A method for evaluating the anti-dissolution durability of fly ash-asphalt pavement materials under coupled environment

Abstract

The present invention discloses a method for evaluating the anti-dissolution and permeation durability of fly ash-asphalt pavement materials under a coupled environment. The main steps include: constructing a coupled test environment for anti-dissolution and permeation durability; preparing asphalt mixture specimens based on the upper, middle, and lower layers of the asphalt pavement, and processing the specimens to collect interlayer leachate; placing the specimens in a simulated coupled environment, implementing the effects of coupled environmental factors, collecting leachate in layers, and testing the types and contents of heavy metal elements in leachates with different numbers; calculating the permeability coefficient and diffusion under different coupling conditions, analyzing the leaching patterns of heavy metal elements in fly ash in the asphalt pavement material carrier, and evaluating the durability of the asphalt pavement material for the control effect of the dissolution and diffusion of heavy metal elements in fly ash through correlation analysis with the coupling factors. The evaluation method and indicators proposed in this patent can provide a relevant basis for accurately evaluating the environmental protection and safety of the resource utilization of fly ash in road engineering.

Description

Technical Field

[0001] The invention relates to the field of road material performance evaluation, and in particular to a method for evaluating the anti-solution and permeation durability of garbage fly ash-asphalt pavement materials under a coupling environment. Background Art

[0002] Fly ash from landfill incineration is a residual product, containing most of the minerals and toxic heavy metals present in the waste. Fly ash cannot be stored for long periods and requires necessary solidification to stabilize its composition before it can be effectively utilized. Currently, the main methods for harmless disposal of fly ash include melting, vitrification, cementation, chemical treatment, and acid or other solvent extraction. However, these methods fail to achieve resource utilization of the fly ash and can only control and solidify the heavy metals within it. Fly ash from landfill incineration has the characteristics of large surface area and rich porosity, which allows for good interaction and bonding with asphalt, making it suitable for resource utilization as mineral powder in asphalt pavement materials. However, the presence of numerous heavy metals within fly ash poses a risk of secondary pollution during its resource utilization in asphalt pavement applications. Therefore, a coupled evaluation method for the anti-solution durability of fly ash-asphalt pavement materials is urgently needed to assess its long-term durability under different environmental conditions. This is crucial for protecting the ecological environment and achieving resource utilization of fly ash. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for evaluating the anti-solution and permeation durability of fly ash-asphalt pavement materials under coupled environments. The method can achieve good and accurate evaluation of the anti-solution and permeation durability of fly ash-asphalt pavement materials under different coupled environments, and will provide a good basis and guarantee for the application and promotion of fly ash-asphalt pavement materials. The specific scheme is as follows:

[0004] A method for evaluating the anti-solution durability of fly ash-asphalt pavement materials under a coupled environment comprises the following steps:

[0005] S1. Construct a coupled test environment for anti-solution and durability;

[0006] S2. Prepare asphalt mixture specimens according to the asphalt pavement structure, immerse and process the specimens to collect interlayer leachate;

[0007] S3. Place the specimen in a simulated coupling environment, implement the coupled environmental factors, and collect leachate in layers. Test the type and content of heavy metal elements in the leachate with different numbers. The numbering rules are as follows:

[0008] The leachate is numbered as C y,x, where y represents the interlayer position, y=1 represents the position between the upper and middle layers, y=2 represents the position between the middle and lower layers, and y=3 represents the bottom position of the lower layer; x represents the plane position, x=1 represents the center of the interlayer, referred to as mark 1, x=2 represents the test point marked on a circle with a diameter of 100 mm, referred to as mark 2, and x=3 represents the test point marked on a circle with a diameter of 200 mm, referred to as mark 3; the leachate collected between the upper and middle layers is marked as C 11 、C 12 、C 13 , the leachate collected in the middle and lower layers are marked as C 21 、C 22 、C 23 , the filtrates collected by the bottom collection device are marked as C 31 、C 32 、C 33 , where the upper middle layer is referred to as layer 1, and the middle and lower layer is referred to as layer 2;

[0009] S4. Calculate the permeability coefficient and diffusivity, analyze the control of asphalt pavement materials on the infiltration of heavy metal elements from fly ash in the longitudinal and horizontal directions under coupling conditions, and evaluate the durability of asphalt pavement materials' control over the three-dimensional diffusion of heavy metal elements from fly ash through correlation analysis with coupling factors.

[0010] The longitudinal heavy metal element leaching index - permeability coefficient K i And the longitudinal concentration gradient difference △Ci at the center point is calculated as follows:

[0011]

[0012] △C i =C2-C1

[0013] where K i is the permeability coefficient, which indicates the average increase in the concentration of heavy metal elements per millimeter when the leachate penetrates vertically downward between layers; h is the height of the leachate between the surface layers; △C i is the longitudinal concentration gradient difference at the center point, indicating the difference in the concentration of heavy metal elements in the leachate at the center point of different layers of the specimen; i = 1, 2, 3, indicating the position through which the leachate passes, i = 1 indicates that the leachate reaches interlayer 1 from interlayer 2, i = 2 indicates that the leachate reaches the bottom layer from interlayer 2, and i = 3 indicates that the leachate reaches the bottom layer from interlayer 1; C2 indicates the heavy metal concentration of the leachate located in the upper layer of the calculated leachate between the two layers, and C1 indicates the heavy metal concentration of the leachate located in the lower layer of the calculated leachate between the two layers;

[0014] Horizontal heavy metal element leaching diffusivity index - diffusivity U y,i, the calculation formula is as follows:

[0015]

[0016] △C y,i =C3-C4

[0017] Among them U y,i is the diffusion degree, which indicates the average increase in the concentration of heavy metal elements in the leachate during horizontal diffusion between layers per millimeter, △C y,i represents the difference in heavy metal concentrations of leachate collected between the same layers; y represents the layer from which the leachate was collected, and y=1, 2, and 3 represent that the leachate was collected in layer 1, layer 2, and the bottom layer, respectively; i=1, 2, and 3 represent that the leachate diffused from marker 1 to marker 2, marker 2 to marker 3, and marker 1 to marker 3, respectively; C3 represents the heavy metal concentration of the marker point near the periphery during the horizontal diffusion of the leachate from the center to the periphery; C4 represents the heavy metal concentration of the marker point near the center during the horizontal diffusion of the leachate from the center to the periphery; l represents the difference in the radius between the two marker points and the center point;

