Study On Synergistic Effect Of Plant Roots And VGC

With the enlargement of urban construction scale and the acceleration of urbanization construction,the ecological balance has been seriously and irreversibly changed.Urban waterlogging disaster prevention and rainwater control have become a hot issue in urban development.Based on this,China proposes to create sponge cities characterized by "natural accumulation,natural infiltration and natural purification".Vegetation growing concrete(VGC)is a new building material which is introduced to construct "sponge city,and takes into account both biocompatibility and engineering function.VGC is a kind of concrete composed of sand-free porous concrete skeleton and plant-growing substrate in the pore,which has certain strength and is suitable for plant growth.In this paper,the preparation technology,mechanical properties,alkali reduction methods,substrates selection and plant compatibility of VGC are studied through experimental analysis,the main conclusions are as follows:(1)The better performance VGC can be prepared by controlling the cement slurry fluidity between 170 and 220 mm,making aggregate even encapsulated in slurry without flowing and cohesion by using "shell-making" stirring process,choosing tamping and vibration combinatorial shaping method,and using film moisturizing maintenance.(2)Porosity plays a decisive role in VGC mechanical properties,porosity of 20%?25%can meet the needs of strength and plant growth.The aggregate quality and cementitious strength at high porosity are the main factors affecting the compressive strength,while the aggregate size and water cement ratio have Iess influence.Adding ultra-fine can improve concrete performance by improving cementitious materials strength,and the best dosage is 40%.The compressive strength of VGC is greatly damaged by fast freezing method.After 50 freeze-thaw cycles,the strength loss rate is 8%?55%,while the damage degree of natural freeze-thaw 1s relatively small.(3)The alkalinity of pore decreases slightly by changing the composition of cementitious material and spraying modified solution.Ferrous sulfate solution soaked for 4 days,oxalic acid solution soaked for 7 days or clear water soaked for 26 days can stabilize the pore pH value to below 8,and there is no large amount of alkaline substance leaching after soaking for 20 hours.(4)In order to achieve better planting effect,the conditions of nutrient,temperature,light,water,acidity and alkalinity needed for plant growth should be satisfied to the maximum extent.As plant growth carrier,VGC needs to be filled with planting substrates to ensure the planting conditions.Among them,the porous base material is mixed with nutrient solution to form mud suspension,which is filled into the pore,and the surface base material is mixed with grass seeds on the concrete surface.Grass species should choose drought-resistant,barren-resistant,alkali-tolerant plants with well-developed roots,such as tall fescue and so on.(5)The results of planting showed that most grass species could grow normally in VGC.After 60 days of turf planting,the roots could penetrate 6 cm thick concrete blocks,but the growth pattern of roots was different from that of soil.(6)The compressive strength of VGC with different proportions decreased significantly to 3.1-4.1 MPa after 30 days of turf planting,and then slowly increased to 5.8-6.8 MPa.The permeability coefficient of VGC increases with the increase of porosity and aggregate size.The permeability after planting is basically the same as that after covering soil,which decreases to 2.3%?3.9%of that of concrete.After planting,aggregate size and porosity have little effect on the frost resistance of planted concrete,and freeze-thaw damage is no longer the main factor to reduce the strength of concrete.