Product Category Rules (PCRs) for Expanded Shale, Clay and Slate Lightweight Aggregate

The Expanded Shale, Clay and Slate Industry is committed to the efficient production and long-term performance of expanded shale, clay and slate (ESCS) lightweight aggregate. The industry and its related association, the Expanded Shale, Clay and Slate Institute (ESCSI), are also committed to the sustainable development of the entire building industry. And ESCSI proves this commitment by being on the forefront of the environmental movement since the late 1990s, when it commissioned its first life-cycle inventory (LCI) of the lightweight aggregate manufacturing process. Since then, the industry has worked to benchmark its environmental performance and continue to reduce its environmental impact through additional research and development of a set of product category rules (PCR) for expanded shale, clay and slate lightweight aggregate.

ESCS Product Category Rules (PCRs)

Anticipating that its members will soon need to produce environmental product declarations (EPDs), ESCSI partnered with UL (as the program operator) to draft a PCR for lightweight aggregate. Along with representatives of ESCSI member companies, the PCR was developed and released in March 2022. PCR development is the prerequisite for creating EPDs. Recognizing that most of the sustainability benefits are derived in the products and construction using the material after it exits the production facility gate, the PCR has been written as a “Cradle to Grave” document. This will lead to cradle to grave EPDs for ESCS.

To access the PCR for Construction Product-Related Products and Services: Part B Expanded Shale, Clay, and Slate Lightweight Aggregate EPD Requirements, please visit to create a free account and download the pdf at no cost.

LCI of Lightweight Aggregate

ESCSI published its first LCI “The Life-Cycle Inventory of the Lightweight Aggregate Manufacturing Process,” by Nisbet and VanGeem over twenty years ago.  Member plants representing an estimated 2.5 million tons of production provided data on energy and materials consumed, and emissions to air, land, and water. Nisbet and VanGeem conducted the study according to the SETAC guidelines, and reported results per average ton (2000 lb.) of lightweight aggregate produced. ESCSI updated the study in 2006, 2022, and 2023 and published Product Category Rules (PCR) by ASTM International in 2015 and UL in 2022.

The 2023 production survey represents 3.175 million tons or nearly 4.73 million cubic yards of processed materials. The 2023 surveyed energy and emissions indicate significant declines due to continuous plant improvements and enhanced process technology efficiencies. An in-progress lifecycle assessment (LCA) and the following industry-average environmental product declaration (EPD) will report cradle-to-grave and beyond footprints for ESCS aggregates and applications (expected 2024). Predefined scenarios are available in the PCR of ESCS conducted by UL in 2022.

For additional information, see ESCSI Info Sheet #9153-23, Environmental Footprints for the Production Process of Expanded Shale, Clay, and Slate (ESCS) Lightweight Aggregate.

Comparison Study of Embodied Energy

Walter P. Moore completed a study in 2012 that compared the embodied energy in the structural system of a steel-framed building with lightweight concrete (LWC) floor slabs on composite steel deck to the same system using normalweight concrete (NWC). Four structural systems were compared, and all the systems had the same floor acceleration; fire rating; and live, wind and seismic loads.

This study only included the embodied energy of the buildings’ structural materials. It excluded any transportation energy impacts as well as the embodied energy in the building envelope (or other systems).

After performing the structural design for each of the building scenarios, a material inventory was created. For the concrete mixture proportions, Walter P. Moore used aggregated data from historical concrete mixture proportions used in its practice across the U.S. Energy intensities of the structural materials were taken from the Inventory of Carbon & Energy, version 2, by Hammond and Jones, which reports embodied energy of materials from a cradle-to-gate basis.

The results showed that one of the LWC scenarios had the lowest total embodied energy at 10,520 MMBTU, while the NWC scenario had a total embodied energy of 10,660 MMBTU. The study found that the energy required to produce LWA was offset by the following:

  • the reduced dead load of the scenario
  • the reduced concrete volume due to improved fire performance
  • thinner steel decks for a given beam spacing due to reduced weight of the concrete floor

Product History

The sustainability movement has created a shift in attitudes and lifestyle awareness that has caused the building industry to evaluate itself from a green perspective. When the ESCSI looked at the uses and manufacturing of ESCS lightweight aggregate from a green perspective, we were pleasantly surprised.

Lightweight aggregate is an environmentally friendly product with unique features that has been successfully used for well over two millennia, with rotary kiln produced ESCS in widespread use for the past ninety years. It has been used in a multitude of applications that contributed to the sustainability of the site and structure long before the current green movement came to the forefront.