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This research was conducted to study the effect of adding waste plastic fibers (WPFs) on the behavior of reinforced concrete (RC) beams. Fifteen simply supported RC beams with a cross section of (100 * 150) mm and a clear span of (1100) mm was tested under two-point loads until failure. Three beams of the total samples were made from the reference mix, and the twelve beams remaining were made from concrete mixes containing WPFs with volumetric percentage ratios (Vf) varying from (0.5% to 2%) of the total volume. These beams were divided into three main groups according to the longitudinal steel reinforcement area ratio (ρ), and these ratios were approximately equal to (ρ max, 0.75 ρ max, ρ min). Test results established that the adding of WPFs, in addition, to decreasing the danger of PET wastes on the environment, leads to increasing the maximum applied load causing ultimate failure, an increment in ductility index and transformation of the mode of failure of the tested beams into a more ductile one for all beams contains such kind of fibers.

The main objective of this research is to investigate the structural behavior and strength of reinforced reactive powder concrete beams with a hollow section subjected under two point concentrated loading. The experimental work consist of ten beams with dimensions (150mm width×200mm height×1000 mm length), eight of them are hollow beams and two solid beams were cast and tested up to failure. The major parameters adopted in the current research includes the hollowness ratio (10% and15%), hollow location (at top or at bottom), and hollow shape (circle or square). The amount of longitudinal and transverse reinforcement, concrete strength and the other parameters were kept constant for all the specimens. The comparisons between all specimens (hollow and solid) are based on the load carrying capacity, deflection, crack pattern and mode of failures. Results showed that the strength capacity of hollow beam when the hollow lies in the bottom is much higher than for top hollow, and the square hollow will lead to more decrease in the beam strength compared with the circular hollow and this is more evident when the hollowness ratio increases from (10% to 15%).

In this research, the effect of the addition of fly ash particles with different weight ratios of 15%, 20%, and 25% as well as the addition steel fibers with different volume fractions of 0.25%, 0.75%, and 1.25% on the mechanical properties of concrete (compressive strength and modulus of rupture) was studied. To carry out this research, ten concrete mixes were prepared, one of which is the reference normal concrete (without any additives), the others contain steel fibers and fly ash as additives with the mentioned volumetric and weight proportions. For each type of concrete mix, three standard 150×300 mm cylinders and three standard prisms 100×100×500 mm were casted, water to cementing material ratio was fixed for all concrete mixes (W/cm = 0.435) and the superplasticizer was used with ratio of 0.98%-1.22% by weight of the cementitious material in mixtures that contain steel fibers and fly ash particles as a partial replacement of cement weight. The results showed that the addition of fly ash particles had little effect on the mechanical properties of normal concrete, while the steel fibers had the greatest effect. The highest increase in compressive strength and flexural strength compared with reference concrete was 61.60% and 78.84%, respectively in the volume fractions 1.25% of steel fiber.