Application of recycled materials in asphalt concrete road structures

Abstract

This invention relates to an asphalt concrete road structure using recycled materials, laid on a roadbed. The asphalt concrete road structure comprises a base layer and a surface layer. The base layer is laid on the roadbed and includes a recycled asphalt concrete layer, which is composed of asphalt concrete scrap, a mixture of asphalt concrete scrap and natural aggregate, or a mixture of asphalt concrete scrap and steel aggregate. The surface layer is laid on the base layer and includes a steel aggregate asphalt concrete layer, which is composed of asphalt concrete mixed with steel aggregate, or asphalt concrete scrap mixed with steel aggregate. Through this configuration, this invention can simultaneously utilize the recycling of asphalt concrete scrap and steel aggregate, forming a multi-layered pavement structure.

Description

Application of recycled materials in asphalt concrete road structures Technical Field

[0001] This work relates to road pavement structure technology, and in particular to an asphalt concrete road structure using recycled materials. Prior Technology

[0002] Most road pavements are made of a mixture of asphalt and natural aggregates, laid on a leveled and compacted subgrade. Through multiple rolling and curing processes, a load-bearing structural layer is gradually constructed. To maintain the road's strength and durability, traditional pavements typically use freshly mixed asphalt concrete as the main material, laid in layers. With increased road repaving and maintenance, existing pavements often need to be removed and repaved, generating large amounts of asphalt concrete scrap. Direct disposal of this scrap not only occupies land but also increases waste disposal and transportation costs.

[0003] To address these issues, the industry has begun developing recycling technologies. This involves crushing and screening asphalt concrete scrap before mixing it into fresh aggregate to replace a portion of the new aggregate, thereby reducing material consumption and achieving resource recycling. Some projects are also experimenting with using recycled asphalt concrete as a road base or subbase material to balance construction quality and cost control, while reducing construction waste.

[0004] On the other hand, byproducts generated during steel manufacturing, such as blast furnace slag and oxide residue, are also considered mineral materials with potential for reuse. After appropriate processing, these byproducts can be incorporated into asphalt concrete for the surface layer to improve skid resistance and wear resistance, or used as base layer aggregate to improve drainage and stability. Existing recycled pavement projects often focus on the application of single recycled materials, such as simply adding asphalt concrete scrap to the asphalt mixture, or only incorporating steel aggregate into the road surface layer. Because different recycled materials have different material properties, neglecting layer configuration and material combination can easily lead to uneven strength of the structural layers or difficulty in controlling construction quality. In practice, there is a lack of structural designs that can simultaneously integrate asphalt concrete scrap and steel aggregate in different layers, allowing recycled materials to perform their respective functions according to layer characteristics, balancing structural stability and reuse efficiency.

[0005] Therefore, in current recycled road pavement technology, how to properly configure the base layer and surface layer materials so that asphalt concrete scrap and steel aggregate can work together, and establish an integrated pavement structure that simultaneously has load-bearing capacity, ease of construction, and environmental protection benefits, remains a direction of continuous attention and improvement in related technical fields. Summary of the Invention

[0006] To address the aforementioned technical issues, the main objective of this invention is to provide an asphalt concrete road structure utilizing recycled materials. By separately configuring asphalt concrete scrap and steel aggregate in different layers of the road, it achieves both recycling and structural reinforcement, thereby extending road life and improving pavement performance.

[0007] To achieve the above objectives, this invention provides an asphalt concrete road structure using recycled materials, laid on a roadbed. The asphalt concrete road structure includes a base layer and a surface layer. The base layer is laid on the roadbed and includes a recycled asphalt concrete layer, which is composed of asphalt concrete scrap, a mixture of asphalt concrete scrap and natural aggregate, or a mixture of asphalt concrete scrap and steel aggregate. The surface layer is laid on the base layer and includes a steel aggregate asphalt concrete layer, which is composed of asphalt concrete mixed with steel aggregate, or asphalt concrete scrap mixed with steel aggregate.

