Enhancing flexural strength of metakaolin-based geopolymer reinforced with different types of fibers

Abstract

Geopolymers are considered as eco-friendly materials and are used as a cement replacement material. However, geopolymer applications are limited due to its low flexural strength. This work improves the flexural strength of geopolymers by using glass fiber (GF) and bamboo fiber (BF) as the reinforcing materials. Metakaolin (MK) is used as a geopolymer precursor. The mixture of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) is used as the alkaline activator. The results show that the interface bond between the reinforced fibers and the geopolymer matrix influences the flexural strength of the composites more than the inherent strength of fibers. Although the inherent strength of BF is lower than that of GF, BF can improve the flexural strength of MK-geopolymer more effectively than GF. The flexural strengths of MK-geopolymer are enhanced by 1.9, 2.5, and 2.6 times when adding 1%, 3%, and 5% by volume of BF, respectively. The rough surface of BF promotes physical interlocking and bonding between BF and the MK-geopolymer matrix. As a result, the flexural and compressive strength of the MK-geopolymer is enhanced by reinforcing with BF. Conversely, GF exhibits poor bonding with the MK-geopolymer matrix. Consequently, the use of GF as the reinforcing material does not improve the flexural and compressive strength of the MK-geopolymer.