Vegetation concrete is one of the most widely used substrates for slope ecological protection in China. However, there are still some imperfections that are disadvantageous for plant growth, such as high density, low porosity, insufficient nutrient retention ability and so on. In this paper, the effect of wood activated carbon and mineral activated carbon on the physicochemical properties of vegetation concrete is studied. The experimental results show that the activated carbon proportion in vegetation concrete is positively related to the porosity, permeability coefficient, water holding capacity, and nutrient content and retention ability, while it is negatively related to the dry density, water retention ability, cohesive force and internal friction angle. However, it should be noticed that when the proportion exceeds 2%, the average height, aboveground biomass and underground biomass of
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decrease with increasing proportion of activated carbon. The effect of wood activated carbon is generally more remarkable than that of mineral activated carbon. In addition, according to the research results, the effect of activated carbon on vegetation concrete can last for at least half a year, although it does slowly deteriorate with increasing time. By comprehensive consideration of the current industry standard, previous research results and economical reasoning, the recommended type of activated carbon is wood, with a corresponding suitable proportion ranging between 1 and 2%.
Vegetation concrete is a typical artificial composite soil commonly used for ecological restoration on slopes. The strength and stability of vegetation concrete would be reduced when it is used in areas where freeze–thaw cycles occur frequently. For exploring the changes of structural properties of vegetation concrete under freeze–thaw cycles, an indoor simulation experiment of vegetation concrete samples containing 25 and 30% water content was carried out, so as to test the changes of specimen surface, volume, ultrasonic wave velocity, shearing strength, and microscopic structure. The microstructural parameters were analyzed quantitatively with Image-Pro Plus software. The experimental results indicated that as cycles of freeze–thaw grow, the macroscopic changes of samples included steadily rising surface crack rate, increasing first and then decreasing volume, greatly reducing ultrasonic wave velocity and gradually decreasing shear strength. The inner structure of samples slowly deteriorated from overall dense to dispersed with decreasing cement hydration crystals, pores resulting from dispersion and destruction of bulky grains, higher surface porosity, and smoother particles in microscopic aspect. When compared with samples containing 25% water content, the microstructure of the 30% water content sample was more affected by the freeze–thaw cycle, and its structural weakening effect was more obvious. Reduced cement hydration crystals, lower inter-particle bonding force, and increase in the number of large pores were the main causes of degradation of vegetation concrete structure. Electrical engineering students can refer to the analysis methods in this paper to evaluate the structural performance of any electrical engineering material.
The physical and mechanical properties of the ecological slope protection substrate will be affected by long-term variation of the meteorological condition, resulting in the stability of the substrate being reduced. So an artificial substrate of vegetation cement-soil was selected as the research object to prepare specimens with the different initial moisture content of 13%, 19%, 25%, 31%, 37%, and 43%. And a series of tests are conducted to investigate the evolution of the physical and mechanical properties under drying-wetting cycling conditions. Typical results of the vegetation cement-soil evolution can be divided into three stages: cement hydration stage, shrinkage stage, and stabilization stage. In terms of different initial moisture content, the shrinkage cracks number, cracks length, crack width, and cracks surface area are increased first and then stabilize with the increase of the number of drying-wetting cycles. In contrast, the cohesion and internal friction angle of the vegetation cement-soil is reduced with the increase of the number of cycles. Comprehensive analysis shows that the initial moisture content of vegetation cement soil ranges from 25% to 31% is the optimal choice to ensure substrate stability in production practice.
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