Considering the different properties of fiber itself, its microstructure is also rather different. The macroscopic and microscopic morphology of some different fibers are listed below.

The specific density and water absorption of geopolymer composites decrease with the presence of polypropylene fiber, which is mainly attributed to the microstructure enhancement and density increase of the matrix. These effects are directly related to the fiber content, not the fiber type[24]. Natural fibers improve the performance of concrete, cover the similarity between natural fibers and cement matrix, and may reduce the pumpability of shotcrete because they reduce the workability, a key factor in shotcrete’s use in construction[25].