Recycled content in road underlay material

Agata—Material may be considered “recycled content” if it meets all of the ISO-14021 criteria:
. . 1. It is “material that would have otherwise been disposed of as waste or used for energy recovery but has instead been collected and recovered [reclaimed] as a material input, in lieu of new primary material, for a recycling or a manufacturing process.”
. . 2. It is “material that has been reprocessed from recovered [reclaimed] material by means of a manufacturing process and made into a final product or into a component for incorporation into a product.
. . 3. It is either pre-consumer material (“material diverted from the waste stream during a manufacturing process,” excluding “reutilization of materials such as rework, regrind or scrap generated in a process and capable of being reclaimed within the same process that generated it”) or post-consumer material (“material generated by households or by commercial, industrial and institutional facilities in their role as end-users of the product which can no longer be used for its intended purpose,” including “returns of material from the distribution chain”).

I assume that, by “coal slate,” you mean, “coal refuse.” As I understand it, coal deposits usually occur layered within other rocks. The rocks are mined and then broken apart to extract the pure coal, leaving behind tons of rock fragments. Mining companies usually dispose of this “refuse” in “gob piles,” in “slate dumps,” and in pits behind dams. If, by reprocessing the material into subbase for paving and concrete, your project diverts the material from its normal waste stream, the material may qualify as pre-consumer recycled content.

The biggest challenge may be that coal refuse often contains traces of coal, sulfur, heavy metals, and acids that can leach out to contaminate soils and groundwater or to interact corrosively with adjacent materials. Before using such materials, your project should consider and address all environmental ramifications.