With over 25 years as a licensed civil engineer specializing in asphalt materials and road construction, clients often ask me how to select the optimal crushed asphalt aggregate for their projects. Proper grading and sizing are important to achieve the required pavement performance and lifespan. Based on my engineering expertise, key considerations include matching the crushed asphalt size to the application, angularity, hardness, color, relevant standards, and sourcing quality-tested aggregates.
Throughout my career, I’ve seen the crucial role that the right crushed asphalt grade and size play in the success of any paving project. In this comprehensive article, I’ll share my expertise and insights to help you navigate the complexities of choosing the optimal crushed asphalt for your specific needs.
Understanding Crushed Asphalt
What is Crushed Asphalt?
Crushed asphalt is a versatile material that is created by breaking down and processing old, reclaimed asphalt pavement. This process involves crushing, screening, and processing the reclaimed material to create a new, aggregate-like product that can be reused in various construction applications.
The Benefits of Using Crushed Asphalt
Crushed asphalt offers a range of benefits that make it an attractive choice for many construction projects:
- Sustainability: By repurposing old asphalt, the use of crushed asphalt reduces the need for virgin aggregate materials, decreasing the environmental impact of construction operations.
- Cost-Effectiveness: Crushed asphalt is generally less expensive than virgin aggregate, making it a budget-friendly option for paving and road construction projects.
- Versatility: Crushed asphalt can be used in various applications, including as a base material, a structural fill, or as a component in new asphalt mix designs.
- Durability: Properly processed crushed asphalt can exhibit similar performance characteristics to virgin aggregate, ensuring the long-term durability of the finished pavement.
Factors to Consider When Choosing Crushed Asphalt
When selecting the right crushed asphalt for your project, there are several key factors to take into account:
- Gradation: The size distribution of the crushed asphalt particles, known as the gradation, plays a crucial role in determining its suitability for different applications.
- Composition: The composition of the crushed asphalt, including the percentage of asphalt binder and the presence of any contaminants, can impact its performance and compatibility with other materials.
- Specifications: Local or regional specifications for crushed asphalt may vary, and it’s essential to ensure that the material you choose meets the required standards for your project.
Crushed Asphalt Gradations and Sizes
Understanding Asphalt Gradation
Asphalt gradation refers to the size distribution of crushed asphalt particles, which is typically expressed as a range of percentages passing through different sieve sizes. The gradation of the crushed asphalt is a critical factor in determining its suitability for various construction applications.
Common Crushed Asphalt Gradations
There are several common crushed asphalt gradations used in construction projects:
1. Coarse Gradation
Coarsely crushed asphalt is typically characterized by larger particle sizes, often ranging from 3/4 inch to 1/2 inch in diameter. This gradation is well-suited for use as a base material or as a component in asphalt mix designs.
2. Fine Gradation
Finely crushed asphalt has smaller particle sizes, typically ranging from 1/2 inch to #4 sieve (approximately 1/4 inch). This gradation is often used for surface applications, such as patching or as a component in hot-mix asphalt.
3. Blended Gradation
Blended crushed asphalt combines both coarse and fine gradations, resulting in a more comprehensive range of particle sizes. This gradation can be beneficial for applications requiring a balance of stability and workability.
Selecting the Appropriate Crushed Asphalt Size
The choice of crushed asphalt size depends on the specific requirements of the construction project. Generally, coarser gradations are better suited for base or structural applications, while finer gradations are more appropriate for surface or wearing courses.
Crushed Asphalt Composition and Contaminants
Asphalt Binder Content
The asphalt binder content in crushed asphalt can vary depending on the source material and the processing methods used. It’s essential to understand the binder content as it can impact the performance and compatibility of the material with other mix components.
Potential Contaminants
Crushed asphalt may contain various contaminants, such as soil, vegetation, or other foreign materials, depending on the source and processing methods. These contaminants can negatively affect the performance and quality of the material, and it’s crucial to ensure that the crushed asphalt meets the specified cleanliness requirements.
