Method for evaluating effective utilization rate of asphalt in reclaimed material

Abstract

The application discloses a method for evaluating effective utilization rate of asphalt in recycled materials, which comprises the following steps: recovering old asphalt and detecting the content of the old asphalt, combining the amount of a recycling agent and new asphalt to calculate the theoretical proportion of the old asphalt, determining the optimal amount of new asphalt through a Marshall test, and then calculating the theoretical effective utilization rate; meanwhile, a correction coefficient based on the performance of asphalt and the road performance of a mixture is constructed, the actual effective utilization rate of the old asphalt in the recycled material is accurately quantified through dynamic weight distribution, the problem of inaccurate evaluation of the utilization rate of the old asphalt and complicated test in the prior art is solved, and a scientific basis is provided for the mix proportion design of high-mixing RAP recycled asphalt mixture.

Description

Technical Field

[0001] This invention relates to the field of road engineering material testing technology, specifically to a method for evaluating the effective utilization rate of asphalt in recycled materials. Background Technology

[0002] With the arrival of the peak season for highway overhauls, research on recycling technologies for reclaimed asphalt pavement (RAP) has become particularly important. In-depth research into RAP recycling technologies can conserve natural resources, protect the ecological environment, and reduce construction costs. Asphalt pavement recycling technology enables waste asphalt pavement materials to meet road performance requirements again, saving significant material resources and funds, reducing project costs, and simultaneously avoiding environmental pollution from waste materials, thus achieving a circular economy in the industry and ecological environmental protection.

[0003] The current standard JTG / T 5521-2019 "Technical Specification for Recycling Asphalt Pavement of Highways" Appendix D stipulates that the grade of new asphalt should be determined by referring to tables or using a blending method based on the RAP asphalt grade and blending ratio. It also stipulates that when the RAP content does not exceed 20%, the amount of new asphalt should be estimated based on experience or formula D.6.1, and the estimated amount of new asphalt P should be used as the final estimate. nb To determine the median value, use a Marshall test to detect P. nb P nb ±0.5, P nb The optimal amount of new asphalt was determined based on the results of using five asphalt dosages of ±1.0. This method assumes that the old asphalt can be fully utilized, which is inconsistent with reality. The experiment is cumbersome and sets many conditions for the use of recycling agents. Moreover, it does not take into account the insufficient effective utilization rate of old asphalt in RAP due to factors such as aging and coating status.

[0004] Researching the effective utilization rate of asphalt in recycled materials is of great significance for achieving efficient resource recycling, environmental protection, cost reduction, and improving construction efficiency and pavement performance. However, the current lack of effective methods for evaluating the effective utilization rate of used asphalt makes it impossible to accurately predict the proportion of reclaimed asphalt (RAP) and the amount of new asphalt, thus hindering the improvement of RAP recycling rates. Therefore, there is an urgent need for an evaluation method that can truly reflect the actual utility of used asphalt to achieve efficient resource recycling. Summary of the Invention

[0005] The main objective of this invention is to provide a method for evaluating the effective utilization rate of asphalt in recycled materials. This invention combines the three major indicators of asphalt with the road performance parameters of the mixture, and constructs correction coefficients for asphalt performance and mixture performance to correct the results of the effective utilization rate of asphalt. By studying high-content RAP recycled asphalt mixtures, the recycling rate of RAP is further improved, thereby achieving efficient recycling of resources and reducing costs.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for evaluating the effective utilization rate of bitumen in recycled materials includes the following steps:

[0008] 1) Recycle the RAP material, separate the old asphalt from the RAP material, and obtain the old asphalt content L0;

[0009] 2) Based on the design requirements, determine the blending ratio of RAP material, the dosage and amount of recycling agent, the amount of new aggregate and the amount of new asphalt, and calculate the percentage T0 of old asphalt in the total asphalt mass.

[0010] 3) Determine the optimal amount of new asphalt by Marshall test and calculate the theoretical effective utilization rate of old asphalt F0;

[0011] 4) After preliminary blending of old asphalt, recycling agent, and new asphalt to obtain blended asphalt, and after mixing new aggregate, RAP material, and new asphalt to obtain mixed asphalt, correction coefficients are constructed based on asphalt properties and mixture properties, and the corrected effective utilization rate F of old asphalt is calculated. The calculation formula is as follows:

[0012] ;

[0013] Wherein, F is the effective utilization rate of the corrected old asphalt; K is the asphalt performance correction coefficient; and γ is the asphalt mixture correction coefficient.

[0014] Preferably, step 1) uses a centrifugal extraction method to separate and extract the old bitumen from the RAP material.

[0015] Preferably, in step 2), the asphalt ratio is initially adjusted according to design requirements, and the type and dosage of the recycling agent are determined. The formula for calculating the dosage of the recycling agent is as follows:

[0016] ;

[0017] Wherein, m1 is the mass of old asphalt added during initial blending; m2 is the mass of recycling agent added during initial blending; and ρ is the amount of recycling agent added during initial blending (by mass ratio).

[0018] Preferably, in step 2), the amount of new asphalt (m3) is initially determined based on the blending ratio of the RAP material, and the percentage (T0) of old asphalt in the total asphalt mass is calculated. The calculation formulas are as follows:

[0019] ;

[0020] Wherein, m3 is the mass of new asphalt added during initial blending; M0 is the estimated amount of asphalt to be produced entirely from new asphalt without the addition of RAP material; m0 is the mass of RAP material calculated according to the RAP material blending ratio; L0 is the content of old asphalt in the RAP material; T0 is the percentage of old asphalt in the total asphalt mass; m1 is the mass of old asphalt added during initial blending; m2 is the mass of recycling agent added during initial blending; and m3 is the mass of new asphalt added during initial blending.

