Bamboo, basalt, glass, and polypropylene fiber-reinforced metakaolin based geopolymers: a comparative study

Geopolymers usually exhibit poor tensile and flexural strengths due to their brittleness and ceramic features, which are easy to cause catastrophic failure limiting their applications. Fibers can be incorporated into geopolymers to improve flexural properties and fracture toughness. In this work, the effects of four types of fibers including bamboo, basalt, glass, and polypropylene (PP) on bulk density, apparent porosity, water absorption, and compressive and flexural strengths of geopolymers were investigated based on alkali-activated metakaolin. The compressive strength of the composites decreased with fiber content. The flexural strength increased under optimum fiber content, and the optimum content of bamboo, basalt and glass fiber was 1%, while that of PP fiber was 0.8%. Compared with pure geopolymer, the maximum improvements in flexural strength were 35.61%, 16.25%, 15.76%, and 11.41% for basalt, glass, bamboo, and PP fiber-reinforced composites, respectively. Parameters such as thermal stability, chemical composition, and amorphous phase of geopolymers were investigated. The fiber distribution and fiber-matrix interface were observed via optical and scanning electron microscopy. The results contribute to our knowledge of fiber-reinforced geopolymer composites, and offer guidance for further investigation of bamboo fiber reinforced metakaolin-based geopolymer.