Method for testing leaching pollution of permeable pavement material in different environments by simulation

Abstract

A method for testing leaching pollution of a permeable pavement material in different environments by simulation, comprises; immersing the permeable pavement material in a leaching agent and collectin

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of leaching pollution testing for permeable pavement in sustainable drainage systems (SuDS), and particularly to a method for testing leaching pollution of a permeable pavement material in different environments by simulation. BACKGROUND

[0002] Permeable pavement materials are road paving materials with water permeability and rich pore structures inside. Compared with traditional hardened pavement, the permeable pavement could effectively reduce water accumulation on the road surface, alleviate urban waterlogging and runoff pollution, and improve road traffic safety and comfort. Therefore, the permeable pavement materials are important for building a sponge city.

[0003] However, whether the components of various permeable pavement materials may have adverse effects on the water environment during rain or immersion has not received widespread attention. As increasing solid wastes such as waste tires, waste rubber, red mud as aluminum smelting solid waste, and waste plastics are used in permeable pavements, there is an urgent need in detection and evaluation of leaching pollution of permeable pavement materials. SUMMARY

[0004] In view of this, the present disclosure provides a method for testing leaching pollution of a permeable pavement material in different environments by simulation. In the present disclosure, the method could simulate various leaching behaviors of the permeable pavement material under different external environmental conditions to achieve accurate testing of the rapid, short-term, and long-term leaching behavior of the permeable pavement material in different environments, and obtained test results could provide decision-making support for relevant industry personnel in determining environmental risks of the material.

[0005] To achieve the above object, the present disclosure provides the following technical solutions:

[0006] The present disclosure provides a method for testing leaching pollution of a permeable pavement material in different environments by simulation, including the following steps:

[0007] immersing the permeable pavement material in a leaching agent and collecting a resulting leachate, where the immersing includes at least one selected from the group consisting of single static 27 10 25 immersion, single dynamic immersion, short-term immersion, and long-term immersion; the single static immersion is conducted for 24 h±6 h, and the single dynamic immersion is conducted for 24 h±6 h; the short-term immersion is conducted for 7 d±l d (day), and the long-term immersion is conducted for 20 d or more; and the leaching agent is one selected from the group consisting of deionized water and an acidic leaching agent; and

[0008] subjecting the resulting leachate to water quality detection and leaching pollution evaluation, wherein a liquid-to-solid ratio of the leaching agent to the permeable pavement material during the immersing is calculated according to equation I: L _ P X I X AX t — — equation I, S h x p x A where L / S represents the liquid-to-solid ratio; P represents an average annual rainfall, in unit of mm / year; I represents an infiltration coefficient of the permeable pavement material; A represents a unit area of contact between the permeable pavement material and the leaching agent; t represents an application time of the permeable pavement material, in unit of year; h represents a thickness of the permeable pavement material, in unit of mm; and p represents a density of the permeable pavement material, in unit of g / cm3.

[0009] In some embodiments, the single static immersion, the single dynamic immersion, the shortterm immersion, and the long-term immersion each are conducted at room temperature.

[0010] In some embodiments, the immersing is conducted in a covered water tank, and the covered water tank is provided with three water sampling ports that are configured to collect the resulting leachate; and the three water sampling ports are arranged at a top surface of the covered water tank, a middle part of a side of the covered water tank, and a lower part of a side of the covered water tank, respectively.

[0011] In some embodiments, the single static immersion includes: placing the permeable pavement material in a water tank containing the leaching agent, subjecting the permeable pavement material to static immersion for 24 h±6 h, and collecting the resulting leachate at the three water sampling ports; and

[0012] the single dynamic immersion includes: placing the permeable pavement material in a water tank containing the leaching agent, subjecting the permeable pavement material to immersion under stirring at a rotation speed of 800 r / min to 1,000 r / min for 6 h±3 h, and then to static immersion for 18 h±3 h, and collecting the resulting leachate at the three water sampling ports.

[0013] In some embodiments, the short-term immersion includes: placing the permeable pavement material in a water tank containing the leaching agent, subjecting the permeable pavement material to 27 10 25 static immersion for 7 d±l d, and collecting the leachate at intervals during the static immersion, wherein from day 0 to day 3, two adjacent leachate collections are conducted at an interval of not more than 18 h, and after the day 3, two adjacent leachate collections are conducted at an interval of not less than 24 h; and each of leachate collections is conducted at the three water sampling ports.

