Preparation method of dry-process SBS (styrene-butadiene-styrene) modified hot in-place recycling asphalt mixture

Abstract

The invention discloses a preparation method of a dry-process SBS (styrene-butadiene-styrene) modified hot in-place recycling asphalt mixture, which comprises the following steps: firstly, weighing limestone with different particle sizes according to a ratio, preheating, heating limestone aggregate, SBS modified asphalt and a waste asphalt mixture, and uniformly mixing to obtain the dry-process SBS modified hot in-place recycling asphalt mixture. The preparation method comprises the following steps: adding a waste asphalt mixture into a stirring pot, adding the SBS modified asphalt and limestone powder into the stirring pot, stirring to obtain a new asphalt mixture, adding the waste asphalt mixture into the stirring pot, stirring, adding the SBS thermal regeneration composite modifier, stirring, adding the new asphalt mixture, and stirring to obtain the SBS modified in-situ thermal regeneration asphalt mixture. The SBS thermal regeneration composite modifier can supplement the degraded SBS component in the old asphalt mixture and restore the performance of old pavement aged asphalt, realizes comprehensive improvement of high and low temperature performance, water damage performance and fatigue cracking performance of the large-mixing-amount waste asphalt mixture by means of the quick-melting high-elasticity SBS component, is simple in addition mode, can be used for site construction, and has good application prospects. And the popularization value is very good.

Description

Technical Field

[0001] This invention relates to the field of in-situ thermal recycling asphalt technology, and more particularly to a method for preparing dry-process SBS modified in-situ thermal recycling asphalt mixture. Background Technology

[0002] In-situ thermal recycling technology is used for surface layers with the highest performance requirements for road surfaces. It involves heating and milling the old asphalt pavement, mixing it on-site with recycling agents, new asphalt, and new aggregates, and then repaving it. The proportion of old asphalt in the mixture can be as high as 80% or more. However, due to loads and environmental effects during the service life of the old asphalt mixture, the asphalt and SBS modifiers continuously age or become ineffective. Except for the improved high-temperature rutting resistance caused by asphalt aging and hardening, other road performance characteristics generally deteriorate. The water stability, spalling resistance, fatigue crack resistance, and low-temperature crack resistance of the asphalt mixture are severely weakened, necessitating targeted improvement measures to achieve the ideal goals of thermal recycling technology.

[0003] The deterioration of RAP (Recycled Asphalt Powder) properties is mainly caused by changes in gradation, asphalt aging, and the degradation and failure of SBS in modified asphalt pavements. Currently, methods for improving the performance of in-situ thermally recycled asphalt mixtures primarily focus on gradation correction and the use of recycling agents to restore the properties of aged asphalt, with limited research on the performance recovery of SBS-modified materials. Since the old asphalt mixture in in-situ thermally recycled asphalt mixtures already contains sufficient asphalt, the addition of a small amount of new asphalt cannot replenish the SBS component in the old asphalt mixture. Therefore, a dry-process method for preparing SBS-modified in-situ thermally recycled asphalt mixtures is needed to address the issues of SBS modification, performance enhancement, and improvement of old asphalt mixtures. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems by providing a method for preparing dry-process SBS-modified in-situ thermally recycled asphalt mixtures. This method involves adding an SBS thermally recycled composite modifier to the old asphalt mixture to supplement the SBS component, thereby improving the road performance of the in-situ thermally recycled asphalt mixture.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: According to one aspect of the present invention, a method for preparing dry-process SBS modified in-situ thermally recycled asphalt mixture is provided, comprising the following steps: S1. Weigh limestone of different particle sizes in proportion and preheat it to obtain limestone aggregate, which includes limestone ore and limestone powder. S2. Heat the mixture of limestone aggregate, SBS modified asphalt, and waste asphalt. S3. Preheat the mixing pot, put the limestone aggregate into the mixing pot for premixing, after the premixing is completed, add SBS modified asphalt and mix, after the mixing is completed, add limestone powder and mix to obtain a new asphalt mixture. S4. Add the waste asphalt mixture to the mixing pot and mix, then add the SBS hot recycling composite modifier and mix, then add the new asphalt mixture and mix to obtain SBS modified in-situ hot recycled asphalt mixture.

