ESCS Lightweight Aggregate

Rotary kiln produced expanded shale, clay and slate (ESCS) structural lightweight aggregate is an environmentally friendly product that saves material, labor and transportation costs, and improves the functionality and service life of concrete, asphalt, geotechnical projects and landscape products and applications. Additionally, using lightweight aggregate will lower the overall energy consumption of structures, thereby reducing the associated life cycle costs throughout the structure’s useful life. These benefits support sustainable development and contribute to projects becoming LEED® certified.

Product Evaluation

The first step toward designing sustainable structures is product evaluation and selection. How is the product made? Is the product an efficient use of the raw materials? How will the product be used and how will it perform? What happens to the product when its useful life is over?

Manufacturing: ESCS is a ceramic material produced by expanding and vitrifying select shales, clays, and slates in a rotary kiln. The process produces a high quality ceramic aggregate that is structurally strong, durable, environmentally inert, low in density, and highly insulative. It is a natural, non-toxic, absorptive aggregate that is dimensionally stable and will not degrade over time.

Lightweight aggregate particles have a low-particle relative density because of their cellular pore system. The cellular structure within the particles is developed by heating certain raw materials to incipient fusion. At this temperature, gases are evolved within the pyroplastic mass, causing expansion, which is retained upon cooling. Strong, durable, lightweight aggregates contain a uniformly distributed system of pores that have a size range of approximately 5 to 300μm, developed in a continuous, relatively crack-free, high-strength vitreous phase. Pores close to the surface are readily permeable and fill with water within the first few hours to a few days of exposure to moisture. Interior pores, however, fill extremely slowly, with many months of submersion required to approach saturation. Interior pores are essentially non-interconnected and a small fraction remain unfilled after years of immersion (ACI 213R-03).

The ceramic nature of the aggregate insures the product is inert and highly resistant to degradation, thereby providing concrete with a key component that has stood the test of time. These same properties also render the product environmentally benign in that it can be reused as fill or base material. In many applications, the aggregate is blended into soils that benefit from the water absorbing characteristics of its porous nature, which provides aeration as well as a nutritional and moisture buffer that help to modify climate and environmental conditions.

No single description of the ESCS aggregate material is all-inclusive, and the reader is urged to consult the individual ESCS manufacturers for physical and mechanical properties of their lightweight aggregates, as well as for the proper use in the various aggregate applications.

Efficient raw material usage: The increased usage of processed lightweight aggregates is evidence of environmentally sound planning, as these products have lower transportation requirements and use raw materials that have limited structural applications in their natural state. This reduces demands on finite resources of quality natural sands, stones and gravels.