Porous geopolymers for thermal insulation: an environmental assessment by LCA methodology

Geopolymers have been extensively studied for their versatility in the construction sector and can be tailored for specific applications by incorporating fillers and partially reactive materials derived from industrial waste streams. In this context, it is essential to assess such systems using well-established methodologies such as Life Cycle Assessment (LCA), to identify potential trade-offs in environmental impact and support the adoption of more sustainable manufacturing practices. This study applies the LCA methodology to an experimental system for producing a porous, metakaolin-based geopolymer paste incorporating ashes derived from the combustion of both vegetal and animal biomasses. The resulting blocks were designed for thermal insulation applications in the construction sector, serving as potential substitutes for traditional inorganic insulation materials, such as autoclaved aerated concrete (AAC). The life cycle inventory (LCI) accounts for all material and energy inputs required for geopolymer production at the laboratory scale, as well as direct emissions and waste flows generated throughout the process. Where necessary, specific datasets were developed for materials not directly included in existing LCI databases (e.g., metakaolin, potassium silicate, biomass ashes). To enhance the representativeness of the production process, inventories were also scaled up to an industrial level using established frameworks and large-scale LCA modeling approaches [1]. The environmental performance of the scaled-up porous geopolymer was then compared to that of a conventional AAC block, adopting a cradle-to-grave approach with a functional unit that ensures equivalent thermal insulation performance. Consistent with previous LCA studies, our results indicate that the alkaline activator (i.e., potassium hydroxide and potassium silicate) is the primary contributor to the overall environmental impact, followed by metakaolin production. Although the production process has been optimized compared to previous studies [2], eliminating high temperature treatments of unburned residues, additional impacts arise from direct energy consumption during mixing, drying, and consolidation. The incorporation of biomass ashes as a partial replacement for metakaolin was found to lower the overall environmental footprint of the geopolymer block. However, a direct comparison with AAC highlights the need for further impact reductions to make geopolymers a truly competitive alternative from an environmental perspective. The findings of this LCA study can support the adoption of more sustainable practices in geopolymer production, while also highlighting the potential benefits of incorporating industrial waste streams into value-added building materials. This study was funded under the National Recovery and Resilience Plan (NRRP), Mission 04 Component 2 Investment 1.5 – NextGenerationEU (Call for tender n. 3277 dated 30/12/2021 - Award Number: 0001052 dated 23/06/2022).