[0006] Preferably, in step S1, the limestone particle size includes five ranges: 13.2-16mm, 9.5-13.2mm, 4.75-9.5mm, 2.36-4.75mm, and less than 0.075mm. The limestone with particle sizes of 13.2-16mm, 9.5-13.2mm, 4.75-9.5mm, and 2.36-4.75mm is limestone ore, and the limestone with a particle size of less than 0.075mm is limestone powder.

[0007] Preferably, the limestone ore with a particle size of 13.2-16 mm accounts for 14.63% of the total mass of limestone, the limestone ore with a particle size of 9.5-13.2 mm accounts for 24.4% of the total mass of limestone, the limestone ore with a particle size of 4.75-9.5 mm accounts for 48.77% of the total mass of limestone, the limestone ore with a particle size of 2.36-4.75 mm accounts for 4.87% of the total mass of limestone, and the limestone powder smaller than 0.075 mm accounts for 7.33% of the total mass of limestone.

[0008] Preferably, in step S1, the preheating conditions are: maintaining the temperature at 105℃±5℃ for a time of not less than 4 hours.

[0009] Preferably, in step S2, the SBS modified bitumen is of type ID, with a penetration of 4-6 mm at 25°C, a softening point ≥60°C, and a ductility ≥20 mm at 5°C.

[0010] Preferably, in step S2, the waste asphalt mixture is obtained by hot milling 4cm of the surface layer of the asphalt pavement, and the old asphalt in the waste asphalt mixture has a penetration of more than 20mm at 25℃ and a viscosity of 2.81Pa·s at 135℃.

[0011] Preferably, in step S2, the heating conditions are as follows: heating is carried out in an oven at 175°C for 1 hour.

[0012] Preferably, in step S3, the premixing and mixing times are both 90 seconds.

[0013] Preferably, in step S3, the SBS thermal regenerated composite modifier includes fast-melting SBS, a regenerator, and a coupling agent.

[0014] Preferably, in step S4, the mixing time for adding the waste asphalt mixture and the mixing time for adding the SBS hot recycling composite modifier are both 90s, and the mixing time for adding the new asphalt mixture is 150s.

[0015] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: This invention can effectively replenish the SBS components that have degraded and failed during the use of asphalt pavement, restore the performance of aged asphalt in waste asphalt mixtures, and achieve a comprehensive improvement in the high and low temperature performance, water damage and fatigue cracking performance of waste asphalt mixtures with large dosage. It can also achieve SBS modification, performance enhancement and improvement of waste asphalt mixtures. At the same time, the dry process addition method is simple and convenient for on-site construction of hot recycled asphalt pavement. Attached Figure Description

[0016] Figure 1 These are data on the effects of SBS hot recycling composite modifier and recycling agent on the dynamic stability of in-situ hot recycled asphalt mixtures in the embodiments and comparative examples of this invention; Figure 2 These are data on the effects of SBS hot-recycled composite modifier and regenerator on the failure strain of in-situ hot-recycled asphalt mixtures in low-temperature bending tests, as shown in the embodiments and comparative examples of this invention. Figure 3 These are data on the effects of SBS hot recycling composite modifier and recycling agent on the splitting residual strength ratio of in-situ hot recycled asphalt mixtures in the embodiments and comparative examples of this invention; Figure 4 These are data on the effects of SBS hot recycling composite modifier and recycling agent on the fatigue life of in-situ hot recycled asphalt mixtures in the embodiments and comparative examples of this invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are merely to provide the reader with a thorough understanding of one or more aspects of the invention, and these aspects of the invention can be achieved even without these specific details.

