Degradation of Geopolymers by Oxalic Acid: A Kinetic Study

TL;DR

This study examines how oxalic acid degrades geopolymers, a sustainable cement alternative, and highlights the need to consider organic acid effects on their long-term durability.

Contribution

The study provides new insights into the degradation kinetics of geopolymers under oxalic acid exposure, a previously underexplored area.

Findings

Geopolymers showed significant structural changes when exposed to oxalic acid.

Mass loss measurements revealed the reaction kinetics of degradation.

Microstructural and chemical analyses confirmed the impact of oxalic acid on geopolymer integrity.

Abstract

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% of carbon emissions. However, their long-term durability in aggressive chemical environments, particularly when up against organic acids, remains insufficient. While mineral and inorganic acid resistance have 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. The results revealed significant alterations in the geopolymers’ structures due to Ox exposure, providing key insights into their vulnerability to organic acid attack. These findings indicate the importance of considering organic acid interactions in long-term performance assessments of geopolymers.

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