2.Role of Fibers in Geopolymer Composites

Steel fibers, glass fibers, basalt fibers, polypropylene fibers, and blended fibers are all fibers currently used in concrete. Given that geopolymers and cement are both brittle materials, fibers play similar roles in geopolymers, mainly the following roles in the polymer such as nano filling and crack bridging. The key factors to be considered while selecting fibers for reinforcement modification of cement or geopolymer composites include: (1) compatibility of material properties with application; (2) adequate fiber-matrix interaction to transfer stress; and (3) optimal aspect ratio to ensure effective post-cracking behavior. The addition of fibers affects the fluidity and mechanical properties of viscous carbides, which depends on the surface properties, shape, types and flexibility of the fibers[8].
At present, the fibers used in geopolymers can be roughly divided into the following three categories, i.e., inorganic fiber, natural fiber and synthetic fiber. To be specific, inorganic fiber mainly includes steel fiber, glass fiber and basalt fiber; natural fiber mainly consists of plant fiber, animal fiber and mineral fiber; and synthetic fiber mainly refers to polyethylene, polypropylene, polyvinyl alcohol fiber, etc. Table 1 lists the main characteristics of common fibers added to geopolymer.
Table1 Characteristics of common fibers