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As permeable concrete contains more pores and larger pore size when improving its water permeability, it will affect its mechanical properties and durability, so it is of great significance to study the mixing ratio of porous concrete. Studying the mixing ratio of porous concrete is of great significance. The subject is studied in depth from the aspects of mechanical properties and water permeability, in order to prepare high-performance permeable concrete with high compressive strength and meet the requirements of infiltration. Firstly. Optimization of the performance of raw materials and mixing ratios of porous concrete, according to the aggregate gradation, aggregate particle size, and other factors on the mechanical properties of porous concrete, to determine its optimal aggregate mixing ratio. Three groups of high-performance pervious concrete specimens with different aggregate particle sizes and pore structures were examined for their real fine structure. Finally, after the preparation of high-performance pervious concrete was completed, the porosity, fractal dimension, equivalent diameter, contour coefficient, and roundness of the specimens were tested to investigate the effects of several factors mentioned above on the permeability coefficient and compressive strength properties of pervious concrete. The results show that the two-dimensional pore diameter is normally distributed, the diameter size is centrally distributed in the range of 0~10mm, and the number of pores in this range accounts for more than 70%. Gradually increasing aggregate particle size leads to an increase in the proportion of large pores inside the specimen. After the compressive strength test and porosity test, it was found that the water permeability coefficient of the porous concrete was the best for the single-grain limestone aggregate with the equivalent diameter range of 5~8mm. The results of this study have theoretical value in enriching and developing high-performance permeable concrete.

Ceramic casting mould is a kind of complex part which is used in the field of investment precision casting to mold the inner and outer structure of casting. With the increase of the complexity of casting, more delicate and complex casting mould is needed to meet the casting demand. However, the traditional ceramic casting method like injection molding has many disadvantages such as high cost, long research and development cycle, and it is difficult to meet the requirements of increasingly complex fine structure molding. As a rapid prototyping method, 3D printing technology can accurately form complex structures. Its application in casting production can not only solve the problem of forming complex structures, but also reduce the production cost and shorten the production cycle. The 3D printing technology in the application of the ceramic mould production was mainly expounded in this article. The research and application of the ceramic mould was introduced from the types and the features of 3D printing ceramic mould material, typical 3D printing mould technology and post-processing method of 3D printing mould technology. The future development of this technology was prospected, it was pointed out that 3D printing technology can effectively solve the molding problem of complex ceramic casting, so as to meet the casting demand of complex hollow structure metal parts.

Steel fiber reinforced concrete (SFRC) is a kind of multiphase composite material and its tensile strength (ft) and fracture toughness (KIC) cannot be easily measured using small samples due to its highly heterogeneous microstructure. In this study, a novel evaluation is proposed for calculating ft and KIC of brittle heterogeneous solids. The results obtained by this method have been confirmed by three-point bending (TPB) test results of 75 notched SFRC beams in which the length of the corrugated steel fibers is 36 mm. Considering the heterogeneity and discontinuous fracture failure characteristic of SFRC samples, a virtual crack propagation calculation model is established, and the accurate prediction of ft and KIC can be obtained by incorporating the model into the Hu-Duan boundary effect model (BEM). The reasonable range of tensile strength of SFRC used in this paper is about 3.77–5.66 MPa. Compared with the median value of this range, the calculation error of BEM is only 7.69 %. By discussing the influence of α-ratio (defined as the ratio between the height W and the initial notch depth a0) on the predicted results, a value that is less affected by the front and rear boundary is obtained, and the value range is 0.16–0.24. Meanwhile, the exact ft and KIC can be obtained by using only 1–2 groups of samples with reasonable α-ratio. Based on the failure curve of SFRC established by using ft and KIC, the theoretical minimum size of samples with different α-ratio is determined under the condition of linear elastic fracture mechanics (LEFM). This method provides a valuable reference for the estimation of concrete mechanical parameters.

Nitride-based ceramic materials have excellent comprehensive properties such as high strength, high modulus, high temperature resistance, thermal shock resistance and wave-transparent performance. They are the main candidates for high-temperature wave-transparent components. The reports about their application are few, and the preparation technologies and properties need to be improved. In this paper, the research progress of nitride ceramics, nitride composite ceramics and nitride ceramic matrix composites was summarized. It is found that the comprehensive properties of porous Si3N4 ceramics, BN-Si3N4 composite ceramics and BNw/Si3N4 composites are excellent, with the dielectric constant less than 5, the dielectric loss less than 0.01, and the room-temperature flexural strength higher than 200 MPa, respectively. In this paper, the existing problems of the studies on the nitride-based ceramic as high-temperature wave-transparent materials were analyzed, which is mainly that the mechanical properties and dielectric properties are difficult to improve in coordination, and the future development direction of the selection of high-temperature wave-transparent material systems and preparation technologies are prospected.

The commercial SAPO-34 zeolite with 0.38 nm pore size and ZIF-8 particles with 0.34 nm aperture size were separately dispersed into different polymer matrix, to prepare the mixed matrix membranes (MMMs) for gas separation. The dispersed situation of the SAPO-34 and ZIF-8 particles in matrix and the influence of the fillers on the separation performance of the membrane had been investigated in this study. The as-synthesized MMMs showed a better trade-off between permeability and selectivity than the pure polymer membrane and the performance could exceed or close to the upper bound line of polymer membrane for CO2 and CH4 separation. The CO2 permeability and CO2/CH4 ideal selectivity of the 6FDA-mDAT MMM containing 40 wt% SAPO-34 zeolite was 190 barrer and ca. 60, respectively. The 6FDA-TrMPD based MMMs containing 20 wt% ZIF-8 provided a permeability of C3H6 and an ideal selectivity of C3H6/C3H8 at 24 barrer and ca. 17, respectively. These separation performances were in a suitable agreement of the theoretical value from Maxwell model.

Silicon carbide matrix composite reinforced by both SiC and carbon fibers [(SiC-C)/PyC/SiC] to alleviate the thermal residual stresses (TRS) between carbon fiber and SiC matrix, then reduce the microcracks in the SiC coating as well as in the matrix, was fabricated by chemical vapor infiltration (CVI) process. Compared with C/PyCHT/SiC composite in which PyC interphase was heat-treated at 1800°C in argon to lower the fracture energy of the interphase, the TRS in SiC matrix and SiC coating was reduced by 69.5% and 62.2%, respectively. Coating cracks density was 50 cracks/m for (SiC-C)/PyC/SiC composite, and 1090 cracks/m for C/PyCHT/SiC composite. Carbon phases could be protected in (SiC-C)/PyC/SiC composite when the composite was subjected to temperatures ranging from 700°C to 1300°C in air for 10 h. The residual strength of (SiC-C)/PyC/SiC composite was higher than those of C/PyCHT/SiC composite below 1200°C. The residual strength of (SiC-C)/PyC/SiC composite was lower than those of C/PyCHT/SiC composite at 1300°C because of the recession of SiC fiber.