Discontinuous organic synthetic fibers mainly play the role of crack resistance and toughening in the mortar. Polypropylene fibers have the characteristics of small density, small diameter, and low Young’s modulus. When they are uniformly distributed in the mortar at a low volume rate, they can obtain obvious crack resistance. Cement products, components or buildings and various plastering mortars, in the process of setting and hardening, due to the change of microstructure and volume, many cracks will inevitably occur, and with the change of shrinkage, temperature and humidity changes, external load changes and expands, so that the cement matrix gradually deteriorates, and the instant brittle fracture of the cement matrix causes the matrix to fail. If the fibers are distributed uniformly and disorderly in the cement mortar matrix, the fibers will restrict and hinder the expansion of micro-cracks when the cement mortar is subjected to external force or internal stress.

Hundreds of millions of fibers are crisscrossed, isotropic, and evenly distributed, just like hundreds of millions of “micro steel bars” are implanted in the matrix of cement mortar, which makes the propagation of cracks blocked by the fibers, and the micro cracks cannot be crossed. These fibers continue to develop and can only detour along the interface between the fiber and the cement matrix. The generation and propagation of cracks require a certain amount of energy. The energy generated by the stress caused by various reasons in the mortar matrix will be exhausted due to the existence of a large number of fibers. Therefore, the existence of a huge number of fibers not only consumes energy, but also relieves stress, thereby preventing the further development of cracks and playing a role in blocking cracks.

The toughness of fiber concrete or mortar is closely related to impact resistance. The low content of synthetic fibers can significantly improve the impact resistance of concrete or mortar.