Synthetic fiber for three-dimensional reinforcement of a cement product

A synthetic fiber for three-dimensional reinforcement of a cement product characterized in that is represents a coaxial core-coat fiber wherein the core comprises a thermoplastic polymer and one or more substance(s) initiating formation of fibrillar crystals in an amount of 0.5 to 3% of total weight of the core and/or one or more high-molecular polymer(s) and/or copolymer(s) in an amount of 3 to 30% of total weight of the core, and the coat comprises either

• a) a thermoplastic polymer resistant to environment having pH>11 and one or more hydrophilic and/or surface active substance(s) in an amount of 3 to 30% of the total weight of the coat, or
• b) a thermoplastic polymer resistant to environment having pH>11 grafted with active or unsaturated monomers of one or different kinds constituting 3 to 25% of the total weight of the coat,
• wherein the surface tension of the coat is at least 45 mN/m, and
• wherein the substance initiating formation of fibrillar crystals in the core represents one or more finely dispersed minerals selected from oxide, nitride, carbide and silicate, and has a mean particle size which is 10 to 50 times smaller than the cross-sectional area of the fiber, and the high-molecular polymer(s) and/or copolymer(s) is selected form polyvinyl alcohol and ethylene vinylacetate having vinylacetate content of not more than 15 wt. %.