[0021] Preferably, in step 3), the formula for calculating the effective utilization rate F0 of old asphalt is:

[0022] ;

[0023] Wherein, F0 is the theoretical effective utilization rate of old asphalt; T1 is the percentage of the old asphalt that is effectively utilized after adding a portion of new asphalt m4, relative to the total mass of asphalt; and T0 is the proportion of old asphalt under the assumption that 100% of the old asphalt is utilized.

[0024] Preferably, in step 4), based on the RAP mix ratio, the median value of the optimal asphalt content Pnb is estimated, and five Marshall specimens with different asphalt contents are prepared. Volumetric parameters and mechanical properties are then tested, and the optimal new asphalt content m is determined based on the results. OAC The calculation formula is:

[0025] Wherein, m4 represents the mass of new asphalt added to compensate for the unused portion of the old asphalt in the mixture, m3 represents the mass of new asphalt added during the initial blending, and m... OAC -Optimal amount of new asphalt.

[0026] Preferably, in step 4), the heated new aggregate and RAP material are mixed for 40-80 seconds, and then new asphalt is added and mixed at a mixing temperature of 150-160℃. After mixing, the mixture is kept warm for 2.5 hours and then cooled to room temperature to obtain the asphalt mixture.

[0027] Preferably, the new aggregate includes at least one of limestone, granite, diabase and basalt.

[0028] Preferably, in step 4), the mass of newly added asphalt is m. OAC The obtained asphalt mixture was extracted to obtain asphalt B. The properties of asphalt B and blended asphalt A were then measured, including penetration, softening point, and ductility. The asphalt performance correction factor K was calculated using the effect of partially used asphalt in the blended asphalt as the numerator and the effect of the used asphalt when it was fully utilized as the denominator. The calculation formula is as follows:

[0029] ;

[0030] In the formula:

[0031] k1, k2, k3 — respectively are the correction coefficients for the effective utilization rate of old asphalt when the asphalt penetration, softening point and ductility are parameters;

[0032] P0 and P1 are the penetration (0.1 mm) of the asphalt after the T0 and T1 ratio reduction, respectively.

[0033] R0 and R1 are the softening points (°C) of asphalt when the T0 and T1 ratios are reduced respectively.

[0034] D0 and D1 are the ductility (cm) of asphalt after the T0 and T1 ratio reduction, respectively.

[0035] q1, q2, and q3 represent the weights of the effects of penetration, softening point, and ductility on the effective utilization rate of asphalt, respectively. ).

[0036] The effective utilization rate of the aforementioned old asphalt is calculated using three main asphalt parameters: penetration, softening point, and ductility. The calculation is compared between the assumption that the old asphalt is fully utilized and the actual situation, and the results are corrected using appropriate coefficients.

[0037] Preferably, in step 4), the masses of newly added asphalt m3 and m are respectively... OAC The performance of asphalt mixtures prepared under certain conditions is tested, including dynamic stability, residual Marshall stability after immersion in water, freeze-thaw splitting strength ratio, and maximum flexural strain. The correction factor γ for asphalt mixture performance is calculated using the effect of partially reused asphalt in recycled asphalt mixtures as the numerator and the effect of fully utilized asphalt as the denominator. The calculation formula is as follows:

[0038] ;

[0039] In the formula:

[0040] γ1, γ2, γ3, γ4 — are the effective utilization rate correction coefficients of old asphalt when the high temperature stability (dynamic stability), water stability (marshall residual stability after immersion, freeze-thaw splitting strength) and low temperature performance (maximum flexural strain) of asphalt mixtures at different proportions are used as parameters.

[0041] DS0 and DS1 represent the dynamic stability (cycles / mm) of asphalt mixtures with reduced T0 and T1 ratios, respectively.

[0042] MSr0 and MSr1 represent the water immersion Marshall residual stability (%) of asphalt mixtures with reduced T0 and T1 ratios.

[0043] R T0 RT1 - The freeze-thaw splitting strength ratio of asphalt mixtures with reduced T0 and T1 ratios (%)

[0044] - These represent the maximum flexural strain of the asphalt mixture after the reduction of T0 and T1 ratios, respectively. ).

[0045] The above-mentioned effective utilization rate of old asphalt is corrected by the performance of asphalt. At the same time, the high temperature stability, water stability and low temperature performance of asphalt mixture are compared between the assumption that the old asphalt is fully utilized and the actual situation. The corresponding coefficients are used to correct the results, making the results more stable and accurate, and providing certain reference and guidance.

[0046] The present invention provides a method for evaluating the effective utilization rate of asphalt in recycled asphalt. By employing reasonable asphalt index parameters, an equation for the effective utilization rate of old asphalt under high RAP (Recycled Asphalt Additive) content is constructed. This equation determines the precise effective utilization rate of old asphalt at a given content. Simultaneously, the calculated utilization rate guides the amount of asphalt added to the asphalt mixture, leading to a more rational design. This method calculates the effective utilization rate of asphalt based on actual results, independent of the aging degree of the RAP material, resulting in more objective results. Verification has shown that the recycled asphalt mixture obtained by this method exhibits excellent road performance, meeting the requirements of technical specifications.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] 1. This invention combines the three major indicators of asphalt with the road performance parameters of the mixture to construct correction coefficients for asphalt performance and mixture performance, thereby correcting the results of asphalt effective utilization rate and making the results closer to reality.