[0018] Furthermore, the step S1 constructs a coupled test environment for anti-solution and permeation durability, specifically:

[0019] The coupling test environmental factors include three indicators: light, temperature, and precipitation;

[0020] The light, temperature and precipitation indicators are simulated and constructed using an ultraviolet light accelerated weathering tester, and a coupled environment is constructed and implemented using a composite effect method;

[0021] The ultraviolet radiation parameters of the illumination were selected from Urumqi, Xinjiang Uygur Autonomous Region, a region with complex climatic conditions and high ultraviolet intensity. A high-pressure mercury lamp was used to simulate the accelerated aging of ultraviolet light. The lamp's spectrum range was between 350-450nm and the power was 1000W. Calculation showed that 6 hours of indoor accelerated ultraviolet aging radiation was equivalent to 1 month of outdoor aging time. The ultraviolet radiation parameters of the illumination were set to simulate an irradiation time of 10-12 years, and the indoor accelerated ultraviolet aging conversion time was 720h-864h.

[0022] The temperature parameters are based on the western region. The highest annual temperature in the western region is generally in July, with an average monthly temperature of around 33°C. Calculations show that when an asphalt pavement is exposed to sunlight, its highest surface temperature is between 60°C and 70°C. Therefore, the temperature setting range is 60°C to 70°C.

[0023] The precipitation parameters simulate the scouring effect of summer rain on the road surface in Hainan. The stability of asphalt pavement decreases under high temperatures in summer, and precipitation will aggravate its damage. The summer precipitation in Hainan is about 672.3 mm, and the total annual precipitation is simulated to be 675 mm. Precipitation is achieved by spraying with sprinklers. The sprinkler sprays 5 mm per minute. Since one year of outdoor UV aging is equivalent to 72 hours indoors, 225 mm or 45 minutes of spraying is required every 24 hours. The spraying time and cycle are set to spray three times every 24 hours and once every 8 hours. The duration of each spray is set to 15 minutes. The total number of spray cycles is determined according to the total aging time. The simulated aging range of 10-12 years is 30-36 cycles.

[0024] In order to analyze the correlation between the concentration of heavy metal elements in leachate and coupling factors through orthogonal experiments, two parameter values ​​were selected for each environmental indicator parameter within the provided range.

[0025] Furthermore, the step S2 is to prepare an asphalt mixture specimen according to the asphalt pavement structure, and immerse and process the specimen to collect the interlayer leachate, specifically:

[0026] The asphalt mixture specimens used common gradation types, including AC, SMA, and OGFC. The mineral gradation and asphalt-stone ratio were selected in accordance with the "Technical Specifications for Highway Asphalt Pavement Construction" (JTGF40-2019). No. 70 matrix asphalt was used, limestone was used as coarse and fine aggregates, and limestone slag and fly ash were used as fillers. According to existing research, the fly ash was mixed using a dry method to replace the slag, and the mass fraction of the fly ash replacing the slag was in the range of 10% to 50% of the mass of the slag.

[0027] The upper, middle and lower asphalt mixture specimens were tested according to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering"

[0028] The thickness of the upper, middle and lower layers is based on the "Highway Asphalt Pavement Design Specifications".

[0029] (JTG D50—2017) design, the upper, middle and lower layers are bonded by spreading adhesive layer oil;

[0030] The lower layer specimen and the middle surface layer specimen were demoulded, and with the center point of the upper surface of the specimen as the center, marked circles with diameters of 200mm and 100mm were made respectively. The center of the circle and any point on the circle were marked with a marker pen. Two straight lines with a spacing of 7-10mm were gradually cut downward at an angle of 3-5° downward from the surface on both sides of each marked position. A Bosch GBH 220 electric hammer equipped with a 6mm×110mm drill bit was used to crush and remove the asphalt mixture within the two straight lines to form a groove for diversion and collection of interlayer leachate. After drilling, a rubber strip with a diameter of 6mm was placed inside the groove. The end of the strip should extend outside the specimen so that it can be subsequently pulled out and inserted into the diversion hose.

[0031] Place the upper, middle and lower layer specimens in a steel mold with a size of 300mm×300mm×Hmm, where H is the total thickness of the upper, middle and lower layer specimens. Sprinkle tack oil between the layers for bonding and fixing to obtain the upper, middle and lower layer asphalt mixture test specimens; demould the upper, middle and lower layer specimens, pull out the rubber strips, and use epoxy resin to bond and fix the leachate collection device at the bottom of the specimen. Use sealant to seal the periphery of the contact position between the bottom of the specimen and the leachate collection device. Wrap the specimen with asbestos cloth on all sides and seal it. Place the sealed specimen in a foam box. Drill a hole at the overlapping position of the foam box and the reserved holes between the upper, middle and lower layer specimens, and insert a silicone hose with a diameter of 6mm to ensure that the hose is inserted into the predetermined position inside the upper, middle and lower layer specimens. Install a collection bag at the end of the hose, and seal the contact position between the hose and the specimen; finally, use sealant to seal the contact position between the upper end of the foam box and the edge of the specimen surface to complete the specimen preparation;

[0032] The specific dimensions of the asbestos cloth are 0.5mm thick, 1250mm long, and H+50mm wide; the outer wall and bottom of the foam box are 30mm thick, and the internal dimensions are 300mm×300mm×H+100mm;

[0033] The leachate collection device is a steel container with an outer dimension of 300mm×300mm×100mm, an outer wall and bottom thickness of 10mm, and contains two annular grooves and a cylindrical groove inside. The annular groove and cylindrical groove wall thickness are 5mm, the large circle radius of the large ring is 105mm, the small circle radius is 90mm, the large circle radius of the small ring is 55mm, the small circle radius is 40mm, and the cylindrical groove radius is 20mm. It is used to collect the bottom leachate;

[0034] The collection bag is made of silicone, with a size of 100mm×50mm and a thickness of 1mm. A cylindrical nozzle with a length of 20mm, an inner diameter of 6mm and a wall thickness of 1mm is set at the top center of the collection bag for connecting to the hose.

