| Since the 21 st century, ecological equilibrium becomes more and more essential for economic construction and social development. And it has receiving serious attention by the government and the whole society. The excavation of land in the process of infrastructure construction and urbanization not only destroy the original ecological balance, but also cause a large number of bare slopes, which leading to some problems such as water and soil loss. In addition, in the process of the original building demolition and rebuilding will produce large amounts of construction waste, caused serious environmental pollution and resource waste. So, the slope protection and construction waste resource utilization is the two major issues.Porous ecological concrete, as a kind of environment-friendly concrete, has received widespread attention because it's many ecological effects. With the development of the related research, the high basicity, nonstandard mixture ratio design and prepar ation technology have been resolved. However, the application of porous ecological concrete is limited because the rapidly losses and lack of nutrient in porous ecological concrete restricts the growth of plants and the effect of greening. This study focus on the fertilizer supply for porous ecological concrete and to solve the problems about lacking of nutrient for plant, topdressing is difficult and low utilization rate of fertilizer. Cementing material with fertilizer slow-release effect was made and recycled aggregate with porous characteristics was used to prepare porous ecological concrete with fertilizer slow-release effect. The main conclusions as following:(1)Both urea and ammonium hydrogen phosphate were extend the setting time of sulphoaluminate cement. The initial setting times were extended about 14 min to 50 min and 5min to 168 min, the final setting extend about 10 min to 53 min and 3min to 313 min, respectively. The hydration rate, cumulative heat release and early compressive strength of sulphoaluminate cement were decreased. The fluidity of cement paste could extend from 87.0mm to 149.3mm when the content of urea was 0.2wt.% to 4.0wt.%. Low-dosage of ammonium hydrogen phosphate could extend the fluidity of cement paste and the more content of ammonium hydrogen phosphate the small fluidity of cement paste will. Urea made limited effect on the compressive strength of hardened cement paste. When the content of urea was from 1.5wt.% to 2.0 wt.%, the compressive strength could up to 124.0MPa, about 2.0% growth. Ammonium hydrogen phosphate made seriously impact on the compressive strength of hardened cement paste. When content was 4.0wt.%, the compressive strength was lost. This is attributed to that ammonium hydrogen phosphate hindered the hydration of cement and the formation of AFt. The presence of urea and ammonium hydrogen phosphate could make cement hardened paste with nitrogen release effect and nitrogen release rate can reach 22.6% to 95.4%. However, the phosphorus cumulative release rate of the cement hardened paste with ammonium hydrogen phosphate is very low, which is only about 0.03%. So, ammonium hydrogen phosphate is not suitable added to the cement.(2)The porosity and permeable coefficient of porous concrete with recycled aggregate are higher than the porous concrete with limestone aggregate and the compressive strength is lower. The suitable water-cement ratio for recycled aggregate to prepare porous concrete is 0.334, which verifying that the water-cement ratio calculation method for different type aggregate put forward in this article is feasible. The porous concrete withe water-cement ratio of 0.334 and aggregate-cement ratio of 5.0, the total poro sity, connected porosity, permeable coefficient and compressive stre ngth of porous concrete is 43.3%, 38.2 %, 2.72cm/s and 5.0MPa, respectively, which is reach the demand of the plant growth. Total porosity in the range of 39.0% to 47.0% and connected porosity in the range of 37.0% to 39.0%, the relationship between total porosity and connected porosity and the relationship between connected porosity and permeable coefficient are linear and the correlation coefficient is 0.9351 and 0.9667, respectively.(3)Through three different mixing processes combined with three different molding processes and synthesizes the compressive strength, porosity and permeable coefficient of recycled aggregate porous concrete, found that two step mixing process combined with compacted molding the most suitable preparation process for recycled aggregate to prepare porous concrete. Under this preparation process, the total porosity, connected porosity, permeable coefficient and compressive strength is 44.1%, 40.9%, 2.88m/s and 4.2MPa, respectively.(4)The presence of urea can improve the dry shrinkage property of the porous concrete with recycled aggregate. When the dosage of urea is 2.0 wt.%, the drying shrinkage rate is about 1.15×10-4, which is similar with porous concrete with limestone aggregate. The addition of ammonium monohydric phosphate makes the dry shrinkage property become poor. Recycled aggregates modified by sulphoaluminate cement paste with the water-cement ratio of 1.0. After drying in air for 7 days and then preparing for porous concrete. After 20 freeze-thaw cycle, the mass loss of porous concrete is 1.69% and antifreeze performance is improved. When curing ages to 28 days, the p H value of porous concrete with urea is about 8.2, which is lower than reference sample. And the p H values of porous concrete with ammonium monohydric phosphate were higher than reference sample.(5)The presence of urea and ammonium hydrogen phosphate could make porous concrete with nitrogen release effect. The nitrogen release effect is obvio us and the higher urea and ammonium hydrogen phosphate content the higher nitrogen cumulative release rate, which is in the range about 16.1% to 92.0%. However, the phosphorus release effect is poor and the release rate is only about 0.01% to 0.030%.(6)Hydroxypropyl methyl cellulose ether can improve the water retention and washing resistance performance of planting material and the optimum additive content is 0.375%. Ryegrass, green scene 5 and festuca arundinacea can well grow in porous ecological concrete with slow-release fertilizer effect. |
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