[0049] 2. This invention dynamically adjusts the weights of penetration, softening point, and ductility based on RAP content and climatic conditions, making the evaluation method applicable to the design of recycled materials in different climatic zones such as high temperature and low temperature. Using this method to guide the mix design of recycled materials can more accurately determine the amount of asphalt and optimize the mix design.

[0050] 3. This invention breaks through the limitation of low RAP content in the current specifications, and can accurately evaluate the effective utilization rate of old asphalt with RAP content of 40% and above, providing support for high-content recycling technology, while realizing efficient recycling of resources and reducing costs. Attached Figure Description

[0051] Figure 1 This is a flowchart of a method for evaluating the effective utilization rate of asphalt in recycled materials according to the present invention. Detailed Implementation

[0052] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0053] Example 1:

[0054] This embodiment takes the AC-20 surface layer of an asphalt pavement project in a high-temperature region as an example. The new asphalt used is domestically produced Grade A 70# asphalt, with a RAP content of 40%. The preliminary estimated design asphalt content of the recycled material is 4.7%. The new aggregate is limestone, and the mass of the asphalt mixture is set at 50 kg. This provides a method for evaluating the effective utilization rate of asphalt in recycled materials (e.g., ...). Figure 1 (As shown), including the following steps:

[0055] 1) Trichloroethylene was used to dissolve the RAP material. Centrifugal extraction and rotary evaporator methods were used to separate and recover the asphalt from the asphalt solution, resulting in an old asphalt content (L0) of 3.6% in the RAP. The mass of old asphalt in 50 kg of asphalt mixture was... ;

[0056] 2) Based on the design requirements of the construction pavement, initially adjust the asphalt ratio and determine the type and amount of recycling agent;

[0057] Asphalt recycling agents are used to improve the performance of aged asphalt. The current standard, "Technical Specification for Recycling of Highway Asphalt Pavement" (JTG / T 5521-2019), classifies asphalt recycling agents into six grades based on their viscosity. Considering the degree of asphalt aging in this project's RAP and the compatibility between the recycling agent and asphalt, the RA-5 type recycling agent from a certain manufacturer, with its lower viscosity and higher activity, was ultimately selected. The test results are shown in Table 1.

[0058] Table 1

[0059]

[0060] Note: Viscosity ratio before and after the film drying oven test = viscosity of the sample film after the drying oven test / viscosity of the sample film before the drying oven test.

[0061] When determining the dosage of the recycling agent, it was added to the old asphalt at four dosages of 10.0%, 12.1%, 14.2%, and 16.3%, respectively. After thorough mixing, the penetration, softening point, and ductility were tested. The improvement effect of different dosages of recycling agent on old asphalt is shown in Table 2.

[0062] Table 2

[0063]

[0064] Note: The performance index test results of the old asphalt in RAP are when the recycling agent content is 0%. Two parallel tests were conducted for each group, and the average value was taken. 10.0%, 12.1%, 14.2%, and 16.3% represent the mass ratio of recycling agent to old asphalt.

[0065] By comparing and analyzing the above test results, it can be concluded that the improvement of old asphalt performance is directly proportional to the amount of recycling agent, and the recycling agent content is determined to be 14.2%.

[0066] The formula for calculating the amount of regenerant is as follows:

[0067] ;

[0068] Wherein, m1 is the mass of old asphalt added during initial blending; m2 is the mass of recycling agent added during initial blending; ρ is the amount of recycling agent added during initial blending (by mass ratio). When ρ=14.2%, the performance of various indicators of old asphalt is significantly improved, which can meet the requirements of 70# asphalt in the specification.

[0069] According to equation (1), we can obtain: ;

[0070] 3) Test the aggregate gradation of RAP material to determine the amount and specifications of new aggregate limestone for each grade, as shown in Table 2;

[0071] Table 3

[0072]

[0073] As shown in the table above, when the RAP material is added to the recycled mixture at a dosage of 40%, it is necessary to add 12% 16-26.5mm crushed stone, 25% 9.5-19mm crushed stone, 10% 4.75-9.5mm crushed stone, 10% 2.36-4.75mm crushed stone and 3% mineral powder by mass ratio. At this time, the aggregate gradation meets the upper and lower limits of the specified gradation and the gradation curve is close to the median.

[0074] When estimating the initial design asphalt content of recycled materials, if relevant data is lacking, the above-mentioned synthetic gradation of new aggregates can be mixed with new asphalt, and the optimal asphalt content of the new asphalt can be determined through experiments. The optimal asphalt content of the new asphalt can then be used as the initial estimated asphalt content.

[0075] 4) The RAP content is 40%. The initial amount of new asphalt is determined in m3, and the initial percentage of old asphalt in the total asphalt mass T0 is calculated.

[0076] ;

[0077] Wherein, m3 is the mass of new asphalt added during initial blending; M0 is the estimated amount of asphalt to be produced entirely from new asphalt without the addition of RAP material; m0 is the mass of RAP material calculated according to the RAP material blending ratio; L0 is the content of old asphalt in the RAP material; T0 is the percentage of old asphalt in the total asphalt mass; m1 is the mass of old asphalt added during initial blending; m2 is the mass of recycling agent added during initial blending; and m3 is the mass of new asphalt added during initial blending.