[0035] The inner diameter of the silicone hose is 4mm, the outer diameter is 6mm, and the length is required to exceed 100mm after being inserted into the test piece. The length of the rubber strip is required to exceed 20mm after being inserted into the test piece.

[0036] The sealing process is performed using a high temperature resistant sealant, such as Aricon SI207 or Aricon SI593, which is sprayed onto the desired location for sealing;

[0037] The fly ash is produced from a waste incineration plant in Guangzhou;

[0038] The tack coat oil is an asphalt emulsion or asphalt solvent specially used for road surfaces, and is characterized by good adhesion and permeability;

[0039] Furthermore, in step S3, the specimen is placed in a simulated coupling environment, the coupling environmental factors are applied, and the leachate is collected in layers to test the type and content of heavy metal elements in the leachate, specifically:

[0040] S3-1. Place the specimen in a UV accelerated weathering tester and adjust the light, temperature, and precipitation parameters set in step S1 through the touch screen panel of the device;

[0041] S3-2. After the coupling is completed, remove the collection bag and the bottom leachate collection device, number the leachate, and test the type and content of heavy metals in the leachate collected at different positions.

[0042] According to the “Determination of 65 Elements in Water Quality by Inductively Coupled Plasma Mass Spectrometry” (HJ 700-2014), the heavy metal content of the leachate was tested using an inductively coupled plasma mass spectrometer (ICP-MS) to obtain the heavy metal types and leaching concentrations of the leachate.

[0043] Furthermore, the step S4 calculates the permeability coefficient and diffusivity under different coupling conditions, and takes K3, U 33 As the main indicator, through the correlation analysis with the coupling factors, the durability of asphalt pavement materials on the three-dimensional diffusion control effect of heavy metal elements in fly ash is clarified, specifically:

[0044] Calculate the permeability coefficient K of different heavy metal elements under different coupling conditions i , diffusion U y,i , analyze the leaching law of heavy metal elements in fly ash in asphalt pavement materials; take the permeability coefficient K3, diffusion degree U 33 As the main indicators, the permeability coefficient K3 and diffusion U of different heavy metal elements under different coupling environments are calculated. 33 The coefficient of variation of the heavy metal elements is used to clarify the degree to which different heavy metal elements are affected by coupling factors;

[0045] The coefficient of variation B of the permeability coefficient K3 K The calculation process is to calculate the average value

[0046]

[0047] in is the average value of K3 under different coupling environmental conditions, N is the total number of working conditions under different coupling conditions, and ∑K3 is the sum of K3 calculated under different coupling conditions;

[0048] Calculate the standard deviation using the following formula:

[0049]

[0050] where δ K is the standard deviation of K3 calculated under different coupling conditions; N is the total number of working conditions under different coupling conditions; i is the number of working conditions under different coupling conditions, where i = 1, 2, 3, ..., N; is the average value of K3 under different coupling conditions;

[0051] Coefficient of variation B K The formula is as follows:

[0052]

[0053] Among them B K is the coefficient of variation of K3 calculated under different coupling conditions; δ K is the standard deviation of K3 calculated under different coupling conditions; is the average value of K3 under different coupling conditions;

[0054] The diffusion U 33 The calculation process of the coefficient of variation is to calculate its average value

[0055]

[0056] in U under different coupling environment conditions 33 The average value of N is the total number of working conditions with different coupling conditions, ∑U 33 is the U calculated under different coupling conditions 33 the sum of;

[0057] Calculate the standard deviation δ U , the calculation formula is as follows:

[0058]

[0059] where δU is the U calculated under different coupling conditions 33 The standard deviation of ; N is the total number of different coupling condition working conditions; i is the number of different coupling condition working conditions, where i = 1, 2, 3, ..., N; U under different coupling conditions 33 The average value of

[0060] Coefficient of variation B U The formula is as follows:

[0061]

[0062] Among them B U is the U calculated under different coupling conditions 33 The coefficient of variation of δ U is the U calculated under different coupling conditions 33 The standard deviation of U under different coupling conditions 33 The average value of

[0063] By the coefficient of variation B k 、B U Evaluation of the permeability coefficient K3 and diffusion degree U of heavy metal elements 33 Degree of influence by coupling environmental factors:

[0064] When the coefficient of variation is less than 0.2, it means that the degree of variation of the data is relatively small, and the data is relatively stable under the coupled environmental factors, indicating that the degree of influence of the coupled environmental factors is small;

[0065] When the coefficient of variation is greater than 0.2 and less than 0.5, it means that the degree of variation of the data is moderate. The data has a certain degree of dispersion under the coupled environmental factors, indicating that the degree of influence of the coupled environmental factors is moderate.

[0066] When the coefficient of variation is greater than 0.5, it means that the degree of variation of the data is relatively large, and the data has a large degree of dispersion under the coupled environmental factors, indicating that it is greatly affected by the coupled environmental factors.

[0067] Each step in the above application method has a strict preparation, detection and evaluation sequence, and improper method steps will seriously affect the characterization results.

[0068] The existing technologies mainly include "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid and Nitric Acid Method" (HJ / T299-2007) and water tank leaching test (EA NEN7375). These two methods simply test the heavy metal leaching amount of fly ash asphalt mixture, and do not take into account the surface structure of the asphalt pavement and the influence of environmental factors on the asphalt pavement material under actual use. The advantage of the present invention is that it proposes an evaluation method for the durability of asphalt pavement material for the three-dimensional diffusion control effect of the dissolution and infiltration of heavy metal elements in garbage fly ash. By preparing asphalt pavement material specimens, designing a coupling environment to couple the specimens, collecting the leachate between the specimen layers and the bottom, and measuring the type and content of heavy metals, the permeability coefficient K defined by this evaluation method is determined. i and diffusion U y,i , which can more accurately evaluate the durability of asphalt pavement materials on the three-dimensional diffusion control effect of heavy metal elements in fly ash under actual conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 It is a flow chart of the technical solution of the present invention.

