With the addition of polypropylene fiber in the mixture of concrete it enhances the toughness and tensile strength. When concrete is by itself it has the tendency to be very brittle especially in the area of a tensile test which is where the fibers come into play to build in where regular concrete lags, which can increase the compressive strength to a dramatic level.
In coastal areas there is a high concentration of chloride ions from the salty air, this creates corrosion with the steel product which produces rust as a result. This rust has the capacity to expand four to ten times larger than the iron causing a large expansion which makes cracks and voids. Polypropylene fibers now are underway in replacing the reinforcing steel in concrete, which has a much greater strength and can reach up to 20k psi.