[0008] According to one embodiment of this invention, the aforementioned steel granules are electric arc furnace oxide slag or converter stone.

[0009] According to one embodiment of the present invention, the steel aggregate content of the aforementioned surface layer is 5% to 30% of the total weight of the asphalt concrete.

[0010] According to one embodiment of the present invention, the steel aggregate content of the aforementioned base layer is 5% to 60% of the total weight of the asphalt concrete.

[0011] According to one embodiment of the present invention, the aforementioned asphalt concrete scrap is crushed and screened to form the base layer of the road.

[0012] According to one embodiment of the present invention, the aforementioned base layer includes a base layer and a bottom layer. The base layer is composed of asphalt concrete scrap, asphalt concrete scrap mixed with natural gradation, or asphalt concrete scrap mixed with steel aggregate. The bottom layer is composed of asphalt concrete scrap, asphalt concrete scrap mixed with natural gradation, or asphalt concrete scrap mixed with steel aggregate, and the bottom layer is laid on the base layer.

[0013] According to one embodiment of the present invention, the aforementioned base layer thickness is generally greater than or equal to the bottom layer thickness, and the bottom layer thickness is greater than the top layer thickness.

[0014] Compared with conventional techniques, this creation has the following advantages: 1. The asphalt concrete road structure using recycled materials in this invention features a multi-layer recycled material configuration design, which can simultaneously utilize two types of recycled materials: asphalt concrete scrap and steel aggregate. This allows each layer of material to perform its corresponding function according to its characteristics, taking into account load-bearing capacity, stability, and service life. 2. The recycled material application of this invention in asphalt concrete road structures utilizes the residual asphalt components and aggregate strength in the asphalt concrete scrap, reducing the need for fresh asphalt and natural aggregates. Furthermore, the high rigidity of the steel aggregate enhances the load-bearing capacity and wear resistance of the pavement layer, achieving the effects of energy conservation, carbon reduction, and recycling. 3. The recycled material application in this invention for asphalt concrete road structures involves setting an adhesive layer between the base layer and the surface layer, which can effectively improve interlayer adhesion, prevent interlayer delamination and cracking, and maintain the overall stability and durability of the road structure. It has good practical application value and promotion potential.

[0015] The following detailed explanation, using specific embodiments and accompanying drawings, will make it easier to understand the purpose, technical content, features, and effects achieved by this invention. Simple Explanation of the Diagram

[0016] Figure 1 is a cross-sectional schematic diagram of an asphalt concrete road structure using recycled materials according to the first embodiment of this invention. Figure 2 is a cross-sectional schematic diagram of an asphalt concrete road structure using recycled materials according to the second embodiment of this invention. Implementation

[0017] Embodiments of this invention will be further explained below with reference to the accompanying drawings. Wherever possible, the same reference numerals in the drawings and description represent the same or similar components. In the drawings, shapes and thicknesses may be exaggerated for simplicity and convenience. It is understood that components not specifically shown in the drawings or described in the description are forms known to those skilled in the art. Those skilled in the art can make various changes and modifications based on the content of this invention.

[0018] Please refer to Figure 1, which is a cross-sectional schematic diagram of the asphalt concrete road structure using recycled materials according to the first embodiment of this invention. The asphalt concrete road structure of this invention is laid on the subgrade 10 and includes a base layer 20 and a surface layer 30. The subgrade 10 can be leveled and compacted to achieve the designed density and uniform load-bearing capacity.

