Study On Design Of Permeable Asphalt Pavement Based On Heavy Metal Pollution Control Of Pavement Runoff

With high concentrations of heavy metals, the road runoff affects the surface water and soil along road sides, and has apparent influence on the health of animals and human being. It has become one of the most important problems for the environmental pollution control. Porous asphalt pavement can be used as an effective tool to mitigate the heavy metal pollution in road runoff, reduce the volume of road runoff during rainfall period, recharge the underground water, and improve the soil conditions under the road. Moreover, it can help save the land and cut down the cost for construction. Therefore, using porous asphalt pavement as a useful engineering measure to remove heavy metals from road runoff is an important development aspect.In this study, a new design method of porous asphalt pavement for removing heavy metals in runoff was firstly set up. The surface course, base course, reservoir structure and filter course were designed based on specific requirements. Then, a special laboratory test system and a corresponding test approach for measuring the permeability of porous asphalt mixture were worked out. The permeability of porous asphalt mixture samples was independently measured and verified. Meanwhile, a laboratory artificial simulation of rainfall system was developed to test the purification ability of porous asphalt pavement to heavy metals in road runoff. The simulation results showed that the porous asphalt pavement designed could satisfy the requirement of removing heavy metals from road runoff during rainfall events and in a 24-hour storage period afterward.The following conclusions are drawn from this study:(1) In order to decrease the volume of road runoff, the objective air void and the optimum asphalt content of porous asphalt mixture were 20.86%~25.00% and 5.6%~6.2%, respectively, considering the characteristics of precipitation in Nanjing city, Jiangsu province of China.(2) A typical structure of porous asphalt pavement with a suitable drainage system was proposed based on the ability to remove heavy metals from road runoff, including a porous asphalt surface course, a porous asphalt base course, a reservoir structure made of single sized basalt aggregate, and a geotextiles layer.(3) The porous asphalt pavement designed had a significant removal rate up to 40.00% of Pb and Zn from initial flush of road runoff. However, during the runoff storage period, the removal rate varied. The percentage removal of Pb reached 81.00% at the initial stage, while the Zn removal rate was continually increasing over time. At the end of the 24-hour storage period, the removal rates of Pb and Zn were 97.00% and 98.03%, respectively.