Polypropylene fiber has two main functions in concrete:
1) Prevent plastic shrinkage cracks in concrete. During the setting and hardening process of concrete, the surface water loss will lead to plastic shrinkage and cracks. The concrete mixed with polypropylene fiber can prevent this kind of cracks.
Because the elastic modulus of polypropylene fiber is lower than that of hardened concrete, the improvement of crack resistance (cracks caused by temperature stress or mechanical load) of hardened concrete is limited, the improvement of tensile and flexural strength is not large, and the toughness of concrete is improved to a certain extent.
2) Improve the fire resistance of hardened concrete. Under the action of high temperature, polypropylene fiber will soften and burn first, forming many holes in the concrete, and the water vaporized by high temperature in the concrete can be discharged along these holes to prevent the water vaporization from forming internal high pressure and causing the concrete to burst, so as to greatly improve the fire resistance time and fire resistance rating of the concrete.
