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.

The study is conducted to perform two goals: The first geal is to produce a lightweight concrete using major components which are locally available with some standard admixtures.Many mixtures are prepared using many ratios of superplasticizer (SP) and silica fume (SF) admixtures to yield a lightweight aggregate concrete, the effects of using different ratios of these admixtures on unit weight, compressive strength and flexural strength are studied individually and accumulatively. The secondis to study the dynamic specifications of normal and lightweight reinforced concrete beams.The results showed that the increasing in dosage of superplasticizer (SP) for (LWAC) increases the density of (LWAC), and the increasing in dosage of silica fume (SF) decreases the density of (LWAC). The experimental impact tests for R.C. beams shows that the lightweight R.C. beams have a better response under impact loading with respect to the maximum dynamic deflection (2.955mm for normal weight beam and 1.58mm for lightweight beam). Also,Impact force transferred to supports reactions of lightweight beams is smaller within 45% than the impact force transferred to reaction of normal weight concrete under the same impact load, and the time to reach 90% damping equal to 1.223 sec and 1.6 sec for lightweight and normalweight R.C. beams respectively. Also, the reinforced concrete beams are tested under repeated impact load up to failure. The tests showed that the no. of blows to cause first crack for lightweight concrete beams more than twice of this for normalweight concrete beams.

In this research, trial mixes were conducted according to Self-Compacted Concrete (SCC) specifications, a mix that gave a higher compressive strength to the age of seven days has been selected. Then after selecting the appropriate mix, concrete samples had poured and were distributed into five groups; each group consists of six cubes, six cylinders, and six prisms. The samples of each group are testing for compressive, tensile splitting, and flexure strengths respectively for the ages of 7, 14, 28, 60, and 90 days respectively. Before of conduction of destructive tests, the samples were tested using ultrasonic waves to determine the relationship between the concrete strength and pulse velocity and in the same way for all ages in above. Experimental results showed that, all concrete mechanical properties have improved, and the maximum improve was in flexural strength followed by compressive strength and tensile splitting strength. The cube compressive strength increased according to (G1 at 7 days curing) from 34.3% to 71.8%, the percentage of increase of tensile strength according to (G1 at 7 days curing) from 16.8% to 64.3% , modulus of rupture increased according to (G1 at 7 days curing) from 34.6% to 98.7% for ages (14, 28, 60, 90 days) respectively. Pulls velocity increased according to (G1 at 7 days curing): For cube from 5.1% to 23.9%, for cylinder from 21.4% to 40.3%, for prisms from 7.1% to 29.2%.