Fly ash, a supplementary cementitious material, is normally used in conjunction with portland cement to improve the durability properties of concrete in the field, such as sea-crossing bridges, high-speed railways, and mass concrete in dams. Currently, these concrete structures are frequently exposed to sulfate environments. The object of this paper is to investigate the relationship among content of calcium hydroxide (CH), formation of gypsum, and compressive strength, as well as the relationship among the formation of ettringite, pore structure, and expansion properties in blend cement paste at long-term sulfate attack, up to 1,110 days. Mercury intrusion porosimetry (MIP) and thermo gravimetric (TG) analysis were used to evaluate the pore structure and content of CH, respectively. The results show that there is a significant negative relationship between CH content and the coefficient of compressive strength during sulfate attack as more gypsum formation is contributed for the loss of strength. Compared to the reference sample, the addition of 20% and 40% fly ash decreased the CH content by 16.7% and 25.1% through the pozzolanic reaction, which reduced the formation of gypsum and prevented the decalcification of calcium silicate hydrate (C-S-H). Crystallization pressure, due to the formation of ettringite in a limited space, is discussed to explain the cracking of cement-based materials. Several harmful pores ($>0.1\mathrm{\mu m}$ ) were formed in the reference sample due to crystal pressure with the formation of ettringite, which caused the expansion and exacerbated the diffusion of sulfate ions. The pozzolanic reaction of fly ash also improved the pore structures and reduced the degree of supersaturation of ettringite by preventing the ingress of external sulfate ions.

Wasted concrete was often used as a recycled aggregate instead natural stone in fresh concrete to reduce the environmental impact in a decade. However, because of the residual mortar interface, the performance of recycled aggregate was weaker. In this paper, the recycled aggregate was prewetted, and the effects of prewetted degree on the workability, strength, and durability of concrete were studied. The properties of the interfacial transition zone (ITZ), including microhardness, pore structure, and width, were also investigated. The results show that the workability intensity increased with the increase in prewetted degree from 0% to 100%, while the strength was first increased and then decreased with the optimal value of 43.3 MPa when the prewetted degree was 50–65%. The water absorption and chloride ion diffusion coefficient were also decreased by approximately 10% at minimum with the prewetted degree around 55% because of the declined fraction of pores larger than 50 μm and smaller porosity. The width of ITZ was first sharply decreased with a prewetted degree of 50–65%, then increased again with higher moisture, while microhardness of the ITZ showed the opposite trend and reached 82.7 MPa at maximum, at 50%. The appropriate moisture (50–65%) improved the pore structure and hydration products with an internal curing effect. When the moisture content was too high, the excess water was released from aggregate to the matrix, causing a higher water–cement ratio at ITZ; the porosity and the number of macrospores were increased to weaken the performance of concrete.

Alkali-activated fly-ash–slag blending materials (AA-FASMs) are gradually being studied and applied more because of their good performance. There are many factors affecting the alkali-activated system, and the effect of single-factor variation on the performance of AA-FASM has been mostly reported; however, there is a lack of unified understanding of the mechanical properties and microstructure of AA-FASM under curing conditions and multiple-factor interaction. Therefore, this study investigated the compressive strength development and reaction products of alkali-activated AA-FASM under three curing conditions including seal (S), dry (D) and water saturation (W). Based on the response surface model, the relationship between the interaction of slag content (W_SG), activator modulus (M) and activator dosage (R_A) on its strength was established. The results showed that the maximum compressive strength of AA-FASM after 28 days of sealed curing was about 59 MPa, while the strengths of dry- and water-saturation-cured specimens decreased by 9.8% and 13.7%, respectively. The seal-cured samples also had the smallest mass change rate and linear shrinkage and the most compact pore structure. Due to the adverse effects from a too-high or too-low modulus and dosage of the activators, the shapes of upward convex, slope and inclined convex were under the interaction of W_SG/M, W_SG/R_A and M/R_A, respectively. The correlation coefficient R² > 0.95 and p-value < 0.05 indicated that the proposed model could be used to predict strength development given the complex factors. Optimal proportioning and curing conditions were found to be W_SG = 50%, M = 1.4, R_A = 50% and sealed curing.

Double liquid grouting materials (DLGMs) are composed of slurry A and slurry B. In response to the need for sustainable development, there is currently a focus on improving the utilization rate of resources. In this paper, industrial solid waste fly ash, slag, and ordinary Portland cement were used to prepare slurry A, while sodium silicate was used as slurry B. Slurry C was made by adding slurry B to slurry A. The mix design parameters of the DLGMs, with large amounts of fly ash, were optimized based on the response surface method. The results showed that the relative content of cement and the reactivity and morphological effect of supplementary cementitious materials (fly ash and slag) were the main factors affecting the operable time, viscosity, and stability of slurry A. The relative content of cement and the sodium silicate modulus were the main factors affecting the operable time of the DLGMs. Compared to the C30F70S0-Z_3.3 group (where C, F, S, and Z represented cement, fly ash, slag, and sodium silicate modulus, respectively), the operable time of the C0F70S30-Z_3.3 group increased by approximately 36 min. As the sodium silicate modulus was lowered to 2.3, the operable time of the C0F70S30-Z_2.3 group increased by about 32 min compared to that of the C30F70S0-Z_2.3 group. The established model and response surface can well reflect the influence of multiple factors on the properties of the DLGMs. When the mass ratio of cement/fly ash/slag in slurry A was 7.5%: 70%: 22.5%, and the sodium silicate modulus and content of slurry B were 2.8 and 10%, respectively, the 28-day compressive strength of the DLGMs can reach up to 11.3 MPa. The content of fly ash was the most significant factor affecting the 28-day compressive strength of the DLGMs, followed by the sodium silicate content. The least influential factor was the sodium silicate modulus. The XRD and SEM results showed that a large amount of Ca²⁺ produced by cement hydration can quickly react with [SiO₄]^4- in sodium silicate to form C-S-H gel. Moreover, it also promoted the hydration of C₃S and C₂S in grouting to produce more C-S-H gel, which was conducive to the alkali activation of slag and fly ash, resulting in a denser microstructure and hence, yielded obvious increases in the compressive strengths of the DLGMs.

V₆O₁₃ thin films were deposited on indium-doped tin oxide (ITO) conductive glass by a concise low-temperature liquid-phase deposition method and through heat treatment. The obtained films were directly used as electrodes without adding any other media. The results indicate that the film annealed at 400 °C exhibited an excellent cycling performance, which remained at 82.7% of capacity after 100 cycles. The film annealed at 400 °C with diffusion coefficients of 6.08 × 10⁻¹² cm²·s⁻¹ (Li⁺ insertion) and 5.46 × 10⁻¹² cm²·s⁻¹ (Li⁺ extraction) in the V₆O₁₃ film electrode. The high diffusion coefficients could be ascribed to the porous morphology composed of ultrathin nanosheets. Moreover, the film endured phase transitions during electrochemical cycling, the V₆O₁₃ partially transformed to Li_0.6V_1.67O_3.67, Li₃VO₄, and VO₂ with the insertion of Li⁺ into the lattice, and Li_0.6V_1.67O_3.67, Li₃VO₄, and VO₂ partially reversibly transformed backwards to V₆O₁₃ with the extraction of Li⁺ from the lattice. The phase transition can be attributed to the unique structure and morphology with enough active sites and ions diffusion channels during cycles. Such findings reveal a bright idea to prepare high-performance cathode materials for LIBs.