Browsing by Author "Deifalla, Ahmed"

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Effect of Using Lightweight Concrete on the Behavior of L and T- Beams under Combined Stresses
(azharcermjournal, 2019) Awad, Ahmed; Deifalla, Ahmed; Seleem, Hosam
This paper presents an experimental investigation for the behavior of flanged reinforced lightweight concrete (LWC) under combined stresses. LWC was obtained through the use of polystyrene foam as a partial aggregate’s replacement to reduce the concrete dry unit weight from 23.0 kN/m3 to 18.1 kN/m3. The experimental work was consisted from two phases; The first phase quantified the mechanical properties of lightweight concrete; namely the compressive and tensile strengths as well as the tension stiffening capability of the concrete mix and The second phase was concerned with testing specimens of lightweight and normal-weight concrete beams (L and T-shaped) under combined stresses for determination of the ultimate resistance, mode of failure, ultimate angle of twist, and load-deflection curve for all tested beams. The experimental program consisted of four full scale T & L beams with cross-section of (150 x 400 mm.). Two T-sections having a width of slab 550 mm and slab thickness of 150 mm, span of 1300 mm, load eccentricity of 50mm, with varying material type (LWC, and NWC). Two L-sections having a width of slab 350 mm and slab thickness of 150 mm, span of 1300 mm, load eccentricity of 50mm, with varying material type (LWC, and NWC).The main variables of this study were the material type, and the shape of cross section. The observed behavior of the light weight concrete specimens up to failure greatly encourages the use of light weight concrete in all structural elements.
Mechanical Properties of Hybrid Steel-Polypropylene Fiber Reinforced High Strength Concrete Exposed to Various Temperatures
(Multidisciplinary Digital Publishing Institute (MDPI), 2022-06-12) Tawfik, Maged; El-said, Amr; Deifalla, Ahmed; Awad, Ahmed
Combining different types of fibers inside a concrete mixture was revealed to improve the strength properties of cementitious matrices by monitoring crack initiation and propagation. The contribution of hybrid fibers needs to be thoroughly investigated, taking into consideration a variety of parameters such as fibers type and content. In this paper, the impact of integrating hybrid steel-polypropylene fibers on the mechanical properties of the concrete mixture was investigated. Hybrid fiber-reinforced high-strength concrete mixtures were tested for compressive strength, tensile strength, and flexural strength. According to the results of the experiments, the addition of hybrid fibers to the concrete mixture improved the mechanical properties significantly, more than adding just one type of fiber for specimens exposed to room temperature. Using hybrid fibers in the concrete mixture increased compressive, tensile, and flexural strength by approximately 50%, 53%, and 46%, respectively, over just using one type of fiber. Furthermore, results showed that including hybrid fibers into the concrete mixture increased residual compressive strength for specimens exposed to high temperatures. When exposed to temperatures of 200 ◦C, 400 ◦C, and 600 ◦C, the hybrid fiber reinforced concrete specimens maintained 87%, 65%, and 42% of their initial compressive strength, respectively. In comparison, the control specimens, which were devoid of fibers, would be unable to tolerate temperatures beyond 200 ◦C, and an explosive thermal spalling occurred during the heating process.