[0070] Figure 2 This is a diagram of the marking positions between asphalt mixture layers of the present invention.

[0071] Figure 3 It is a three-dimensional diagram of the bottom leachate collecting device of the present invention.

[0072] Figure 4 This is a top view of the bottom leachate collection device.

[0073] Figure 5 It is a three-dimensional diagram of the test piece of the present invention. Specific implementation methods

[0074] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0075] S1. Conduct simulation construction of the coupling environment;

[0076] S2. Asphalt pavement material specimens use an upper layer of AC-13, a middle layer of AC-20, and a lower layer of AC-25, with thicknesses of 4, 6, and 8 cm. Coarse and fine aggregate, mineral powder, and fly ash are weighed according to the design gradation requirements for each specimen and then heated in a preheated oven at 200°C for 6 hours. The asphalt is then heated in an oven preheated at 180°C. The mold is then placed in the oven for heating. The asphalt mixer is preheated for approximately 10 minutes. The preheated coarse and fine aggregates are added to the mixer and dry-mixed for 60 seconds. A predetermined amount of asphalt is then added and stirred for 90 seconds. Finally, the mineral powder and fly ash are added and stirred for another 90 seconds, for a total mixing time of 4 minutes.

[0077] Prepare a lower mold with internal dimensions of 300mm x 300mm x 80mm and heat it in an oven. Line the heated mold with oil-absorbing paper to prevent the mixture from sticking to the inner walls. Use a spatula to shovel the mixed mixture into the mold. Place the asphalt mixture into the mold from the sides toward the center, with the center slightly higher than the surrounding area. Next, use a preheated small compacting hammer to tamp the mold with the poured asphalt mixture in a circular motion from the sides toward the center, forming a convex arc. When the asphalt mixture reaches compaction temperature, insert a thermometer and place a piece of cut plain paper on the surface. Preheat the rollers to 100°C before forming. Furthermore, place the rutting plate containing the asphalt mixture on the compaction tester platform, gently lower the rollers, and adjust the total load to 9 kN (linear load 300 N / cm). Turn on the wheel rolling tester and pre-roll the asphalt twice in one direction (a total of four times). After unloading the load, raise the rolling wheel and rotate the rutting plate in the opposite direction. Repeat the same rolling operation, but test the rolling before rolling. The rutting plate is rolled 24 times. After rolling, remove the paper on the surface with tweezers, mark the rolling direction on the upper surface with a marker, and cure the specimen at room temperature for 12 hours to obtain the lower layer asphalt mixture.

[0078] The middle and upper layer specimens were made by the above method. The size of the middle layer specimen was 300mm×300mm×60mm, and the size of the upper layer specimen was 300mm×300mm×40mm. The lower layer specimen and the middle layer specimen were demoulded, and the center point of the upper surface of the specimen was used as the center of the circle to make marking circles with diameters of 200mm and 100mm respectively. The center of the circle and any point on the circle were marked with a marker pen. The Dongcheng angle grinder S1M-FF09-100S was used to gradually cut two symmetrical straight lines with a spacing of 7mm on both sides of each marked position at an angle of 4° downward with the surface as the reference plane. The Bosch GBH equipped with a 6mm×110mm drill bit was used. A 220 electric hammer is used to crush and remove the asphalt mixture within two straight lines to form a groove for diversion and collection of interlayer leachate. After drilling is completed, a rubber strip with a diameter of 6 mm is placed inside the groove (to prevent the adhesive layer oil from filling and clogging the groove). The end of the strip should extend 20 mm outside the specimen so that the strip can be pulled out and inserted into the diversion hose.

[0079] Place the upper, middle, and lower layer specimens in a steel mold with a size of 300mm×300mm×180mm, and spread tack oil between the layers for bonding and fixing to obtain the upper, middle, and lower layer asphalt mixture test specimens; demould the upper, middle, and lower layer specimens, pull out the rubber strips, and use epoxy resin to bond and fix the leachate collection device at the bottom of the specimen. Use sealant to seal the periphery of the contact position between the bottom of the specimen and the leachate collection device. Wrap the specimen with asbestos cloth on all sides and seal it. Place the sealed specimen in a foam box, drill a hole at the overlapping position of the reserved hole between the foam box and the upper, middle, and lower layer specimens, and insert a silicone hose with a diameter of 6mm to ensure that the hose is inserted into the predetermined position inside the upper, middle, and lower layer specimens. Install a collection bag at the end of the hose, and seal the contact position between the hose and the specimen with sealant Aricsen SI207; finally, use sealant Aricsen SI207 to seal the contact position between the upper end of the foam box and the edge of the specimen surface to complete the specimen preparation;

[0080] S3. Place the specimen in a UV accelerated weathering tester and set the light, temperature, and precipitation parameters as shown in Table 1. The coupling factors are then applied. After the test, collect the leachate in layers in a glass and label it using the following numbering rules:

[0081] Number C y,x , where y represents the interlayer position, y=1 represents the interlayer position between the upper layer and the middle layer, y=2 represents the interlayer position between the middle layer and the lower layer, and y=3 represents the bottom position of the lower layer; x represents the plane position, x=1 represents the center of the interlayer, referred to as mark 1, x=2 represents the test point marked on a circle with a diameter of 100 mm, referred to as mark 2, and x=3 represents the test point marked on a circle with a diameter of 200 mm, referred to as mark 3;

[0082] The leachate collected between the upper and middle layers is marked as C 11 、C 12 、C 13 , the leachate collected in the middle and lower layers are marked as C 21 、C 22 、C 23 , the filtrates collected by the bottom collection device are marked as C 31 、C 32 、C 33 ;

[0083] The heavy metal content of the leachate was tested using inductively coupled plasma mass spectrometry (ICP-MS) according to the "Determination of 65 Elements in Water Quality by Inductively Coupled Plasma Mass Spectrometry" (HJ 700-2014). The heavy metal types and leaching concentrations of the leachate are shown in Table 2.