[0019] In this embodiment, the base layer 20 is laid on the subgrade 10 and includes a recycled asphalt concrete layer 21. The recycled asphalt concrete layer 21 can be formed from asphalt concrete scrap, asphalt concrete scrap mixed with natural gradation, or asphalt concrete scrap mixed with steel aggregate. Further explanation: the asphalt concrete scrap can be asphalt concrete that has been excavated or removed during road repaving or maintenance works. The particle size can be distributed between 0.075mm and 25mm, and the main components include aggregate and asphalt binder. Before use, it must be crushed and screened to remove impurities and adjust the particle size distribution. For the particle size distribution requirements of general road construction, the particle size distribution of the asphalt concrete scrap can be controlled to approximately 90% passing through a 19mm sieve, approximately 50% passing through a 4.75mm sieve, and approximately 5% passing through a 0.075mm sieve, thereby ensuring both gradation density and compactness. Before use, asphalt concrete scraper material must be crushed and screened to remove impurities and excessively large particles. A suitable amount of virgin material or mineral powder can be mixed in to improve its bonding properties. The porosity of the recycled layer should be controlled between 15% and 25%, and the moisture content should be maintained at the optimum compaction moisture content ±2% to ensure compaction effect and stability.

[0020] If a mixed-structure design is adopted, steel aggregate can be incorporated at a ratio of 5% to 60% of the total weight of the asphalt concrete. The steel aggregate used in this design is electric arc furnace slag or converter ash, or other stabilized steelmaking furnace slag. The steel aggregate is used after crushing, magnetic separation for iron removal, and stabilization. The particle size of the steel aggregate can be between 4.75mm and 37.5mm. The addition of steel aggregate improves overall rigidity and enhances heat resistance and durability. During paving, a layered paving method can be adopted, with each layer not exceeding 30cm in thickness. Each layer is compacted using a vibratory roller to achieve a design density of 95% or higher. The thickness can be adjusted according to the road grade and design requirements.

[0021] The surface layer 30 is laid on the base layer 20 and includes a steel-aggregate asphalt concrete layer 31. The steel-aggregate asphalt concrete layer 31 is composed of asphalt concrete mixed with steel aggregates, or asphalt concrete scrap mixed with steel aggregates. The steel aggregates can be electric arc furnace slag or converter stone, and their addition amount is approximately 5% to 30% of the total weight of the asphalt concrete. After crushing and screening, the steel aggregates have a rough surface and high strength, which can improve the skid resistance, wear resistance, and deformation resistance of the asphalt concrete. During mixture preparation, the heating temperature and mixing time can be controlled; for example, the heating temperature can be controlled at 135°C to 163°C, and the mixing time at 30 to 60 seconds, so that the asphalt and steel aggregates are evenly coated. During construction, a paver is used for even paving, and steel-wheeled and rubber-tired rollers are used alternately for compaction to ensure surface density and smoothness.

[0022] Please refer to Figure 2, which is a cross-sectional schematic diagram of the asphalt concrete road structure using recycled materials according to the second embodiment of this invention. In this embodiment, the base layer 20 can be subdivided into two layers: a base layer 22 and a subbase layer 23, with the subbase layer 23 laid on the base layer 22. In one configuration, the base layer 22 is composed of asphalt concrete scrap, and the subbase layer 23 is composed of asphalt concrete scrap mixed with natural gradation or steel aggregate; in another configuration, the base layer 22 can be composed of asphalt concrete scrap mixed with natural gradation, and the subbase layer 23 can be composed of asphalt concrete scrap, or asphalt concrete scrap mixed with steel aggregate; in yet another configuration, the base layer 22 can be composed of asphalt concrete scrap mixed with steel aggregate, and the subbase layer 23 can be composed of asphalt concrete scrap, or asphalt concrete scrap mixed with natural gradation; in yet another configuration, both the base layer 22 and the subbase layer 23 can be composed of asphalt concrete scrap, or both can be composed of asphalt concrete scrap mixed with natural gradation, or both can be composed of asphalt concrete scrap mixed with steel aggregate. The bottom layer 23 serves as a support layer, primarily providing load-bearing capacity; the base layer 22 provides intermediate buffering and stabilization. The mixing ratio of steel aggregate can be adjusted according to traffic load and climate conditions; in high-traffic sections, the mixing ratio can be increased to enhance rigidity.

