Jianghuai Zhan

This research systematically evaluated the durability performance of low-carbon cement concrete prepared with industrial solid wastes under harsh service conditions. Measurements included mechanical properties and drying shrinkage. Microstructural characterization was carried out using SEM-EDS, MIP, and TG-DTG, revealing a synergistic relationship between microstructural changes and the resulting mechanical and durability behavior of the concrete. The experimental results indicated that adding 25% fly ash (FA) lowered the compressive strength of the CF-25 and BF-25 concrete by 11.30% and 11.39%, respectively, while reducing drying shrinkage by roughly 9.2–9.5%. In comparison, incorporating 5% silica fume (SF) had contrasting effects. It significantly improved the compressive strength of the CS-5 and BS-5 concrete by 18.92% and 9.94%, respectively, but at the cost of increasing drying shrinkage by 6.30% and 18.68%, respectively. Fractal dimension analysis based on thermodynamic relationships showed that the pore structure fractal dimension (Ds) ranged from 2.88 to 2.93. Group C exhibited a higher Ds (2.93) than Group B (2.90), indicating a more intricate pore network associated with greater C-S-H gel formation. With FA addition, Ds decreased to 2.91601 for CF-25 but rose to 2.93244 for BF-25. With SF addition, Ds fell to 2.91182 for CS-5 and 2.88102 for BS-5. Micro-mechanistic analysis revealed that the limited pozzolanic activity of FA at early ages resulted in insufficient hydration products and increased porosity. In contrast, SF contributed to a dense, highly polymerized gel structure and an optimized pore size distribution through its strong pozzolanic reactivity and nano-filling action. The distinct chemical properties of high-calcium and low-calcium cementitious systems further accentuated the differential influences of these supplementary cementitious materials.

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 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.