Fiber Reinforced Concrete (FRC) has been used widely due to its advantages over plain Concrete such as high energy absorption, post cracking behavior, flexural and impact strengths, arresting shrinkage crack.This research discusses the effect of increasing the percentage of polypropylene fiber on flexural toughness and strength of FRC. Three percentages of polypropylene fiber were substituted in 1% Steel fiber Reinforced Concrete (SFRC). Finally, the mechanical properties of three types of hybrid fiber Reinforced Concretes were compared with each other and with Steel fiber Reinforced Concrete by measuring their flexural toughness and flexural strength. A four-point bending test was adopted to determine the effect of hybrid fibers on crack arresting and post crack behavior.The research results show that the more the percentage of polypropylene fiber which is substituted in SFRC is, the less the amount of energy absorption and flexural toughness with FRC will be.

Concrete incorporating Steel fibers poses difficulty in mixing, transporting, placing and compacting that may lead to voids in hardened Concrete. The determination of fresh fiber Reinforced Concrete properties is therefore, important for satisfactory performance in hardened state. The present experimental study investigates effect of three fiber properties volume fraction of fiber, aspect ratio of fiber and diameter of fiber- on the rheological properties of high performance Concrete with a parallel plate rheometer. The test result shows that yield stress and plastic viscosity are adversely affected by all the three parameters. Fiber volume concentration has the highest effect on the measured rheological parameters whereas fiber diameter has the least effect.

In the present study, a new method for retrofitting Reinforced Concrete beam is introduced in which Steel-Concrete composite jackets containing Steel fiber is used. For this purpose, 75% of the peripheral surface of Reinforced Concrete beams was initially Reinforced using Steel plates and bolts, and Steel fiber Reinforced Concrete was used between the Steel plates and the peripheral surfaces of the beam. Thus, due to the relatively high tensile strength of Concrete Reinforced with Steel fibers, not only the cross-section and moment of inertia of the beam will increase, but the tensile strength of the beam will also increase. The variables studied were Steel fiber value (0, 1 and 2% by volume of Concrete) and type of retrofitting (Concrete jacket, Steel-Concrete composite jacket, and carbon fiber Reinforced polymer (CFRP) sheet). Thus, 8 Reinforced Concrete beams were constructed and their response to four-point loading was compared by examining the parameters such as crack load, yield load, ultimate load, ductility, stiffness, and energy absorption capacity. The results showed that Steel fiber-Reinforced composite jackets delay the formation of the first crack in Concrete and the yield of Steel rebars with confinement and they result in an increase in energy absorption capacity of the beams by 89 to 129% depending on the amount of Steel fiber. On the other hand, the use of Steel-Concrete composite jackets, due to their higher flexural stiffness, exhibits higher flexural capacity compared to Steel-Reinforced Concrete jackets and CFRP sheets. They have a much better performance in terms of ductility.

In order to select the most suitable Concrete for the construction of high-rise buildings, method of analytic hierarchy process (AHP) based on expert knowledge has been used.In this study conducted a series of laboratory works, to compare the effect of Steel fibers used in various categories of resistance on Concrete behavior parameters. Mixing the samples is set for the three categories of resistance 25, 35 and 45 MPa. Strength parameters that are chosen to identify Concrete actions are tensile strength, impact strength, compressive strength and flexural strength. Also the samples in each resistance category are made with four fibers quantity: without fibers, 15, 25 and 35 kg fibers per cubic meter. The results suggest that using of Steel fibers, increases the impact resistance, time of the first crack and ultimate strength of Concrete significantly. Also the addition of this type of fibers, increases tensile strength and flexuralstrength but don’t have significant effect on the compressive strength of Concrete.

Cementitious matrices are the fragile materials that possess a low tensile strength. The ‎addition of fibers randomly distributed in these matrices improves their resistance to ‎cracking, substantially. However, the incorporation of fibers into a plain Concrete ‎disrupts the granular skeleton and quickly causes problems of mixing as a result of the ‎loss of mixture workability that will be translated into a difficult Concrete casting in ‎site. This study was concerned on the on hand with optimizing the fibers Reinforced ‎Concrete mixes in the fresh state, and on the other hand with assessing the mechanical ‎behavior of this mixture in the hardened state, in order to establish a compromise ‎between the two states. In the first part of this paper, an experimental study of an ‎optimization method of fibers Reinforced Concrete while taking into account of some ‎parameters related to the matrix e.g. volume of the admixture, volume of incorporated ‎fibers and the volume of water and, cement (W, C) in function of workability time are ‎presented. Finally, test specimens of mixture optimized by this method have been ‎tested in compression and tension due to bending. The results have been compared ‎with those of mixture test specimens optimized by Baron-Lesage method‏.‏