[0014] In some embodiments, the long-term immersion includes: placing the permeable pavement material in a water tank containing the leaching agent, subjecting the permeable pavement material to static immersion for 20 d or more, and collecting the leachate at intervals during the static immersion, wherein from day 0 to day 7, leachate collections are conducted according to a leachate collection process of the short-term immersion, and after the day 7, two adjacent leachate collections are conducted at an interval of not less than 7 d; and each of leachate collections is conducted at the three water sampling ports.

[0015] In some embodiments, the acidic leaching agent is a sulfuric acid-nitric acid mixed solution with a pH value of 5.5±0.1.

[0016] In some embodiments, an indicator of the water quality detection is one selected from the group consisting of a pollutant concentration and a pH value.

[0017] In some embodiments, the leaching pollution evaluation is conducted by a degree of damage, and the degree of damage is calculated according to equation II:

[0018] 1 equation II;

[0019] where Ki represents a degree of damage caused by a pollutant i; Ti represents a maximum concentration of the pollutant i in the resulting leachate within a specified period of time, in unit of mg / kg; and Bi represents a baseline level of the pollutant i, in unit of mg / kg.

[0020] The present disclosure provides a method for testing leaching pollution of a permeable pavement material in different environments by simulation, including the following steps: immersing a permeable pavement material in a leaching agent and collecting a resulting leachate, where the immersing comprises at least one selected from the group consisting of single static immersion, single dynamic immersion, short-term immersion, and long-term immersion; the single static immersion is conducted for 24 h±6 h, and the single dynamic immersion is conducted for 24 h±6 h; the short-term immersion is conducted for 7 d±l d, and the long-term immersion is conducted for 20 d or more; and the leaching agent is selected from the group consisting of deionized water and an acidic leaching agent; and subjecting the resulting leachate to water quality detection and leaching pollution evaluation. Compared with the prior art, embodiments of the present disclosure have the following beneficial effects: 27 10 25

[0021] (1) In the present disclosure, the method could comprehensively and systematically cover the leaching process of the permeable pavement material. The comprehensiveness lies in that the method covers single static immersion, single dynamic immersion, short-term immersion, and long-term immersion, which could simulate rapid, short-term, and long-term leaching behavior of the permeable pavement material under rainwater infiltration, external disturbance, and different immersion times. Further, the leaching agent is deionized water or acidic leaching agent, which could simulate the leaching behaviors of the permeable pavement under natural rainfall or acid rain conditions. Also, the systematicity lies in proposed standardized test steps, including preparation of the permeable pavement material, preparation of the leaching agent, calculation of the liquid-to-solid ratio, selection of an appropriate immersion process, collection of leachate, water quality detection of the leachate, and leaching pollution evaluation.

[0022] (2) Furthermore, the method according to the present disclosure could accurately characterize the leaching behaviors of the permeable pavement material. The calculation method for parameters involved in each immersion process is specified, and is as close to the actual application scenario as possible. This method includes preparing different types of the leaching agent to simulate different environmental conditions, calculating the liquid-to-solid ratio based on local rainfall conditions and application scenario characteristics, and optimizing the immersion time and interval of leachate collections corresponding to different immersion processes.

[0023] (3) In addition, the leachate collected by the method of the present disclosure has a stable composition and thereby results in accurate test results. The degree of damage Ki is calculated based on a maximum leaching amount of pollutants in the leachate of the permeable pavement material under different environmental conditions, so as to evaluate the leaching risk. The test results are intuitive and could provide decision-making support for industry-related personnel to determine environmental risks of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 shows a flow chart of a method for testing leaching pollution of a permeable pavement material in different environments by simulation according to an embodiment of the present disclosure.

[0025] FIG. 2 shows a schematic diagram of an immersion experimental device for testing leaching pollution of a permeable pavement material according to an embodiment of the present disclosure.

[0026] FIG. 3 shows changes of total nitrogen (TN) in the leachate of the permeable asphalt pavement material in Example 1 of the present disclosure after short-term immersion in different environments.

