348
4000.008
Not Given
Concrete Information
Paper
Portland Cement Association
1962
1-7
Y
Structural lightweight-aggregate concrete is defined as concrete that has a 28-day compressive strength in excess of 2,000 psi and an air-dry unit weight of less than 115 lb per cubic foot. This type of concrete should not be confused with very lightweight concretes used primarily for insulating purposes. Such concretes have a unit weight range of 20 to 70 lb. per cubic foot. Because their compressive strengths seldom exceed 1,000 psi, they are not discussed in this article.In 1917, a process of producing expanded shale lightweight aggregate was introduced by Stephen J. Hayde. He discovered that certain types of shale, clay, and slate expand when exposed to high temperatures in a rotary kiln and produce a sound, hard, lightweight aggregate.
Structural lightweight aggregates are usually classified according to their manufacturing process because the processes produce aggregates with different physical properties. Shale, clay, and slate are expanded commercially by the rotary kiln process or by the sintering process. Blast-furnace slag is expanded while in a molten state by treating it with water.