material was really mortar, i.e. cement mixed with inert materials. The oldest cement was probably mud, which, like the burnt calcareous material used in Egypt, would not last in a wet climate. The Greeks and Romans required cement that would withstand rain and set under water; they pre- pared hydraulic cement from volcanic tuff, and from use of that at Pozzuoli, a suburb of Naples, it was named Pozzolana. After the fall of Rome the art of preparing good lime was lost until the twelfth century. Builders then began to im- prove mortar, but hydraulic cement was not rediscovered until 1756, when Smeaton was designing the third Eddystone Lighthouse. The cement in its predecessor had been pro- tected from water by metal bands. Smeaton set himself to prepare a cement that would resist water and be as hard as the stones it joined; he succeeded by burning equal parts of the earthy Liassic limestones of Glamorganshire, and of volcanic tuff, known as Trass, from the extinct volcanoes of the Rhine. Cements are divided into two main groups. In the first the action depends upon the replacement of some constituent, usually moisture or carbon dioxide, which has been expelled by heat; as it is replaced the cement becomes hard or * sets.” 18

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