Keramzit

the most widely used type of artificial porous filler in the USSR for lightweight concretes (less frequently keramzit is used as a heat-insulating and sound-insulating filler in structural components of various types of buildings).

Keramzit is produced by roasting fusible, swelling clay ores along with slightly swelling clay ores and additives (such as solar oil, sawdust, peat, or a sulfate-alcohol mash); the roasting is done in rotary furnaces. In its structure a keramzit grain represents a glasslike porous mass (with spherically formed closed pores), with a thin, sintered outer covering. Keramzit is produced primarily in the form of gravel (with grain sizes ranging from 5 to 40 mm) and less frequently in the form of crushed stone; it can also be made by crushing large chunks of keramzit gravel or pieces of a swollen mass of keramzit. A gravel form of keramzit sand (with grains less than 5 mm) is obtained by roasting the raw material in kilns of a “fluidized bed” or together with clay ores being roasted in rotary furnaces. The density of keramzit gravel ranges from 150 to 800 kg per cu m, its compression strength varies from 0.3 to 6 meganewtons per sq m (3–60 kilograms-force per sq cm), and its water absorption is from 10 to 25 percent; it can resist at least 15 cycles of alternate freezing and melting.