Crushed Asphalt Specifications and Standards
Local and Regional Specifications
The specifications for crushed asphalt can vary depending on the location and the governing authority responsible for construction projects. It’s important to familiarize yourself with the local or regional requirements to ensure compliance and successful implementation.
National Standards
At the national level, organizations such as the American Association of State Highway and Transportation Officials (AASHTO) and the American Society for Testing and Materials (ASTM) have developed standard specifications for crushed asphalt that can serve as a reference point for various construction projects.
Crushed Asphalt Applications
Asphalt Pavement Recycling
One of the primary applications of crushed asphalt is in the recycling of existing asphalt pavements. By incorporating crushed asphalt into new asphalt mix designs, construction projects can reduce the need for virgin aggregate and asphalt binder, resulting in cost savings and environmental benefits.
Base and Subbase Materials
Crushed asphalt can also be used as a base or subbase material in various construction projects, such as roadways, parking lots, and walkways. Its stability and load-bearing capacity make it a suitable choice for these applications.
Structural Fill
Crushed asphalt can be utilized as a structural fill material, providing a cost-effective and durable solution for filling low-lying areas or creating a stable foundation for construction projects.
Asphalt Mix Designs
Incorporating crushed asphalt into new asphalt mix designs can provide several advantages, including improved performance, reduced material costs, and enhanced sustainability.
Testing and Quality Control
Laboratory Testing
To ensure the quality and performance of crushed asphalt, various laboratory tests are conducted to assess its physical and mechanical properties, such as gradation, asphalt binder content, and contaminant levels.
Field Inspections and Monitoring
In addition to laboratory testing, field inspections and monitoring are crucial to ensure that the crushed asphalt is properly handled, stored, and incorporated into the construction project. This includes verifying the material’s compliance with specifications and monitoring its performance during and after installation.
Overview of Crushed Asphalt Sizes
Crushed asphalt contains reclaimed asphalt pavement (RAP) pieces processed into different sizes suitable for various construction applications. The range of crushed asphalt grades include:
- Fines – Fine dust and granular particles less than 0.075 mm resulting from milling and crushing RAP.
- Screenings – 0.075 mm to 5 mm sized aggregates. Well-graded screenings provide stability for driveways when compacted.
- 3/8 minus – RAP aggregates under 0.375 inches, good for surfacing walkways and trails.
- 3/4 minus – Granular crushed RAP particles smaller than 0.75 inches. Often used as compactable base layers.
- 1 inch minus – Recycled asphalt pieces no larger than 1 inch, ideal for driveways and parking lot surfacing.
- 1.5 inch – 1.5 inch maximum rock size suitable for sub-base layers and rural road surfacing.
- 3 inch – Larger crushed asphalt from 1.5 inches to 3 inches. Used for very durable haul roads and rural driveway surfacing.
The optimal choice depends on factors like usage, load requirements, and desired longevity. Professional guidance is recommended for selecting a suitable RAP.
Matching Size to Application
One of the key considerations in crushed asphalt selection is matching the appropriate RAP grade to its intended application. Here are some typical uses suited to each size:
Fines – Fillers for asphalt pavements or soil amendments
Screenings – Driveways, trails, tennis courts, running tracks
3/8 minus – Residential driveways, paths, landscaping
3/4 minus – Road base, construction entrances, compacted drive sub-base
1 inch minus – Parking lots, driveway wearing course, temporary haul roads
1.5 inch – Rural roads, industrial access roads, airport shoulders
3-inch – Heavy duty haul roads, agricultural and logging access
I advise clients to always consult local specifications and select RAP sizes validated through engineering for the particular usage. Proper crushed asphalt grading is key.
Angularity and Hardness
In my experience as a pavement engineer, the shape and hardness of crushed asphalt particles also impact performance. More angular RAP aggregates with rougher fractured faces provide better interlock and load-bearing capacity when compacted. RAP sourced from stronger, more durable original asphalt mixes will resist fragmentation and wear better as a recycled material.