[0027] FIG. 4 shows changes of pH value in the leachate of the permeable asphalt pavement material in Example 2 of the present disclosure after long-term immersion in different environments. 27 10 25 DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The present disclosure provides a method for testing leaching pollution of a permeable pavement material in different environments by simulation, including the following steps:

[0029] immersing the permeable pavement material in a leaching agent and collecting a resulting leachate, wherein

[0030] the immersing comprises at least one selected from the group consisting of single static immersion, single dynamic immersion, short-term immersion, and long-term immersion; the single static immersion is conducted for 24 h±6 h, and the single dynamic immersion is conducted for 24 h±6 h; the short-term immersion is conducted for 7 d±l d, and the long-term immersion is conducted for 20 d or more; and the leaching agent is selected from the group consisting of deionized water and an acidic leaching agent; and subjecting the resulting leachate to water quality detection and leaching pollution evaluation wherein a liquid-to-solid ratio of the leaching agent to the permeable pavement material during the immersing is calculated according to equation I: L _ P X I X AX t — — equation I, S h x p x A where L / S represents the liquid-to-solid ratio; P represents an average annual rainfall, in unit of mm / year; I represents an infiltration coefficient of the permeable pavement material; A represents a unit area of contact between the permeable pavement material and the leaching agent; t represents an application time of the permeable pavement material, in unit of year; h represents a thickness of the permeable pavement material, in unit of mm; and p represents a density of the permeable pavement material, in unit of g / cm3.

[0031] FIG. 1 shows a flow chart of the method for testing leaching pollution of a permeable pavement material in different environments by simulation according to the present disclosure, including preparation of the permeable pavement material, preparation of the leaching agent, calculation of liquid-to-solid ratio, selection of appropriate immersion process (single static immersion, single dynamic immersion, short-term immersion, and long-term immersion), collection of leachate, water quality detection of the leachate, and leaching pollution evaluation. The present disclosure is described in detail below with reference to FIG. 1.

[0032] In the present disclosure, a permeable pavement material is immersed in a leaching agent and then a resulting leachate is collected. There is no special requirement on a type of the permeable 27 10 25 pavement material, and those well known to those skilled in the art could be used. In specific embodiments, the permeable pavement material is a permeable asphalt pavement material. In some embodiments, a permeable pavement material specimen is prepared according to a formula of the permeable pavement material, and then subjected to an immersion test. In some embodiments, the permeable pavement material specimen is a cylindrical specimen. In some embodiments, the permeable pavement material specimen has a diameter of 101.6 cm and a height of 6.4 cm. In the present disclosure, there are no special requirements on a preparation method of the permeable pavement material specimen. In specific embodiments, a Marshall Compaction method is adopted. In specific embodiments, a permeable pavement material specimen is first prepared, a leaching agent is then selected and prepared, an appropriate immersion process is selected according to actual demands and a leachate is collected, and then water quality detection of the leachate and leaching pollution evaluation are conducted.

[0033] In some embodiments of the present disclosure, the leaching agent is deionized water or an acidic leaching agent. In some embodiments, the acidic leaching agent is a sulfuric acid-nitric acid mixed solution. In some embodiments, the sulfuric acid-nitric acid mixed solution has a pH value of 5.5±0.1, preferably 5.5. In specific examples, concentrated sulfuric acid and concentrated nitric acid are mixed, and then a resulting mixed acid is added into deionized water such that a pH value of a resulting mixture is 5.5 by adjustment, thus obtaining the sulfuric acid-nitric acid mixed solution. In some embodiments, a mass ratio of the concentrated sulfuric acid to the concentrated nitric acid is 2:1. In some embodiments of the present disclosure, deionized water is used as the leaching agent to simulate the leaching of a permeable pavement material under normal natural conditions. In some embodiments of the present disclosure, the sulfuric acid-nitric acid mixed solution is used as the leaching agent to simulate the leaching of a permeable pavement material under acid rain conditions. The type of acid rain in China is a mixture of sulfuric acid and nitric acid. Therefore, a sulfuric acid-nitric acid mixed solution that serves as the acidic leaching agent is more in line with the actual situation and would result in more accurate simulation results.

[0034] In the present disclosure, the liquid-to-solid ratio of the leaching agent to the permeable pavement material during the immersion is determined according to the local rainfall status and application scenario characteristics, and it is obtained by calculation according to equation I: L _ P X I XAX t

[0035] — — --------------- equation I; where S hx pxA

[0036] L / S represents the liquid-to-solid ratio; P represents an annual rainfall; I represents an infiltration coefficient of the permeable pavement material; A (A on a right side of the equation) 27 10 25 represents a unit area of contact between the permeable pavement material and the leaching agent; t represents an application time of the permeable pavement material; h represents a thickness of the permeable pavement material; and p represents a density of the permeable pavement material. In specific embodiments, P specifically represents an average annual rainfall in unit of mm / year; t is in unit of year; h is in unit of mm; and p is in unit of g / cm3. In some embodiments, I is preferably 20%. In some embodiments, L / S is an integer.

[0037] In the equation I of the present disclosure, PxIxAxt specifically represents a volume of the leaching agent required for the material per unit area, and hxpx A represents a dry basis weight of the permeable pavement material per unit volume; in actual calculation, the equation I could be simplified to equation 1-1: L _PxIxt

[0038] $ equation I-1.

