Novel green bio-composite geopolymeric thermo-plasters for innovative building applications: upcycling spent coffee ground

This study proposes the reuse of spent coffee ground and biomass fly ash in the development of green geopolymeric thermo-plastering for innovative building applications. The former waste is the major residue of the brewing process, that is usually used as fertilisers or disposed of in landfill with extreme harmfulness for the natural environment. The latter is an industrial waste generated during the Kraft paper-pulp process, that is usually landfilled. The mortar is produced with a combination of metakaolin (30 wt.%) and biomass fly ash (70 wt.%), and natural siliceous sand filled with spent coffee ground (up to 17.5 wt.%). The high amount of reused waste makes the material an optimum candidate for the Environmental Minimum Criteria (CAM) assessment as ruled by the National Action Plan on Green Public Procurement. The overall manufacturing process occurred at ambient conditions (20 °C, 65% RH) contributing to the materials sustainability. 28-days cured specimens were analysed to assess the material engineering properties and delineate the possible applications in construction. Finally, virtual energy simulations were implemented to study the possible energetic performance benefits in a simplified building model. The major results are that the used wastes considerably improve the technological material performance making it suitable for effective use in construction. While the slurry workability is significantly affected by the waste introduction, and the mechanical resistance is still high, the thermal conductivity outlines a possible energy application. All considering, coffee waste can be effectively reused to manufacture green bio-composite materials with satisfactory performance considering the main requirements of a building making them exploitable in various applications in construction, especially in energy-saving functions, in line with the European directives towards zero-energy building.