[0078] Based on the asphalt mixture weight being 50 kg, the RAP content being 40%, and the preliminary estimated design asphalt content being 4.7%, we know that m0 = 20 kg. ;

[0079] According to formula (2), m3 = 1.5278 kg; according to formula (3), T0 = 30.64%.

[0080] 5) The old asphalt, recycling agent, and new asphalt extracted in step 1) are blended according to the T0 ratio to obtain preliminary blended asphalt, namely Asphalt A. The penetration P0, softening point R0, and ductility at 15℃ D0 of Asphalt A are measured, as shown in Table 4:

[0081] Table 4

[0082]

[0083] Note: When the ductility at 15℃ does not exceed 150cm, the actual measured value shall be recorded.

[0084] 6) Based on the design drawings and specifications, and with a RAP content of 40%, estimate the optimal asphalt content P. nb =4.7% is the median (the estimated optimal asphalt content includes both old asphalt and the added recycling agent in the RAP mix), and five different asphalt contents (P) were prepared. nb P nb ±0.5%, P nb Marshall specimens were prepared at ±1.0% intervals (0.5%), and their volumetric and mechanical properties were tested. Based on the results, the optimal asphalt content (OAC) was determined to be 4.86%, and the actual required mass of new asphalt to be added was m. OAC ;

[0085] Calculations show that:

[0086]

[0087] 7) After the calculation is completed, heat the new aggregate to 160°C in the oven and the RAP material to 110°C. Keep the mixing pot at 155°C and mix the RAP and limestone for 1 minute. Add a certain amount of new asphalt to the mixing pot and stir for another 2 minutes. After mixing, keep the mixture in the oven at 155°C for 2.5 hours and then let it cool naturally to room temperature.

[0088] 8) Control the amount of new asphalt added, and separately control the mass of new asphalt added (m3 and m). OAC Under these conditions, the dynamic stability DS0 and DS1, the water-immersed Marshall residual stability MSr0 and MSr1, and the freeze-thaw splitting strength ratio R of the asphalt mixture are tested. T0 and R T1 Maximum bending tensile strain and The test results are shown in Table 5:

[0089] Table 5

[0090]

[0091] 9) The mass of new asphalt added (m) OAC The obtained asphalt mixture was extracted and separated to obtain B asphalt. The penetration P1, softening point R1 and ductility D1 of B asphalt were tested, and the results are shown in Table 6.

[0092] Table 6

[0093]

[0094] Note: When the ductility at 15℃ does not exceed 150cm, the actual measured value shall be recorded.

[0095] 10) T0 represents the proportion of old asphalt assuming 100% utilization. However, in actual production, the old asphalt adhering to the surface of the old aggregate in RAP cannot be fully utilized. Therefore, a portion of new asphalt (m4) needs to be added to compensate for the old asphalt's role in the mixture. Theoretically, the effective utilization rate of old asphalt can be expressed by the following formula:

[0096] ;

[0097] Wherein, F0 is the theoretical effective utilization rate of old asphalt; T1 is the percentage of the effective utilization of old asphalt relative to the total mass of asphalt after adding a portion of new asphalt m4; and m4 is the mass of new asphalt added to compensate for the ineffective use of some old asphalt in the mixture.

[0098] According to equations (5) and (4), we can calculate that...

[0099]

[0100] 11) The effective utilization rate F0 of old asphalt calculated in step 10) is under theoretical conditions, but the actual proportion of complete uniform performance is difficult to determine, and the mechanism of asphalt mixture is very complex. Therefore, it is necessary to use the performance of asphalt and the performance of asphalt mixture to correct and calibrate the theoretical effective utilization rate formula.

[0101] ;

[0102] Wherein, F is the modified effective utilization rate of old asphalt; K is the asphalt performance correction coefficient; and γ is the asphalt mixture correction coefficient.

[0103] 12) The effective utilization rate correction coefficient K of old asphalt is obtained by taking the effect of a portion of the old asphalt in the blending of asphalt as the numerator and the effect of the old asphalt when it is fully utilized as the denominator, and the ratio of the two is as follows:

[0104] ;

[0105] Where: k1, k2, k3 – are the correction coefficients for the effective utilization rate of old asphalt when the penetration, softening point, and ductility of asphalt are used as parameters; P0, P1 – are the penetration of asphalt when the T0 and T1 ratios are reduced, respectively; R0, R1 – are the softening point of asphalt when the T0 and T1 ratios are reduced, respectively; D0, D1 – are the ductility of asphalt when the T0 and T1 ratios are reduced, respectively; q1, q2, q3 – are the weights of the influence of penetration, softening point, and ductility on the effective utilization rate of asphalt (q1+q2+q3=1), and the values ​​are taken from Table 7:

[0106] Table 7

[0107]

[0108] Based on the high-temperature region and the RAP doping value, we can obtain: q1=0.45, q2=0.35, q3=0.20.

[0109] According to formulas (7) to (10), we can calculate that: k1=1.0556, k2=0.9802, k3=1.1170, K=1.0415.

