After the incorporation of polypropylene fibers, impermeability of concrete progress, chloride lax coefficient increases, carbonation depth increases, which is not the same because the media is not the same in the transmission mechanism is not the same aperture. Water in the concrete pore size greater than 100nm pores transmission to soak mainly because of the capillary effect after filling water pressure water soaked fit Darcy equation; when the diameter less than 100nm, water has been unable to constitute viscous flow (layer in the hole Perhaps the turbulent flow), the media is a relocation of a molecular ion perhaps, that because of lax adsorption. When a certain ion concentration difference exists in the concrete table can move along at a low concentration of high concentration at the pore walls to lax mainly fit Fick law. Incorporation of fiber cut off water permeable pores larger path, but adds fiber and cement paste interface is less than 100nm pores, chloride and carbonation coefficient lax add depth that is due to this, so aggressive media the existence of an environment is not conducive to maintaining the use of synthetic fiber reinforced [3].

Polypropylene fiber and composite swell agents use:

    Polypropylene fibers and cuts and swelling agents can avoid concrete cracking, impermeability of concrete progress talent, but they are different. Mechanism is not the same: the vast majority of domestic and foreign agents are swollen sulphoaluminate type, it is usually 8% to 12% equivalent alternative cementitious materials. Swelling agent with cement hydration reaction constitutes swell ettringite crystals in steel and ortho constraint to establish in concrete 0.2 ~ 0.7MPa preload stress, improved stress conditions concrete progress their crack function; ettringite Stone has filled, the effect of blocking the pores, improves the hole layout of concrete, down the total porosity and permeability function of concrete progress. These results are mainly through chemical effects occur, while polypropylene fiber is entirely physical effects to cut through concrete cracks, progress impermeability caliber.

    Construction conditions are not the same: swelling agent for the maintenance conditions are very harsh, as long as the moist environment to achieve better talent cracking, impermeability effect, if poorly maintained and even then may not see its effect Destructive Enthusiasm; and polypropylene fiber for construction and maintenance No extra demand conditions, the use of very convenient. Time is not the same as promoting effects: swelling agent without help avoid cracking the plastic concrete, hardened concrete progress can only crack function. The swelling usually normal concrete at 1 ~ 7d wet maintenance time, should develop swelling rate of 70% to 80%, in order to compensate for self-generated concrete and cement hydration heat shortening occurs shrink; 7 ~ 28d of the swelling rate forward 20% to 30% in order to compensate for shrinkage of the concrete. The polypropylene fiber is able to reduce and avoid cracks in concrete and plastic settlement cracks that have been hardened concrete crack resistance dedication not only from a limited slack and impedance effects.

    So on the basis of polypropylene fibers and swelling characteristics of the respective agents they use complex, concrete progress can not crack the same time function, reduce and avoid the occurrence of cracks in concrete, in order to ensure project quality.