الفهرس 
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Abstract
Concrete is a non-homogeneous material and it has high compressive strength but it is weak in tension. In conventional concrete, micro-cracks develop before structure is loaded because of drying shrinkage and other causes of volume change. When the structure is loaded, the micro cracks open up and propagate, results in inelastic deformation in concrete. Adding fibers to plain concrete is considered one of many solutions to improve the properties of concrete. In this study an experimental investigation is carried out by adding steel fibers (S.F) with (1mm) diameter and (50 mm) long i.e. aspect ratio (l/d=50) to plain concrete to study it is effect on fresh and hardened properties of concrete (unit weight, workability, compressive strength, tensile strength, flexural strength, flexural toughness, abrasion resistance, water permeability and absorption). The tested variables are the characteristics of concrete (fcu30MPa and fcu40MPa), the steel fibers content (0.4%, 0.5%, and 0.6%) by volume of concrete, and the tensile reinforcement. The results show increases in compressive strength by (6%, 12 % and 17%) for fcu30 MPa and by (8%, 13% and 16%) for fcu40 MPa for fiber content 0.4%, 0.5% and 0.6 respectively. The tensile strength increases by (38%, 59% and 67%) for fcu30 and by (21%, 35% and 53%) for fcu40 respectively. Abrasion resistance is increased by (14%, 29% and 31%) for fcu30 and by (6%, 25% and 26%) for fcu40 respectively. The absorption of concrete is also enhanced by (7%, 14% and 26%) for fcu30 and by (25%, 33% and 55%) for fcu40. The enhancing in water permeability of concrete is (17%, 28% and 44%) for fcu30 and (20%, 40% and 47%) for fcu40 respectively. The flexural strength is enhanced by (10%, 15% and 20%) for fcu30 and by (12%, 37% and 40%) for fcu40 respectively. Adding steel fibers enhanced behavior of concrete slab by change its failure mode from sudden brittle mode of failure into more ductile and improves the behavior of load deflection curve and increases the toughness of concrete. It was observed that increases volume fraction of steel fiber has a little effect on the unit weight of concrete. Workability decreases when adding steel fiber volume fraction compared to control mix.