[0018] This invention provides a method for preparing dry-process SBS-modified in-situ thermally recycled asphalt mixture, the technical solution of which is as follows: A method for preparing dry-process SBS-modified in-situ thermally recycled asphalt mixture includes the following steps: S1. Limestone of different particle sizes is weighed and mixed in proportion and then preheated to obtain limestone aggregate, which includes limestone ore and limestone powder.

[0019] Specifically, limestone is used to prepare new asphalt mixtures. Limestone aggregates are obtained by mixing limestone of different particle sizes. These aggregates have the following particle size ranges: 13.2-16 mm, 9.5-13.2 mm, 4.75-9.5 mm, 2.36-4.75 mm, and less than 0.075 mm. Limestone with particle sizes of 13.2-16 mm, 9.5-13.2 mm, 4.75-9.5 mm, and 2.36-4.75 mm is used as limestone raw material. Limestone with a particle size less than 0.075 mm is used as limestone powder. Of the total mass of limestone aggregate, limestone ore with a particle size of 13.2-16mm accounted for 14.63%, limestone ore with a particle size of 9.5-13.2mm accounted for 24.4%, limestone ore with a particle size of 4.75-9.5mm accounted for 48.77%, limestone ore with a particle size of 2.36-4.75mm accounted for 4.87%, and limestone powder smaller than 0.075mm accounted for 7.33%. The limestone aggregates of different particle sizes were weighed according to the specified proportions and then preheated. Preheating of the limestone aggregates involved placing the aggregates in an oven and maintaining a temperature of 105℃±5℃ for at least 4 hours.

[0020] S2. Heat the mixture of limestone aggregate, SBS modified asphalt, and waste asphalt. Specifically, limestone aggregate, SBS modified asphalt, and waste asphalt mixture are heated. Heating involves placing these materials in a 175℃ oven and maintaining the temperature for 1 hour. The limestone aggregate is the preheated limestone aggregate from step S1. The SBS modified asphalt is of type ID, with a penetration of 4-6 mm at 25℃, a softening point of at least 60℃, a ductility of at least 20 cm at 5℃, and a residual ductility of at 5℃ of at least 15 cm after aging in a rotating film oven. The SBS modified asphalt is melted by placing it in a 175℃ oven and heating it to a molten state. The waste asphalt mixture is obtained by hot milling 4 cm of the surface layer of the asphalt pavement. The waste asphalt mixture has an SMA-13 ​​structure. The asphalt content and gradation of the waste asphalt mixture are determined by the combustion method. The asphalt content of the waste asphalt mixture is 6.2%, and the gradation of the waste asphalt mixture is shown in Table 1 below. Table 1 As shown in the table above, the gradation of the waste asphalt mixture has a relatively high passing rate through a sieve with a mesh size of 1.18-4.75. The old asphalt extracted from the waste asphalt mixture was obtained using the centrifugal separation method and the rotary evaporator method according to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering". The old asphalt in the waste asphalt mixture has a penetration of greater than 20 mm at 25℃ and a viscosity of 2.81 Pa·s at 135℃.

[0021] S3. Preheat the mixing pot, put the limestone aggregate into the mixing pot for premixing, after the premixing is completed, add SBS modified asphalt and mix, after the mixing is completed, add limestone powder and mix to obtain a new asphalt mixture.

[0022] Specifically, the mixing pot is preheated at 170℃ for 1 hour. The preheated limestone aggregate is then added to the mixing pot and mixed for 90 seconds to ensure uniformity. SBS modified asphalt is then added and mixed for 90 seconds. Finally, the preheated limestone powder is added and mixed for 90 seconds to obtain the new asphalt mixture. The gradation of the new asphalt mixture is shown in Table 2 below. Table 2 S4. Add the waste asphalt mixture to the mixing pot and mix, then add the SBS hot recycling composite modifier and mix, then add the new asphalt mixture and mix to obtain SBS modified in-situ hot recycled asphalt mixture.

