A multi-element solid waste-based asphalt pavement stress absorbing layer material and a preparation method thereof

Abstract

This invention discloses a high-performance stress-absorbing layer for asphalt pavement based on multi-component solid waste, along with its preparation and construction methods, belonging to the field of highway asphalt pavement technology. The stress-absorbing layer material, by weight percentage, comprises: 10-35% 0.01-2.36mm RAP, 35-60% 2.36-4.75mm RAP, 4.5-8.0% new asphalt, 7.5-12.5% ​​waste rubber powder, 2-6% waste fiber material, and 2-7% filler. This invention completely replaces natural aggregates with high-content RAP, synergistically utilizing various solid wastes to construct a triple-composite toughening system. This fundamentally solves the technical bottleneck of insufficient toughness and easy cracking of high-content RAP. The resulting material possesses excellent anti-reflective cracking performance, high and low temperature performance, and water stability. It has high solid waste utilization rate, low engineering cost, and its preparation and construction processes are compatible with existing conventional highway engineering equipment, making it easy to scale up and promote. It can be widely used in the construction of stress-absorbing layers for asphalt pavements.

Description

Technical Field

[0001] This invention belongs to the field of highway asphalt pavement technology, specifically relating to a stress-absorbing layer material for asphalt pavement and its preparation method, particularly a stress-absorbing layer material and its preparation method that uses multi-element solid waste as the main raw material and has both high toughness and excellent anti-reflective cracking performance. Background Technology

[0002] By the end of 2024, the total length of highways in China exceeded 5.49 million kilometers. Large quantities of used asphalt mixtures are generated during major and medium-scale road repairs, road upgrades, restoration of road surface functions, and laying of municipal pipelines. These used asphalt mixtures occupy land resources and pollute the ecological environment. Although the asphalt in the used asphalt mixture is aged, it still has a binding effect, and the aggregates in the road surface (basalt, limestone, etc.) still have good properties, high strength, and wear resistance. Utilizing used asphalt mixtures is an economical, environmentally friendly technology that meets the requirements of sustainable development and is a hot topic in current research. However, it is currently difficult to fully utilize RAP fines. In recent years, with the continuous improvement and development of green and sustainable asphalt pavements, researching how to efficiently utilize recycled materials (such as RAP) to prepare high-performance stress-absorbing layers will be a key path to protect the environment and reduce costs.

[0003] Stress-absorbing layers (RAPs) are flexible intermediate layers laid between the road base and surface layers. They can absorb and disperse stress through high elastic deformation capacity to prevent reflective cracking. However, the materials currently used in stress-absorbing layers face the challenges of high performance requirements and high cost. As an intermediate layer in the structural layers, stress-absorbing layers are very thin, therefore, the performance requirements for their materials are very high. Their binders must have high elasticity and good high and low temperature performance. Current research focuses on using RAPs in asphalt pavement base layers or ordinary surface layers. However, because the aged asphalt in RAPs hardens and becomes brittle, its use in stress-absorbing layers, which require extremely high toughness, presents technical bottlenecks such as insufficient toughness and easy cracking, thus limiting the application of high-proportion RAPs.

[0004] Currently, there is a lack of research on RAP stress-absorbing layer mixtures. Due to its high stiffness and low toughness, fine RAP particles are difficult to replace natural aggregates in the preparation of stress-absorbing layers. Solid wastes such as RAP, waste rubber powder, and waste fiber materials are generated in large quantities and are difficult to dispose of. Therefore, a synergistic solution for high-performance stress-absorbing layers and solid waste disposal is needed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a multi-element solid waste-based asphalt pavement stress-absorbing layer material and its preparation method. It aims to solve the technical problem of insufficient toughness and easy cracking of stress-absorbing layer caused by the hardening and brittleness of aged asphalt due to high-content RAP fine aggregate, and realize the high-value-added resource utilization of RAP fine aggregate.