[0110] 13) The effective utilization rate correction coefficient γ of old asphalt is obtained by taking the effect of a portion of old asphalt (asphalt ratio T1) in the recycled asphalt mixture as the numerator and the effect of old asphalt when it is fully utilized (asphalt ratio T0) as the denominator. The calculation formula is as follows:

[0111] ;

[0112] Wherein: γ1, γ2, γ3, and γ4 are correction coefficients for the effective utilization rate of old asphalt when the dynamic stability, water-immersed Marshall residual stability, freeze-thaw splitting strength, and maximum flexural strain of asphalt mixtures at different proportions are used as parameters; DS0 and DS1 are the dynamic stability of asphalt mixtures mixed with asphalt at reduced T0 and T1 proportions, respectively; MSr0 and MSr1 are the water-immersed Marshall residual stability of asphalt mixtures mixed with asphalt at reduced T0 and T1 proportions, respectively; R T0 R T1 - The freeze-thaw splitting strength ratio of asphalt mixtures with reduced T0 and T1 ratios, respectively; - These represent the maximum flexural strain of the asphalt mixtures with reduced T0 and T1 ratios, respectively.

[0113] According to formulas (11) to (15), we can calculate that: γ1=0.8986, γ2=1.0088, γ3=1.0174, γ4=1.1067, γ=1.0079.

[0114] Finally, substituting the asphalt performance correction coefficient K and the asphalt mixture correction coefficient γ into formula (6) in step 10), the effective utilization rate of old asphalt can be obtained: .

[0115] Example 2:

[0116] The engineering background of this embodiment is the same as that of Embodiment 1. Taking the AC-20 surface layer in an asphalt pavement project in a high-temperature area as an example, the new asphalt uses domestic Class A 70# asphalt with a RAP content of 70%, and the new aggregate uses limestone. The preliminary estimate of the asphalt content in the recycled material is 4.7%, and the mass of the asphalt mixture is set at 50 kg. A method for evaluating the effective utilization rate of asphalt in recycled materials is provided, including the following steps:

[0117] 1) Trichloroethylene was used to dissolve the RAP material. Centrifugal extraction and rotary evaporator methods were used to separate and recover the asphalt from the asphalt solution, resulting in an old asphalt content (L0) of 3.6% in the RAP. The mass of old asphalt in 50 kg of asphalt mixture was... ;

[0118] 2) Based on the design requirements of the construction pavement, initially adjust the asphalt ratio and determine the type and dosage of the recycling agent;

[0119] In this embodiment, RA-5 type recycling agent was selected. The dosage test of the recycling agent was the same as in Example 1. Comparative analysis of the test results showed that the improvement in the performance of old asphalt was directly proportional to the dosage of recycling agent. The optimal recycling agent dosage ρ was determined to be 14.2%. When ρ = 14.2%, the performance of various indicators of the old asphalt was significantly improved, meeting the requirements for 70# asphalt in the specification. Therefore, the dosage of the recycling agent is: ;

[0120] 3) Test the aggregate gradation of RAP material to determine the dosage and specifications of each grade of new aggregate, as shown in Table 8;

[0121] Table 8

[0122]

[0123] As shown in Table 8, when the RAP content in the recycled mixture is increased to 70%, only two grades of new aggregates and mineral powder need to be added, with proportions of 16%, 11% and 3% (by mass), respectively. At this time, the aggregate gradation needs to meet the upper and lower limits of the specified gradation and the gradation curve needs to be close to the median.

[0124] If relevant data is lacking when estimating the initial design asphalt content of recycled materials, the above-mentioned synthetic gradation of new aggregates can be mixed with new asphalt, and the optimal asphalt content of the new asphalt can be determined through experiments. The optimal asphalt content of the new asphalt can then be used as the initial estimated asphalt content.

[0125] 4) The RAP content is 70%. The initial amount of new asphalt is determined in m3, and the initial percentage of old asphalt in the total asphalt mass T0 is calculated.

[0126] ;

[0127] 5) The old asphalt, recycling agent, and new asphalt extracted in step 1) are blended according to T0 to obtain preliminary blended asphalt, namely Asphalt A. The penetration P0, softening point R0, and ductility at 15℃ D0 of Asphalt A are measured, as shown in Table 9:

[0128] Table 9

[0129]

[0130] Note: When the ductility at 15℃ does not exceed 150cm, the actual measured value shall be recorded.

[0131] 6) Based on the design drawings and specifications, and with a RAP content of 70%, estimate the optimal asphalt content P. nb =4.7% is the median (the estimated optimal asphalt content includes both old asphalt and the added recycling agent in the RAP mix), and five different asphalt contents (P) were prepared. nb P nb ±0.5%, P nb Marshall specimens were prepared at ±1.0% intervals (0.5%), and their volumetric and mechanical properties were tested. Based on the results, the optimal asphalt content (OAC) was determined to be 5.08%, and the actual required mass of new asphalt to be added was m. OAC ;

[0132] Calculations show that:

[0133] ;

[0134] 7) After the calculation is completed, heat the new aggregate to 160°C in the oven and the RAP material to 110°C. Keep the mixing pot at 155°C and mix the RAP and limestone for 1 minute. Add a certain amount of new asphalt to the mixing pot and stir for another 2 minutes. After mixing, keep the mixture in the oven at 155°C for 2.5 hours and then let it cool naturally to room temperature.

