In-situ lunar construction technology is critical for future lunar base development, and the production of geopolymers from lunar regolith—a novel cementitious material with concrete-like properties—has become a vital approach for achieving in-situ resource utilization. This study systematically investigated the influence of basalt fiber content (0–0.4%) on the mechanical properties of lunar regolith simulant geopolymers by controlling key parameters including curing temperature (20 °C and 80 °C), duration (1 d and 7 d), and alkali activator type (strong alkaline solution: a mixture of sodium hydroxide and sodium silicate, and weak alkaline solution: sodium silicate solution). Through testing of 144 specimens, the results revealed that strong alkali-activated specimens with 0.3% fibers cured at 20 °C for 7 d showed optimal ductility with compressive strength of 2.85 MPa and flexural strength of 0.53 MPa, exhibiting characteristic flat stress-strain curves. Specimens with 0.2% fibers under high-temperature curing at 80 °C for 1 d achieved maximum compressive strength of 44.76 MPa and flexural strength of 1.60 MPa but demonstrated brittle failure behavior. Weak alkali-activated specimens containing 0.1% fibers cured at 80 °C for 7 d attained superior comprehensive performance with peak flexural strength reaching 3.88 MPa, showing excellent fiber-matrix synergy. These findings provide important theoretical foundations for optimizing lunar construction materials through customized fiber reinforcement and curing strategies.

Bimetallic steel, as a layered composite material formed by metallurgically bonding two dissimilar metals, combines the excellent corrosion resistance of the cladding layer with the superior mechanical properties (such as high strength and toughness) of the base layer. It has been widely applied in demanding fields like marine engineering, the petrochemical industry, and energy equipment, where comprehensive material performance is critical. This paper provides a structured review of the research progress and application status of bimetallic steel. First, mainstream fabrication techniques, such as explosive welding and roll bonding, along with their effects on interfacial bonding quality, are analyzed. Subsequently, key material characteristics, including welding performance, mechanical properties, and corrosion behavior, are discussed. Furthermore, the component-level bearing performance and failure mechanisms under various loading conditions are evaluated. Finally, by synthesizing existing research, current knowledge gaps in areas like long-term service life assessment, adaptability to extreme environments, and efficient intelligent manufacturing are identified, and future development trends are outlined. This review provides important academic reference and engineering guidance for deepening the understanding of bimetallic steels and promoting their safer, more reliable, and cost-effective application in major engineering projects.

Geopolymer concrete contains inorganic aluminosilicate polymer gels formed through the activation of industrial solid wastes. This study investigated the effects of fly ash (FA) and silica fume (SF) on the durability and microstructure of geopolymer concrete exposed to freeze–thaw cycles and single-side salt erosion. Five mixtures were prepared using Baioheng geopolymer cement, with FA replacement levels of 15% and 25% and SF replacement levels of 3% and 5%. Mechanical tests, freeze–thaw tests, single-side salt-freezing tests, SEM-EDS, XRD, and CT analysis were conducted to evaluate the relationship between macroscopic performance and inorganic polymer gel structure. The results showed that 25% FA reduced compressive strength and freeze–thaw resistance, mainly due to insufficient reaction products and increased defect connectivity. In contrast, 3% SF improved the 56 d compressive strength by 13.24%, maintained the relative dynamic elastic modulus at 86.64% after 100 freeze–thaw cycles, and limited the mass loss to 0.72%. SEM-EDS and XRD results indicated that appropriate SF addition increased the Si/Al ratio and promoted the formation of C-(A)-S-H/N-A-S-H-related gel products, leading to a denser inorganic polymer matrix. However, excessive SF weakened the improvement effect, possibly due to local heterogeneity and dispersion difficulty. These results indicate that controlling the composition and spatial distribution of inorganic aluminosilicate polymer gels is essential for improving the salt-frost durability of geopolymer concrete.