[0084] S4. Calculate the longitudinal heavy metal element leaching index - permeability coefficient K i and the longitudinal concentration gradient difference △C at the center point i , the calculation formula is as follows:

[0085]

[0086] △C i =C2-C1

[0087] where K i is the permeability coefficient, which indicates the average increase in the concentration of heavy metal elements per millimeter when the leachate penetrates vertically downward between layers; h is the height of the leachate between the surface layers; △C i is the longitudinal concentration gradient difference at the center point, indicating the difference in the concentration of heavy metal elements in the leachate at the center point of different layers of the specimen; i = 1, 2, 3 indicate the position through which the leachate passes, i = 1 indicates that the leachate reaches interlayer 1 from interlayer 2, i = 2 indicates that the leachate reaches the bottom layer from interlayer 2, and i = 3 indicates that the leachate reaches the bottom layer from interlayer 1; C2 indicates the heavy metal concentration of the leachate in the upper layer between the two layers, and C1 indicates the heavy metal concentration of the leachate in the lower layer between the two layers.

[0088] Horizontal heavy metal element leaching diffusivity index - diffusivity U y,i , the calculation formula is as follows:

[0089]

[0090] △C y,i =C3-C4

[0091] Among them U y,iis the diffusion degree, which indicates the average increase in the concentration of heavy metal elements in the leachate during horizontal diffusion between layers per millimeter, △C y,i represents the difference in heavy metal element concentrations in the leachate collected between the same layers; y represents the layer where the leachate is collected, and y=1, 2, and 3 represent that the leachate is collected in layer 1, layer 2, and the bottom layer, respectively; i=1, 2, and 3 represent that the leachate diffuses from marker 1 to marker 2, marker 2 to marker 3, and marker 1 to marker 3, respectively; C3 represents the leachate concentration at the outermost marker point during the horizontal diffusion of the leachate from the center to the periphery; C4 represents the leachate concentration at the innermost marker point during the horizontal diffusion of the leachate from the center to the periphery; l represents the difference in the radius from the two marker points to the center point, and the permeability coefficient K is obtained. i , diffusion U y,i , this embodiment takes U y,3 As the main indicator of interlayer horizontal diffusion, it is shown in Table 3.

[0092] Take the permeability coefficient K3 and the diffusivity U 33 As the main indicators, the permeability coefficient K3 and diffusion U of different heavy metal elements under different coupling environments are calculated. 33 The coefficient of variation of the heavy metal elements is used to clarify the degree to which different heavy metal elements are affected by coupling factors;

[0093] The coefficient of variation B of the permeability coefficient K3 K The calculation process is to calculate the average value

[0094]

[0095] in is the average value of K3 under different coupling environmental conditions, N is the number of working conditions under different coupling conditions, and ∑K3 is the sum of K3 calculated under different coupling conditions;

[0096] Calculate the standard deviation δ K , the calculation formula is as follows:

[0097]

[0098] where δ k is the standard deviation of K3 calculated under different coupling conditions; N is the number of working conditions under different coupling conditions; i is the number of working conditions under different coupling conditions, where i = 1, 2, 3, ..., N; is the average value of K3 under different coupling conditions;

[0099] Coefficient of variation B v The formula is as follows:

[0100]

[0101] Among them BK is the coefficient of variation of K3 calculated under different coupling conditions; δ K is the standard deviation of K3 calculated under different coupling conditions; is the average value of K3 under different coupling conditions;

[0102] The diffusion U 33 The coefficient of variation B U The calculation process is to calculate the average value

[0103]

[0104] in U under different coupling environment conditions 33 The average value of N is the number of working conditions with different coupling conditions, ∑U 33 is the U calculated under different coupling conditions 33 the sum of;

[0105] Calculate the standard deviation δ U , the calculation formula is as follows:

[0106]

[0107] where δ U is the U calculated under different coupling conditions 33 The standard deviation of ; N is the number of different coupling condition working conditions; i is the number of different coupling condition working conditions, where i = 1, 2, 3, ..., N; U under different coupling conditions 33 The average value of

[0108] Coefficient of variation B U The formula is as follows:

[0109]

[0110] Among them B U is the U calculated under different coupling conditions 33 The coefficient of variation of δ U is the U calculated under different coupling conditions 33 The standard deviation of U under different coupling conditions 33 The average value of

[0111] By the coefficient of variation B k 、B U Evaluation of the permeability coefficient K3 and diffusion degree U of heavy metal elements 33 Degree of influence by coupling environmental factors:

[0112] When the coefficient of variation is less than 0.2, it means that the degree of variation of the data is relatively small, and the data is relatively stable under the coupled environmental factors, indicating that the degree of influence of the coupled environmental factors is small;

[0113] When the coefficient of variation is greater than 0.2 and less than 0.5, it means that the degree of variation of the data is moderate. The data has a certain degree of dispersion under the coupled environmental factors, indicating that the degree of influence of the coupled environmental factors is moderate.

[0114] When the coefficient of variation is greater than 0.5, it means that the degree of variation of the data is relatively large, and the data has a large degree of dispersion under the coupled environmental factors, indicating that it is greatly affected by the coupled environmental factors.

