Impact of Surface Treatment on the Strengthening of Geopolymer Composites Reinforced with Short Sisal Fibers

This paper presents a first-time investigation into the effects of an eco-friendly sodium bicarbonate fiber treatment on the mechanical properties of metakaolin-based geopolymers reinforced with short sisal fibers. For this purpose, geopolymer composites were initially manufactured by replacing different weight contents (0.5–2.0 wt.%) of aggregate (river sand) with untreated natural fibers. Subsequently, sisal fibers were soaked for 120 h in varying concentrations of aqueous NaHCO₃ solutions (2.5–10 wt.%) to assess the influence of solution concentration on the performance of 2% fiber-reinforced geopolymer composites. All the manufactured composites were characterized through quasi-static compression, flexural, and Brazilian tests. The experimental results revealed that both increasing the fiber content and pre-treating the sisal fibers significantly affect the mechanical response of the geopolymer composites.