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This work created a fireproof sandwich structure in which the face sheets were made of expanded vermiculite and expanded perlite‐filled geopolymer composites and embedded basalt fiber mats and the core material was rock wool in designing the lightweight and cost‐effective fire‐resistant structure for steel bridges with excellent retardant and heat‐insulating performance. The effects of adding 5%, 10%, 15%, and 20% expanded vermiculite and expanded perlite to the geopolymer on mechanical properties and the thermal conductivity were investigated to obtain the optimized material mixtures for preparing the face‐sheets material of the sandwich panel. Then, the fireproof sandwich structures were fabricated and exposed to 800°C for 3 h to study the structural integrity, backfire side temperature, and mass loss ratio. The results indicated that adding 10 wt% expanded vermiculite and 10 wt% expanded perlite to the geopolymer achieved the retention of compressive strength of 66.5% after being exposed to 800°C, and the geopolymer mixtures showed a low thermal conductivity of 0.1942 W/(mK). The TOPSIS evaluation analysis reveals that the proposed fireproof sandwich panel had the highest integrated performance considering the structural weight, insulation properties, and cost. The findings of this work may provide some insights into fireproof and insulating applications in bridge engineering. [ABSTRACT FROM AUTHOR]

This study develops sustainable and recyclable basalt fiber (BF)‐reinforced flexible plastic low‐temperature polyamide (L‐PA) filaments for fused deposition modeling (FDM)‐3D printing and optimizes fabrication parameters to achieve eco‐friendliness, high mechanical performance, and lightweight FDM‐fabricated composite parts. Herein, 15 wt% fiber‐filled composite filaments were prepared by an extrusion process. Three manufacturing parameters, including printing temperature, printing speed, and layer height, were investigated for their effects on the tensile and compression properties through Taguchi L9 orthogonal experiments. To obtain a suitable printing temperature range, the thermal behaviors of the composite filaments were characterized by differential scanning calorimetry, thermogravimetric analysis, and melt flow factor measurements. In addition, the FDM‐printed specimen surface and tensile fracture interface after tensile tests were observed and analyzed by SEM. Results show that the printing temperature has the greatest effect on the mechanical properties of the BF/L‐PA composites, followed by the layer height, whereas the printing speed has the least effect. This indicates that better mechanical properties can be obtained at higher printing temperatures and lower layer heights. Compared with neat L‐PA, adding BF to L‐PA improves the tensile modulus, tensile strength, and specific energy absorption per volume without sacrificing ductility, showing the maximal increases of 176.6%, 142.0%, and 172.2%, respectively, as compared with neat L‐PA. A SEM micrograph reveals that the primary factors for these improvements are the fibers acting as reinforcement filling in the L‐PA matrix and the good bonding properties between the adjacent infills in a single layer and among successive layers. [ABSTRACT FROM AUTHOR]

Highlights Structural supercapacitors (SSCs) are a promising solution for reducing the weight of structures. In order to improve the electrochemical performance of carbon fiber (CF) electrodes, a new technique for carbon fiber electrodes modified with polypyrrole (PPy) and carbon nanotubes (CNTs) with friendly preparation methods was developed. The mixture of PPy and CNT produced a significant synergistic effect in increasing the capacitance of the electrode. PPy/CF electrode was optimized by adjusting parameters. The areal capacitance of the CNT‐PPy/CF electrode achieves 1789.84 mF/cm2 at a scanning speed of 10 mV/s, which is 159 times higher compared with the CF electrode. Furthermore, the CNT‐PPy/CF electrode exhibits good electrical conductivity, mechanical flexibility, and cycle stability. In terms of mechanical properties, the monofilament tensile strength of CNT‐PPy/CF is improved by 9.5% compared to CF after treatment at 550°C. In addition, the SSC was fabricated using two pieces of electrodes, the PEGDGE/EMIMTFSI/LiTFSI as the electrolyte and a piece of basalt fiber fabric as the separator. The capacitance of SSC with CNT‐PPy/CF as electrodes is 38 times higher than that with CF as electrodes, and the power density is 1.23 mW/cm−3 at the energy density of 18.36 μWh/cm−3. The results demonstrate the CNT‐PPy/CF electrode provides an excellent electrode for the high‐performance SSC. A novel modification method for CF electrodes was developed using CNTs and PPy. The synergistic effect of PPy and CNT is exhibited. CNT‐PPy/CF provides excellent electrodes for the high‐performance SSC. PPy synthesized with dopant NaSSA exhibits excellent electrochemical performance. CNT‐PPy/CF exhibits excellent electrochemical and mechanical performance. [ABSTRACT FROM AUTHOR]