Study On The Influence Mechanism Of Void Characteristics On The Removal Of Lead Ion From The Permeable Asphalt Surface Structure

The 50% of the heavy metal?Pb?in the receiving water is from the road runoff.According to the research,Pb is present in the form of granular and dissolved lead ions(Pb²⁺)in water,in which the dissolved lead is less,but the bioavailability is strong and the granular lead can be transformed into dissolved water.Lead ions(Pb²⁺)is closely related to vehicle emission,tire wear,fuel,lubricating oil drip and brake wear,Pb²⁺ can not be degraded easily and gathered in biological body,and then enters the body through food chain transmission,eventually cause poisoning to human body.Therefore,it is very necessary to use in situ treatment technology to effectively reduce the runoff Pb.Permeable asphalt pavement is an eco-friendly pavement structure,As the structure layer is in the form of porous structure,it can meet the road performance and facilitate the rapid infiltration of water into the soil base,so that during the heavy rainfall,reduce the adverse effect caused by pavement water,and in the process of rainwater infiltration,have the effectiveness of water purification.In this paper,soluble heavy metals Pb as a representative pollutant.we first study the permeable asphalt mixture based on the effective removal of pavement runoff pollutants,and determine the target porosity by indoor road performance test and water permeability test.Secondly,we use CT technology,VGStudio MAX and Matlab to study the space distribution characteristics of permeable asphalt mixture.Finally,we establish mathematical model between the characteristic parameters of the voids and the removal rate of Pb²⁺ by simulating the rainfall experiment in the room,and analyze the influence mechanism of the characteristic parameters on the removal of Pb²⁺.The main conclusions are as follows:?1?Results indicated that the distribution curve of voidage,void volume and equivalent diameter was symmetrical,maximum value at each end and minimum value at the central-cross section,but which was contrary to the number of voids.specific surface area and fractal dimension along the specimen height has no significant change.?2?The effect of target porosity on the void volume,the number of voids,specific surface area and fractal dimension of the permeable asphalt mixture is basically the same.The larger target porosity,the larger parameter value.The effect on the equivalent diameter is opposite.?3?At the same cross-section,equivalent diameter showed a significantly positive relation with voidage and a good negatively correlation with the number of voids.The void specific surface area and fractal dimension have a good linear positive correlation,there was a high degree of consistency in the curves along the height direction;there has no significant correlation between the other parameters.?4?The voidage can be used as a separate parameter when describing the total volume of the void's distribution characteristics along the height of the specimen,however,it is necessary to use the parameters such as the equivalent diameter and the number of voids in the description ofvoid distribution characteristics along the height of the specimen.Fractal dimension and specific surface area parameters in description the distribution characteristics of the trend,because of the trend of more than 90% is similar,so you can choose one of the parameters as a description of the characteristics of the void.?5?There was a positive correlation between the voidage,specific surface area,void volume,fractal dimension parameters and the ability to remove Pb²⁺ from the permeable asphalt surface structure,but it showed the opposite relationship for equivalent diameter.The number of voids has no significant effect on the ability to remove Pb²⁺.