Concrete needs more investigations and development to improve its properties and provide it high performance to resist impact loads, penetration and perforation which resulted from projectiles of modern destructive weapons, which affect many military structures such as slabs of airports, runways, protective shelters, and fortification structures. An experimental program was carried out to investigate the efficiency of two strengthening techniques , using additives to fresh concrete using

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... end steel fibers with aspect ratio (l/d=50) , and new shape of steel fibers (spiral steel fiber) of spiral diameter 15 mm with wire diameter 1 mm . The steel fibers were added with different volume fractions (1%, 2% and 3%) for both hooked-ends and spiral steel fibers. The specimens were tested to study the mechanical properties and behavior of concrete, which included penetration depths, crater diameters. It was observed that adding steel fibers to plain concrete prevents its shattering, disintegration, and also decreases spalling when opposed to hard projectiles. Also adding steel fibers "hooked-ends" with 1% volume content improves penetration resistance to hard missiles and reduce penetration depth about 30%, while there is no significant reduction in penetration depth when increase fibers fraction to 2% "by volume". But there is descending in penetration resistance if we increase steel fibers content to 3% "by volume".