[0039] In specific embodiments of the present disclosure, a specific volume of the leaching agent could be obtained by combining the liquid-to-solid ratio obtained according to equation I with the dry basis weight of the permeable pavement material.

[0040] In some embodiments of the present disclosure, the immersion includes at least one of single static immersion, single dynamic immersion, short-term immersion, and long-term immersion. In some embodiments, the single static immersion is conducted for 24 h±6 h, preferably 24 h. In some embodiments, the single dynamic immersion is conducted for 24 h±6 h, preferably 24 h. In some embodiments, the short-term immersion is conducted for 7 d±l d, preferably 7 d. In some embodiments, the long-term immersion is conducted for 20 d or more, preferably 20 d to 30 d, and more preferably 20 d to 28 d. In the present disclosure, the single static immersion and single dynamic immersion are conducted to simulate the rapid leaching behavior of the permeable pavement material, the short-term immersion is conducted to simulate the short-term leaching behavior of the permeable pavement material, and the long-term immersion is conducted to simulate the long-term leaching behavior of the permeable pavement material.

[0041] In some embodiments of the present disclosure, the immersion is conducted in a covered water tank. In some embodiments, the covered water tank is provided with three water sampling ports for collecting the leachate; and the three water sampling ports are arranged at a top surface of the covered water tank (namely, on a water tank cover, denoted as a water sampling port 1), a middle part of a side of the covered water tank (denoted as a water sampling port 2), and a lower part of a side of the covered water tank (denoted as a water sampling port 3), respectively. In some embodiments, the water sampling port 1 is arranged at a center of the water tank cover. In some embodiments, the water 27 10 25 sampling ports 2 and 3 are arranged on opposite sides of the covered water tank, respectively. In some embodiments, the covered water tank is made of acrylic. In some embodiments, the covered water tank has a dimension of 24 cmx24 cm><30 cm. Before the test, the covered water tank needs to be cleaned with deionized water and wiped dry. In some embodiments, during the immersion, in order to prevent water evaporation, a top part of the covered water tank is mulched with a layer of transparent plastic wrap, and then covered. FIG. 2 shows a schematic diagram of an immersion test device for leaching pollution of the permeable pavement material in the present disclosure.

[0042] In some embodiments of the present disclosure, the single static immersion, the single dynamic immersion, the short-term immersion, and the long-term immersion each are conducted at room temperature. The specific operation modes of the single static immersion, single dynamic immersion, short-term immersion, and long-term immersion are described in detail below.

[0043] In some embodiments of the present disclosure, the single static immersion includes: placing the permeable pavement material in a water tank containing the leaching agent, subjecting the permeable pavement material to static immersion for 24 h±6 h, and collecting the leachate at the three water sampling ports.

[0044] In some embodiments, the single dynamic immersion includes: placing the permeable pavement material in a water tank containing the leaching agent, subjecting the permeable pavement material to immersion under stirring for 6 h±3 h, and then to static immersion for 18 h±3 h, and collecting the leachate at the three water sampling ports. In some embodiments, the stirring is conducted at a rotation speed of 800 r / min to 1,000 r / min and preferably 850 r / min to 950 r / min. In some embodiments, the stirring is conducted using an electric stirrer. Dynamic immersion by combining stirring and standing could achieve rapid leaching and stable release of soluble substances inside the material, and a resulting leachate has a more stable composition, thereby resulting in more accurate test results.

[0045] In some embodiments of the present disclosure, the short-term immersion includes: placing the permeable pavement material in a water tank containing the leaching agent, subjecting the permeable pavement material to static immersion for 7 d±l d, and collecting the leachate at intervals during the static immersion, wherein from day 0 to day 3, two adjacent leachate collections are conducted at an interval of not more than 18 h, and after the day 3, two adjacent leachate collections are conducted at an interval of not less than 24 h; and each of leachate collections is conducted at the three water sampling ports. In some embodiments, from day 0 to day 3, the interval between two leachate collections ranges from 3 h to 18 h. In some embodiments, from day 0 to day 3, leachate collections are conducted 4 to 6 times in total, preferably 6 times. In some embodiments, after day 3, 27 10 25 the interval between two leachate collections ranges from 24 h to 48 h. In some embodiments, leachate collections after day 3 (namely, day 4 to day 7±1) are conducted 1 to 2 times, preferably 2 times in total. In some embodiments, the last leachate collection is conducted on the last day of immersion. In some embodiments, as the immersion time increases, the interval between each of leachate collections is longer. In specific examples, the static immersion is conducted for 7 d, from day 0 to day 3, the leachate is collected at 1 h, 6 h, 12 h, 24 h, 42 h, and 54 h after the start of immersion. In some embodiments, on day 4 to day 7, the leachate is collected on day 5 and day 7 after the start of immersion.

