Sherif Yehia

This article presents two innovative methods to enhance electromagnetic (EM) shielding in nonbearing masonry walls constructed from normal-weight concrete (NC) hollow blocks. Two different block sizes are investigated, 400 × 200 × 200 mm³ and 400 × 200 × 150 mm³. The first method involves filling hollow NC blocks with either NC or two conductive concrete mixes (M1 and M2), incorporating carbon and fiber additives. It achieves shielding effectiveness of 20–36 dB across 1–10 GHz, significantly exceeding that of NC-filled blocks (1–25 dB). The second method applies a 2 cm fiber-reinforced conductive composite (FRCC) coating, in planar or corrugated configurations, to one or both sides of masonry walls. Double-sided FRCC coatings, particularly with corrugated surfaces, deliver superior SE up to 50 dB, compared to 10–25 dB for uncoated walls, with scattering reducing reflections. Simulations using ANSYS high-frequency structure simulator confirm these findings, indicating power transmission of less than 1% for FRCC-coated walls and up to 96% absorption for conical corrugated designs. Both methods demonstrate robust EM-shielding across diverse frequencies and illumination directions, offering practical solutions for nonbearing masonry walls in civil engineering applications requiring enhanced EM interference protection.

The advancement of high-power microwave technology has indeed brought about the possibility of E-bombs, also known as electromagnetic pulse (EMP) bombs. These weapons emit an electromagnetic pulse that can disable electrical circuitry within a specific radius. As the frequency spectrum becomes more congested with various technologies operating in similar frequency bands, the need for shielding against interference becomes crucial. One promising solution is the use of conductive concrete, which is created by incorporating conductive components into a traditional concrete mixture. This conductive concrete has shown excellent shielding properties and improved electrical characteristics. To assess and quantify its effectiveness, the relative complex permittivity of the concrete mixture needs to be estimated. In this paper, the authors propose a method for estimating the relative complex permittivity of the concrete mixture. This was achieved by measuring the scattering parameters of concrete samples using a rectangular waveguide within the C-band frequency range. The scattering parameters provide valuable information about how electromagnetic waves interact with the concrete. A dielectric mixing model was developed to determine the relative complex permittivity. This model takes into account the volume percentage and the dielectric properties of the individual constituents present in the concrete mixture. By applying this model and obtaining the complex permittivity of the mixture, it becomes possible to calculate the required thickness of the conductive concrete mix needed to achieve the desired levels of electromagnetic attenuation and shielding.

In this paper, the mechanical properties and bond strength of composite samples that consist of a conductive concrete (CC) layer and a self-consolidated concrete (SCC) layer are investigated. The bond strength study includes two parameters: (1) surface preparation and (2) casting and testing directions. The surface preparation study shows that, compared to the other methods in this study, the shear key method is the most suitable surface preparation method to fully utilize the CC in a composite. Moreover, the casting direction study reveals that the strength is heavily dependent on the type of test used along with CC’s layer positioning. The flexural strength study confirms that positioning the CC mix in the tensile region is beneficial since it can increase the flexural strength of a structure because of the hybrid steel fibers included in the mixture. Finally, different codes/specifications and published theoretical results are used to predict the CC’s mechanical properties, and the predictions are not as accurate as the SCC predictions, which can be attributed to the presence of conductive fillers in the CC mix.