[0115] According to the permeability coefficient K under different coupling conditions i , diffusion U y,i As shown in Table 3, the leaching law of heavy metal elements in fly ash in asphalt pavement material carrier is analyzed; the permeability coefficient K3 and the diffusion degree U 33 As the main indicator, the coefficient of variation was calculated to clarify the degree to which different heavy metal elements were affected by the coupled environment, as shown in Tables 4 and 5;

[0116] Table 1 Orthogonal experimental design for experiments under coupling environment

[0117]

[0118] Table 2 Heavy metal leaching concentrations between fly ash and asphalt pavement material layers under coupled environmental conditions

[0119]

[0120] Table 3 Interlayer permeability coefficient K of fly ash-asphalt pavement materials under coupled environment i , diffusion U y,i

[0121]

[0122] Table 4 Permeability coefficient K3 of heavy metal elements in fly ash-asphalt binder under different coupled simulation environments

[0123]

[0124] Table 5 Diffusivity U of heavy metal elements in fly ash-asphalt binder under different coupled simulation environments 33

[0125]

[0126] The specific standard referenced in Table 2 is the "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007). Comparing the leachate heavy metal concentrations with the regulatory limits in Table 2 reveals that all meet the regulatory limits. Table 3 shows that under the coupled environment, the permeability coefficients K1, K2, and K3 of the asphalt pavement material for different heavy metal elements are all greater than 0, with similar values ​​for K1, K2, and K3. This indicates that the heavy metal concentration gradually increases during the longitudinal penetration of the asphalt specimen, and the increase is relatively stable, indicating that the longitudinal leaching of heavy metal elements from fly ash into the asphalt pavement material is relatively stable under the coupled factors. Similarly, the diffusion coefficients are mostly greater than 0 and relatively stable, indicating that the heavy metal concentration gradually increases during the longitudinal penetration of the asphalt specimen, and the increase is relatively stable, indicating that the horizontal diffusion of heavy metal elements from fly ash into the asphalt pavement material is relatively stable under the coupled factors. This indicates that the asphalt pavement material has a strong three-dimensional barrier effect on the heavy metal elements in fly ash.

[0127] Table 4 shows the coefficient of variation of the elemental permeability coefficient, K3, of fly ash-asphalt pavement materials under different coupled simulated environments. The variation ranges from 46.01% to 57.70%, with an average coefficient of variation of 52.39%, reaching a high level of bias. Cr (59.70%) has the highest coefficient of variation, indicating that its longitudinal leaching is most affected by the environment. Zn (46.01%) exhibits moderate variation, while Cu (54.23%), Pb (53.39%), and Cr (59.86%) exhibit high variation. This indicates that the longitudinal leaching of heavy metals from fly ash-asphalt pavement materials is significantly affected by the environment.

[0128] Table 5 shows the diffusion rate U of heavy metal elements in fly ash-asphalt binder under different coupled simulation environments. 33 The coefficient of variation of the chromium (56.31%) is the largest, indicating that the horizontal diffusion of element Cu is most affected by the environment. The coefficients of variation for Cu (56.14%) and Cr (56.31%) are both large, indicating high variation. The coefficients of variation for Zn (22.17%) and Pb (38.07%) are relatively stable, indicating moderate variation and less affected by coupling. This indicates that the horizontal diffusion of heavy metals in fly ash from fly ash-asphalt pavement materials is less affected by the coupled environment than the vertical diffusion. In summary, the asphalt pavement material's control over the three-dimensional diffusion of heavy metal elements in fly ash is significantly affected by the environment.

[0129] From Tables 1 to 5, it can be seen that the asphalt pavement material is greatly affected by the coupling environment in terms of the three-dimensional diffusion control effect of heavy metal elements in fly ash. However, the concentrations of heavy metal element leachate between the layers of fly ash-asphalt pavement material meet the requirements of the "Hazardous Waste Identification Standard - Leaching Toxicity Identification" (GB 5085.3-2007), and the longitudinal leaching and horizontal diffusion are relatively stable under different coupling environments.

[0130] The present invention provides a method for evaluating the anti-solution and permeation durability of fly ash-asphalt pavement materials under a coupled environment. The evaluation method of the present invention defines the following parameters: permeability coefficient K i , diffusion U y,i Through the correlation analysis with the coupling factors, the durability of asphalt pavement materials on the three-dimensional diffusion control effect of heavy metal elements in fly ash can be clarified.

[0131] As described above, the method for evaluating the anti-solution and permeation durability of fly ash-asphalt pavement materials in a coupled environment provided by the present invention is introduced in detail. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; any simple modifications, changes and equivalent structural changes made to the above embodiments based on the technical essence of the invention are still within the scope of protection of the technical solution of the present invention.

Claims

1. A method for evaluating the anti-solution durability of fly ash-asphalt pavement materials under a coupled environment, characterized in that: include: S1. Construct a coupled test environment for anti-solution and durability; S2. Prepare asphalt mixture specimens based on the asphalt pavement structure and process the specimens to collect interlayer leachate; S3. Place the specimen in a simulated coupling environment, implement the coupled environmental factors, and collect leachate in layers. Test the type and content of heavy metal elements in the leachate with different numbers. The numbering rules are as follows: The leachate is numbered as C y,x , where y represents the interlayer position, y=1 represents the position between the upper and middle layers, y=2 represents the position between the middle and lower layers, and y=3 represents the bottom position of the lower layer; x represents the plane position, x=1 represents the center of the interlayer, referred to as mark 1, x=2 represents the test point marked on a circle with a diameter of 100 mm, referred to as mark 2, and x=3 represents the test point marked on a circle with a diameter of 200 mm, referred to as mark 3; the leachate collected between the upper and middle layers is marked as C 11 、C 12 、C 13 , the leachate collected in the middle and lower layers are marked as C 21 、C 22 、C 23 , the filtrates collected by the bottom collection device are marked as C 31 、C 32 、C 33 , where the upper middle layer is referred to as layer 1, and the middle and lower layer is referred to as layer 2; S4. Calculate the permeability coefficient and diffusivity, analyze the control of asphalt pavement materials on the infiltration of heavy metal elements from fly ash in the longitudinal and horizontal directions under coupling conditions, and evaluate the durability of asphalt pavement materials' control over the three-dimensional diffusion of heavy metal elements from fly ash through correlation analysis with coupling factors. The longitudinal heavy metal element leaching index - permeability coefficient K i and the longitudinal concentration gradient difference △C at the center point i , the calculation formula is as follows: △C i =C2-C1 where K i is the permeability coefficient, which indicates the average increase in the concentration of heavy metal elements per millimeter when the leachate penetrates vertically downward between layers; h is the height of the leachate between the surface layers; △C i is the longitudinal concentration gradient difference at the center point, indicating the difference in the concentration of heavy metal elements in the leachate at the center point of different layers of the specimen; i = 1, 2, 3, indicating the position through which the leachate passes, i = 1 indicates that the leachate reaches interlayer 1 from interlayer 2, i = 2 indicates that the leachate reaches the bottom layer from interlayer 2, and i = 3 indicates that the leachate reaches the bottom layer from interlayer 1; C2 indicates the heavy metal concentration of the leachate located in the upper layer of the calculated leachate between the two layers, and C1 indicates the heavy metal concentration of the leachate located in the lower layer of the calculated leachate between the two layers; Horizontal heavy metal element leaching diffusivity index - diffusivity U y,i , the calculation formula is as follows: △C y,i =C3-C4 Among them U y,i is the diffusion degree, which indicates the average increase in the concentration of heavy metal elements in the leachate during horizontal diffusion between layers per millimeter, △C y,i It represents the difference in heavy metal element concentration of leachate collected in the same layer; y represents the layer where the leachate is collected, and y=1, 2, and 3 represent that the leachate is collected in layer 1, layer 2, and the bottom layer, respectively; i=1, 2, and 3 represent that the leachate diffuses from marker 1 to marker 2, marker 2 to marker 3, and marker 1 to marker 3, respectively; C3 represents the heavy metal concentration of the marked point near the periphery during the horizontal diffusion of the leachate from the center to the periphery; C4 represents the heavy metal concentration of the marked point near the center during the horizontal diffusion of the leachate from the center to the periphery; l represents the difference in the radius between the two marked points and the center point.

