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This paper reports the development of green bio-composite mortars, obtained reusing spent coffee ground (SCG), an agri-food residue, in the light of the Circular Economy approach. This process can boost the sustainability in Construction and proposes an alternative to SCG disposal in landfill, potentially dangerous to humans and the environment. For the first time, specimens were produced and compared using different blends of conventional hydraulic binders (ordinary Portland cement and natural hydraulic lime); SCG partially substituted sand (up to 15 wt.%, with a 2.5% increment) for the aggregate mix. The manufacturing process was performed at ambient conditions (20°C, 65% RH) resulting highly sustainable, and consisted of simple operative steps reproducible in a real building site. The prepared mixes were fully characterised to assess their technological potentials in construction. Morphology analysis, performed by Scanning Electron Microscopy (SEM), showed SCG addition led to a more compact structure. Considering the functional properties, results widely range on binder blend base, offering various concrete applications; it was observed that with SCG addition, despite a decrease in the bulk density (up to 26%), the mechanical performance still remained suitable for proper masonry applications, according to the relevant standards (class of resistance M2.5-M10). A light water imbibition increase was registered (about 5%) while a significant decrease of the capillarity index was seen. Moreover, a robust thermal conductivity reduction was observed (up to 72%), making the mortars highly suitable for energy-saving uses in building. Finally, a reduction in the manufacturing cost (up to 8%) was calculated, granting significant financial saving in light of the industrial symbiosis. These encouraging results showed that reusing SCG not only provides numerous benefits to the overall building performance and management but it is also a valid alternative to usual SCG disposal. The high amount of reused bio-waste significantly widens the knowledge of greener and more efficient building sector, making the prepared mortars promising candidates for the Minimum Environmental Criteria certification, in light of the recent EU regulations, and in line with the principles of the Circular Economy.

Spent coffee ground, the residue obtained from the brewing process, is the primary unavoidable (inedible) waste from the coffee consumption. As coffee production and beverage consumption are increasing worldwide, a more sustainable waste management is required since the usual disposal in landfill is a liability to both humans and the environment. This paper is aimed at showing a possible alternative reuse of coffee ground wastes in novel green building materials intended for thermo-plastering applications in construction, in a circular economy context. Coffee waste was used in various percentages (up to 17.5%) to assess the engineering performance of the produced bio-composite mortars. The main results showed that just a little amount of coffee waste determines a bulk density decrease up to 15.4% (making the products comparable to a structural lightweight conglomerate or a light plastering mortar), an extensive drop in mechanical performance (still maintaining acceptable values for the considered plastering application) and in thermal conductivity (up to 47%). Moreover, a multi-criteria analysis, not only able to consider the materials performance, but also aspects related to the environmental impact and the economic drawback, has been implemented resulting that the preferable mix would contain 10% waste. Finally, preparatory virtual energy simulations were implemented to analyse the performance of that mix in a simplified architectural model, revealing a sufficient energy improvement and a more efficacy in cold climates. All considering, coffee waste can be effectively reused to manufacture green bio-composite thermo-plasters with adequate energy performance considering the main requirements of a building application published