[0006] To achieve the above objectives, the present invention provides a multi-component solid waste-based asphalt pavement stress-absorbing layer material, comprising the following components by weight percentage: 0.01-2.36mm recycled asphalt pavement (RAP): 10-35%; 2.36-4.75mm recycled asphalt pavement (RAP): 35-60%; New asphalt: 4.5-8.0%; Waste rubber powder: 7.5-12.5%; Waste fiber materials: 2-6%; Filler: 2-7%. The stress-absorbing layer is generally designed to be thin, belonging to an ultra-thin flexible intermediate layer. The maximum nominal aggregate size must be strictly limited: if coarse aggregate is used, problems such as uneven compaction of the ultra-thin layer, coarse aggregate breaking through the structural layer, discontinuous interlayer contact, and excessive flatness will occur, directly losing the core functions of stress dispersion and anti-reflective cracking. 2.36-4.75mm RAP is the core of the mixture's skeleton. This size of RAP aggregate has a thinner aged asphalt film on its surface, and the basalt / limestone skeleton of the aggregate body is fully preserved, forming a stable interlocking skeleton structure. This solves the core defects of all-fine aggregate mixtures, such as poor high-temperature stability and easy rutting and shoving, providing basic stiffness and bearing capacity for the ultra-thin stress-absorbing layer, while ensuring that the structure does not loosen during compaction and that construction and workability are controllable. 0.01-2.36mm RAP is the core for controlling the filling density and toughness of the mixture. This particle size is the most difficult RAP fine aggregate to dispose of in the industry. It has a higher content of aged asphalt adhering to its surface, which can fill the gaps in the skeleton formed by 2.36-4.75mm aggregates, control the porosity of the mixture within the optimal range, and improve the density, water stability and anti-aging performance. At the same time, the aged asphalt of this particle size can be precisely modified and restored to its properties through recycling agents. It can be fused with new asphalt and waste rubber powder to form a high-toughness mortar, which is the core carrier for achieving high elastic deformation and anti-reflective cracking function of stress absorption layer, and also realizes the high-value utilization of RAP fine aggregate.

[0007] Furthermore, the 0.01-2.36mm and 2.36-4.75mm RAP aggregates are all subjected to impurity removal, preheating treatment, and recycling treatment using asphalt recycling agents; the asphalt recycling agents include one or more combinations of waste vegetable oil, waste rubber and plastic pyrolysis oil, and asphalt recycling agents of type RA-1, RA-5, RA-25, RA-75, RA-250, and RA-500, and the amount added is 5%-15% of the mass of aged asphalt in the RAP fine aggregates.

[0008] Furthermore, the particle size of the waste adhesive powder is 0.01-2mm; the waste fiber material includes one or more of waste carbon fiber, waste glass fiber, waste polyester fiber, and waste nylon fiber, with a length of 2-6mm; the filler includes one or more of metallurgical slag powder, fly ash powder, limestone powder, and silicate cement, with a fineness ≥150 mesh.

[0009] Furthermore, the waste fiber material undergoes pretreatment, specifically by: surface activation and dispersion of the waste fiber material, followed by ultrasonic dispersion treatment in a silane coupling agent solution, and then filtration, washing, and drying to obtain the final product.

[0010] Furthermore, the concentration of the silane coupling agent solution is 0.5-2.0%; the ultrasonic power of the ultrasonic dispersion treatment is 350-400W, and the time is 1h.

[0011] On the other hand, the present invention also provides a method for preparing the multi-component solid waste-based asphalt pavement stress-absorbing layer material as described above, characterized by comprising the following steps: S1. RAP particles are crushed and sieved to 0.01-2.36mm and 2.36-4.75mm, and then dried at 95±5℃; S2. Mix the sieved RAP fine aggregate with asphalt recycling agent and recycle it at a temperature not exceeding 60°C to reduce the softening point of the aged asphalt in the RAP fine aggregate and obtain recycled RAP fine aggregate. S3. The recycled RAP fines and waste rubber powder are kept at a first temperature, and the new asphalt is kept at a second temperature, wherein the first temperature is lower than the second temperature; S4. Dry mix the heat-insulated recycled RAP fines and waste rubber powder, then add new asphalt and mix, then add waste fiber materials and fillers and mix again to obtain a multi-element solid waste-based asphalt pavement stress-absorbing layer mixture.

