The following info pertains to usual monofilament or fibrillated polypropylene fibers (not the structural ones).
Use polypropylene fibers….
1) For the reduction of plastic shrinkage cracks. This phenomenon evolves mainly during the first 6 hours after concrete or mortar casting.
2) For the reduction of plastic settlement cracks (evolving mainly the first 3 hours).
3) As a secondary, triaxial reinforcement to intercept early crack formation.
4) For the production of thin section building elements.
5) For better impact resistance and shattering behavior.
6) To increase abrasion resistance in concrete floors. Polypropylene fibers reduce bleeding and surface cracking. Much dusting is produced by crack edges’ fracturing.
7) In combination with air entraining agents to improve concrete’s behavior to freeze-thaw cycles. The synergistic effect of these materials is powerful!!
8) To give extra protection against carbonation and reinforcement corrosion.
9) For longer life and higher concrete durability.
10) To reduce explosive spalling in case of fire e.g. in tunnels.
11) To reduce rebound of sprayed concrete (increases cohesiveness).
12) To reduce cracking and water permeability in screeds and mortars.
Don't use polypropylene fibers...
(1) for less water permeable concrete. PP fibers could only marginally contribute to this. To reduce concrete water permeability it's much easier to use:
- a PCE superplasticizer to attain a water-to-cement ratio not more than 0,45
- some pore blockers as for example silica fume
- integral waterproofers based on esters of stearates. These products line concrete pores with hydrophobic substances and reduce intermolecular adhesion forces between pore walls and water.
-integral waterproofers based on proprietary,penetrating salts:crystallization process
(2) to replace any kind of structural steel and rebars. Use only fibrillated fibers of great length (25-40mm) at increased quantities (at least 1,5 Kg/m3) to replace traditional wire-mesh for slabs-on-grade.
Monofilament fibers? Just forget about it!!
(3) to control crack formation due to external stresses
(4) to increase compressive strength
(5) to reduce thickness of slabs-on-grade
(6) to avoid the obligation to abide by proper concrete practices.