Fibers for use in concrete have been produced from steel, plastic, glass and natural materials in various shapes and sizes. Steel fibers, up to about four percent by volume, increase the "first crack flexural strength" of concrete up to 2.5 times the strength of the unreinforced materials and slightly increase the compressive strength. Splitting tensile strength of mortar reinforced with steel fibers has been reported to be about 2.5 times that of the unreinforced mortar when three percent fiber by volume was used and two times when 1.5 percent was used. Direct tensile strength of mortar reinforced with 1.5 percent steel fibers is reported to be about 1.4 times that of unreinforced material. Steel fibers reinforced concrete has been used for refractories, pavements, overlays, patching, concrete armor for jetties and mine tunnels. Tests indicate that steel fibers can be used in place of stirrups for shear reinforcement of frames, beams and flat slabs. It can also be added in small amounts, such as .25 percent, to selected zones of prestressed concrete to assure a minimum allowable tensile stress to eliminate much of the secondary reinforcement.