[0012] Furthermore, in step S3, the first temperature is 140-150℃, the second temperature is 170-190℃, and the holding time is 5 hours for both. The surface of the RAP fine aggregate is coated with a layer of recycled aged asphalt. Although a recycling agent has been added, the molecular chains of this asphalt layer are still relatively fragile compared to new asphalt, and its thermal stability is poor. If the RAP temperature is too high, the lightweight components in the recycling agent will volatilize more quickly, weakening its effect of softening the old asphalt. At the same time, the residual asphalt may undergo secondary short-term thermal aging at high temperatures, becoming hard and brittle again, rendering the previous recycling work futile. Controlling the RAP temperature at around 140-150℃ keeps it in a softened state, facilitating subsequent mixing, while avoiding thermal damage to the recycled asphalt, thus locking in the recycling effect. The new asphalt mainly acts as a binder in the mixture and needs to be evenly coated on the surface of each solid particle. Asphalt is a temperature-sensitive material; the higher the temperature, the lower the viscosity. The high temperature of 170-190℃ ensures that the new asphalt has excellent fluidity, allowing it to spread rapidly upon being added to the mixing pan. If the new asphalt is too cold, it will be too viscous and unable to disperse quickly and evenly, resulting in uneven mixing or localized thin asphalt films, affecting interlayer adhesion. Simultaneously, when the high-temperature new asphalt encounters the low-temperature RAP / rubber powder mixture, heat is transferred from the new asphalt to the RAP surface. This temperature difference produces two positive effects: first, the hot new asphalt preferentially adsorbs and coats the relatively low-temperature RAP and rubber powder surfaces, forming a new asphalt shell; second, this shell isolates the internal aged asphalt from direct contact with the outside environment, allowing the mixture to exhibit the excellent bonding properties of the new asphalt macroscopically, while retaining the physical properties of the RAP and rubber powder internally, forming a core-shell-like reinforced structure.

[0013] In step S4, the temperature for both dry mixing and blending is 150-200℃, the dry mixing time is 80-100s, the blending time after adding new asphalt is 80-100s, and the re-mixing time after adding waste fiber materials and fillers is 80-100s.

[0014] On the other hand, the present invention also provides a method for constructing a stress-absorbing layer material prepared using the above-described material or method, characterized by comprising the following steps: (1) Clean and dry the base layer; (2) The multi-component solid waste-based asphalt pavement stress-absorbing layer mixture is laid; (3) Compact the paved mixture with 1-2 passes for the initial compaction and 1-2 passes for the final compaction.

[0015] Furthermore, the thickness of the stress-absorbing layer is 1.5-2.5 cm.

[0016] Furthermore, steel wheel rollers are used for static compaction or small-amplitude vibratory compaction.

[0017] The beneficial effects of this invention are: To achieve the synergistic high-value utilization of diverse solid wastes, this invention completely replaces natural aggregates with RAP aggregates, with RAP content as high as 50%-75%. At the same time, it synergistically disposes of various solid wastes such as waste rubber powder, waste fiber materials, and industrial slag, significantly reducing the mining of natural aggregates, effectively alleviating the environmental pressure of solid waste disposal, and significantly reducing the raw material cost and engineering construction cost of stress-absorbing layers.

[0018] A triple-composite toughening system was constructed, consisting of internal regeneration of the asphalt regenerator, external toughening with waste rubber powder, and reinforcement with waste fibers to inhibit cracking. This system fundamentally solves the technical bottleneck of high-content RAP aged asphalt exhibiting high brittleness and insufficient toughness. Specifically, the asphalt regenerator penetrates into the interior of the aged RAP asphalt, restoring its ductility and rheological properties and repairing its internal molecular structure. The waste rubber powder, combined with new asphalt, forms a rubber asphalt system, significantly improving the material's macroscopic flexibility and deformation capacity. The waste fibers form a three-dimensional network structure within the mixture, effectively inhibiting the generation and propagation of microcracks. The synergistic effect of these three components enables the resulting stress-absorbing layer material to achieve toughness equal to or even exceeding that of some traditional SBS-modified asphalt stress-absorbing layers, exhibiting excellent resistance to reflective cracking.