[0135] 8) Control the amount of new asphalt added, and separately control the mass of new asphalt added (m3 and m). OAC Under these conditions, the dynamic stability DS0 and DS1, the water-immersed Marshall residual stability MSr0 and MSr1, and the freeze-thaw splitting strength ratio R of the asphalt mixture are tested. T0 and R T1 Maximum bending tensile strain and The test results are shown in Table 10:

[0136] Table 10

[0137]

[0138] 9) The mass of new asphalt added (m) OAC The obtained asphalt mixture was extracted and separated to obtain B asphalt. The penetration P1, softening point R1 and ductility D1 of B asphalt were tested, and the results are shown in Table 11.

[0139] Table 11

[0140]

[0141] Note: When the ductility at 15℃ does not exceed 150cm, the actual measured value shall be recorded.

[0142] 10) T0 represents the proportion of old asphalt assuming 100% utilization. However, in actual production, the old asphalt adhering to the surface of the old aggregate in RAP cannot be fully utilized. Therefore, a portion of new asphalt (m4) needs to be added to compensate for the old asphalt's role in the mixture. Theoretically, the effective utilization rate of old asphalt can be expressed by the following formula:

[0143] ;

[0144] 11) The effective utilization rate F0 of old asphalt calculated in step 10) is under theoretical conditions, but the actual proportion of complete uniform performance is difficult to determine, and the mechanism of asphalt mixture is very complex. Therefore, it is necessary to use the performance of asphalt and the performance of asphalt mixture to correct and calibrate the theoretical effective utilization rate formula.

[0145] ;

[0146] Wherein, F is the modified effective utilization rate of old asphalt; K is the asphalt performance correction coefficient; and γ is the asphalt mixture correction coefficient.

[0147] 12) The effective utilization rate correction coefficient K of old asphalt is obtained by taking the effect of a portion of the old asphalt in the blending of asphalt as the numerator and the effect of the old asphalt when it is fully utilized as the denominator, and the ratio of the two is as follows:

[0148] ;

[0149] Based on the high-temperature region and RAP dosage, the values ​​obtained from Table 7 are: q1=0.50, q2=0.30, q3=0.20.

[0150] 13) The effective utilization rate correction coefficient γ of old asphalt is obtained by taking the effect of a portion of old asphalt (asphalt ratio T1) in the recycled asphalt mixture as the numerator and the effect of old asphalt when it is fully utilized (asphalt ratio T0) as the denominator. The calculation formula is as follows:

[0151] ;

[0152] Finally, substituting the asphalt performance correction factor K and the asphalt mixture correction factor γ into the formula in step 11), the effective utilization rate of old asphalt can be obtained: .

[0153] The experimental results show that, when the raw materials, RAP material, and mix proportions remain unchanged, this method can be used to find the variation law of asphalt effective utilization rate under different RAP content. That is, the asphalt effective utilization rate increases with the increase of RAP material content. When the RAP recycled material content exceeds a certain critical value, the asphalt effective utilization rate may begin to decrease. This invention patent can find the critical value of asphalt effective utilization rate change under the same raw materials and mix proportions, thereby maximizing the RAP material content and using it to guide construction.

[0154] Example 3:

[0155] This embodiment takes the AC-16 surface layer in an asphalt pavement project in a high-temperature region as an example. The new asphalt is domestically produced Grade A 90# asphalt, with a RAP content of 60%. The preliminary estimated design asphalt content of the recycled material is 5.2%. The new aggregate is limestone, and the mass of the asphalt mixture is set at 50 kg. This embodiment provides a method for evaluating the effective utilization rate of asphalt in recycled materials, including the following steps:

[0156] 1) Trichloroethylene was used to dissolve the RAP material. Centrifugal extraction and rotary evaporator methods were used to separate and recover the asphalt from the asphalt solution, resulting in an old asphalt content (L0) of 4.0% in the RAP. The mass of old asphalt in 50 kg of asphalt mixture was... ;

[0157] 2) Based on the design requirements of the construction pavement, initially adjust the asphalt ratio and determine the type and amount of recycling agent;

[0158] Asphalt recycling agents are used to improve the performance of aged asphalt. The current standard, "Technical Specification for Recycling of Highway Asphalt Pavement" (JTG / T 5521-2019), classifies asphalt recycling agents into six grades based on their viscosity. Considering the degree of asphalt aging in this project's RAP and the compatibility between the recycling agent and asphalt, a RA-1 type recycling agent from a certain manufacturer, with lower viscosity and stronger compatibility, was ultimately selected. The test results are shown in Table 12.

[0159] Table 12

[0160]

[0161] Note: Viscosity ratio before and after the film drying oven test = viscosity of the sample film after the drying oven test / viscosity of the sample film before the drying oven test.

[0162] When determining the dosage of the recycling agent, it was added to the old asphalt at four dosages of 11.0%, 13.4%, 15.3%, and 17.6%, respectively. After thorough mixing, the penetration, softening point, and ductility were tested. The improvement effect of different dosages of recycling agent on old asphalt is shown in Table 13.

[0163] Table 13

[0164]

[0165] Note: The performance index test results of the old asphalt in RAP are when the recycling agent content is 0%. Two parallel tests were conducted for each group, and the average value was taken. 11.0%, 13.4%, 15.3%, and 17.6% represent the mass ratio of recycling agent to old asphalt.

