| As an eco-friendly pavement structure,porous asphalt pavement is made up of continuous porous mixtures and built through a special process.The porous mixture is not only taking advantage of proper intensity,breathability and water permeability,but also providing the function of purifying the contamination of runoff,as well as reducing road temperature and changing the outdoor environment humidity of the city.However,there still many shortcomings in permeable asphalt pavement,such as purification of runoff pollutants,rainwater seepage and temperature reduction.In order to investigate the characteristics of purification of runoff pollutants,rainwater seepage and the temperature reduction in asphalt pavement,a reasonable permeable asphalt pavement structure will be proposed and analyzed on the base of laboratory experiments and numerical simulations.Firstly,a purifying experimental table was designed and established in laboratory to investigate the purification effect of runoff pollutants in the permeable asphalt pavement.The results show that the purification effect of runoff pollutant reaches the best when the porosity is 0.20,and the effective time of decontamination is 5 years.The compaction degree is directly related to the purification result.Under the circumstances of fully compacted,when the porosity exceeds 0.25,the internal voids microstructure has a significant impact on the decontamination of organic matter.When the effective height of the asphalt mixture is more than 10 cm,the purification reaches its best result.When the amount of ceramsite in the asphalt mixture is 40%,it has the best purification ability.The filter layer composed of fine sand,slag and ceramic aggregate has the best purification effects.The thicker the filter layer is,the better the purification effect of the filter layer composed of fine sand,slag and ceramsite is on the runoff pollutants.However,when the filter layer is fine sand,the thickness of filter layer has little influence on the purification of runoff pollutants.The filter layer made by the combination of fine sand,slag and ceramsite has a better effect on the purification result than those filter layer made by one material.The 20 cm filter layer of slag and ceramsite has the best purification ability on heavy metal pollutants.The experiment investigates the purification law of porous asphalt pavement.The results show that the COD and SS are mainly cleaned by the surface layer and the permeable base of the permeable asphalt pavement.The surface layer,permeable base,aquifer and filter layer play a key role for the purification of heavy metals Pb and Zn.Secondly,a rainwater seepage numerical model on the permeable asphalt pavement was established according to the principle of porous media seepage theory and calibrated by exploiting the experiment data.Then,the influences of intensity of precipitation,the porosity of each layer and the size of the structure on the permeable asphalt pavement were investigated and analyzed.The results indicate that rain type has the most obvious effect on the permeable asphalt pavement;under the rain type I(with the rainfall intensity of 18.8mm/h),the permeation rate is higher than other rain types.When the porosity is ranging from 0.15 to 0.25,the porosity of permeable asphalt concrete layer has a lesser impact on the permeability of the permeable asphalt pavement.When the porosity of graded gravel and sand cushion is bigger than 35%,it has a small impact on the permeability of permeable asphalt pavement.When the macadam base of large voids asphalt stabilized crushed stone is ranging from 6cm to 8cm,the macadam base of asphalt stabilized crushed stone has a small impact on the permeability of permeable asphalt pavement.When the structure of permeable asphalt pavement is at the seepage stability period(seepage duration>150min),the thickness of permeable asphalt concrete layer is less than 5cm,the thickness of the graded gravel layer is less than 15 cm,the thickness of sand cushion layer is between 5cm-15 cm,each thickness of layer has a small impact on the permeation rate.Finally,the numerical model of the temperature reduction of the permeable asphalt pavement is established based on above purification efficiency and the seepage law of rainwater.The study also carries out simulation research on cooling characteristics.This paper analyzes the temperature distribution characteristics of the permeable asphalt pavement at different times during the day,the influence of water permeability and the porosity for cooling characteristics of the permeable asphalt pavement.The results show that the temperature distribution through the permeable asphalt pavement thickness is remarkably affected by the solar radiation intensity.It reaches the peak values during 12:00-13:00 at noon.The temperature change in the macropore stabilized macadam base is the most obvious.In the process of structure design of this region,the structural thermal stress damage caused by the change of road surface temperature should be fully considered.At the same time,the moisture content of the permeable asphalt pavement has obvious influence on the internal temperature distribution,and the void fraction has little effect on its temperature distribution.The temperature of the permeable asphalt pavement is obviously reduced with the increase of the water content,and the water content considerably affects the temperature distribution of the permeable asphalt pavement with depth less than 45 cm.For reducing the temperature of the pavement,permeable asphalt pavement should be given priority to use in areas with large solar radiation intensity and more rainwater,which can reduce the pavement temperature and the discharge of runoff pollutants,improve the city outdoor environmental temperature and humidity.The above research results on purification of runoff pollutants,rainwater seepage and reducing temperature for permeable asphalt pavement will provide theoretical foundation for the structure design of permeable asphalt pavement a nd reduction of the runoff contamination and temperature in China. |
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