Search

To investigate the effects of wet–heat–salt coupling environment (WHSCE) and the content of polyvinyl alcohol (PVA) fibers on the durability of cementitious composites (CC), a series of durability tests were carried out. In this study, the salt concentration in the WHSCE was set to 5%, the temperature at 50°C, and the relative humidity at 100%. Six different contents of PVA fibers were set up in the test for exploring their effects on the durability (impermeability, chloride ion penetration resistance, freeze–thaw resistance, and chloride salt erosion resistance under dry and wet cycle conditions) of CC. The results showed that durability of CC under the WHSCE was enhanced regardless of the content of PVA fibers added. At the PVA fiber amount of 1.2%, the impermeability pressure, electric flux, mass loss rate, compressive strength loss rate, and compressive strength corrosion resistance coefficient under the WHSCE reached the optimal values. This indicated that the durability of CC was most favorable when the amount of PVA fibers was 1.2% since many engineering structures are subject to erosion by various factors in the ocean, which can inevitably affect the service life of the purchase. In this study, the effect of PVA fiber content on the durability of CC in complex environment is studied, which provides experimental data and analytical ideas for improving engineering located in the ocean, hoping to provide a theoretical basis for their subsequent application in practical engineering.

Graphene oxide (GO) is a two-dimensional derivative of graphene material, with carboxy, hydroxy group functional groups at the middle of the sheets, and oxygen-containing functional groups at sheet edges. It has multiple advantages, such as high strength, hydrophilicity, and strong reactivity. With the development of construction materials, GO has been widely used as a nano-reinforced material in cement-based composites (CBCs). Based on a large amount of relevant literature, the preparation and dispersion behavior of GO-reinforced CBC are summarized. Besides, the impact of GO on the workability, volume stability, mechanical performance, and durability of CBC are discussed. Moreover, the influencing mechanism of GO on the hydration of CBC is expounded. From the findings of this review, the following conclusions can be drawn: the fluidity of CBC will be decreased when GO is evenly dispersed in the cement slurry, which results in a loss of workability of CBC. Meanwhile, the addition of GO improves the volume stability of CBC, while the tensile, compressive, and flexural strengths are all improved to varying degrees. The improvement of GO on the durability of CBC is mainly reflected in the corrosion resistance and permeability resistance. In addition, problems existing in the current research are summarized and future perspectives are put forward. The review work in this article could offer important guidance for further research and implementation of GO-doped CBC in practical engineering.

As a promising novel route towards highly efficient optoelectronic devices, based 3D core-shell light emitting diodes (LEDs) have attracted increased attention in recent years. In comparison to conventional 2D thin film LED, the 3D LED systems using a core-shell geometry with high aspect ratio are a breakthrough in technology with lots of advantages. In this paper, we review our developed growth strategies of these LED systems on and sapphire substrates. A catalyst free selective area growth of 3D core-shell LED systems was realized using patterned substrates by metal organic vapor phase deposition in a convenient continuous-flux growth mode. We have recently suggested that the surface polarity plays a crucial role for the morphology of 3D structure growth. In order to analyze the surface polarity of 3D submicron or micron structures, Kelvin probe force microscopy and selective etching techniques have been developed. During the growth of submicron rods and micron columns on patterned /sapphire templates, mixed polarity effects could be detected. A new "truncated pyramid + column" growth method was developed to effectively avoid the formation of mixed polarity and realize single N-polar 3D devices. Transmission electron microscopy and spatially and spectrally resolved cathodoluminescence measurements evidently prove the core-shell structure of 3D LED systems. [ABSTRACT FROM AUTHOR]