What is ESC? It is a unique, ceramic lightweight aggregate prepared by expanding select minerals in a rotary kiln at temperatures over 2000°F. The production and raw materials selection processes are strictly controlled to insure a uniform, high quality product that is structurally strong, stable, durable and inert, yet also lightweight and insulative. ESC structural grade aggregate is composed of a strong, ceramic, vitreous material encapsulating a system of general non-interconnected pores. Although, the particle density is approximately 1/2 of natural aggregates, this aggregate when used in concretes acheive usual structural strengths.
The term "Lightweight Aggregate" describes a range of special use aggregates that have a relative density considerably below ordinary sand and gravel which were at one time used in almost all concrete.
Lightweight aggregates range from the extremely light materials used for insulative and non-structural concrete (Vermiculite and Perlite, relatively low strength concrete can be made with these aggregates weighing as little as 20 pounds per cubic food) all the way to ES&C used for high performance structural concrete. Since the lightness of these aggregates derives from the air-trapped in each individual particle, the more air that is trapped per particle unit the lighter the weight and the better the insulation, but, conversely, the lower the strength.
In the manufacturing process of ES&C there are few variations in the way the material is prepared for the rotary kiln. In one option the raw material is pre-sized before entering the kiln so that only limited crushing after burning is necessary. Still another variation consists of extruding or pelletizing fine raw material as a means of pre-sizing the raw kiln feed. Combinations of these variations are found throughout the industry.
Although statistics are not available, it is estimated that expanded shale, clay or slate aggregate produced by the rotary kiln method is used for more than 95 percent of the structural lightweight concrete placed today.