Low carbon bio-based building materials from organic waste. A closed-loop production model within circular neighborhoods

75% of natural resources consumption occurs in cities, which produce 50% of global waste and 60-80% of greenhouse gas emissions (EMF, 2019): a circular city would allow a 10-fold CO2 reduction, cutting emissions related to building and energy production (ICESP, 2019). In this perspective, the scale of the circular neighbourhood is relevant: an eco-district in terms of energy efficiency and use of renewable sources, but structured with attention to all resource flows and oriented towards zero-waste. At the neighbourhood scale, the organic waste stream represents a significant share of the overall waste production: residual biomasses, produced both within and near the eco-district, are a strategic supply basin for various purposes, with the dual advantage of saving on waste disposal operations and gaining energy, biofuels, bio-materials and bio-products. In particular, organic waste can be used in the production of bio-based building materials in several applications: partial replacement of inorganic elements with organic components; total replacement of inorganic elements with organic components; replacement of petrochemical coatings with biochemical and bioaromatic components; design of new products based on organic elements also in interaction with inorganic elements in composite products. In this sense, the use of bio-based building materials represents an important opportunity to reduce the impacts of construction materials (Ecorys, 2014; EMF, 2015). This contribution systematises the outcomes of four researches: the first, of national relevance (PRIN 2017), working on key enabling technologies for the built environment with a view to climate mitigation, opened to a subsequent research (PON 2014-2020), which specifically addressed the relationship between climate neutrality, green technologies and circular communities and developed a framework of integrated strategies for circular neighbourhoods’ design. Related to this research are two ongoing activities. One is aimed at investigating the contribution of a circular and local management of the organic waste stream to the transition towards climate neutrality at the neighbourhood scale. The second research line investigates in particular the potential of using organic waste in the production of low-carbon bio-based and hybrid (organic and inorganic) building materials, within a local closed-loop production model. The objective of the integrated research lines is to combine decarbonisation and circularity goals, through a multi-scalar life-cycle design approach, by identifying the most innovative applications for organic waste in a 'zero km' production of building materials and components, with a focus on the interactions, at the end of life, of organic and inorganic elements. The research lines adopted different methodologies, in distinct key steps: interconnected literature reviews; analysis of numerous international best practices at the neighbourhood scale; analysis of the main resource flows within neighbourhoods; study on the main types of biomass produced in and around the neighbourhoods, and of collection, transformation and reuse technologies; in-depth study of the reuse of organic waste for the production of bio-materials for construction; selection and systematisation of case studies of innovative architectural and design products made from organic waste; definition of a closed-loop production model for low-carbon bio-based materials applicable to the neighbourhood scale in relation to the context (urban/provincial). Decarbonisation, in such a model, first envisioned in the Circular Amsterdam project (Circle Economy, TNO, Fabric, 2016), is achieved both by reducing emissions related to the disposal of organic residuals and by cutting CO2 in the local production of bio-based materials/products compared to traditional production systems of the equivalent fossil/non-renewable materials.