The utilization of recycled coarse aggregate (RCA) from construction and demolition waste (CDW) is a sustainable solution to protect the fragile natural environment and save the diminishing natural resources. The current study was aimed at exploring the impact resistance and mechanical properties of recycled aggregate concrete (RAC) affected by hooked-end steel fiber (HF) and crimped steel fiber (CF). Fifteen concrete mixtures considering different RCA substitution ratio, steel fiber dosage, and steel fiber shapes were designed. Meanwhile, a statistical analysis method-based Weibull distribution was introduced to evaluate the variations of impact test results, presented using a reliability function. Lastly, the microstructural morphologies of interfacial transition zones at the cement paste/aggregate and cement paste/fiber interfaces were observed using a scanning electron microscope (SEM). The experimental results showed that the impact resistance and mechanical properties mildly decreased with the increase in substitution ratio of RCA, whereas they conclusively increased with the increase in steel fiber content. Steel fiber recycled aggregate concrete (SFRAC) with 1.5% steel fiber content had the best impact resistance, and its initial cracking times and final failure times were 3.25–4.75 and 8.78–29.08 times those of plain RAC, respectively. HF has better impact resistance than CF. The SEM observations of microstructures indicated that the hardened cement paste of natural aggregate concrete (NAC) was more compact than that of RAC. Steel fiber had a better connection with the cement paste interface than that of aggregate and cement paste owing to better thermal conductivity. This research could be a guide for SFRAC as a structural material in practical engineering, steering the construction industry toward the circular economy.

Metal laminated composites are widely used in industrial and commercial applications due to their excellent overall performance. In this study, the copper/graphene-aluminum-copper/graphene (Cu/Gr-Al-Cu/Gr) laminated composites were prepared by ingenious hot pressing design. Raman, optical microscope (OM), scanning electron microscope (SEM), van der Pauw (vdP), and X-Ray Diffractometer (XRD) were used to investigate the graphene status, interface bonding, diffusion layer thickness, electrical conductivity, Miller indices and secondary phases, respectively. The results demonstrate that the Cu-Al interfaces in the Cu/Gr-Al-Cu/Gr composites were free of pores, cracks and other defects and bonded well. The number of graphene layers was varied by regulating the thickness of the Cu/Gr layer, with the Cu/Gr foils fabricated by chemical vapor deposition (CVD). The electrical conductivity of the composite was significantly improved by the induced high-quality interfaces Cu/Gr structure. The increased number of graphene layers is beneficial for enhancing the electrical conductivity of the Cu/Gr-Al-Cu/Gr composite, and the highest conductivity improved by 20.5% compared to that of raw Al.

In order to reduce the manufacturing cost of foamed ceramics and expand the application scope of industrial solid waste, in this study, a new type of environment-friendly foamed ceramics was prepared using direct high-temperature foaming with waste silicomanganese slag (SMS) and fly ash (FA) as raw materials and silicon carbide (SiC) as a foaming agent. The influence of SMS content, SiC content, and sintering temperature on the characteristics and microstructure of the specimen were explored. More concretely, the compressive strength, pore morphology, bulk density, and crystalline composition of the foamed ceramics were discussed. The foaming mechanism was also further analyzed. The results showed that including 20% SMS significantly reduced the melt’s viscosity and stimulated bubble expansion. This, in turn, facilitated the creation of a porous structure. Moreover, it was noted that samples containing 20% SMS exhibited an anorthite phase when sintered at 1110 °C, resulting in enhanced compressive strength. The bulk density and compressive strength of the foamed ceramics decreased with an increase in the sintering temperature and SiC content. This trend was primarily attributed to the higher total porosity and the insufficient support of the pore wall to the matrix. The best all-around performance was achieved with 20 wt% SMS, 80 wt% FA as raw material, SiC addition of 1.0 wt%, and a sintering temperature of 1100 °C. Under these conditions, the compressive strength, bulk density, and total porosity of the foamed ceramics were 8.09 MPa, 0.57 g/cm³, and 71.04%, respectively. Taken together, the outstanding porous structure and mechanical properties of this foamed ceramic make it suitable for use as insulation or for building partition materials.

In order to study the axial compression behavior of rectangular concrete short columns that have been strengthened with basalt fiber-reinforced polymer sheets, the axial compression test were conducted on 15 groups specimens. The parameters are the cross aspect ratio and the number of basalt fiber-reinforced polymer layers. As the aspect ratio increases, the confined effect of basalt fiber-reinforced polymer decreases. The strength of one ply of basalt fiber-reinforced polymer decreases as the aspect ratio increases, the range is not very obvious, but the two ply of basalt fiber-reinforced polymer has the obvious decreasing tendency. With the increase in aspect ratio, the square and rectangular section columns of basalt fiber-reinforced polymer confined have a certain size effect. When the aspect ratio is 1.0, the values of f_cc/f_c0 by one ply of basalt fiber-reinforced polymer and two ply of basalt fiber-reinforced polymer are 1.14 and 1.50, respectively. And when the ratio is 2.0, the values of f_cc/f_c0 are 1.06 and 1.16. The confined effect is best when the aspect ratio is 1.0, while there is no significant effect with the ratio of 2.0. Results of the theoretical analysis compared with the experimental results show good agreement.

This paper reports the development of a novel bio-inspired composite sandwich panel (BCSP) with fiber metal laminate (FML) face sheets and a dual core to improve the low-velocity impact behavior based on the woodpecker’s head layout as a design template. The dynamic response of BCSP under impact load is simulated and analyzed by ABAQUS/Explicit software and compared with that of the composite sandwich panel (CSP) with a single foam core. The impact behavior of BCSP affected by these parameters, i.e., a different face sheet thickness, rubber core thickness and foam core height, was also reported. The results show that BCSP has superior impact resistance compared to CSP, with a lower damage area and smaller deformation, while carrying a higher impact load. Concurrently, BCSP is not highly restricted to any particular region when dealing with stress distributions. Compared to CSP, the bottom skin maximum stress value of BCSP is significantly reduced by 2.4–6.3 times at all considered impact energy levels. It is also found that the impact efficiency index of BCSP is 4.86 times higher than that of CSP under the same impact energy, indicating that the former can resist the impact load more effectively than the latter in terms of overall performance. Furthermore, the impact resistance of the BCSP improved with the increase in face sheet thickness and rubber core thickness. Additionally, the height of the foam core has a notable effect on the energy absorption, while it does not play a significant role in impact load. From an economic viewpoint, the height of the foam core retrofitted with 20 mm is reasonable. The results acquired from the current investigation can provide certain theoretical reference to the use of the bio-inspired composite sandwich panel in the engineering protection field.