[0046] In some embodiments of the present disclosure, the long-term immersion includes: placing the permeable pavement material in a water tank containing the leaching agent, subjecting the permeable pavement material to static immersion for 20 d or more, and collecting the leachate at intervals during the static immersion, where from day 0 to day 7, leachate collections are conducted preferably according to a leachate collection process of the short-term immersion, and after the day 7, two adjacent leachate collections are conducted at an interval of not less than 7 d; and each of leachate collections is conducted at the three water sampling ports, from day 0 to day 7, the leachate could be collected according to a leachate collection process of the short-term immersion, and the interval and number of times of leachate collections are not described repeatedly here. In some embodiments, after day 7, the interval of two adjacent leachate collections ranges from 7 d to 14 d. In some embodiments, leachate collections are conducted 2 to 3 times in total, preferably 2 times in total. In some embodiments, the last leachate collection is conducted on the last day of immersion. In some embodiments, as the immersion time increases, the interval between each of leachate collections is longer. In specific examples, the immersion is conducted for 28 d in total, from day 0 to day 7, the leachate is collected at 1 h, 6 h, 12 h, 24 h, 42 h, 54 h, day 5, and day 7 after the start of immersion. In some embodiments, after day 7, the leachate is collected on day 20 and day 28 after the start of immersion.

[0047] In the present disclosure, during the short-term immersion and long-term immersion, the leachate is collected at a relatively short interval in the early stage of immersion, and at a relatively long interval in the later stage. The above intervals are in line with the component leaching law of the permeable pavement material, i.e., the early stage of immersion is a rapid leaching stage, and the interval of leachate collections should be appropriately shortened; the later stage of immersion is a stable stage, and the component concentrations do not change much, so that the interval of collections should be extended.

[0048] In the present disclosure, after obtaining the leachate, the leachate is subjected to water quality detection and leaching pollution evaluation. In some embodiments, an indicator of the water quality detection is a pollutant concentration or a pH value. In specific examples, the water quality detection is conducted according to a type of pollutants in the permeable pavement material, and the type of pollutants includes nitrogen and heavy metals, etc. There are no special requirements on a detection method, and methods well known to those skilled in the art may be used. In specific examples, the type of pollutants could be estimated by material composition and then determined by the single dynamic immersion or single dynamic immersion.

[0049] In the present disclosure, three leachates are collected at the three water sampling ports each time. In some embodiments, pollutant concentrations or pH values in the three leachates are separately measured, and then averaged, and an average value is taken as a pollutant concentration or pH value at that time point. By testing the leachates collected at different time points, the change of the pollutant concentration or pH value in the leachate over time could be obtained.

[0050] In the present disclosure, the leaching pollution evaluation is specifically conducted by a degree of damage, and the degree of damage is obtained by calculation according to equation II: 27 10 25

[0051] ! equation II;

[0052] where Ki represents a degree of damage caused by a pollutant i; Ti represents a maximum concentration of the pollutant i in the leachate within a certain period of time, in unit of mg / kg; and Bi represents a baseline level of the pollutant i, in unit of mg / kg. Bi could be calculated with reference to a surface water quality standard limit in China.

[0053] In the present invention, a higher Ki value indicates a greater degree of damage and thereby a greater leaching risk.

[0054] In the present disclosure, the degree of damage Ki is calculated based on a maximum leaching amount of pollutants in the leachate of the permeable pavement material under different environmental conditions, so as to evaluate the leaching risk. The test results are intuitive and could provide decisionmaking support for industry-related personnel to determine environmental risks of the material.

[0055] The technical solutions of the present disclosure will be clearly and completely described below in conjunction with specific examples of the present disclosure. Obviously, the described examples are only a part of, not all of, the examples of the present disclosure. All other examples obtained by a person of ordinary skill in the art based on the examples of the present disclosure without creative efforts shall fall within the scope of the present disclosure.

[0056] Example 1 - Simulation of TN leaching of a permeable asphalt pavement material under short-term immersion in different environments

[0057] 1) Preparation of the permeable asphalt pavement material: the main raw materials were composed of asphalt, coarse and fine aggregates, and filler. The asphalt was high-viscosity modified asphalt, the coarse and fine aggregates were both basalt, the filler was limestone powder, an asphalt-to-aggregate ratio was 5.0%, and a total porosity of the permeable asphalt pavement material was controlled at 20%.