[0019] With excellent comprehensive road performance, this invention effectively ensures the dense skeleton structure of the mixture through the discontinuous gradation design of dual-grade RAP and the optimized selection of fillers. At the same time, it significantly improves the high-temperature stability, water stability and interlayer adhesion of the material. The comprehensive performance meets the performance requirements of stress-absorbing layer materials in the "Technical Specification for Construction of Highway Asphalt Pavement". It can be widely used in the paving of asphalt pavement stress-absorbing layers in new highways and major and medium-sized road reconstruction projects.

[0020] The preparation and construction processes are simple and controllable. The preparation method of this invention is compatible with existing conventional asphalt mixture mixing equipment, and the construction method is fully compatible with existing asphalt pavement paving and compaction processes. No new special equipment is required, the process parameters are stable and controllable, and it is easy to promote and apply on a large scale, thus having broad market application prospects. Detailed Implementation

[0021] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0022] I. Experimental Design Principles and Basic Conditions 1.1 Standardize basic raw materials

[0023] 1.2 Standardized test methods and evaluation indicators Specimen preparation: The test was carried out in strict accordance with the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011). Marshall specimens were compacted on both sides 75 times. Rutting specimens were 300×300×50mm in size. Low temperature bending test specimens were 250×30×35mm in size. Core evaluation indicators: Marshall properties: stability, flow value (basic mechanical properties); High temperature stability: Dynamic stability at 60℃ (resistance to rutting); Water stability: Freeze-thaw splitting strength ratio (TSR) (resistance to water damage); Core crack resistance performance: -10℃ low temperature bending limit failure strain (toughness and resistance to reflective cracks, core index of stress absorption layer). Mixing and molding process: Unless otherwise specified, dry mix for 90 seconds, mix with new asphalt for 90 seconds, and mix with fiber and filler for 90 seconds. The mixing temperature was 180℃, and the specimen molding temperature was 170℃.

[0024] II. Implementation Examples and Comparative Examples Table 1. Component design of the embodiments (weight percentage, %)

[0025] Table 2 Comparative Design

[0026] III. Test Results Table 3 Performance test results of each embodiment and comparative example

[0027] III. Experimental Data Analysis and Inventive Concept Verification The experimental data above show that the ultimate failure strain of Example 1 reached 4120 με, which is 1.92 times that of the conventional natural aggregate mixture (Comparative Example 1), far exceeding the crack resistance requirements of the stress absorption layer; the dynamic stability reached 4860 cycles / mm, which is 2.89 times that of Comparative Example 1, and the high-temperature rutting resistance was excellent; the TSR reached 92.3%, and the water stability was far higher than the standard threshold.

[0028] By comparing Examples 1-3, Comparative Example 5, and Comparative Examples 8-9, Comparative Example 5, which uses ungraded full-size RAP, showed a 34% decrease in ultimate failure strain and a 41% decrease in dynamic stability compared to Example 1. This is because ungraded RAP cannot form a stable skeleton interlocking-dense filling structure, insufficient coarse material content leads to poor high-temperature stability, and large fluctuations in fine material result in insufficient uniformity of the binder, leading to a significant decrease in toughness. This verifies the necessity of a precise two-size classification design. In Comparative Example 8, RAP was over-mixed to 80%, resulting in a sharp decline in various properties and failure to meet the specifications. This is because excessive RAP caused the total amount of aged asphalt to exceed the control range of the toughening system, increasing the brittleness of the mixture. In Comparative Example 9, the RAP content was less than 40%. Although the performance met the standards, it lost the core innovative value of high-proportion solid waste disposal, demonstrating the rationality of the 50%-75% total RAP content range in this invention.

