Study On Nutrient Holding Capability And Physical Parameters Of The Vegetation Concrete Under Freeze-thaw Cycles

In the application of the vegetation concrete substrate for the slope repair in the high-cold areas,the freeze-thaw cycle is the main reason for the loose,collapsing and shedding of the ecological slope protection substrate.The repeated freeze-thaw cycle damages the pore structure of the substrate,reduces its fertilizer protection performance,and then affects the effect of the slope repair.Based on this,this paper takes the vegetation concrete as the research object,selects the number of freeze-thaw cycle as the influence factor,and carries out the simulation experiments in the freeze-thaw cycle,and probes into the change of the nutrient holding capacity and physical parameters of the vegetation concrete with different water content gradient under different freeze-thaw cycles,and the fixing ability and substance of various available nutrients.The relationship between parameters is studied.The experimental samples of vegetation concrete with different initial water content gradient（18%and 24%）were prepared in the experiment,and 64 freeze-thaw cycles were simulated with a programmable constant temperature and constant humidity test box.The nutrients of the base material after the freeze-thaw cycle were studied,including the organic matter,total nitrogen,ammonia nitrogen,nitrate nitrogen,total phosphorus,available phosphorus,total potassium and available potassium.The results showed that the content of organic matter increased first and then decreased,the content of total nitrogen decreased first,and the content of nitrate nitrogen decreased gradually.The content of ammonia nitrogen,available phosphorus and available potassium increased,and the content of total phosphorus and total potassium did not change.Then,the leaching experiment was carried out on the base material after freeze-thaw cycle,and the nutrient content of the sample after leaching was measured.According to the comparison of the nutrient content of the samples before and after leaching,the results showed that the content of total phosphorus and total potassium before and after the leaching was basically unchanged with the increase of the number of freeze-thaw cycle,and the leaching loss rate of other nutrients increased gradually.The nutrient holding capacity of the base material gradually decreased.Then 4 physical indexes,aggregate,particle gradation,disintegration and permeability,were selected to study the effect of freeze-thaw cycle on the physical parameters of the base material with different initial water content.The content of aggregate in different initial water content,the content of water stable aggregate,the content of micro aggregate and the composition of particle size at different levels were obtained by dry sieve method,wet sieving method and suction tube method.According to the content of aggregate and particle gradation above,the index of 0.25mm aggregate content(R_0.25),aggregate average weight diameter（MWD）,geometric mean diameter（GMD）,dispersion rate,agglomeration degree and structural failure rate are used as the substrate structure characteristics index,indicators such as the permeability coefficient and disintegration coefficient are to study the physical characteristics of substrates.According to the experimental study,it is found that the freeze-thaw cycle causes the large particle size to break into small particle size because of the frost heave effect.The average weight diameter of the substrate gradually decreases with the number of freeze-thaw cycles,which is less than the 0.25mm aggregate content and the particle.The compasition gradually increased,and the aggregate content and particle composition of the other large particle sizes decreased to varying degrees.With different initial water content,the hydration reaction degree of cement in the curing process is different,and then the structural characteristics of the substrate before the freeze-thaw cycle effect of the substrate are different.Moreover,with the increase of moisture content,the effect of freeze-thaw cycle on the structural properties of substrates is also increasing.Finally,in order to further explore the nutrient holding capacity of the vegetation concrete base material under the freeze-thaw cycle,8 kinds of nutrient indexes were used as the main component analysis index with the change of the freeze-thaw cycle times,and the nutrient leaching rate of the base material was analyzed and sorted by the principal component analysis method,and the nutrient fixation of the base material was obtained.The contribution rate of capacity and comprehensive evaluation were carried out.The results showed that nutrient leaching and loss of substrate increased with the increase of freeze-thaw cycles.In order to investigate the relationship between the material retention and physical parameters of the base material,the relationship between the nutrient holding capacity and the 12 physical parameters were analyzed,and the physical parameters were found to be the most relevant to the fixation capacity of each nutrient,which indicated the direction for improving the properties of the base material.