This study investigated the post-fire resistances of 6063-T5 aluminium alloy angle section stub columns (SCs). The post-fire mechanical properties of 6063-T5 aluminium alloy were assessed using tensile coupon tests. Instead of exhibiting a yield plateau, the stress–strain curves indicated a shift from an elastic to a strain-hardening phase. The impacts of elevated-temperature exposure on the residual elastic modulus were negligible. Strength properties decreased while ductile properties increased within the elevated-temperature range of 200 to 450 °C, with a subsequent strength increase observed beyond 450 °C. After the SC tests, gradual decreases in ultimate resistance were observed within 200–450 °C, followed by an increase beyond 450–500 °C. These trends in the ultimate resistance closely paralleled those strength characteristics observed in the stress–strain curves. As regards the failure mode, all specimens experienced local buckling after exposure to the range of elevated temperatures. The failure mode, ultimate resistance, and load–end shortening curve were used to evaluate a numerical modelling approach that was created to simulate the residual resistance of SCs after exposure to different elevated temperatures was applied. The EC9, ADM-2020, AS/NZS 1664, and GB 50429-2007 were among the design approaches that were evaluated using the experimental and numerical data. Due to the increased strain-hardening behaviour caused by elevated temperatures, the existing design methods proved excessively conservative when applied to the direct prediction of ultimate resistances of 6063-T5 aluminium alloy angle section SCs. The modified design provisions in light of the observed post-fire strain-hardening behaviour improved the accuracy in predicting the residual bearing capacity of 6063-T5 aluminium alloy angle section SCs, which showed better agreement with test and numerical results, offering enhanced applicability for post-fire design.

This study systematically investigated the durability of low-carbon concrete under severe service conditions using industrial solid wastes. The mechanical properties and carbonation resistance (including carbonation depth, compressive strength after carbonation, and splitting tensile strength after carbonation) were tested. Multi-scale characterization techniques, including XRD, SEM-EDS, and nanoindentation, were employed to investigate the microstructure. This approach revealed a synergistic mechanism linking microstructural evolution to the concrete’s macroscopic mechanical and durability performance. Results showed that incorporating 25% fly ash (FA) reduced compressive strength by 11.30% and 11.39% in CF-25 and BF-25 mixes, respectively, and increased carbonation depth by 58.46% in CF-25. In contrast, the addition of 5% silica fume (SF) produced different effects. It significantly enhanced the compressive strength of the CS-5 and BS-5 mixes by 18.92% and 9.94%, respectively. Furthermore, it improved the micromechanical properties of the interfacial transition zone (ITZ) and reduced its thickness. Micro-mechanistic analysis revealed that the low pozzolanic activity of FA at early ages led to insufficient hydration products, higher porosity, and a weaker ITZ. Conversely, SF, through its high pozzolanic reactivity and nano-filling effect, promoted a dense, highly polymerized gel structure and optimized pore size distribution. The distinct chemical characteristics of high-calcium and low-calcium cementitious systems further amplified the differential effects of these supplementary materials.

This study investigated the effects of freeze–thaw cycles on unreinforced and basalt fiber-reinforced lunar regolith simulant (LRS) geopolymer. Specimens were subjected to 0, 3, 6, and 10 freeze–thaw cycles. Compressive strength, flexural strength, elastic modulus, peak strain, and failure mode were measured. Damage degree and gain ratio were used to evaluate fiber reinforcement. Results showed that the unreinforced LRS geopolymer exhibited considerable fluctuation in compressive strength during freeze–thaw cycles. Its compressive strength first increased, then decreased; its flexural strength continuously declined; and its elastic modulus and peak strain showed opposite trends, with typical brittle failure. In contrast, basalt fiber-reinforced LRS geopolymer demonstrated superior frost resistance. Its compressive strength increased continuously with freeze–thaw cycles, reaching 23.5% after 10 cycles. Its flexural strength decreased but stabilized, with a damage level of only 16.0% after 10 cycles, significantly lower than that of the unreinforced group (26.1%). Its elastic modulus increased continuously while peak strain decreased gradually, with failure exhibiting some ductile characteristics. Gain ratio analysis showed compressive and flexural strength gain ratios of 1.92 and 1.69, respectively, after 10 cycles, indicating significant reinforcement. Among three classical constitutive models (Guo Zhenhai, Saenz L.P., and Carreira D.J.), the Guo Zhenhai model provided the best fit for stress–strain curves of both geopolymer types under all freeze–thaw conditions, making it the recommended constitutive model. This study provides theoretical support for LRS geopolymer applications in extreme environments such as the lunar surface.