Influence of spent catalyst (Ecat) on the partial replacement of metakaolin in geopolymers

mechanical and microstructural properties

Abstract

The production of Portland cement generates significant environmental impacts, accounting for approximately 8% of global CO₂ emissions. As an alternative, geopolymers allow for the incorporation of industrial waste, notably the spent fluid catalytic cracking (SFCC) catalyst, derived from petroleum refining and currently destined for landfills. This study evaluated the physicochemical characteristics of SFCC and its potential for application in geopolymer matrices, in which metakaolin was partially replaced by contents of 0% (Ref), 10% (SFCC 10%), 20% (SFCC20%), 30% (SFCC 30%), and 40% (SFCC 40%). The influence of these contents was evaluated through water absorption and compressive strength tests, X-ray diffraction, and thermogravimetry. The results demonstrated that SFCC possesses suitable characteristics for synthesis, including a high surface area (105 m²/g) and a rich composition of SiO₂ (36.5%) and Al₂O₃ (51.2%). Formulations with SFCC maintained mechanical strength equivalent to the reference sample and exhibited an increase in the amorphous phase proportional to the addition of the waste. In the thermogravimetric analysis, the 40% sample showed the highest total mass loss (17.4%), indicating that thermal stability may be compromised at higher contents. Overall, formulations with up to 20% SFCC maintained satisfactory performance.