Effect Of Controlling Sustained Release Of Planting Concrete And Its Effect On Plant Growth Performance

With the development of “The Belt and Road Initiative” infrastructure construction,such as roads,railways and embankments will inevitably destroy the original landforms and plant cover,causing soil erosion,uncovered hills and damage to roadbeds and dams.Bare mountain ecological disorder,the serious loss of nutrients and the ever-increasing reciprocity have accelerated the vicious cycle.Planted concrete with solid soil slope protection and restoration of the mountain landscape came into being.However,the traditional planting concrete is seriously deficient in “cultivation”,and the survival rate of herbaceous plants is low,and it is not suitable for environments with severe nutrients such as bare mountain.Therefore,there is an urgent need to develop a new type of planting concrete to realize the regreening of barren nutrients such as bare hills.In this paper,the long-term fertilizer effect sustained-release characteristics of planting concrete were achieved by use of Osmocote and IBDU as slow-release fertilizers.The former is a capsule structure and is surrounded by a semipermeable membrane,which can effectively control the release of fertilizer efficiency;the latter is slightly soluble at room temperature.In water,the release of fertilizer is slow.At the same time,large-aperture(>3mm)planting concrete was designed and matched with the growth of vinelike Euonymus fortunei.The vines of this plant grow fast,have many branches,and have high green coverage.What's more,it can firmly fix to the concrete surface through aerial roots,even interspersed inside the concrete.So it is suitable for planting steep slopes.The main conclusions are as follows:(1)The incorporation of Osmocote and IBDU both prolonged the setting time of sulphoaluminate cement,the initial setting time was extended by 4 min to 108 min and 2 min to 20 min respectively,and the final setting time was extended by 9 min to 141 min and 2 min to 33.5min,respectively.Incorporation of Osmocote increases the cement paste fluidity from 160 mm to 275 mm,and the addition of IBDU increases the cement paste fluidity from 160 mm to 185 mm.The two fertilizers were added,both will make the early compressive strength of sulphoaluminate cement reduce,but the impact on the late strength is not obvious.From the analysis of hydration heat,the X-ray diffraction pattern of hydrated products and the TG-DSC curve,the addition of fertilizers slows down the rate of hydration of sulphoaluminate cement,and the cumulative heat release also decreases to a certain extent.After the addition of fertilizer,no new hydration minerals were found,and ettringite(AFt)is the main hydration product.With the increase of fertilizer content,the formation of ettringite is gradually reduced,that means the addition of fertilizers to some extent hinder the formation of ettringite(AFt).(2)The sulphoaluminate cement hardened paste has a certain sustained release effect to both fertilizers,and the cumulative release rate is proportional to the fertilizer dosage.When the content of Osmocote was 5.0wt.%,and it was cured to 140 days,the accumulated release rate of nitrogen could reach 94.29%.However,the phosphorus release rate and cumulative release rate are low,and when cured to 140 days,the highest cumulative release rate of phosphorus is only about 0.012%.When the content of IBDU was 5.0wt.%,and it was cured to 140 days,the accumulated release rate of nitrogen was 66.85%.It can be seen that Osmocote can better provide the nutrients needed in the early stage of plant growth,while the IBDU can better meet the demand for nutrients in the later stage of plant growth.(3)When the ratio of w/c is 0.22 and the ratio of g/c is 5.0,the total porosity of the planting concrete can reach 34.85% and the connected porosity is 31.7%.what's more,the ratio of the internal pore diameter is greater than 3mm is 80.80%,and the permeability coefficient is 3.29cm/s.The compressive strength of concrete at 28 days is 8.3 MPa.(4)Since the addition of both fertilizers can reduce the water demand of sulphoaluminate cement,the amount of water added to the planting concrete can be reduced.The optimal w/c ratio for preparing fertilizer-suspended planting concrete is 0.21,and when the fertilizer dosage was 3.5wt.%,the performance of planting concrete was the best.(5)Both fertilizers can promote the growth of plants.When the fertilizer content is 5.0wt.%,the performance indexes of Euonymus fortunei grow best.When the amount of Osmocote was 5.0wt.%,and the plants were grown to 100 days,the growth of stem length,root growth,and relative water content of leaves increased by 44.08%,15.38%,and 3.66%,respectively,compared with the blank samples.At 140 days,leaf chlorophyll content and nitrogen content in leaves increased by 6.50% and 16.83%,respectively,compared with blank samples.When the amount of IBDU was 5.0 wt.%,and the plants were grown to 100 days,the growth of stems,root growth and relative water content of leaves increased by 19.59%,10.26% and 2.03%,respectively,compared to the blank samples.At 140 days,leaf chlorophyll content and nitrogen content in leaves increased by 4.92% and 12.29%,respectively,compared with blank samples.Therefore,it can be seen that in the early stage of plant growth,the regulation of the growth of the plant by Osmocote is better than that of the IBDU,but the difference is not significant.