2. The evaluation method according to claim 1, wherein Step S1 constructs a coupled test environment for anti-solution and permeation durability, and the specific environmental technical indicators are: The coupling test environmental factors include three indicators: light, temperature, and precipitation; The light, temperature and precipitation indicators are simulated and constructed using an ultraviolet light accelerated weathering tester, and a coupled test environment is constructed and implemented using a composite effect method; The ultraviolet radiation parameters of the illumination were selected from Urumqi, Xinjiang Uygur Autonomous Region, a region with complex climatic conditions and high ultraviolet intensity. A high-pressure mercury lamp was used to simulate the accelerated aging of ultraviolet light. The lamp's spectrum range was between 350-450nm and the power was 1000W. Calculation showed that 6 hours of indoor accelerated ultraviolet aging radiation was equivalent to 1 month of outdoor aging time. The ultraviolet radiation parameters of the illumination were set to simulate an irradiation time of 10-12 years, and the indoor accelerated ultraviolet aging conversion time was 720h-864h. The temperature parameters are based on the western region. The highest annual temperature in the western region is generally in July, with an average monthly temperature of around 33°C. Calculations show that when an asphalt pavement is exposed to sunlight, its highest surface temperature is between 60°C and 70°C. Therefore, the temperature setting range is 60°C to 70°C. The precipitation parameters simulate the scouring effect of summer rain on the road surface in Hainan. The stability of asphalt pavement decreases under high temperatures in summer, and precipitation will aggravate its damage. The summer precipitation in Hainan is about 672.3 mm, and the total annual precipitation is simulated to be 675 mm. Precipitation is achieved by spraying with sprinklers. The sprinkler sprays 5 mm per minute. Since one year of outdoor UV aging is equivalent to 72 hours indoors, 225 mm or 45 minutes of spraying is required every 24 hours. The spraying time and cycle are set to spray three times every 24 hours and once every 8 hours. The duration of each spray is set to 15 minutes. The total number of spray cycles is determined according to the total aging time. The simulated aging range of 10-12 years is 30-36 cycles. In order to analyze the correlation between the concentration of heavy metal elements in leachate and coupling factors through orthogonal experiments, two parameter values ​​were selected for each environmental indicator parameter within the provided range.

3. The evaluation method according to claim 1, wherein: In step S2, asphalt mixture specimens are prepared according to the asphalt pavement structure, and the specimens are processed to collect interlayer leachate, specifically: The asphalt mixture specimens used common gradation types, including AC, SMA, and OGFC. The mineral gradation and asphalt-stone ratio were selected in accordance with the "Technical Specifications for Highway Asphalt Pavement Construction" (JTGF40-2019). No. 70 matrix asphalt was used, limestone was used as coarse and fine aggregates, and limestone slag and fly ash were used as fillers. According to existing research, the fly ash was mixed using a dry method to replace the slag, and the mass fraction of the fly ash replacing the slag was in the range of 10% to 50% of the mass of the slag. The upper, middle, and lower asphalt mixture specimens were prepared according to the wheel rolling method in the "Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering" (JTGE20-2019). The thickness of the upper, middle, and lower layers was designed according to the "Design Code for Highway Asphalt Pavement" (JTG D50-2017). The upper, middle, and lower layers were bonded by spreading tack coat oil. The lower layer specimen and the middle surface layer specimen were demoulded, and marked circles with diameters of 200mm and 100mm were made with the center point of the upper surface of the specimen as the center of the circle. The center of the circle and any point on the circle were marked with a marker pen. Two parallel straight lines with a spacing of 7-10mm were gradually cut downward at an angle of 3-5° downward from the surface on both sides of each marked position. A Bosch GBH 220 electric hammer equipped with a 6mm×110mm drill bit was used to crush and remove the asphalt mixture within the two straight lines to form a groove for diversion and collection of interlayer leachate. After drilling, a rubber strip with a diameter of 6mm was placed inside the groove. The end of the strip should extend outside the specimen so that it can be subsequently pulled out and inserted into the diversion hose. Place the upper, middle and lower layer specimens in a steel mold with a size of 300mm×300mm×Hmm, where H is the total thickness of the upper, middle and lower layer specimens. Sprinkle tack oil between the layers for bonding and fixing to obtain the upper, middle and lower layer asphalt mixture test specimens; demould the upper, middle and lower layer specimens, pull out the rubber strips, and use epoxy resin to bond and fix the leachate collection device at the bottom of the specimen. Use sealant to seal the periphery of the contact position between the bottom of the specimen and the leachate collection device. Wrap the specimen with asbestos cloth on all sides and seal it. Place the sealed specimen in a foam box. Drill a hole at the overlapping position of the foam box and the reserved holes between the upper, middle and lower layer specimens, and insert a silicone hose with a diameter of 6mm to ensure that the hose is inserted into the predetermined position inside the upper, middle and lower layer specimens. Install a collection bag at the end of the hose, and seal the contact position between the hose and the specimen; finally, use sealant to seal the contact position between the upper end of the foam box and the edge of the specimen surface to complete the specimen preparation; The specific dimensions of the asbestos cloth are 0.5mm thick, 1250mm long, and H+50mm wide; the outer wall and bottom of the foam box are 30mm thick, and the internal dimensions are 300mm×300mm×H+100mm; The leachate collection device is a steel container with an outer dimension of 300mm×300mm×100mm, an outer wall and bottom thickness of 10mm, and contains two annular grooves and a cylindrical groove inside. The annular groove and cylindrical groove wall thickness are 5mm, the large circle radius of the large ring is 105mm, the small circle radius is 90mm, the large circle radius of the small ring is 55mm, the small circle radius is 40mm, and the cylindrical groove radius is 20mm. It is used to collect the bottom leachate; The collection bag is made of silicone, with a size of 100mm×50mm and a thickness of 1mm. A cylindrical nozzle with a length of 20mm, an inner diameter of 6mm and a wall thickness of 1mm is set at the top center of the collection bag for connecting to the hose. The inner diameter of the silicone hose is 4mm, the outer diameter is 6mm, and the length is required to exceed 100mm after being inserted into the test piece. The length of the rubber strip is required to exceed 20mm after being inserted into the test piece. The sealing process is performed using a high temperature resistant sealant, which includes Aricson SI207 and Aricson SI593, and is sealed by spraying it to the desired position.

