The turbine rotor component is one of the core components of gas turbine engine (GTE). Based on the inspiration from nature spider web as one of excellent toughness and collaborative bearing characteristics, we proposed an idea of preparing ceramic matrix composites (CMCs) turbine blisk, which has a spider web structure (SWS) preform. We invented a new method of designing SWS preform and prepared SWS-SiC/SiC turbine blisk. The SWS-SiC/SiC turbine blisk was tested via super-spin experiments in room temperature. The results show that its breaking speed reaches to 118 000 r/min (at a blade tip speed of 702.84 m/s), which is 3.09 times greater than that of the conventional 2D-C/SiC turbine disk, and 1.86 times greater than that of the target speed (85 000 r/min) of a GTE turbine blisk. The results of target speed test indicate that the first order frequency, second order frequency and third order frequency of SWS-SiC/SiC turbine blisk can be reduced by 0.41%, 0.03% and 0.26%, respectively.

In order to explore the mechanism of action of fiber in alkali-activated materials, 26 groups of fiber reinforced alkali-activated mortar (FRAAM) were prepared at different length to diameter ratios, volume contents of polypropylene fiber (PPF) and water-binder ratios. The influence of fiber reinforced index (I) on the slump spread, flow rate, apparent density, ultrasonic wave velocity, compressive strength, bending strength, and crack fractal dimension of FRAAM was investigated. The results show that the effect of water-binder ratio on the plastic viscosity of FRAAM is more dominant than that on the yield stress. When I is less than critical I (I_c, i.e., 100), the influence of fibers is slight, the distance between fibers is far, and the workability of FRAAM is basically not affected. However, fibers are difficult to limit the cracking of mortar and improve its mechanical properties. When I is between I_c (i.e., 100) and dense I (I_d, i.e., 350), the flexural strength, compressive strength and fracture fractal dimension of FRAAM improve, and the FRAAM can still flow freely under dead weight. When I is higher than I_d (i.e., 350), significant fibrous clumps degrade the FRAAM workability, resulting in a poor compactness and a reduced compressive strength. The I thresholds of PPF-FRAAM are 100 and 350 for loose and tight packing, respectively, and the optimal volume fraction of PPF is between 100/(l/d) and 350/(l/d).

The microstructure of magnesium silicate hydrates pastes in different Mg/Si molar ratios was investigated by X-ray diffraction, Fourier transform infrared spectroscopy, solid-state nuclear magnetic resonance and thermogravimetric analysis, respectively. The results reveal that the formed magnesium silicate hydrates (M-S-H) is a main structure of layered tetrahedra with some chain tetrahedra and branching chain tetrahedra. The layered tetrahedra is dominated by Q³_a at a higher Mg/Si molar ratio, and the layered tetrahedra is Q³_b at a lower Mg/Si molar ratio. The contents of Q¹, Q² and Q³, especially Q² in the system of MgO-SiO₂-H₂O, all increase as the Mg/Si molar ratio increases. Also, the content of magnesium hydroxide (MH) increases, the content of unreacted Q⁴ silica decreases rapidly, the degree of hydration reaction increases, the degree of gel order and the degree of gel polymerization decrease. At a long age, the decomposition rate of MH increases, and the complexity of the gel structure increases, and the prolonged hydration time is conducive to the formation of diversified layered silicon-oxygen tetrahedral structures and the occurrence of M-S-H polymerization. The water structures of M-S-H are free, confined and structural water. The hydroxyl group is bonded with Mg²⁺ ions or combined with adsorbed water. Chain tetrahedra and branching chain tetrahedra are linked to hydroxyl groups, but Q³ silicate sites are not directly linked to hydroxyl groups. The molar ratio of Mg and Si or structural water and Si in a gel is a fixed value.

The effect of tetrasodium hydroxyethylidene diphosphonate (HEDP.Na4) on the fresh and hardening properties of alkali-activated slag materials (AASM) was investigated. Compared with the control group, the initial and final setting time of AASM made with HEDP.Na4 are delayed by 43.8% and 25.0%, respectively. The mini slump of AASM with HEDP.Na4 is increased by 15% and its yield stress is decreased from 57.2 Pa to 26.6 Pa, as compared with AASM without HEDP.Na4. In addition, the compressive and flexural strengths at 3 days of AASM with HEDP.Na4 are reduced, but those at 28 days are increased by 15% and 11.6%, compared with AASM without HEDP.Na4. HEDP.Na4 can reduce the early hydration heat, modify the pore structure, and reduce the total porosity of AASM matrix. Comprehensively, HEDP.Na4 effectively improves the early working performance of AASM and the later hardening performance slightly. This research can provide a guidance for the application of AASM in construction engineering.

