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 hooked-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".