Alkali treatment of bamboo fibers improves the mechanical properties of metakaolin geopolymer

Abstract

Metakaolin geopolymers have limited applications owing to high brittleness. To address this issue, herein, metakaolin geopolymer composites were fabricated by modifying the surface of bamboo fibers with NaOH solution. The mechanical properties of these composites were examined by varying the alkali-treated bamboo fiber content (1%, 3%, 5%, and 7%) and curing period (1, 3, and 7 days). When the mass fraction of alkali-treated bamboo fiber was 3%, the toughness of the composite material was the best. These composites exhibited higher tensile strength, flexural strength, and uniaxial compression strain at break compared to the metakaolin geopolymer, with increases of 15%, 18%, and 360%, respectively. Compared with the metakaolin geopolymer, the composites underwent plastic fracture instead of brittle fracture. The mineral composition and microstructure of alkali-treated composite materials, metakaolin geopolymer, and bamboo fibers were analyzed using FTIR, XRD, and SEM/EDS. The findings show that (1) after alkali treatment, the surface roughness of the bamboo fiber increased, and the binding force between the fiber and matrix was enhanced by friction retardation and (2) the alkali-treated bamboo fibers effectively bridged, deflected, and hindered the matrix cracks. These findings demonstrate that alkali-treated bamboo fibers considerably enhance the tensile strength of the geopolymers and widen their range of applications.