Activator-related effects of sodium hydroxide storage solution in standard testing of fly ash geopolymer mortars for alkali–silica reaction

• Published in: Materials and structures Vol. 55; no. 1
• Main Authors: Naghizadeh, A., Ekolu, S. O.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 2022; Springer Nature B.V
• Subjects: Alkali-silica reactions; Building construction; Building Materials; Caustic soda; Cement; Civil Engineering; Engineering; Fly ash; Geopolymers; Machines; Manufacturing; Materials Science; Mortars (material); Original Article; Portland cements; Prisms; Processes; Silicon dioxide; Sodium hydroxide; Solid Mechanics; Theoretical and Applied Mechanics; Mortars; Fly ash; Alkali–silica reaction; Geopolymers; Ordinary Portland cement
• ISSN: 1359-5997; 1871-6873
• DOI: 10.1617/s11527-021-01875-8

Sodium hydroxide (NaOH) is used as storage solution in standard testing of Portland cement mortars for alkali–silica reaction (ASR). Various researches also similarly use NaOH storage solution for ASR testing of geopolymer binders. However, NaOH is coincidentally an alkali activator of geopolymers. So, questions arise regarding the potential activator-related effects of NaOH when employed as storage solution for ASR testing of geopolymer mortars. The present study compared the ASR response behaviour of fly ash-based geopolymer (FA-GPC) binder with that of ordinary Portland cement (OPC). FA-GPC and OPC mortar prisms of 25 × 25 × 285 mm size were prepared using highly reactive aggregate, then the mortars were subjected to ASTM C1260 (2014) accelerated ASR mortar bar test, under varied concentrations of 0.5M to 3M NaOH storage solution. Analytical studies were conducted using X-ray diffraction and scanning electron microscopy. Findings showed that ASR expansion of FA-GPC mortars was very low or negligible as expected, while corresponding OPC mortars gave high expansion behaviour. Indeed, the 14-day expansion of OPC mortars in standard 1M NaOH storage solution, was 2.0 to 2.5 times greater than that of FA-GPC mortars. But upon increase in concentration of the storage solution beyond 1M NaOH, FA-GPC mortars showed steady corresponding growth in expansion, owing to alkali attack rather than ASR. Evidently, NaOH storage solution being itself an alkali activator, causes secondary geopolymerization with a constant risk potential that may or may not lead to disruptive alkali attack, depending on the solution’s concentration.