Fiber-reinforced cement-based composite materials are a research hotspot in the field of cement-based materials such as mortar and concrete, and are also an effective means to improve the crack resistance of mortar and concrete. Adding various fibers to the dry-mixed mortar is an important means to improve the crack resistance of the mortar, improve the mortar’s anti-burst, freeze-thaw resistance, impact resistance and abrasion resistance, and it is also an important measure to improve the overall performance of the mortar. At present, the fibers that can be used in dry-mixed mortar to improve crack resistance are mainly alkali-resistant glass fibers and organic synthetic fibers such as polypropylene fibers and polyvinyl alcohol fibers. At present, the fiber widely used in mortar is mainly special modified polypropylene fiber with special surface treatment. It is made of high-quality raw materials and the polypropylene fiber with special treatment on the fiber surface can ensure the strength, dispersion and cohesiveness of the material with the cement collective.
Because polypropylene fiber has a wide range of raw materials, low production costs, and good alkali resistance, it is currently widely used in various mortars and various concrete projects to improve the crack resistance and durability of mortar and concrete. The diameter of this polypropylene fiber is usually less than 60 microns and the length is less than 20 mm. The volume ratio of mortar concrete is usually less than 0.1%, which mainly reduces the early plastic shrinkage cracking and settlement cracking of mortar and concrete, and improves the impact resistance of mortar. Due to the small diameter of this fiber, it is often called polypropylene fine fiber or PP fine fiber in the world. At present, there is still a kind of polypropylene coarse fiber with a diameter of more than 100 microns and a length of more than 40 mm in the market, which is also called polypropylene structural fiber. When the volume addition rate of this coarse fiber in concrete is greater than 0.5%, it can play a similar role to steel fiber.