After high-temperature treatment, both nano-titanium dioxide-modified concrete and ordinary concrete exhibit typical splitting failure. High-temperature heating reduces the mechanical properties and brittleness of concrete and improves the ductility of concrete. The stress–strain relationship of the specimens was obtained through the uniaxial compression test of ordinary concrete and nano-titanium dioxide-modified concrete cube specimens under normal temperature and high-temperature conditions. In addition, the relationship between temperature and damage variables was established, and the unified constitutive model containing damage variables after room temperature and high-temperature treatment of ordinary concrete and nano-titanium dioxide-modified concrete were established. It provides a reference for future research on the mechanical properties of high-performance concrete structures after high temperatures (fire).
The soil and water conservation practices of ecological restoration (ER), fish scale pit (FP), furrow and ridge tillage across the slope (FR), shrub strips (SS), and vegetation-covered ridge (VR) are characteristic of the Jixing small watershed of the low mountain and hilly region of Jilin Province, Northeast China. This study aims to elucidate the effects of soil and water conservation practices on soil conditions after the short-term implementation of practices. Soil samples were collected from five soil and water conservation sites (ER, FP, FR, SS, and VR) and two controls (BL and CT) to investigate their properties. To evaluate the influence of soil and water conservation practices on soil quality, an integrated quantitative index, soil quality index (QI), was developed to compare the soil quality under the different soil and water conservation practices. The results show that not all soil and water conservation practices can improve the soil conditions and not all soil properties, especially soil organic carbon (SOC), can be recovered under soil and water conservation practice in short-term. Moreover, the QI in the five soil and water conservation practices and two controls was in the following order: ER > VR > BL > FR > CT > SS > FP. ER exhibited a higher soil quality value on a slope scale. In the low mountain and hilly region of Northeast China, ER is a better choice than the conversion of farmlands to planted grasslands and woodlands early in the soil and water conservation program.
The black soil of Northeast China has a strong adhesion ability because of its unique physical properties, and the soil often adheres to the surface of the grouser shoes of tracked vehicles during the operation. The adhesion performance depends largely on structure parameters of the grouser shoes. The grouser height, the grouser thickness, and the grouser splayed angle were selected as structure parameters. The adhesion force and adhesive soil mass were selected as indicators of adhesion performance. Therefore, the mathematical model between structure parameters and response indicators was established by the response surface method (RSM). The optimal parameters combination was that the grouser height was 20 mm, grouser thickness was 6.34 mm, and grouser splayed angle was 40.45°. The average data of verification experiments occurred when the adhesion force reached 1.11 kPa and adhesive soil mass reached 22.68 g. Compared with the average value of un-optimized experiment results, the adhesion force and adhesive soil mass reduced by 12.84% and 4.63%, respectively. The relative error of the predicted values and measured values was less than 5%, proving the reliability of the regression models. This study could provide a reference method for parameters optimization, and a new structure of the grouser shoes of tracked vehicles will be designed to reduce adhesion.
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