The present study aimed to evaluate the comparative deterioration mechanism of sulfate solution on the fly ash based geopolymer paste (GP) by soaking in 8% Na2SO4 and 8% MgSO4 solutions up to 120 days. X-ray CT, SEM, EDS, XRD, FTIR and TGA/DTG were used to characterize the changes in microstructure and products under sulfate attack. Furthermore, the corrosion solution was also analyzed by ICP-OES and pH analysis. The results showed that Na2SO4 and MgSO4 induced distinctly different deterioration behaviors. After 120 days of immersion, the compressive strength loss rates reached 40.2% and 34.0% in Na2SO4 and MgSO4 solutions, respectively. Na2SO4 exposure mainly caused surface exfoliation and significant alteration of the sodium aluminosilicate hydrate (N-A-S-H) gel structure, accompanied by the formation of analcime-containing phases and salt crystallization. In contrast, MgSO4 exposure promoted the transformation of N-A-S-H gel into magnesium aluminosilicate hydrate (M-A-S-H) gel and induced crystallization-related crack development. Although MgSO4 attack generated more visible cracking, Na2SO4 resulted in greater strength deterioration. These findings indicate that the deterioration of GP in Na2SO4 solution is governed primarily by gel alteration and exfoliation, whereas MgSO4 attack involves both gel transformation and crystallization-induced cracking. The study provides new insights into the sulfate attack mechanisms of fly ash-based geopolymers and supports their durability assessment in sulfate-rich environments.
- Open Access
- Article
Comparative Investigation on Performance of Fly Ash-Based Geopolymer Paste Subjected to Na2SO4 and MgSO4 Solution
Author Information
Received: 09 Apr 2026 | Revised: 19 Aug 2026 | Accepted: 31 Aug 2026 | Published: 14 Sep 2026
Abstract
Keywords
fly ash-based geopolymer paste | compressive strength | sulfate attack | durability | deterioration mechanism
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