[0029] By progressively comparing Comparative Examples 2-4 with Example 1, Comparative Example 2, without any toughening measures, showed that the ultimate failure strain of the mixture with 70% RAP content was only 1480 με, far below the specification requirements. This directly demonstrates the industry pain point of insufficient toughness and easy cracking of high-content RAP used in stress-absorbing layers. Comparative Example 3, using only internal regeneration with a recycling agent, increased the ultimate failure strain from 1480 με to 2060 με, restoring it to the level of ordinary asphalt mixtures. This indicates that the recycling agent can effectively repair the performance of aged asphalt, but internal regeneration alone cannot meet the high toughness requirements of stress-absorbing layers. Comparative Example 4, with the addition of waste rubber powder for external toughening on the basis of the recycling agent, further increased the ultimate failure strain to 2980 με, and the dynamic stability exceeded 3000 cycles / mm. This indicates that waste rubber powder can significantly improve the macroscopic flexibility and high-temperature stability of the rubber paste, but without fiber reinforcement, it still cannot achieve the optimal crack resistance effect. Example 1 fully utilizes a triple composite system of internal regeneration, external toughening, and reinforced crack-resistant reinforcement. The ultimate failure strain jumps to 4120 με, which is 38.3% higher than Comparative Example 4 and 178% higher than Comparative Example 2. This proves that the three components are not simply superimposed, but rather form a significant synergistic effect: the regenerator repairs the interfacial bonding performance of aged asphalt, providing a basis for the swelling of rubber powder and fiber anchoring; the rubber powder enhances the overall deformation capacity of the asphalt and disperses the stress at the crack tip; and the fibers form a three-dimensional network to prevent the propagation of microcracks. The synergistic effect of these three components fundamentally solves the brittleness problem of high-content RAP.

[0030] Comparing Example 1 and Comparative Example 6, Comparative Example 6, which uses a full-component 180℃ constant-temperature insulation, showed a 37.9% decrease in ultimate failure strain, a 37.2% decrease in dynamic stability, and a 10.6% decrease in TSR compared to Example 1. This is because prolonged exposure to 180℃ high temperature led to a large amount of volatilization of the lightweight components of the recycling agent, secondary thermal aging of the aged asphalt, and complete loss of internal recycling effect; waste rubber powder underwent molecular chain thermal degradation under prolonged high temperature, resulting in a significant reduction in elasticity and toughening effect; the asphalt film on the AP surface carbonized at high temperature, reducing the interfacial adhesion between aggregate and asphalt, and drastically deteriorating the water stability and durability of the mixture. In contrast, the gradient insulation design in Example 1 not only locked in the recycling effect and rubber powder elasticity through low-temperature insulation but also ensured the mixing fluidity of the new asphalt through high-temperature insulation, perfectly resolving the contradiction between maintaining the recycling effect and mixing adhesion performance.

[0031] Comparative Example 7 used untreated fibers, and the ultimate failure strain decreased by 14.6% compared with Example 1. This was because the interfacial adhesion between the unmodified fibers and the asphalt mortar was poor, making it easy for slippage and pull-out to occur, thus failing to fully exert the reinforcement and crack-prevention effect. This verified the necessity of the silane coupling agent pretreatment process.

[0032] In summary, the dual-grade RAP gradation design achieves efficient absorption of RAP fines while constructing a stable and dense skeletal structure, providing a fundamental guarantee for the comprehensive performance of the material. The triple composite toughening system, consisting of internal regeneration of the regenerator, external toughening of waste rubber powder, and reinforcement and crack resistance of waste fibers, produces a significant synergistic effect, fundamentally solving the industry pain points of insufficient toughness and easy cracking of high-dosage RAP. The differentiated gradient insulation process and fiber surface pretreatment process further lock in and amplify the effect of the core toughening system, ensuring the long-term road performance of the mixture.

