Study On Prefabricated Permeable Pavement Base Material And Overall Operating Efficiency In Large Parking Lots

Permeable pavement is one of the commonly used technologies in sponge city construction,which has a good capacity of retaining and purifying pavement runoff.Parking lots have multiple problems,such as complex load change,long paving cycle,fragility,difficult maintenance,heavy runoff pollution,and so on.Based on these characteristics,this paper developed a prefabricated permeable pavement structure,which has advantages of great bearing capacity,convenient construction,easy maintenance,as well as strong ability to intercept pollution.It has great practical significance for the construction and maintenance of parking lots,especially large parking lots.The test studied the influence of aggregate gradation on the mechanical properties and water permeability of permeable concretes.The group with the best comprehensive performance was selected from the five groups of different aggregate gradation,and was used as permeable pavement base.The results show that the performance of all the permeable concrete test blocks can meet the requirements of relevant specifications.The compressive strength of 7d is 5.14MPa～9.63MPa,the compressive strength of 28d is 5.97MPa～15.26MPa,the porosity is 17.4%～25.9%,the permeability coefficient is 0.61cm/s～1.32cm/s,and the loss of dry and wet circulation strength is 0.20MPa～2.38MPa.The optimal aggregate gradation is20%of 4.75mm～9.5mm aggregate,50%of 9.5mm～19mm aggregate,and 30%of19mm～31.5mm aggregate.The hydrological effects of four types of prefabricated permeable pavements were compared through artificial simulated rainfall experiments.All these permeable pavement structures share the same surface layer which is made of clay permeable brick.Natural sand and medium sand are used as leveling materials,and permeable prefabricated blocks differ in structural forms as type a and type b.According to difference of the leveling materials and permeable base prefabricated block structures,prefabricated permeable pavements are divided into typeⅠ（natural sand+type a permeable concrete prefabricated block）,typeⅡ（natural sand+type b permeable concrete prefabricated block）,typeⅢ（medium sand+type a permeable concrete prefabricated block）,and typeⅣ（medium sand+type b permeable concrete prefabricated block）,respectively.The results show that under the same condition of rainfall,the ranking of runoff control ability is typeⅠ>typeⅡ>typeⅢ>typeⅣ.The leveling material has a great influence on the hydrological effect of permeable pavement,and natural sand is superior to medium sand.The structure form of prefabricated base block has little influence on the hydrological effect of permeable pavement,and type a is slightly better than type b.Under the condition of extreme rainfall（rainfall intensity is 2 mm/min,rainfall duration is 2h,rainfall break is 1d）,runoff control of typeⅠand typeⅡprefabricated permeable pavement structure can still reach 44.0%and 42.7%.Under the condition of storm rainfall（rainfall intensity is 1mm/min,rainfall duration is 1h,rainfall break is 7d）,runoff control of typeⅠand typeⅡprefabricated permeable pavement can reach 97.8%and 95.4%,respectively.The water quality effects of the four types of prefabricated permeable pavement structures were compared.The results show that the ranking of removal efficiency of SS is typeⅢ>typeⅣ>typeⅡ>typeⅠ;the removal efficiency of COD is typeⅣ>typeⅡ>typeⅠ>typeⅢ;the removal efficiency of NH₃-N is typeⅣ>typeⅢ>typeⅡ>typeⅠ;the removal efficiency of TN is typeⅢ>typeⅣ>typeⅡ>typeⅠ;the removal efficiency of TP is typeⅣ>typeⅡ>typeⅢ>typeⅠ;and comprehensive pollutant reduction ability is typeⅣ>typeⅢ>typeⅡ>typeⅠ.The leveling material has a great influence on the pollutant reduction ability of permeable pavement,and medium sand is superior to natural sand.The structure form of base prefabricated block has little influence on the pollutant reduction ability of permeable pavement,and type b is slightly better than type a.Under the condition of the maximum runoff pollution concentration（SS is 155.0 mg/L,the COD is 115.0 mg/L,NH₃-N is 1.27 mg/L,TN is 9.57mg/L,TP 0.54 mg/L）,the removal rate of the above pollution factors by typeⅣprefabricated permeable pavement structure are 77.4%,60.0%,22.1%,44.2%,81.5%,respectively.Based on comprehensive comparison of the mechanics,runoff reduction,and pollutant reduction performance of the four prefabricated permeable pavement structures,typeⅡpermeable pavement has the best comprehensive performance.It shows no obvious deformation when carrying heavy loads,its runoff control rate under heavy rain is 95.4%,and its removal rates of SS,COD,NH₃-N,TN and TP are 68.1%,49.1%,33.7%,51.7%and 62.8%,respectively.After optimization of its natural sand size in the leveling layer,typeⅡprefabricated permeable pavement structure is used for the construction of permeable pavement in parking lots.The conclusion of this practical experiment is basically consistent with the results of the laboratory experiment,which proves the feasibility of its engineering application,and on this basis,the economic analysis of engineering application is carried out.