This specification covers lightweight aggregates intended for use in concrete not exposed to the weather, in which the prime consideration is the thermal insulating property of the resulting concrete. Two general types of lightweight aggregate are group I aggregates, which are prepared by expanding products, such as perlite or vermiculite, and group II aggregates which are prepared by expanding, calcining, or sintering products such as blast-furnace slag, clay, diatomite, fly ash, shale, or slate; and aggregates prepared by processing natural materials, such as pumice, scoria, or tuff. The thermal insulating properties of concrete made from the lightweight aggregate under test shall conform to the maximum average thermal conductivity indicated in the specification. To ensure reasonable uniformity in the gradation of successive shipments of lightweight aggregates, fineness modulus determination shall be made periodically. The aggregate shall be composed predominantly of lightweight cellular and granular inorganic material. The test methods for insulating concrete properties include specimen preparation, then concrete density determination, and determinacy of thermal conductivity. When lightweight aggregates covered by this specification are delivered in packages, the name of the manufacturer, type of aggregate, and minimum mass and approximate volume of the contents shall be plainly indicated thereon.