Expanded shale is one of several artificial lightweight aggregates currently used in the production of lightweight concrete. Its use has become rather widespread through recent improvements in production techniques, mix designs, placement methods, and air entrainment. However, various types of lightweight concrete as such is not of recent origin, having been used in this country for more than a half century.

Expanded shale aggregates are produced by heating a suitable shale to the point of fusion. Gases within the shale expand and thus form thousands of tiny air cells within the mass which are retained upon cooling and solidification. The finished product is a highly cellular aggregate. Burning takes place in rotary kilns under controlled temperatures ranging from 1900 to 2200°F.

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No. 102

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