The geological significance of novel anthropogenic materials: Deposits of industrial waste and by-products

Industrial wastes and by-products are increasingly (re-)used as filling material in constructions. To enhance awareness among the geological community of the growing and widespread occurrence of deposits that contain these “novel anthropogenic materials”, this paper reviews three volumetrically important materials: (1) ash remaining from the incineration of household waste (Municipal Solid Waste Incineration bottom ash), (2) slag from steel production, and (3) the stony aggregate fraction of construction and demolition waste. We review their origin, main geochemical weathering reactions, and influence on the natural geogenic environment. These materials have properties that set them apart from the geogenic materials that they replace and overlie. They are formed under high-temperature conditions, are thermodynamically unstable, and may exhibit physical and chemical changes on relatively short timescales, an aspect relatively new for mapping geologists. Because knowledge of deposits in the shallow urban subsurface is increasingly important for urban planning, more articulation and detail in the classification of novel anthropogenic materials is necessary.