The main objective of this research was studied the flexure behavior of hybrid reinforced concrete beams combining reactive powder concrete (RPC) and lightweight concrete (LWC). The experimental work consists of casting and testing in flexure seven simply supported reinforced concrete beams. The dimensions of (7) beams were geometrically similar, having rectangular cross-section, of dimensions (125×200×1600) mm. Lightweight concrete was used in tension layer and reactive powder concrete was used in compression layer for all hybrid concrete beams. The main variables were; type of concrete (LWC and RPC), thicknesses of RPC layer (h R =0, 50, 100 and 200) mm and longitudinal reinforcement ratios (ρ= 0.0033 and 0.0227). The type of LWC used in the experimental work was porecilenite aggregate. The results showed that the characteristic strength (first and ultimate loads) was increased when the thickness of RPC layer was increased. In addition to that, these parameters were decreased the values of deflection. All beams failed by flexure mode without any shear cracks which achieved by yielding of tensile steel in the tension zone. Also, for all hybrid beams, the slip was absent between the concrete layers. Finally, the reinforcement ratio (ρ) had more effective factor of all parameter used to increase the stiffness value of the beams which increased the characteristic strength and reduced the deflection values.

An experimental study was conducted to investigate the behavior of composite concrete beams damaged and cracked under pure torsion, and then repaired by external strengthening. This was achieved using high strength Carbon Fiber Reinforced Polymer (CFRP) laminates bonded with epoxy four composite modify reactive powder concrete (MRPC) I-beams. Different types of section (Solid & with opening) were tested to obtain the effect of amount of CFRP laminate on beams ultimate torque behavior, angle of twist and failure modes. The results obtained showed that a significant effect of external high strength CFRP laminates on effectively restore of section solid, the range of 89.8% to 91.2% of ultimate torsional strength effectively restored as well as effectively restoring of section opening by 83.48%-86.67% of ultimate torsional strength. The repaired beams give high efficiency in ultimate torsional strength, and indicate that the adopted technique gives a good torsional strength.

The strength of concrete columns is controlled by the strength of the material and the geometry of the cross section. The use of Reactive Powder Concrete RPC technology has proven most popular with superior strength, stiffness and durability being the major advantages. An experimental investigation was carried into the behavior of RPC columns subjected to axial load with initial eccentricity. Twelve columns were prepared with 120mm square section at the midsection and were hunched at the ends to apply eccentric loading. The specimens were tested up to failure to evaluate the effects of the variation of the concrete type (normal or RPC), presence of steel fibers and longitudinal steel ratio. Experimental data on strength, lateral displacement and failure mode was obtained for each test. The comparative analysis of the experimental results showed that the use of RPC caused substantial variation in the ultimate strength and failure modes. Also, inclusion of steel fibers in RPC was an effective way to prevent spalling of the concrete cover and increase the ductility, as well as, high ratio of longitudinal reinforcement delays the buckling of the columns and increases strength.

In this research an investigation has been done on eight reinforced concrete beams. Each beam was strengthened by bolted steel plates attached to their bottom side, of which length and thickness ratio varied, except one beam which has been tested without steel plate as controlling test. Two limits have been introduced upon the maximum plate area used and its minimum length. The first limit is to insure a ductile tension failure, and the latter is to prevent loss of interaction between the two components. Bolts with head were used to provide suitable connection through the specimens of concrete beams and the steel plates through predrilled holes in the steel plates. All beams have similar dimensions and tested simply supported over an effective length of 1600 mm and loaded with central load. Test results show that the plated beam gain an increase in strength over that of unplated beam of about 145%. Also, beams with relatively thin plates, the plate length has little effect upon the ultimate strength, however, for beams with thicker plates the results show a decrease in strength of about 16%.

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