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 αf and concrete matrix strength αc were put forward and determined by regression analysis of experimental data. Calculated results agree well with the experimental results.

A tunable three band absorber has been proposed and investigated in the terahertz (THz) with graphene strips. Three perfect absorption is elaborately analyzed with the electrical field and the induced surface current distribution. Owing to the unique character of graphene, the position and intensity of three peaks are flexibly regulated with different Fermi energy and chemical potential. Meanwhile, an on to off modulation of the perfect absorption is achieved when the polarization angle varies from 0 to 90°, and the modulation degree of three resonant peaks can simultaneously approach 100%, which are much higher than the previous work. Moreover, the tunable absorption is examined with different geometry parameters and intermediate medium. Such highly tunable absorber with our proposed design has numerous application potential in the controllable optical switchers, filters, detectors, and sensors.

No abstract