ESCS Lightweight Aggregate

ESCS Product

Expanded shale, expanded clay and expanded slate (ESCS) lightweight aggregate is prepared by expanding select minerals in a rotary kiln at temperatures over 1000° C. The production and raw material selection processes are strictly controlled to insure a uniform, high quality lightweight aggregate.

ESCS gives designers greater flexibility in creating solutions to meet the challenges of dead load, energy requirements, terrain, seismic conditions, construction schedules and budgets in today’s market environment. ESCS is an environmentally friendly product that saves material, labor and transportation costs, and improves the functionality and service life of the products in which it is used.

Brief History of ESCS and ESCSI

For over a century, ESCS has been used successfully in more than 50 different types of applications. The most notable among these are lightweight concrete masonry units, high-rise buildings, concrete bridge decks, high performance marine platforms, asphalt bituminous surface treatments, lightweight chip seal, soil conditioner and lightweight  geotechnical fills.

ESCS as manufactured by the rotary kiln process was originally developed in 1908 and patented by Stephen J. Hayde in 1918 as Haydite®. Today, it is available throughout most of the world.

The Expanded Shale, Clay and Slate Institute (ESCSI) was founded in 1952 and is the international trade association for manufacturers of ESCS lightweight aggregate. ESCSI promotes the extensive use of ESCS lightweight aggregate. Based on research and development, educational material is disseminated to all phases of the building industry. The institute works closely with other technical organizations, ACI, ASTM, etc. to maintain product quality, life-safety and professional integrity throughout the construction industry and related building code bodies.


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. ESCS 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).

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.

From a sustainability Perspective

The first step toward designing sustainable structures is product evaluation and selection. This includes manufacturing, raw material, product uses, performance and its recycle potential.

The ceramic nature of the aggregate insures that the product is inert and highly resistant to degradation, thereby providing concrete and other uses with a key component that has stood the test of time. These same properties also render the product environmentally friendly in that it can be recycled and reused in other applications. Additional information is available in the Sustainability Without Compromise section of this website

ESCSI 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 sand, stone and gravel.

For ESCS embodied energy information, read ESCSI Info Sheet #9153, Embodied Energy to Manufacture Expanded Shale, Clay and Slate Lightweight Aggregate (Jan. 2015).