[0023] Specifically, the preheated waste asphalt mixture is added to the mixing pot and mixed for 90 seconds to ensure uniform dispersion. Then, the SBS hot recycling composite modifier is added and mixed for 90 seconds. Next, the well-mixed new asphalt mixture is added and mixed for 150 seconds. Finally, the dry-process SBS modified in-situ hot recycled asphalt mixture is prepared.

[0024] SBS hot-recycling composite modifiers consist of fast-melting SBS, a recycling agent, and a coupling agent. The SBS used is a fast-melting type of SBS. The proportions of the SBS hot-recycling composite modifier are 4%, 5%, 6%, and 8% of the old asphalt.

[0025] Dry-process SBS-modified in-situ thermally recycled asphalt mixtures consist of 80-96% waste asphalt mixture, 0-16% new asphalt mixture, and 4-8% SBS thermally recycled composite modifier (from waste asphalt). The gradation of the dry-process SBS-modified in-situ thermally recycled asphalt mixture is SMA-13. The optimal asphalt-aggregate ratio of the recycled asphalt mixture is determined according to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering," measuring and calculating the bulk relative density, aggregate void ratio, effective asphalt saturation, flow value, porosity, and stability of the recycled asphalt mixture. The waste asphalt mixture is adjusted to meet the specifications by adding new asphalt mixture. The optimal asphalt-aggregate ratio for in-situ thermally recycled asphalt mixtures is 6.4%.

[0026] The gradation of in-situ thermally recycled asphalt mixtures is shown in Table 3 below: Table 3 This application also includes dry-process SBS modified in-situ thermally recycled asphalt mixtures, wherein the recycled asphalt mixtures include waste asphalt mixtures, new asphalt mixtures, and SBS thermally recycled composite modifiers.

[0027] This application also includes an application method for on-site construction of in-situ thermal recycling, the method comprising the following steps: S1. Preparatory work: Preparatory work includes the treatment of the construction starting point and the treatment of road surface markings.

[0028] S2. Road surface heating and milling: Road surface heating and milling includes two processes: road surface heating and hot milling. The road surface heating uses hot air heating technology. Before hot milling, the road surface temperature is not lower than 180℃ and not higher than 200℃.

[0029] S3. Addition of SBS hot-recycled composite modifier: After the milling process, the SBS hot-recycled composite modifier is added by using an aggregate screw to collect the waste asphalt mixture after hot milling and the SBS hot-recycled composite modifier into a continuous trapezoidal cross-section material mound, so that the waste asphalt mixture and the SBS hot-recycled composite modifier can be fully integrated.

[0030] S4. New asphalt mixture mixing: New asphalt mixture mixing is the process of fully blending fresh asphalt mixture, waste asphalt mixture and SBS hot recycling composite modifier into recycled material, which is then lifted by a material lifting device to a mixing pot for forced mixing. The mixing temperature is controlled above 160℃.

[0031] S5. Paving and compaction: Paving and compaction is the process of paving the road surface with a uniformly mixed recycled asphalt mixture. Compaction is carried out in three stages: initial compaction, intermediate compaction and final compaction. The recycled asphalt mixture is a dry-process SBS modified in-situ hot recycled mixture that is uniformly mixed with fresh asphalt mixture, waste asphalt mixture and SBS hot recycling composite modifier.

[0032] S6. Road surface inspection in construction sections: Road surface inspection in construction sections includes water seepage, smoothness, friction coefficient, texture depth, core sampling, retroreflective brightness coefficient of road markings, and thickness.

[0033] In this embodiment, after the on-site construction of the in-situ thermal recycling began, a freeze-thaw splitting test was conducted on a uniformly mixed dry SBS modified in-situ thermal recycled asphalt mixture. The results of the freeze-thaw splitting test are shown in Table 4. Table 4 Results of freeze-thaw splitting tests on in-situ recycled asphalt mixtures After on-site sampling, the freeze-thaw splitting strength ratio of the prepared dry-process SBS modified in-situ hot recycled asphalt mixture met the requirements of the "Specification for Design of Highway Asphalt Pavement" JTG D50-2017, and it has better resistance to water damage.