[0033] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A multi-element solid waste-based asphalt pavement stress-absorbing layer material, characterized in that, By weight percentage, it includes the following components: 0.01-2.36mm recycled asphalt pavement (RAP): 10-35%; 2.36-4.75mm recycled asphalt pavement (RAP): 35-60%; New asphalt: 4.5-8.0%; Waste rubber powder: 7.5-12.5%; Waste fiber materials: 2-6%; Filler: 2-7%.

2. The multi-element solid waste-based asphalt pavement stress-absorbing layer material according to claim 1, characterized in that, The 0.01-2.36mm and 2.36-4.75mm RAP aggregates have all undergone impurity removal, preheating treatment, and recycling treatment using asphalt recycling agents. The asphalt recycling agents include one or more combinations of waste vegetable oil, waste rubber and plastic pyrolysis oil, and asphalt recycling agents of type RA-1, RA-5, RA-25, RA-75, RA-250, and RA-500, and the amount added is 5%-15% of the mass of aged asphalt in the RAP fine aggregates.

3. The multi-element solid waste-based asphalt pavement stress-absorbing layer material according to claim 1, characterized in that, The waste adhesive powder has a particle size of 0.01-2mm; the waste fiber material includes one or more of waste carbon fiber, waste glass fiber, waste polyester fiber, and waste nylon fiber, with a length of 2-6mm; the filler includes one or more of metallurgical slag powder, fly ash powder, limestone powder, and silicate cement, with a fineness ≥150 mesh.

4. The multi-element solid waste-based asphalt pavement stress-absorbing layer material according to claim 1 or 3, characterized in that, The waste fiber material is pretreated specifically by: surface activation and dispersion of the waste fiber material, followed by ultrasonic dispersion treatment in a silane coupling agent solution, and then filtration, washing, and drying.

5. The multi-element solid waste-based asphalt pavement stress-absorbing layer material according to claim 4, characterized in that, The concentration of the silane coupling agent solution is 0.5-2.0%; the ultrasonic power of the ultrasonic dispersion treatment is 350-400W, and the time is 1h.

6. A method for preparing a multi-component solid waste-based asphalt pavement stress-absorbing layer material as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. RAP particles are crushed and sieved to 0.01-2.36mm and 2.36-4.75mm, and then dried at 95±5℃; S2. Mix the sieved RAP fine aggregate with asphalt recycling agent and recycle it at a temperature not exceeding 60°C to reduce the softening point of the aged asphalt in the RAP fine aggregate and obtain recycled RAP fine aggregate. S3. The recycled RAP fines and waste rubber powder are kept at a first temperature, and the new asphalt is kept at a second temperature, wherein the first temperature is lower than the second temperature; S4. Dry mix the heat-insulated recycled RAP fines and waste rubber powder, then add new asphalt and mix, then add waste fiber materials and fillers and mix again to obtain a multi-element solid waste-based asphalt pavement stress-absorbing layer mixture.

7. The preparation method according to claim 6, characterized in that, In step S3, the first temperature is 140-150℃, the second temperature is 170-190℃, and the heat preservation time is 5h for both. In step S4, the dry mixing and blending temperatures are both 150-200℃, the dry mixing time is 80-100s, the blending time after adding new asphalt is 80-100s, and the re-mixing time after adding waste fiber materials and fillers is 80-100s.

8. A method for constructing a stress-absorbing layer prepared using the material according to any one of claims 1-5 or the method according to any one of claims 6-7, characterized in that, Includes the following steps: (1) Clean and dry the base layer; (2) The multi-component solid waste-based asphalt pavement stress-absorbing layer mixture is laid; (3) Compact the paved mixture with 1-2 passes for the initial compaction and 1-2 passes for the final compaction.

9. The construction method according to claim 8, characterized in that, The thickness of the stress-absorbing layer is 1.5-2.5 cm.

10. The construction method according to claim 8, characterized in that, Static compaction or small-amplitude vibratory compaction is carried out using steel wheel rollers.

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