Study On The Removal Effect Of Structure Characteristics Of Porous Asphalt Pavement To Dissolved Pb

A large number of pollutants with Pb deposit on road surface with traffic,which will flow with runoff or penetrate into pavement structure in rainfall event,the pollutant eventually infiltrates into the underground,causing great harm to the environment.The dissolved Pb is main occurrence state of element lead,with the characteristics of high active and nondegradable.Admittedly,porous asphalt pavement is a low impact development technology which with strong purification ability to heavy metal in road runoff.Thus,the study on the removal effect of structure characteristics of porous asphalt pavement to dissolved Pb would not only help to relieve the waterlogging with urban surface runoff,but also promote the protection of water environment.In this study,the goal porosity of pavement structure was firstly determined in indoor test,according to the characteristics of rainfall and road runoff in Nanjing area and applying the relationship between pavement permeability coefficient and porosity.Secondly,a typical porous asphalt pavement structure was designed through aggregate screening and mix designing in gradations experiments.The lead pollution characteristics of road sediment and road runoff in different function areas in Nanjing were analyzed and evaluated,which provided for the preparation of artificial rainwater solution with a reasonable concentration of Pb2 +.And then,several different structure combination of porous asphalt pavements were designed with different thickness,materials and filter courses.Meanwhile,in order to test the purification ability of porous asphalt pavement to dissolved Pb in road runoff,a laboratorial simulation of rainfall system was developed.The test results showed that after 24-hour storage period,the porous asphalt pavement designed could satisfy the standard of removing dissolved Pb from road runoff.Several results were mainly obtained from above studies:1.For decrease the volume of road runoff,the objective void fraction and the reasonable asphalt content of porous asphalt mixture were 18.74%~25.00% and 5.1%~5.7%,respectively,considering the characteristics of precipitation in Nanjing area.2.The relation between the characteristics of Pb pollutant accumulation in road sediment and previous days without rain was analyzed by regression.The relation between the characteristics of dissolved Pb in road runoff and previous days without rain was analyzed by regression.3.The limestone aquifer is superior to basalt in removing Pb2 + pollution in initial road runoff.The removal rate of dissolved Pb can reach 44.67% at the end of no water storage experiment.The geotextile offers a benefit to remove dissolved Pb,and the Polyester staple fiber geotextile is better than Polypropylene knitted geotextile.4.In this study,a typical structure of porous asphalt pavement with the best ability to remove dissolved Pb from road runoff includes a PAC-16 porous asphalt surface course,a LSPM-25 porous asphalt base course,a Polyester staple fiber geotextile filter course,and a reservoir structure made of single sized limestone aggregate.At the end of the 24-hour storage period,the removal rates of Pb was 98.30%.