[0058] 2) The gradation of the permeable asphalt pavement material is shown in Table 1. All specimens were prepared using a Marshall Compaction method (compacted 50 times on both sides).

[0059] Table 1 Gradation of the permeable asphalt pavement material Permeable asphalt pavement material Percentage (%) passing the following sieve openings (mm) Sieve opening size (mm) 16 13.2 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075 Passing rate (%) 100 95 65 20 15 12 10 7.8 4.5 4.5 27 10 25

[0060] 3) Two leaching agents were prepared, including deionized water and an acidic leaching agent. The preparation of the acidic leaching agent was as follows: H2SO4 and HNO3 were mixed at a mass ratio of 2:1, and a resulting mixed acid was then added into deionized water, with about 2 drops of the resulting mixed acid per 1 L of water, such that a pH value of the resulting system was adjusted to 5.5 to obtain the acidic leaching agent.

[0061] 4) According to the rainfall characteristics of Shanghai urban area, an average rainfall was 674 mm / year, and an infiltration coefficient of the material was 20%; an application time was 15 years; a thickness of the permeable asphalt mixture was 63.5 mm; a density of the material was 2.1 g / cm3, and the liquid-to-solid ratio was determined to be 15:1 by calculation according to equation I.

[0062] 5) The prepared permeable asphalt mixture specimen (with a diameter of 101.6 mm, and a height of 6.4 cm) was placed in a homemade covered acrylic water tank. To prevent water evaporation, the water tank was mulched with a layer of transparent plastic wrap and then covered. A cumulative immersion time was 7 d, leachate collections were conducted at 1 h, 6 h, 12 h, 24 h, 42 h, 54 h, 5 d, and 7 d, and each of the leachate collections was conducted at a water sampling port 1, a water sampling port 2, and a water sampling port 3 of the water tank, respectively.

[0063] 6) Referring to HJ 636-2012 "potassium persulfate digestion UV spectrophotometric method", the TN content of the leachate was determined using a HACH-DR3900 spectrophotometer, a DRB200 digestion device, and a HACH prefabricated reagent.

[0064] 7) The changes in TN content in the leachate of the permeable asphalt pavement material under short-term immersion in different environmental conditions were plotted. The results are shown in FIG. 3. As shown in FIG. 3, the leaching concentration of TN was low when deionized water was used as the leaching agent, indicating that the leaching risk was low under normal rainfall conditions; 27 10 25 when an acidic leaching agent was used, the leaching concentration of TN was high at the beginning of immersion, indicating that the leaching risk of TN was high under acid rain conditions.

[0065] Example 2 - Simulation of pH change of a permeable asphalt pavement material under long-term immersion in different environments

[0066] 1) Preparation of the permeable asphalt pavement material: the main raw materials were composed of asphalt, coarse and fine aggregates, and filler. The asphalt was high-viscosity modified asphalt, the coarse and fine aggregates were both basalt, the filler was limestone powder, and an asphalt-to-aggregate ratio was 5.0%. The gradation, porosity, and preparation method of the permeable asphalt pavement material were the same as those in Example 1.

[0067] 2) Two leaching agents were prepared, including deionized water and an acidic leaching agent. The preparation of the acidic leaching agent was as follows: H2SO4 and HNO3 were mixed at a mass ratio of 2:1, and a resulting mixed acid was then added into deionized water, with about 2 drops of the resulting mixed acid per 1 L of water, such that a pH value of the resulting system was adjusted to 5.5 to obtain the acidic leaching agent.

[0068] 3) According to the rainfall characteristics of Shanghai urban area, an average rainfall was 674 mm / year, and an infiltration coefficient of the material was 20%; an application time was 15 years; a thickness of the permeable asphalt mixture was 63.5 mm; a density of the material was 2.1 g / cm3, and the liquid-to-solid ratio was determined to be 15:1.

[0069] 4) The prepared permeable asphalt mixture specimen (with a diameter of 101.6 mm and a height of 6.4 cm) was placed in a homemade covered acrylic water tank. To prevent water evaporation, the water tank was mulched with a layer of transparent plastic wrap and then covered. A cumulative immersion time was 28 d, and immersion water samples were collected at 1 h, 6 h, 12 h, 24 h, 42 h, 54 h, 5 d, 7 d, 20 d, and 28 d, respectively.