[0166] By comparing and analyzing the above test results, it can be concluded that the improvement in the performance of old asphalt is directly proportional to the amount of recycling agent. Furthermore, the recycling agent dosage ρ is determined to be 15.3%. When ρ = 15.3%, the performance of various indicators of the old asphalt is significantly improved, meeting the requirements for 90# asphalt in the specification. Therefore, the recycling agent dosage is:

[0167] 3) Test the aggregate gradation of RAP material to determine the dosage and specifications of each grade of new aggregate, as shown in Table 14;

[0168] Table 14

[0169]

[0170] As shown in the table above, when the RAP material is added to the recycled mixture at a rate of 60%, only three grades of new aggregates and mineral powder need to be added, with the following mass ratios: 10.4% 4.75-9.5mm crushed stone, 12% 2.36-4.75mm crushed stone, 15% 0-2.36mm crushed stone, and 3% mineral powder. At this time, the aggregate gradation meets the upper and lower limits of the specified gradation and the gradation curve is close to the median.

[0171] When estimating the initial design asphalt content of recycled materials, if relevant data is lacking, the above-mentioned synthetic gradation of new aggregates can be mixed with new asphalt, and the optimal asphalt content of the new asphalt can be determined through experiments. The optimal asphalt content of the new asphalt can then be used as the initial estimated asphalt content.

[0172] 4) The RAP content is 60%. The initial amount of new asphalt is determined in m3, and the initial percentage of old asphalt in the total asphalt mass T0 is calculated.

[0173] ;

[0174] 5) The old asphalt, recycling agent, and new asphalt extracted in step 1) are blended according to T0 to obtain preliminary blended asphalt, namely Asphalt A. The penetration P0, softening point R0, and ductility at 15℃ D0 of Asphalt A are measured, as shown in Table 15:

[0175] Table 15

[0176]

[0177] Note: When the ductility at 15℃ does not exceed 150cm, the actual measured value shall be recorded.

[0178] 6) Based on the design drawings and specifications, and with a RAP content of 60%, estimate the optimal asphalt content P. nb =5.2% is the median (the estimated optimal asphalt content includes both old asphalt and the added recycling agent in the RAP mix), and five different asphalt contents (P) were prepared. nb P nb ±0.5%, P nb Marshall specimens were prepared at ±1.0% intervals (0.5%), and their volumetric and mechanical properties were tested. Based on the results, the optimal asphalt content (OAC) was determined to be 5.63%, and the actual required mass of new asphalt to be added was m. OAC ;

[0179] Calculations show that:

[0180] ;

[0181] 7) After the calculation is completed, heat the new aggregate to 160°C in the oven and the RAP material to 110°C. Keep the mixing pot at 155°C and mix the RAP and limestone for 1 minute. Add a certain amount of new asphalt to the mixing pot and stir for another 2 minutes. After mixing, keep the mixture in the oven at 155°C for 2.5 hours and then let it cool naturally to room temperature.

[0182] 8) Control the amount of new asphalt added, and separately control the mass of new asphalt added (m3 and m). OAC Under these conditions, the dynamic stability DS0 and DS1, the water-immersed Marshall residual stability MSr0 and MSr1, and the freeze-thaw splitting strength ratio R of the asphalt mixture are tested. T0 and R T1 Maximum bending tensile strain and The test results are shown in Table 16:

[0183] Table 16

[0184]

[0185] 9) The mass of new asphalt added (m) OAC The obtained asphalt mixture was extracted and separated to obtain asphalt B. The penetration P1, softening point R1 and ductility D1 of asphalt B were tested, and the results are shown in Table 17.

[0186] Table 17

[0187]

[0188] Note: When the ductility at 15℃ does not exceed 150cm, the actual measured value shall be recorded.

[0189] 10) T0 represents the proportion of old asphalt assuming 100% utilization. However, in actual production, the old asphalt adhering to the surface of the old aggregate in RAP cannot be fully utilized. Therefore, a portion of new asphalt (m4) needs to be added to compensate for the old asphalt's role in the mixture. Theoretically, the effective utilization rate of old asphalt can be expressed by the following formula:

[0190] ;

[0191] 11) The effective utilization rate F0 of old asphalt calculated in step 10) is under theoretical conditions, but the actual proportion of complete uniform performance is difficult to determine, and the mechanism of asphalt mixture is very complex. Therefore, it is necessary to use the performance of asphalt and the performance of asphalt mixture to correct and calibrate the theoretical effective utilization rate formula.

[0192]

[0193] Wherein, F is the modified effective utilization rate of old asphalt; K is the asphalt performance correction coefficient; and γ is the asphalt mixture correction coefficient.

[0194] 12) The effective utilization rate correction coefficient K of old asphalt is obtained by taking the effect of a portion of the old asphalt in the blending of asphalt as the numerator and the effect of the old asphalt when it is fully utilized as the denominator, and the ratio of the two is as follows:

[0195] ;

[0196] Based on the high-temperature region and RAP dosage, the values ​​obtained from Table 7 are: q1=0.50, q2=0.30, q3=0.20.

[0197] 13) The effective utilization rate correction coefficient γ of old asphalt is obtained by taking the effect of a portion of old asphalt (asphalt ratio T1) in the recycled asphalt mixture as the numerator and the effect of old asphalt when it is fully utilized (asphalt ratio T0) as the denominator. The calculation formula is as follows:

[0198] ;

[0199] Finally, substituting the asphalt performance correction factor K and the asphalt mixture correction factor γ into the formula in step 11), the effective utilization rate of old asphalt can be obtained: .