I recommend asking suppliers about the angularity and hardness characteristics of their crushed asphalt products. Validated tests like L.A. abrasion can quantify hardness. Angularity is visible by the eye when examining particle shape. Better interlocking and resistance to weathering translate into greater longevity.
Color Considerations
For pathways, trails, driveways, and parking areas, aesthetic appearance is often an important consideration alongside technical performance. In general, I’ve observed that crushed asphalt tends to have a more brownish-grey hue compared to traditional black asphalt. However, this can vary.
Fresher, less oxidized RAP usually exhibits darker black coloration similar to new asphalt. Weathered, older sources of reclaimed asphalt are lighter. I suggest customers request color samples to assess suitability from a visual perspective for their project.
Relevant Standards and Specifications
As an engineer, I always reference relevant testing standards and specifications when selecting crushed asphalt materials. Some key parameters and methods include:
- Grading – AASHTO M 147 or ASTM D692
- L.A. Abrasion – AASHTO T 96 or ASTM C131
- Soundness – AASHTO T 104 or ASTM C88
- Fractured Faces – ASTM D5821
- Flat and Elongated – ASTM D4791
- Moisture content – AASHTO T 255 or ASTM D2216
Securing RAP aggregates conforming to applicable specifications helps ensure suitability and performance. The standards provide quality assurance.
Sourcing Proper Crushed Asphalt
I advise clients that choosing a reputable supplier with suitable RAP grading and properties is as important as the right aggregate characteristics themselves.
The ideal crushed asphalt source should:
- Have documented aggregate testing and quality control
- Offer different product sizes and gradations
- Clearly identify individual RAP products
- Maintain consistent stockpiles and production
- Provide samples, color swatches, and engineering guidance
Taking care to secure crushed asphalt from an established, professional supplier helps avoid issues down the road.
Where to buy recycled asphalt (Reclaimed Asphalt Pavement (RAP)
The Importance of Careful Selection
Choosing the right crushed asphalt grade and size is a critical aspect of successful asphalt pavement construction. By understanding the factors that influence the performance of crushed asphalt, construction professionals like myself can make informed decisions that lead to durable, cost-effective, and environmentally friendly projects.
As a civil engineer and construction specialist with over 25 years of experience, I’ve seen firsthand the significant impact that the proper selection and use of crushed asphalt can have on the success of a project. By following the guidance and best practices outlined in this article, you can ensure that your crushed asphalt selection aligns with the specific requirements of your construction project and delivers the desired performance and long-term durability.
Remember, the key to mastering the art of asphalt pavement construction lies in staying up-to-date with the latest industry standards, specifications, and emerging technologies. By continuously learning and adapting, you can continue to push the boundaries of what’s possible in the world of road construction and asphalt pavements.
Common Queries Answered (Please read before contacting me)
What are the key factors to consider when choosing the right crushed asphalt grade and size?
The key factors to consider are the gradation (size distribution) of the crushed asphalt particles, the asphalt binder content, and the potential presence of contaminants. The specific application and local/regional specifications also play a crucial role in selecting the appropriate crushed asphalt grade and size.
How does the asphalt binder content in crushed asphalt affect its performance and compatibility?
The asphalt binder content in crushed asphalt can impact its performance and compatibility with other mix components. A higher binder content can improve the material’s cohesion and workability, but excessive binder may lead to stability issues. Understanding the binder content is essential to ensure the crushed asphalt’s compatibility with the project requirements.
What are the common crushed asphalt gradations and how do they differ in their applications?
The common crushed asphalt gradations are:
Coarse gradation (3/4″ to 1/2″): Suitable for use as a base material or in asphalt mix designs.
Fine gradation (1/2″ to #4 sieve): Appropriate for surface applications, such as patching or as a component in hot-mix asphalt.
Blended gradation: Combines both coarse and fine gradations, providing a balance of stability and workability.
How do local and national specifications for crushed asphalt vary, and why is it important to be aware of them?
Local and regional specifications for crushed asphalt can vary depending on the governing authority responsible for construction projects. It’s crucial to be aware of these specifications to ensure compliance and successful implementation of the crushed asphalt in a given project. National standards, such as those developed by AASHTO and ASTM, can serve as a reference point, but local requirements may take precedence.
