Soils from scratch; creating value from construction and demolition fines.

Vast quantities of construction and demolition (C&D) wastes are generated annually during large civil engineering projects. Larger sized material is neatly repurposed as aggregates, but smaller ‘fines’ are often landfilled at great effort and cost. However, these fines (typically < 10mm particle size) are ideally suited to the creation of technical substrates and soils. Mineralogically such fines can differ from ‘natural soils’, for example, by the presence of elevated concentrations of gypsum, derived from plaster. However, they often also contain substantial volumes of topsoil and, as such C&D fines often prove fertile and viable as soils or soil forming materials.

Figure 1: C&D greenwaste compost being used as a growing media.

In urban areas, soil sealing - where impervious surfaces cover natural soils, effectively halt all ecosystem services that the soils they cover provided. The application of soils in raised beds and planters is gathering favour for greenspace creation, microclimate climate regulation and associated biodiversity gains in areas of sealed ground. Since C&D fines are generated primarily in urban areas, research has been undertaken to logically utilize these fines close to their source, together with urban organic wastes such as green and food waste compost, to create ‘technosols’. Making and applying soils and substrates in this way can effectively reduce waste transportation and disposal, and associated carbon emissions, whilst providing urban areas with some of the functions that lost soils used to provide.

Figure 2: Natural topsoil compared to C&D greenwaste compost.

Initial trials published in the journal Agronomy demonstrate that mixtures of C&D and greenwaste composts (Figure 1) are viable plant growth media, with biomass yield and rooting densities similar to, or exceeding those of, ‘natural’ topsoil (Figure 2). Such trials lead to the tantalizing prospect of creating ‘designer soils’ by choosing base materials with idealized nutrients and pH. Such ‘technosols’ may also offer an alternative to cropping high grade agricultural land for bioenergy crops, where biproducts, such as anaerobic digestates and composts, are used to form new technosol batches.

For more information on the results of this trial see; https://doi.org/10.3390/agronomy11040649