[0034] Comparative Example 1 In the comparative example, a common regenerator was selected to replace the SBS thermal regeneration composite modifier.

[0035] In the comparative example, the preparation steps of the in-situ thermal recycled asphalt mixture are as follows: S1. Weigh the five grades of limestone aggregates (13.2-16mm, 9.5-13.2mm, 4.75-9.5mm, 2.36-4.75mm and less than 0.075mm) according to the proportions and put them into an oven for preheating. Keep them at 105℃±5℃ for no less than 4 hours. S2. Place the preheated aggregate, SBS modified asphalt and waste asphalt mixture into a 175℃ oven for heating and keep it warm for 1 hour before use. Heat the ordinary recycling agent in a 145℃ oven before use. S3. Preheat the mixing pot at 170℃ for 1 hour and set aside. Put the preheated aggregate into the mixing pot and premix for 90 seconds to make it uniform. Then add SBS modified asphalt and mix for 90 seconds. Finally, add the preheated mineral powder and mix for 90 seconds to obtain the new asphalt mixture. S4. Add the preheated waste asphalt mixture to the mixing pot and mix for 90 seconds to disperse it evenly. Then add the ordinary recycling agent and mix for 90 seconds. Next, add the mixed new asphalt mixture and mix for 150 seconds. Finally, the geothermal recycled asphalt mixture is prepared.

[0036] Dry-process SBS modified in-situ thermal recycled asphalt mixtures and ordinary recycled asphalt mixtures were subjected to rutting tests, low-temperature bending beam tests, freeze-thaw splitting tests, and fatigue tests in accordance with the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering". The corresponding test data are as follows: Figure 1-4 As shown.

[0037] exist Figure 1 It can be clearly observed that the dry-process SBS modified in-situ hot recycled asphalt mixture exhibits excellent high-temperature performance, meeting the requirements of the "Specification for Design of Highway Asphalt Pavement" JTG D50-2017. The high-temperature performance of the dry-process SBS modified in-situ hot recycled asphalt mixture shows a trend of first increasing and then decreasing with the increase of SBS hot recycling composite modifier dosage. Compared with ordinary recycling agents, its high-temperature performance increases by -6.37%, 23.04%, 18.55%, and -24.32%, respectively.

[0038] exist Figure 2 It can be clearly observed that the low-temperature flexural failure strain of dry-process SBS modified in-situ hot recycled asphalt mixtures all meet the requirements of the "Specification for Design of Highway Asphalt Pavement" JTG D50-2017. Compared with ordinary recycling agents, SBS hot recycled composite modifier can effectively improve the low-temperature performance of waste asphalt mixtures. Compared with in-situ hot recycled asphalt mixtures with ordinary recycling agents, the low-temperature failure strain of dry-process SBS modified in-situ hot recycled asphalt mixtures increased by 19.4%, 34.5%, 17.2%, and 11.3%, respectively.

[0039] exist Figure 3 It can be clearly observed that the residual strength ratios of the dry-process SBS modified in-situ hot recycled asphalt mixtures in the freeze-thaw splitting test all meet the requirements of the "Specification for Design of Highway Asphalt Pavement" JTG D50-2017. The residual strength ratio shows a decreasing trend with the increase of SBS hot recycling composite modifier dosage. Compared with in-situ hot recycled asphalt mixtures with ordinary recycling agents, the splitting residual strength ratios of dry-process SBS modified in-situ hot recycled asphalt mixtures increase by 6.9%, 5.6%, 3.3%, and 3.0%, respectively.