4. The evaluation method according to claim 2, wherein: In step S3, the specimen is placed in a simulated coupling environment, the coupling environmental factors are applied, and the leachate is collected in layers to test the type and content of heavy metal elements in the leachate, specifically: S3-1. Place the specimen in the UV accelerated weathering tester and adjust the lighting, temperature, and precipitation parameters using the touchscreen panel. S3-2. After the coupling is completed, remove the collection bag and the bottom leachate collection device, number the leachate, and test the type and content of heavy metals in the leachate collected at different positions. According to the “Determination of 65 Elements in Water Quality by Inductively Coupled Plasma Mass Spectrometry” (HJ 700-2014), the heavy metal content of the leachate was tested using an inductively coupled plasma mass spectrometer (ICP-MS) to obtain the heavy metal types and leaching concentrations of the leachate.

5. The evaluation method according to claim 1, wherein: Step S4 calculates the permeability coefficient and diffusion under different coupling conditions, analyzes the leaching pattern of heavy metal elements in fly ash in the asphalt pavement material carrier, and further clarifies the durability of the asphalt pavement material for the three-dimensional diffusion control effect of heavy metal elements in fly ash through correlation analysis with coupling factors. Specifically, Calculate the permeability coefficient K of different heavy metal elements under different coupling conditions i , diffusion U y,i , analyze the leaching law of heavy metal elements in fly ash in asphalt pavement materials; take the permeability coefficient K3, diffusion degree U 33 As the main indicators, the permeability coefficient K3 and diffusion U of different heavy metal elements under different coupling environments are calculated. 33 The coefficient of variation of the heavy metal elements is used to clarify the degree to which different heavy metal elements are affected by coupling factors; The coefficient of variation B of the permeability coefficient K3 k The calculation process is to calculate the average value in is the average value of K3 under different coupling environmental conditions, N is the total number of working conditions under different coupling conditions, and ∑K3 is the sum of K3 calculated under different coupling conditions; Calculate the standard deviation δ K , the calculation formula is as follows: where δ K is the standard deviation of K3 calculated under different coupling conditions; N is the total number of working conditions under different coupling conditions; i is the number of working conditions under different coupling conditions, where i = 1, 2, 3, ..., N; is the average value of K3 under different coupling conditions; Coefficient of variation B K The formula is as follows: Among them B K is the coefficient of variation of K3 calculated under different coupling conditions; δ K is the standard deviation of K3 calculated under different coupling conditions; is the average value of K3 under different coupling conditions; The diffusion U 33 The coefficient of variation B U The calculation process is to calculate the average value in U under different coupling environment conditions 33 The average value of N is the total number of working conditions with different coupling conditions, ∑U 33 is the U calculated under different coupling conditions 33 the sum of; Calculate the standard deviation δ U , the calculation formula is as follows: where δ U is the U calculated under different coupling conditions 33 The standard deviation of ; N is the total number of different coupling condition working conditions; i is the number of different coupling condition working conditions, where i = 1, 2, 3, ..., N; U under different coupling conditions 33 The average value of Coefficient of variation B U The formula is as follows: Among them B U is the U calculated under different coupling conditions 33 The coefficient of variation of δ U is the U calculated under different coupling conditions 33 The standard deviation of U under different coupling conditions 33 The average value of By the coefficient of variation B K 、B U The size of the permeability coefficient K3 and diffusion degree U of different heavy metal elements are evaluated 33 Degree of influence by coupling environmental factors: When the coefficient of variation is less than 0.2, it means that the degree of variation of the data is relatively small, and the data is relatively stable under the coupled environmental factors, indicating that the degree of influence of the coupled environmental factors is small; When the coefficient of variation is greater than 0.2 and less than 0.5, it means that the degree of variation of the data is moderate. The data has a certain degree of dispersion under the coupled environmental factors, indicating that the degree of influence of the coupled environmental factors is moderate. When the coefficient of variation is greater than 0.5, it means that the degree of variation of the data is relatively large, and the data has a large degree of dispersion under the coupled environmental factors, indicating that it is greatly affected by the coupled environmental factors.

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