The growth of crystal in the initial stage have an impact on the quality of crystal in the subsequent growth. In this paper, the surface and micropipes morphology of SiC in the initial stage of growth was investigated by optical microscopy. At 8×10⁴ Pa and 1 800-2 100 ℃, the growth step appears on the seed crystal surface due to the atomic migration. Also, the micropipes seriously disturbe the movement of normal step flow, and a circular pit occurs around the micropipes. And no polytype transformation occurs at the micropipes. At 2×10⁴ Pa and 2 150-2 300 ℃, multiple SiC nuclei are formed in the center of the seed crystal surface. Obvious stress regions appear near the crystal edge due to the existence of micropipes. The stress is mainly in the region close to the micropipes and towards the crystal edge, indicating that the step flow moves from the center to the edge. In addition, SiC substrate was also characterized by atomic force microscopy, indicating that atom steps with different orientations appear on the substrate surface, which may originate from the step morphology of the crystal grown in the initial stage.

The durability problem of concrete structures is severe in deicing salt and marine areas. The coarsen of pore structure caused by freeze-thaw cycles (FTCs) can promote chloride transport. The pore solution can freeze into ice during the decrease of freezing temperature and consequently block chloride transport. Also, the change of chloride concentration affects the phase transition of pore solution and then chloride transport. This paper proposed a model considering freezing rate of porous solution during FTCs to analyze the effect of icing on the ionic transport. A multi-phase numerical model for coupling the binary actions of freeze-thaw and chloride transport was proposed and also verified via multiple third-party experiments. The results indicate that the freezing rate and chloride concentration increase with the increase of FTCs, and the temperature and duration of FTC both have an impact on the chloride transport. In addition, the increase of solution concentration also accelerates the chloride transport and the concrete structure deterioration although it is conducive to the decrease of pore freezing temperature and freezing rate.

Glass ion exchange method is still widely used in emerging fields such as information display, aerospace, high-speed railway and optical communication, and its corresponding research is in the ascendant. Previous research work on the ion exchange mainly focuses on the mechanism of glass ion exchange to find new ion exchange pairs, which provides a theoretical support to realize higher mechanical and optical properties of glass, the optimization of ion exchange process parameters and the use of modern means such as auxiliary electric field to realize independent control of ion exchange and improve ion exchange rate. Different performance evaluation indexes are proposed for different application scenarios of ion exchange. The performance indexes of ion exchange reinforced glass mainly include surface compressive stress and layer of depth, while the performance index of waveguide glass is mainly refractive index gradient. This review summarized recent research progress on glass ion exchange based on the aspects above.

Thaumasite form of sulfate attack (TSA) in cement-based materials frequently occurs from transportation and hydraulic engineering in western China. The damage and concealment from TSA in cement-based materials are greater than those of conventional ettringite type and gypsum type sulfate attack. In this review, the physical and chemical properties of thaumasite were summarized, and the methods for characterizing thaumasite were also represented. Meanwhile, the different mechanisms of thaumasite formation and affecting factors of TSA were analyzed. The prevention and suppression measures of TSA were introduced. In addition, some aspects for future studies on TSA were also discussed.

The distribution and orientation of fibers in the matrix have a great impact on the characteristics of strain hardening, multiple cracking and crack self-healing of engineered cementitious composites (ECC). Based on recent work on ECC fiber distribution, this review briefly introduced the characterization parameters and methods of fiber distribution. Effect of fiber distribution on the mechanical properties of ECC was represented from micro- to macro-scale. Three factors affecting ECC fiber distribution are fiber characteristics, matrix characteristics and molding process. In addition, some problems in the current research of ECC fiber distribution were also discussed, and the future research aspects were given.

The accelerated carbonation on the properties of recycled concrete aggregates is important for the recycling of waste concrete, sequestration of CO₂ and reduction of carbon emissions. In this review, the mechanism of accelerated carbonation on the recycled concrete aggregates and the physical properties and microstructure changes of recycled concrete aggregates enhanced by accelerated carbonation were introduced. Some factors for efficient CO₂ treatment on the properties of recycled concrete aggregates were summarized. The physical properties, durability and microstructure improvement of recycled concrete containing CO₂ treated recycled concrete aggregates were analyzed. In addition, the perspectives for future research were also proposed.