[0040] exist Figure 4 It can be clearly observed that the fatigue life of dry SBS modified in-situ hot recycled asphalt mixtures shows a trend of first increasing and then decreasing. Compared with in-situ hot recycled asphalt mixtures with ordinary recycling agents, the fatigue life of dry SBS modified in-situ hot recycled asphalt mixtures increases by -9.1%, 24.6%, 16.7% and 8.0%, respectively.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing dry-process SBS modified in-situ thermally recycled asphalt mixture, characterized in that: Includes the following steps: S1. Weigh limestone of different particle sizes in proportion and preheat it to obtain limestone aggregate, which includes limestone ore and limestone powder. S2. Heat the mixture of limestone aggregate, SBS modified asphalt, and waste asphalt. S3. Preheat the mixing pot, put the limestone aggregate into the mixing pot for premixing, after the premixing is completed, add SBS modified asphalt and mix, after the mixing is completed, add limestone powder and mix to obtain a new asphalt mixture. S4. Add the waste asphalt mixture to the mixing pot and mix, then add the SBS hot recycling composite modifier and mix, then add the new asphalt mixture and mix to obtain SBS modified in-situ hot recycled asphalt mixture.

2. The method for preparing dry-process SBS modified in-situ thermal recycled asphalt mixture according to claim 1, characterized in that: In step S1, the limestone particle size includes five ranges: 13.2-16mm, 9.5-13.2mm, 4.75-9.5mm, 2.36-4.75mm, and less than 0.075mm. The limestone with particle sizes of 13.2-16mm, 9.5-13.2mm, 4.75-9.5mm, and 2.36-4.75mm is limestone ore, and the limestone with a particle size of less than 0.075mm is limestone powder.

3. The method for preparing dry-process SBS modified in-situ thermally recycled asphalt mixture according to claim 2, characterized in that: The limestone ore with a particle size of 13.2-16 mm accounts for 14.63% of the total mass of limestone, the limestone ore with a particle size of 9.5-13.2 mm accounts for 24.4% of the total mass of limestone, the limestone ore with a particle size of 4.75-9.5 mm accounts for 48.77% of the total mass of limestone, the limestone ore with a particle size of 2.36-4.75 mm accounts for 4.87% of the total mass of limestone, and the limestone powder smaller than 0.075 mm accounts for 7.33% of the total mass of limestone.

4. The method for preparing a dry-process SBS modified in-situ thermally recycled asphalt mixture according to claim 1, characterized in that: In step S1, the preheating conditions are to maintain the temperature at 105℃±5℃ for no less than 4 hours.

5. The method for preparing a dry-process SBS modified in-situ thermally recycled asphalt mixture according to claim 1, characterized in that: In step S2, the SBS modified bitumen is of type ID, with a penetration of 4-6 mm at 25°C, a softening point ≥60°C, and a ductility ≥20 mm at 5°C.

6. The method for preparing dry-process SBS modified in-situ thermal recycled asphalt mixture according to claim 1, characterized in that: In step S2, the waste asphalt mixture is obtained by hot milling 4cm of the surface layer of the asphalt pavement. The old asphalt in the waste asphalt mixture has a penetration of more than 20mm at 25℃ and a viscosity of 2.81Pa·s at 135℃.

7. The method for preparing dry-process SBS modified in-situ thermal recycled asphalt mixture according to claim 1, characterized in that: In step S2, the heating conditions are as follows: heating is carried out in an oven at 175°C for 1 hour.

8. The method for preparing dry-process SBS modified in-situ thermally recycled asphalt mixture according to claim 1, characterized in that: In step S3, the premixing and mixing times are both 90 seconds.

9. The method for preparing a dry-process SBS modified in-situ thermally recycled asphalt mixture according to claim 1, characterized in that: In step S3, the SBS thermal regeneration composite modifier includes fast-melting SBS, a regenerator, and a coupling agent.

10. The method for preparing a dry-process SBS modified in-situ thermally recycled asphalt mixture according to claim 1, characterized in that: In step S4, the mixing time for adding the waste asphalt mixture and the mixing time for adding the SBS hot recycling composite modifier are both 90s, and the mixing time for adding the new asphalt mixture is 150s.

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