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The area where lies west of Taihang Mountain, east of Qinghai Lake, south of Daqing Mountain, north of Qinling Mountain, including a portion or most of the area in the middle reach of the Yellow river is regarded as a big natural region part. Especially, in midland and northwestward is Loess Plateau, which is rugged and suffused by hillocks and ravines, with hostile ecological environment and poor vegetation cover, is covered with sand soil with poor scourresistance and water retention, such as brown soil, light Heilu soil, general Heilu soil, glutinous Heilu soil, lithoid loess, lacunaris loess, red arenaceous mud rock, gritstone, grit. It is unfit for plants growing, and then application of the sterile soil is confined for its low intensity, poor water tolerance and low activity as building material. Based on the research of local soil character, this article attempts to investigate the activation of soil from the middle Yellow River valley and preparation of earth concrete and degradable earth concrete, in order to find a new building material with well behavior for the new rural construction. From the research of experiment, some original conclusions are as follows:1. From the investigation and analysis of the soil in seven areas where water loss and soil erosion is more serious in the middle reach of the Yellow River, the constitution and physical status of soil is clearly as follows: Most of particles are powdery, and contain little organic matter and scarcely any nutrients but excessive quartz showed in chemical and mineralogical analysis, which cause soil’s low activity. This appears most clear in Yulin and Shenmu on the edge of desert.2. To use phosphoric acid as activator can significantly enhance soil’s activity, adhesion stress and water-resistance: Phosphoric acid can activate the soil effectively. As the experiment shows, samples composed of soil added into phosphoric acid show higher compressive strength than it composed of pure soil. The more phosphoric acid in it, the higher compressive strength and better water-resistance it shows. The infrared and microcosmic analysis shows that phosphoric acid, which can change the hydroxyl on the surface of soil, reacts with calcium carbonate in the soil to create calcium phosphate crystalloid, which distributes around soil particles to cement the soil.3. The earth concrete which activated by phosphoric acid have favorable mechanical and physical properties, especially favorable water-resistance: As the experiment shows, the compressive strength and water-resistance can be effectively carried out by stabilized with either cement or lime. Moreover, lime-earth concrete which mixed with phosphoric acid has finer performance than ordinary lime-earth concrete: when the ratio was about 4%, the compressive strength was 19.4MPa at 28 d hydration period, and the softening coefficient was 0.95. However, the result shows that physical properties of the earth concrete could be reduced with higher phosphoric acid.4. Proposed the design to ecological degradable earth concrete: Ecological degradable earth concrete based on active system、bonding system and degradable plant fiber reinforced system. On the basis of compressive strength, taken degradable of the inorganic or organic reinforced system and plant fiber system, let the cycle of earth-earth concrete-earth come true.
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