In Situ Fabrication of a Superhydrophobic ORMOSIL Coating on Wood by an Ammonia–HMDS Vapor Treatment

A superhydrophobic ORMOSIL (organically modified silicate) coating was in situ fabricated on a wood surface by ammonia–hexamethylisilazane (HMDS) vapor treatment. The wood was immerged in tetraethoxysilane (TEOS), and then the TEOS absorbed on the wood surface was hydrolyzed and condensed to hydrophobic SiO2 nanoparticles with ammonia and HDMS vapor treatment. The effect of the treatment temperature and time on the hydrophobicity of wood was investigated. At a treatment temperature of 50 °C, a superhydrophobic surface was achieved on the wood with a treatment time longer than 2 h. SEM images indicated that there were SiO2 nanoparticles fabricated on the wood surface, and FTIR revealed that the hydrophobic –Si(CH3)3 groups were incorporated on the wood surface. The ORMOSIL-modified wood possessed improved liquid repellency. The water absorption decreased significantly from 72.3% to 31.9% after modification

Investigation of the Fracture Characteristics of a Cement Mortar Slab under Impact Loading Based on the CDEM

For brittle and quasi-brittle materials such as rock and concrete, the impact-resistance characteristics of the corresponding engineering structures are key to successful application under complex service environments. Modeling of concrete-like slab fractures under impact loading is helpful to analyze the failure mechanism of an engineering structure. In this paper, simulation models of impact tests of a cement mortar slab were developed, and a continuum–discontinuum element method (CDEM) was used for dynamic analysis. Concretely, the cracking simulations of a mortar slab when considering the hammer shape and impact velocity were conducted, and the impact process and failure results of the slab structure were analyzed. The results showed that the top fracture area of the mortar slab was significantly smaller than that of slab bottom under impact loadings of the drop hammer. The impact velocity was an important factor that affected the mortar slab’s cracking. With the increase in the initial impact velocity, the effective fracture area of the slab structure increased significantly; the impact force and rupture degree of the mortar slab also showed a linear growth trend. The shapes of the impact hammerhead also had a significant effect on the crack model of the mortar slab. The effective fracture zones of slab structures were close under circular and square hammers, while the effective fracture zone was significantly larger under a rectangular hammer impact. The peak value (45.5 KN) of the impact force under a circular hammer was significantly smaller than the peak value (48.7 KN) of the impact force under the rectangular hammer. When considering the influence of the stress concentration of the impact hammerhead, the maximum impact stress of the rectangular hammer was 147.3 MPa, which was significantly greater than that of the circular hammer impact (maximum stress of 87.5 MPa). This may have meant that the slab structures were prone to a directional rupture that mainly propagated along the long axis of the rectangular hammerhead. This impact mode is therefore more suitable for rehabilitation and reconstruction projects of slab structures

Investigation of the Fracture Characteristics of a Cement Mortar Slab under Impact Loading Based on the CDEM

For brittle and quasi-brittle materials such as rock and concrete, the impact-resistance characteristics of the corresponding engineering structures are key to successful application under complex service environments. Modeling of concrete-like slab fractures under impact loading is helpful to analyze the failure mechanism of an engineering structure. In this paper, simulation models of impact tests of a cement mortar slab were developed, and a continuum-discontinuum element method (CDEM) was used for dynamic analysis. Concretely, the cracking simulations of a mortar slab when considering the hammer shape and impact velocity were conducted, and the impact process and failure results of the slab structure were analyzed. The results showed that the top fracture area of the mortar slab was significantly smaller than that of slab bottom under impact loadings of the drop hammer. The impact velocity was an important factor that affected the mortar slab's cracking. With the increase in the initial impact velocity, the effective fracture area of the slab structure increased significantly; the impact force and rupture degree of the mortar slab also showed a linear growth trend. The shapes of the impact hammerhead also had a significant effect on the crack model of the mortar slab. The effective fracture zones of slab structures were close under circular and square hammers, while the effective fracture zone was significantly larger under a rectangular hammer impact. The peak value (45.5 KN) of the impact force under a circular hammer was significantly smaller than the peak value (48.7 KN) of the impact force under the rectangular hammer. When considering the influence of the stress concentration of the impact hammerhead, the maximum impact stress of the rectangular hammer was 147.3 MPa, which was significantly greater than that of the circular hammer impact (maximum stress of 87.5 MPa). This may have meant that the slab structures were prone to a directional rupture that mainly propagated along the long axis of the rectangular hammerhead. This impact mode is therefore more suitable for rehabilitation and reconstruction projects of slab structures

