# Constructed Technosols: A Strategy toward a Circular Economy
## 4 Waste Materials in Technosols Design
### Aging  
The chemical-physical properties of the soil can evolve over time modifying the plant growth and ecosystem functions. Porosity in a soil depends on packing density, particle shape, and size distribution and cementing, and it can change in the early stages of soil evolution [117], particularly due to climate and biological activity [118]. A study by [PERSON] et al. [105] reveals the importance of studying the pedogenesis of Technosols, and in particular the soil structuration. They investigated for two years the pore system evolution of a constructed soil obtained by stratifying green-waste compost, paper-mill sludge, and thermally treated industrial soil. They quantified macro- and micro-porosity parameters with image analysis techniques: pores number, their surface area, perimeter, distance, volume, eccentricity, index of connectivity, equivalent diameter, and shape factor. After two year of experimentation, the percentage of macro-porosity and the mean pore surface area decreased significantly, whereas the pore number raised, indicating soil compaction. This phenomenon causes some negative effects, such as a reduction of water infiltration and drainage and an increase in bulk density. To develop accurate models to predict the evolution of soil structure, the authors proposed also to consider in addition the biological parameters, such as biodiversity, fauna abundance, plant and microbial activity [105].  
This approach has been used in the study by [PERSON] et al. [40], focused on the evolution of fauna colonization in constructed technosols. Macro and meso fauna plays an important role in the evolution of the structure of soils, as it is considered one of the main actors in the ecologic rehabilitation of disturbed soils [119]. They applied two different constructed technosols in the urban area of Roubaix, France. One prepared with a top horizon of silt, a middle layer of fine backfill and a bottom layer of coarse backfill; in the second one, green waste compost was added to the top layer. Different management practices were conducted to establish the most favorable for the fauna development. In all soils, the colonization by macrofauna was observed to be relatively slow, as expected in disturbed soils. The taxa abundances and specific richness increased over the time and the establishment of herbaceous cultures, such as flowering meadow and lawn, showed a positive effect on the fauna development, with a greater abundance and richness of taxa. The closeness of one plot with a railway hedgerow (a potential ecological corridor) involved a more intense fauna colonization, with an abundance of Collembola and earthworms. Such models, able to describe and predict the evolution of the soils, surely have extreme utility in designing sustainable strategies for soil regeneration and assess pollutants spreading in restored sites.  
Unfortunately, there is still a lack of competence in the area. For this reason, [PERSON] et al. [120] conducted a study to define a framework to develop models focusing in particular on pedogenetic processes. Technosol evolution plays an important role also in the better understanding of the soil pedogenesis in general. The study revealed that the evolution of these artificial soils is very similar to the natural soils, but pedogenetic processes occur faster in unusual assemblages with very high spatial heterogeneity. To model the Technosol evolution, they proposed to couple tridimensional, multi-scale, and dynamic representation with mathematical model approaches (like partial different equations) with the addiction of plant related processes [120].