Steel fiber reinforced concrete (SFRC) has gained popularity in the last decades attributed to the improvement of brittleness and low tensile strength of concrete. This study investigates the effect of three shapes of steel fibers (straight, hooked end, and corrugated) with four contents (0.5%, 1%, 1.5%, and 2%) on the mechanical properties (compression, splitting tension, shear, and flexure) of concrete. Thirteen groups of concrete were prepared and investigated experimentally. Test results indicated that steel fiber had significant reinforcement on mechanical properties of concrete. When the steel fiber content increases from 0.5% to 2.0%, the compressive strengths increase about 4–24%, splitting tensile strengths increase about 33–122%, shear strengths increase about 31–79%, and flexural strengths increase about 25–111%. Corrugated steel fiber has the best reinforced effect on strength of SFRC, hooked end steel fiber takes the second place, and straight steel fiber is the least. Calculated formulas of compressive, splitting tensile, shear, and flexural strengths were established with consideration of the bonding properties between concrete and steel fiber. Influence factors of steel fiber (α_f) and concrete matrix strength (α_c) were put forward and determined by regression analysis of experimental data. Calculated results agree well with the experimental results.

A wideband folded reflectarray antenna (FRA) based on single-layered polarization rotating metasurface (PRM) is proposed. The FRA is composed of a wideband polarization grid (PG), a wideband PRM and a wideband circular waveguide as the primary source. First, a wideband polarization rotating unit cell consisting of rhombus-shaped metal patch etched on dielectric substrate is designed, which can be used to rotate polarization of the reflective wave 90° relative to that of the incident wave. The element and its mirror image can provide 0°, 90°, 180° and 270° phase shifts with 2-bit phase quantization and relatively higher polarization conversion rates in the Ku band. Due to the introduction of PG and PRM, the distance between the PG surface and the feed phase center can be reduced to about 1/2 of the distance between the imaginary feed and PRM reflectarray. Finally, a wideband FRA consisting of 315 elements with circular aperture is designed, fabricated and measured. The measured results indicate that the proposed antenna achieves 39.5% 3-dB gain bandwidth with 25.5 dBi peak gain at 15 GHz. Its maximum aperture efficiency is about 40%. Low-profile and wideband features of the FRA make it be a candidate in the wireless communication systems.

Recycled aggregate concrete (RAC) is a sort of green, low carbon, environmental protection building material, its application is of great significance to the low carbonization of the construction industry. The performance and strength of RAC are much lower than natural aggregate concrete (NAC), which are the key factors restricting its application. Class F fly ash is a cementitious material that is considered environmentally hazardous. In this paper, appropriate water-binder (w/b) ratios were found through a mortar expansion test at first. The compressive strength of recycled mortar incorporated with class F fly ash was further studied. On this basis, the mechanical properties of nine groups of fully recycled aggregate concrete (FRAC) with a w/b ratio of 0.3, 0.35, and 0.4, and fly ash replacement ratios of 0, 20%, and 40%, were studied. The influence of the w/b ratio and fly ash replacement ratio on mechanical properties was analyzed and compared with previous research results. In addition, the conversion formulas between the splitting tensile strength, flexural strength, and compressive strength of FRAC were fitted and established. The research results have a certain guiding significance for the mixture design of FRAC and further application of class F fly ash.