[0070] 5) The pH values of the immersion water samples were measured with a pH meter at room temperature, and the results were accurate to 1-2 decimal places.

[0071] 6) The pH changes of the leachate of the permeable asphalt pavement material under longterm immersion in different environmental conditions were plotted. The results are shown in FIG. 4. According to FIG. 4, the acidic leaching agent could greatly accelerate the leaching of TN within 24 h after immersion, and the degree of TN leaching of the permeable asphalt itself is gradually weakened with the extension of time. The pH value of the leachate was generally stabilized to around 8.0 after 20 d.

[0072] Example 3 - Risk evaluation for TN leaching of a permeable asphalt pavement material under short-term immersion in different environments

[0073] 1) concentrations of TN in leachates at different immersion time points obtained in Example 1 were used as basic data, in unit of mg / L;

[0074] 2) referring to the "Environmental quality standards for surface water GB3838-2002", the baseline level of TN pollutant (Btn) was 2.0 mg / L; and

[0075] 3) the degree of damage Ki was calculated based on a maximum leaching amount of pollutants in the leachate of the permeable pavement material under different environmental conditions, so as to evaluate the leaching risk, as shown in the following equation: 27 10 25

[0076]                  2 *

[0077] where Ktn represents a degree of damage of the pollutant TN; and Ttn represents a maximum concentration of TN in the leachate in a short period of time. Ttn was 3.5 mg / L when deionized water was used as the leaching agent and 23.8 mg / L when an acidic leaching agent was used.

[0078] By calculation, the Ktn was 0.75 when deionized water was used as the leaching agent, and the Ktn was 10.9 when the acidic leaching agent was used.

[0079] The evaluation results indicated that the permeable asphalt pavement material had a greater short-term leaching risk when the acidic leaching agent was used.

[0080] Example 4 - Determination of heavy metal leaching components in single dynamic immersion of a permeable asphalt pavement material prepared from steel slag aggregate

[0081] 1) Preparation of a steel slag-based permeable asphalt pavement material: the main raw materials were composed of asphalt, coarse and fine aggregates, and filler. The asphalt was high-viscosity modified asphalt, both of the coarse and fine aggregates were steel slag from Donghai Steel Group, Tangshan, China, the filler was limestone powder, an asphalt-to-aggregate ratio was 5.0%, and a total porosity of the permeable asphalt pavement material was controlled at 20%.

[0082] 2) The gradation of the permeable asphalt pavement material is shown in Table 2. All specimens were prepared using a Marshall Compaction method (compacted 50 times on both sides).

[0083] Table 2 Gradation of the permeable asphalt pavement material Porous asphalt pavement material Percentage (%) passing the following sieve openings (mm) Sieve opening size (mm) 16 13.2 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075 Passing rate (%) 100 96.8 64.9 30.9 24.9 17.3 13.4 11.1 10.0 8.8

[0084] 3) The permeable pavement material was placed in a water tank containing a leaching agent (deionized water) and the water tank was then covered and placed at room temperature. The leaching agent in the water tank was stirred at high speed (at a rotation speed of 1,000 r / min) with an electric stirrer for 6 h. The permeable pavement material was then subjected to static immersion for 18 h, and leachate collections were conducted at three water sampling ports, respectively. The corresponding water quality detections were conducted according to the type of pollutants. Results of the resulting three leachates were averaged.

[0085] 4) Since the steel slag contained a lot of metal elements, this example mainly studied the leaching of various metal pollutants. The detection indicators included Pb, Zn, Cr, Cu, Al, Cd, and pH. The results are shown in Table 3. It was finally determined that the main heavy metal components leached from the permeable asphalt pavement material prepared with steel slag aggregate included Al and Cd. 27 10 25

[0086] Table 3 Test results of various indicators Pollutants Detected or not Pb Less than limit of detection Zn Less than limit of detection Cr Less than limit of detection Cu Less than limit of detection Al 0.090 mg / L Cd 0.020 mg / L pH 10.54

[0087] In summary, the present disclosure designs a method for testing leaching pollution of a permeable pavement material in different environments by simulation. The method mainly includes single static immersion, single dynamic immersion, short-term immersion, and long-term immersion. Each of the immersion processes involves determination of the following parameters: leaching agent, liquid-to-solid ratio, immersion time, and intervals of leachate collection. Further, the test follows the following steps: preparation of the permeable pavement material, preparation of the leaching agent, calculation of the liquid-to-solid ratio, selection of an appropriate immersion process, collection of leachate, water quality detection of the leachate, and leaching pollution evaluation. The method could achieve accurate testing of the rapid, short-term, and long-term leaching behavior of the permeable pavement material in different environments, and obtained test results could provide decision-making support for relevant industry personnel in determining environmental risks of the material.

