Analyses of concrete microcosmic structure in multi-media environment

The structure of concrete generally serves in multi-media environments; various environments act differently on concrete. The compound action of some severe environments will threaten the duration of concrete and decrease the service life of a concrete structure if improperly handled. In this paper the microstructure of concrete is observed by using Scanned Electric Microscope (SEM) through contrasting experiments in media of acid, alkali and salt with that of freezing-thawing in the same medium environment. This study is to supply a certain basis for changing traditional thinking of mechanical design and to combine construction reliability design with durability of concrete design.

The impacts of urbanization on soil erosion in the Loess Plateau region

The accelerated urbanization has resulted in new soil erosion in the Loess Plateau region since the 1980s. A concept of urban erosion and its impacts on environment are discussed. The experimental studies and field investigations show that those loose silt and earth piles formed by urban construction can be eroded seriously: Under stormy rain, the amount of sediment from steep man-dumped slope is 10.8–12.2 times that of from uncovered slope land; the result of experiments with the wind tunnel also shows that the damage to the surface structure of dry loess can cause serious soil erosion by wind in some cities of the region. Even if in the urban built-up area, there are many loose sandy soil, mud and silt, which are washed into rivers by city’s ground flow in the rainy season. So, anthropogenically induced soil erosion has made soil erosion more serious around the urban areas. And the urban eroded environment has several characteristics such as fragility, complexity, seasonality and quick variability. Urban areas witness a quick economic growth and have more construction projects than rural areas, which brings more intensive changes of environments during a short period of time or adds some new elements to the erosion system. Therefore erosion has experienced more intensive impact by human activities. So, the possible impact of urbanization on erosion environment must be taken into consideration when designing or planning to exploit natural resources or to develop urban areas in the Loess Plateau.

The Erosion Effect of Kapton Film in a Ground-based Atomic Oxygen Irradiation Simulator

In order to investigate the effect of space environmental factors on spacecraft materials, a ground-based simulation facility for space atomic oxygen（AO） irradiation was developed in our laboratory. Some Kapton film samples were subjected to AO beam generated by this facility. The Kapton films before and after AO exposure were analyzed comparatively using optical microscopy, scanning electronic microscopy, atomic force microscopy, high-precision microbalance, and X-ray photoelectron spectroscopy. The experimental results indicate that the transmittance of Kapton film will be reduced by AO irradiation notably, and its color deepens from pale yellow to brown. Surface roughness of the AO-treated sample is already increased obviously after AO irradiation for 5 hours, and exhibits a flannel-like appearance after 15 hours’ exposure in AO beam. The imide rings and benzene rings in kapton molecule are partially decomposed, and some new bonds form during AO irradiation. The mass loss of kapton film increases linearly with the increase of AO fluence, which is resulted from the formation of volatile products, such as CO, CO2 and NOx. The breakage in structure and degradation in properties of AO-treated Kapton film can be attributed to the integrated effect ofimpaction and oxidization of AO beam. The test results agree well with the space flight experimental data.

Erosion–corrosion behavior of austenitic cast iron in an acidic slurry medium

A series of austenitic cast iron samples with different compositions were cast and a part of nickel in the samples was replaced by manganese for economic reason. Erosion–corrosion tests were conducted under 2wt% sulfuric acid and 15wt% quartz sand. The results show that the matrix of cast irons remains austenite after a portion of nickel is replaced with manganese.（Fe,Cr）3C is a common phase in the cast irons, and nickel is the main alloying element in high-nickel cast iron; whereas,（Fe,Mn）3C is observed with the increased manganese content in low-nickel cast iron. Under erosion–corrosion tests, the weight-loss rates of the cast irons increase with increasing time. Wear plays a more important role than corrosion in determining the weight loss. It is indicated that the processes of weight loss for the cast irons with high and low nickel contents are different. The erosion resistance of the cast iron containing 7.29wt% nickel and 6.94wt% manganese is equivalent to that of the cast iron containing 13.29wt% nickel.

Interactions between soil conservation and dryland farming of heterogeneously eroding areas in Loess Hills,China

The unidirectional impacts of soil conservation on dryland farming and local livelihood have been well studied.However,there are gaps in literature regarding the interactions among factors,such as labor force and financial capital,in response to soil conservation,as well as the influence of such interactions on the relationships between environmental projects and agricultural development.By combining the Chinese Soil Loss Equation(CSLE)model and statistical analyses,this study investigated the spatiotemporal characteristics of soil erosion while also identifying the controlling factors that affect crop and livestock farming.The aim was to reveal how these factors interacted to influence agriculture in two case study areas between 2000 and 2017.The results showed that soil erosion substantially declined as a consequence of soil conservation,while the output from crop farming increased,indicating that there was a synergy between soil conservation and dryland farming in both the districts,over time;and factors facilitating crop farming,such as labor force,agricultural machinery,and irrigation,appeared to exert an adverse effect on livestock farming in both areas,implying a tradeoff between livestock and crop farming in the context of programs such as the Grain for Green Program(GGP)in the Loess Hills.Such a tradeoff is a result of the competition for cropland and labor that exists due to grazing prohibition and rural-urban migration.Therefore,policy-related resolutions are required to address the land use conflicts and migration-related rural labor losing due to implementation of the GGP in the Loess Hills.