The story of Pittsburgh: Cement and concrete

Cement and concrete (Vol. 1, nr. 8)

Bibliographic data

Multivolume work

Identifikator:: 1831622599

Document type:: Multivolume work

Title:: The story of Pittsburgh

Place of publication:: Pittsburgh

Publisher:: First National Bank

Year of publication:: 1919-1930

Collection:: Economics Books

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Volume

Identifikator:: 1831623277

URN:: urn:nbn:de:zbw-retromon-239793

Document type:: Volume

Title:: Cement and concrete

Volume count:: Vol. 1, nr. 8

Place of publication:: Pittsburgh

Publisher:: First National Bank

Year of publication:: 1921

Scope:: [ca. 18] Seiten

Digitisation:: 2022

Collection:: Economics Books

Usage license:: Get license information via the feedback formular.

Chapter

Document type:: Multivolume work

Structure type:: Chapter

Title:: Materials Carefully Proportioned and Chemically Combined

Collection:: Economics Books

MATERIALS CAREFULLY PROPORTIONED AND CHEMICALLY COMEINED Chemists analyze the materials, determine the amount of each to be used, set and seal interlocking automatic scales which in turn feed the materials to mills for grinding. Before mixing, the limestone and slag or other raw material must be crushed, dried and ground. Day in and day out, huge machines crunch hungrily their diet of stone and other materials and pass their mechanically-mixed grist along. At the same time, coal crushers, driers and grinders are at work preparing coal dust as finely ground as the rock dust. After the materials are ground, proportioned and mixed, they pass into rotary kilns. A modern cement kiln is a steel tube lined with fire brick. It is as long as a residence lot and more than large enough in diameter for a man to walk through. There are twenty such kilns in the Universal plant at Pittsburgh, set side by side in a building as long as an average city block. Into one end of each kiln goes a con- stant stream of powdered, mixed materials while into the other, forced along by compressed air, goes a stream of coal dust. Upon its entrance to the kiln, the powdered coal is ignited and travels through the long kiln hissing and burning as from an inferno. This burning produces a temperature of about 2800 degrees Fahrenheit which heats the materials to the point of incipient fusion and combines them chemically. In this process, the powdered materials are burned into nodules of “clinker” ranging from the size of a small pea to that of a walnut. This “clinker” has no setting or binding qualities and can be kept indefinitely. To make it useful as cement, it again must be ground, this time so fine that 789, of it will pass a 200-mesh sieve, that is, a sieve con- taining 200 openings per linear inch or 40.000 openings per square inch. While this fineness is considered one of the important qualities of portland cement, there are certain limits within which it must be confined in order to obtain best results in concrete. If not fine enough, the cement is not active, while if too fine, it becomes too quick in setting or too costly

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