[0088] The above descriptions are merely preferred embodiments of the present disclosure. It should be noted that a person of ordinary skill in the art may further make several improvements and modifications without departing from the principle of the present disclosure, but such improvements and modifications should be deemed as falling within the scope of the present disclosure. 27 10 25

Claims

27 10 251. A method for testing leaching pollution of a permeable pavement material in different environments by simulation, comprising the steps ofimmersing the permeable pavement material in a leaching agent and collecting a resulting leachate, whereinthe immersing comprises at least one selected from the group consisting of single static immersion, single dynamic immersion, short-term immersion, and long-term immersion; the single static immersion is conducted for 24 h±6 h, and the single dynamic immersion is conducted for 24 h±6 h; the short-term immersion is conducted for 7 d±l d, and the long-term immersion is conducted for 20 d or more; and the leaching agent is one selected from the group consisting of deionized water and an acidic leaching agent; andsubjecting the resulting leachate to water quality detection and leaching pollution evaluation, wherein a liquid-to-solid ratio of the leaching agent to the permeable pavement material during the immersing is calculated according to equation I:L _ P X I X AX t— — --------------- equation I,S h X p X Awhere L / S represents the liquid-to-solid ratio; P represents an average annual rainfall, in units of mm / year; I represents an infiltration coefficient of the permeable pavement material; A represents a unit area of contact between the permeable pavement material and the leaching agent; t represents an application time of the permeable pavement material, in units of year; h represents a thickness of the permeable pavement material, in units of mm; and p represents a density of the permeable pavement material, in units of g / cm3.

2. The method as claimed in claim 1, wherein the single static immersion, the single dynamic immersion, the short-term immersion, and the long-term immersion each are conducted at room temperature.

3. The method as claimed in claim 1, wherein the immersing is conducted in a covered water tank, and the covered water tank is provided with three water sampling ports configured to collect the resulting leachate; andthe three water sampling ports are arranged at a top surface of the covered water tank, a middle part of a side of the covered water tank, and a lower part of a side of the covered water tank,respectively.27 10 254. The method as claimed in claim 3, whereinthe single static immersion comprises: placing the permeable pavement material in the covered water tank containing the leaching agent, subjecting the permeable pavement material to static immersion for 24 h±6 h, and collecting the resulting leachate at the three water sampling ports; andthe single dynamic immersion comprises: placing the permeable pavement material in the covered water tank containing the leaching agent, subjecting the permeable pavement material to immersion under stirring at a rotation speed of 800 r / min to 1,000 r / min for 6 h±3 h, and then to static immersion for 18 h±3 h, and collecting the resulting leachate at the three water sampling ports.

5. The method as claimed in claim 3, wherein the short-term immersion comprises:placing the permeable pavement material in the covered water tank containing the leaching agent, subjecting the permeable pavement material to static immersion for 7 d±l d, and collecting the resulting leachate at intervals during the static immersion,wherein from day 0 to day 3, two adjacent leachate collections are conducted at an interval of not more than 18 h, and after the day 3, two adjacent leachate collections are conducted at an interval of not less than 24 h; and each of leachate collections is conducted at the three water sampling ports.

6. The method as claimed in claim 3 or 5, wherein the long-term immersion comprises:placing the permeable pavement material in the covered water tank containing the leaching agent, subjecting the permeable pavement material to static immersion for 20 d or more, and collecting the resulting leachate at intervals during the static immersion,wherein from day 0 to day 7, leachate collections are conducted according to a leachate collection process of the short-term immersion, and after the day 7, two adjacent leachate collections are conducted at an interval of not less than 7 d; and each of leachate collections is conducted at the three water sampling ports.

7. The method as claimed in claim 1, wherein the acidic leaching agent is a sulfuric acid-nitric acid mixed solution with a pH value of 5.5±0.1.

8. The method as claimed in claim 1, wherein an indicator of the water quality detection is one selected from the group consisting of a pollutant concentration and a pH value.

9. The method as claimed in claim 1 or 8, wherein the leaching pollution evaluation is conducted by a degree of damage, and the degree of damage is calculated according to equation II:- Brequation II,where Ki represents a degree of damage caused by a pollutant i; Ti represents a maximum concentration of the pollutant i in the resulting leachate within a specified period of time, in unit of mg / kg; and Bi represents a baseline level of the pollutant i, in unit of mg / kg.27 10 25

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