Geopolymer Degradation by Oxalic Acid: A Kinetic Study

The increasing need for sustainable construction materials has prompted research into alternatives to Ordinary Portland Cement (OPC), a major contributor to global CO₂ emissions. Geopolymers, synthesized via alkali activation of aluminosilicate precursors such as metakaolin and fly ash are a promising alternative reducing up to 80% carbon emissions. However, their long-term durability under aggressive chemical environments, particularly against organic acids, remains insufficient. While mineral and inorganic acid resistance has been studied, the impact of naturally occurring organic acids like oxalic acid (Ox) —commonly found in soils and organic-rich sediments—has received limited attention. Ox is known to chelate metal ions and alter mineral phases, potentially affecting the integrity of geopolymer matrices. This study investigates the degradation behavior of geopolymers under continuous exposure to Ox (0.2, 0.4, and 0.6 M) at 25 °C using a flow-through reactor. Mass loss over time was monitored to determine reaction kinetics, while SEM, FT-IR, XRD, and EDS analyses were conducted to evaluate microstructural and chemical changes. Results revealed significant alterations in geopolymer structure due to Ox exposure, providing key insights into their vulnerability to organic acid attack. These findings remark the importance of considering organic acid interactions in the long-term performance assessment of geopolymers.