[0023] Before laying the base course 22, the surface of the subgrade 10 can be moderately moistened to facilitate compaction. After paving, a vibratory roller should be used to compact each layer to ensure uniform density and thickness. The base course 23 can be constructed using the same method. During construction of each layer, cement, lime, or asphalt emulsion can be added as needed for stabilization treatment to improve material bonding. In terms of layer thickness, the thickness of the base course 22 can be greater than or equal to the thickness of the base course 23, while the thickness of the base course 23 can be greater than the thickness of the surface course 30, giving the upper layer good shear resistance and the lower layer a supporting effect. During construction, the number of compaction cycles and the layer thickness ratio can be adjusted according to the road grade and load conditions to ensure structural stability and service life. For example, the thickness of the base course 22 can be set to 50 to 100 cm, and the thickness of the base course 23 is approximately 20 to 40 cm. During the paving process, different particle size distributions can be used for each layer. For example, the base course 23 uses a coarser particle size distribution, while the base course 22 uses a finer particle size distribution to facilitate compaction and save carbon emissions.

[0024] This invention discloses an asphalt concrete road structure utilizing recycled materials, integrating the reuse of asphalt concrete scrap with the application of steel aggregates. This allows for a rational distribution of materials in each layer according to their function, forming a multi-layered structure with load-bearing capacity and skid resistance. Furthermore, the mix proportions can be adjusted according to local climate and traffic conditions. This road structure not only reduces the use of new materials and construction costs but also lowers carbon emissions and extends road lifespan. Its design concept balances recycling and structural safety, making it suitable for urban roads, arterial roads, parking lots, and various pavement projects requiring load-bearing and durability, demonstrating high practicality and widespread application value.

[0025] Although the present invention has been described in detail above, those skilled in the art will understand that various modifications and changes can be made to the present invention without departing from its spirit and scope. The scope of the present invention is not limited to the detailed description above, but should fall within the scope of the patent application.

[0026] 10: Roadbed 20: Basal layer 21: Recycled asphalt concrete layer 22: Grassroots 23: Bottom layer 30: Surface layer 31: Steel-reinforced aggregate asphalt concrete layer

Claims

1. An asphalt concrete road structure using recycled materials, laid on a roadbed, the asphalt concrete road structure comprising: a base layer laid on the roadbed, the base layer comprising a recycled asphalt concrete layer, the recycled asphalt concrete layer being composed of asphalt concrete scrap, the asphalt concrete scrap being mixed with natural gradation, or asphalt concrete scrap being mixed with steel aggregate; and a surface layer laid on the base layer, the surface layer comprising a steel aggregate asphalt concrete layer, the steel aggregate asphalt concrete layer being composed of asphalt concrete mixed with steel aggregate, or asphalt concrete scrap mixed with steel aggregate.

2. The asphalt concrete road structure as described in claim 1, wherein the steel aggregate is electric arc furnace slag or converter stone.

3. The asphalt concrete road structure as described in claim 1, wherein the steel aggregate content of the surface layer is 5% to 30% of the total weight of the asphalt concrete.

4. The asphalt concrete road structure as described in claim 1, wherein the steel aggregate content of the base layer is 5% to 60% of the total weight of the asphalt concrete.

5. The asphalt concrete road structure as described in claim 1, wherein the asphalt concrete shavings are crushed and screened to form the road base layer.

6. The asphalt concrete road structure as claimed in claim 1, wherein the base layer comprises a base course and a subbase course, the base course being composed of asphalt concrete scrap, asphalt concrete scrap mixed with natural gradation, or asphalt concrete scrap mixed with steel aggregate, the subbase course being composed of asphalt concrete scrap, asphalt concrete scrap mixed with natural gradation, or asphalt concrete scrap mixed with steel aggregate, and the subbase course being laid on the base course.

7. The asphalt concrete road structure as described in claim 6, wherein the thickness of the base course is greater than or equal to the thickness of the subbase course, and the thickness of the subbase course is greater than the thickness of the surface course.

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