The polypropylene fibers are hydrophobic, which do not absorb the water, and are non-corrosive. Moreover, the polypropylene fibers have excellent resistance against alkali, chemicals and chloride and have low heat conductivity. By these characteristics polypropylene fibres have therefore no significant effect on the water demand of the fresh concrete. They do not intervene the hydration of cement and hence do not influence unfavorably the effects of all constituents in the concrete mixture.