[0200] The test results of this embodiment show that when the raw materials, RAP material, and mix proportions change, the effective utilization rate of asphalt in the RAP recycled material also changes. However, it also conforms to the rule that the effective utilization rate of asphalt increases with the increase of RAP recycled material content. When the RAP recycled material content exceeds a certain critical value, the effective utilization rate of asphalt may begin to decrease. This invention patent can find the critical value of the change in the effective utilization rate of asphalt under the same raw materials and mix proportions, thereby maximizing the RAP material content and using it to guide construction.

[0201] It should be noted that this invention is a method for evaluating the effective utilization rate of asphalt in recycled materials, applicable to hot recycling at the plant, but not applicable to in-situ hot recycling or cold recycling at the plant. The initially estimated asphalt content can also be replaced by the optimal asphalt content when using only fresh asphalt for the same gradation.

[0202] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for evaluating the effective utilization rate of asphalt in recycled materials, characterized in that, Includes the following steps: 1) Recycle the RAP material, separate the old asphalt from the RAP material, and obtain the old asphalt content L0; 2) Based on the design requirements, determine the blending ratio of RAP material, the amount and dosage of recycling agent (m2), the amount of new aggregate and the amount of new asphalt (m3), and calculate the percentage of old asphalt in the total asphalt mass (T0). 3) Determine the optimal amount of new asphalt (m) through Marshall tests. OAC Calculate the theoretical effective utilization rate of old asphalt, F0; 4) The blended asphalt obtained by initially mixing old asphalt, recycling agent, and new asphalt, and the mixed asphalt obtained by mixing new aggregate, RAP material, and new asphalt, are compared separately. Based on the asphalt properties and mixture properties, correction coefficients are constructed respectively, and the corrected effective utilization rate F of old asphalt is calculated. The calculation formula is as follows: ； Wherein, F is the corrected effective utilization rate of old asphalt; K is the asphalt performance correction coefficient; and γ is the asphalt mixture performance correction coefficient. In step 2), the asphalt ratio is initially adjusted according to design requirements, and the type and dosage of the recycling agent are determined. The formula for calculating the dosage of the recycling agent is as follows: ； Wherein, m1 is the mass of old asphalt added during initial mixing; m2 is the mass of recycling agent added during initial mixing; and ρ is the amount of recycling agent added during initial mixing. In step 2), based on the RAP mix ratio, the initial amount of new asphalt (m3) is determined, and the percentage (T0) of old asphalt in the total asphalt mass is calculated. The calculation formulas are as follows: ； Wherein, m3 is the mass of new asphalt added during initial blending; M0 is the estimated amount of asphalt to be produced entirely from new asphalt without the addition of RAP material; m0 is the mass of RAP material calculated according to the RAP material blending ratio; L0 is the content of old asphalt in the RAP material; T0 is the percentage of old asphalt in the total asphalt mass; m1 is the mass of old asphalt added during initial blending; and m2 is the mass of recycling agent added during initial blending. In step 3), the formula for calculating the effective utilization rate F0 of old asphalt is: ； Wherein, F0 is the theoretical effective utilization rate of old asphalt; T1 is the percentage of the old asphalt that is effectively utilized after adding a portion of new asphalt m4, relative to the total mass of asphalt; T0 is the proportion of old asphalt under the assumption that 100% of the old asphalt is utilized. In step 4), the mass of newly added asphalt is m. OAC The obtained asphalt mixture is extracted and separated to obtain asphalt B. After being blended according to the T0 ratio, preliminary blended asphalt A is obtained. The properties of asphalt B and blended asphalt A are measured separately, including penetration, softening point and ductility. The asphalt performance correction coefficient K is calculated with the properties of asphalt B as the numerator and the properties of blended asphalt A as the denominator. In step 4), the masses of newly added asphalt m3 and m are respectively... OAC The performance of asphalt mixtures mixed under the following conditions is tested: including dynamic stability, residual Marshall stability after immersion in water, freeze-thaw splitting strength ratio, and maximum flexural strain; with the mass of new asphalt as m. OAC The performance of the asphalt mixture is calculated using the properties of the asphalt mixture being mixed as the numerator and the properties of the asphalt mixture being mixed with new asphalt mass of m3 as the denominator, with the performance of the asphalt mixture being mixed as the numerator.

2. The method for evaluating the effective utilization rate of asphalt in recycled materials according to claim 1, characterized in that, Step 1) uses a centrifugal extraction method to separate and extract old bitumen from RAP material.

3. The method for evaluating the effective utilization rate of asphalt in recycled materials according to claim 1, characterized in that, In step 3), the optimal asphalt content P is estimated based on the RAP blending ratio. nb To determine the median value, five Marshall specimens with different asphalt contents were prepared, and their volumetric parameters and mechanical properties were tested.

4. The method for evaluating the effective utilization rate of asphalt in recycled materials according to claim 1, characterized in that, In step 4), the heated new aggregate and RAP material are mixed for 40-80 seconds, and then the new asphalt is added and mixed at a temperature of 150-160℃. After mixing, the mixture is kept warm for 2.5 hours and then cooled to room temperature to obtain the asphalt mixture.

5. The method for evaluating the effective utilization rate of asphalt in recycled materials according to claim 4, characterized in that, The new aggregate includes at least one of limestone, granite, diabase and basalt.

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