Study on the microstructure and properties of TiB2-CoCrFeNiW0.2 metal ceramic composites prepared by pressureless sintering

Three types of TiB2-HEA ceramic composite were prepared using a non-equimolar ratio CoCrFeNiW0.2 high entropy alloy (HEA) as a binder, mechanical alloying (MA), and 1600 °C pressureless sintering (PS) processes. The phase analysis results indicate the presence of TiB2, FCC, and TCP phases in the TiB2-HEA composite. A detailed study was conducted on the microstructure of TiB2-HEA composite. The results indicate that there is a certain solid solubility between TiB2 and HEA. The Ti and B elements in TiB2 will enter HEA, and the elements in HEA will also enter TiB2. Along with the discovery of many lattice distortion regions in TiB2, a diffraction pattern of P-43m cubic structure was also observed in HEA. HEA has good wettability with TiB2, so it can not only inhibit the grain growth of TiB2, but also improve the performance of TiB2-HEA composite by utilizing the inherent excellent properties of HEA. There are both intergranular and transgranular fractures in the TiB2-HEA composite. The relative density, flexural strength, Vickers hardness, fracture toughness, and electrical resistivity of TiB2-30 wt%HEA are 99.7%, 680 MPa, 18.6 GPa, 6.4 MPa m1/2, and 5.7 × 10−7 Ω m, respectively

The impact fracture characteristics of concrete slabs under different hammerhead shapes, impact velocities and concrete strengths

To ensure the normal use of concrete slab structures, it is important to understand the impact fracture charac-teristics of concrete slabs. In this paper, the fracture processes of concrete slabs under different hammerhead shapes, impact velocities and concrete strengths are simulated based on a continuum-discontinuum element method (CDEM), and the fracture mechanisms of concrete slabs are discussed by analyzing the fracture forms, fracture degree, hammerhead stress and support reaction. The research results show that concrete slabs with lower tensile strength and larger cohesion easily generate bifurcation and unidirectional cracks due to impact tensile failure. However, concrete slabs with larger tensile strength and smaller cohesion are prone to generate dispersion cracks due to impact shear failure. As the tensile strength increases and the cohesive strength de-creases, the fracture degree of the concrete slab under impact loading increases from 0.00795 to 0.01434; however, the impact reaction of the support slab markedly decreases from 53,998 N to 47,636 N, which indicates the bearing performance of fracture concrete slab increases. With an increasing of impact velocity (3 similar to 5 m/s), the dynamic responses of concrete slab are more obvious, the final fracture degree of the concrete slab linearly increases from 0.00658 to 0.01587, the impact stress of the hammerhead obviously increases from 1.04e8 to 1.86e8 Pa, and the impact reaction linearly increases from 40,801 N to 57,432 N. For different impact velocities and concrete strengths, the hammerhead shapes also have a significant influence on concrete fracture. In conclusion, compared with the impact modes of square and circular hammers, rectangular hammer impact easily directionally fractures the concrete slab structures with different strengths

Compaction Characteristics of Cold Recycled Mixtures with Asphalt Emulsion and Their Influencing Factors

The objective of this study is to investigate the compaction characteristics of cold recycled mixtures with asphalt emulsion (CRME) using the Superpave gyratory compactor (SGC) method. Five characteristic parameters were proposed and calculated including the compaction energy index, the compaction energy index, three compaction energy indicators at different compaction stages. The influence of these parameters and material compositions were analyzed for the pavement performance. The difference between SGC and Marshall double-sided compaction/heavy compaction method was compared. The results show that the proposed parameters can better reflect the compaction characteristics of CRME, and the mixture effect with SGC of 50 gyrations was close to that with 75 blows using the Marshall compaction. The asphalt emulsion contents and compaction temperatures had a significant effect on compaction characteristics, but the effect of aggregate gradations was not significant. The appropriate asphalt emulsion and the new aggregate content can increase the capability of the CRME to resist the permanent deformation. The optimum mixing water content of CRME obtained by the SGC method was reduced by 18%, but the density increased by 3.5%, compared with the heavy compaction method. Finally, a new idea to determine the optimum emulsified asphalt content of CRME was provided through analyzing the compaction characteristic parameters