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2 Archives of Civil and Mechanical Engineering

2 2021

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Long-term behavior of normal weight concrete containing hybrid nanoparticles subjected to gamma radiation

Al-Tersawy Sherif H., El-Sadany Rasha A., Sallam H. E. M.

Archives of Civil and Mechanical Engineering

2021

Vol. 21, no. 1

153--170

Since a lot of medical facilities are made from normal weight concrete (NWC), it became an important task to improve the radiation shielding properties of such concrete in a confrontation to radiation with special emphasis on gamma radiation type. Therefore, an experimental program was conducted to investigate the effect of nanoparticles addition on gamma radiation shielding, physical properties, and mechanical properties of NWC. Nano silica (NS), nano hematite (NH), nano titania (NT), and their hybridization were added to NWC with four different percentages of 0.5, 0.75, 1.0, and 2.0% from the cement weight. A total of sixteen concrete mixes with nanoparticles in addition to a control mix were made. The long-term effects of gamma radiation on samples representing all concrete mixes were studied to find out the consequence of exposure to gamma rays over long periods (250 and 500 days) on their mechanical properties. The experimental results showed that the single addition of each of NS, NH, or NT particles and their combination up to 2.0% improved the physical properties, compressive strength, and attenuation coefficient of NWC. The results of the hybrid nano addition showed that the synergistic phenomenon occurred in some cases. Furthermore, the scanning electron microscopy technique (SEM) was used to prove the enhancement in the microstructure of NWC as a result of the addition of NS, NH, NT, and their combination.

Flexural behavior of functionally graded concrete beams with different patterns

Othman M. A., El-Emam H. M., Seleem M. H., Sallam H. E. M., Moawad M.

Archives of Civil and Mechanical Engineering

2021

Vol. 21, no. 4

568--583

Flexural behavior of functionally graded concrete (FGC) beams was experimentally investigated. Fourteen sets of beams, including full depth (FD) fiber-reinforced concrete (FRC) and FGC with different patterns and fiber volume fractions (Vf%), were investigated under three-point bending. These patterns consisted of three layers with a constant middle part of lightweight concrete. The upper layer in the compression zone was either normal strength concrete or FRC having different Vf%. The lower layer in the tension zone was made from either FD FRC has the same Vf% or functionally graded FRC. The fibers used were hooked end steel fibers with Vf% of 0.5, 1.0, and 1.5%. The experimental results were also analyzed numerically and analytically. The experimental results showed that the flexural strength of FGC patterns ranged between 94 and 100% from that of FD FRC beams. However, their toughness indices ranged between 49 and 93% of the corresponding value of FD FRC beams. These ratios depend on Vf% and the presence of fibers in the compression zone. The effect of Vf% is more obvious in the descending part of the load–deflection curve than the ascending part due to the presence of fibers bridging phenomenon following the maximum load. Vf% is more pronounced in the descending portion in all FGC patterns than in the FD FRC beams. There is a good agreement between the experimental results and those predicted by analytical and numerical models.