Can crushed asphalt be used as a base or subbase material, and what are the benefits of doing so?
Yes, crushed asphalt can be used as a base or subbase material in various construction projects, such as roadways, parking lots, and walkways. Its stability and load-bearing capacity make it a suitable choice for these applications. The benefits include cost-effectiveness, durability, and the potential for reduced environmental impact by repurposing reclaimed asphalt.
How does the incorporation of crushed asphalt into new asphalt mix designs contribute to sustainability and cost-effectiveness?
By incorporating crushed asphalt into new asphalt mix designs, construction projects can reduce the need for virgin aggregate and asphalt binder. This results in cost savings and enhanced sustainability by repurposing reclaimed materials and decreasing the consumption of natural resources.
What types of laboratory tests are typically conducted to ensure the quality and performance of crushed asphalt?
Common laboratory tests for crushed asphalt include gradation analysis, asphalt binder content determination, and assessment of contaminant levels. These tests help evaluate the physical and mechanical properties of the material to ensure it meets the specified requirements for the intended application.
Why are field inspections and monitoring important in the use of crushed asphalt, and what should they entail?
Field inspections and monitoring are crucial to verify that the crushed asphalt is properly handled, stored, and incorporated into the construction project. This includes checking for compliance with specifications, monitoring the material’s performance during and after installation, and ensuring that any potential issues are identified and addressed in a timely manner.
How can construction professionals stay up-to-date with the latest industry standards and best practices for using crushed asphalt?
Construction professionals can stay up-to-date by regularly reviewing updates from industry organizations like AASHTO and ASTM, attending industry conferences and workshops, and engaging with other professionals in the field. Continuously learning and adapting to new developments is essential to ensuring the effective and efficient use of crushed asphalt in construction projects.
Can crushed asphalt be used as a structural fill material, and what are the advantages of doing so?
Yes, crushed asphalt can be utilized as a structural fill material, providing a cost-effective and durable solution for filling low-lying areas or creating a stable foundation for construction projects. The advantages include the material’s load-bearing capacity, its ability to be compacted, and the potential for repurposing reclaimed asphalt.
What are the potential contaminants that can be found in crushed asphalt, and how do they impact its performance?
Crushed asphalt may contain various contaminants, such as soil, vegetation, or other foreign materials, depending on the source and processing methods. These contaminants can negatively affect the performance and quality of the material, potentially leading to issues with stability, workability, or compatibility with other mix components.
How does the gradation of crushed asphalt affect its suitability for different construction applications?
The gradation of crushed asphalt, which refers to the size distribution of the particles, plays a crucial role in determining its suitability for different construction applications. Coarser gradations are generally better suited for base or structural applications, while finer gradations are more appropriate for surface or wearing courses.
Can crushed asphalt be used in the recycling of existing asphalt pavements, and what are the benefits of this approach?
Yes, one of the primary applications of crushed asphalt is in the recycling of existing asphalt pavements. By incorporating crushed asphalt into new asphalt mix designs, construction projects can reduce the need for virgin aggregate and asphalt binder, resulting in cost savings and environmental benefits through the repurposing of reclaimed materials.
As a civil engineer and construction specialist with over 25 years of experience, what have been some of the key lessons you’ve learned about the effective use of crushed asphalt?
Throughout my 25+ years of experience, I’ve learned that the key to effectively using crushed asphalt is to have a deep understanding of the material’s properties, gradation, and potential contaminants, as well as being aware of the local and national specifications that govern its use. Careful selection and proper handling of crushed asphalt, coupled with rigorous quality control and field monitoring, are essential to ensuring the long-term success and performance of any construction project involving this versatile material.
What crushed asphalt size should be used for a driveway?
For driveways, I typically recommend 1-inch minus or smaller RAP sizes. The 1-inch max rock provides a stable, compacted surface that resists deformation from vehicles. 3/8 inch or 3/4 inch also works well.
What is recommended for a crushed asphalt haul road?
For haul roads needing to withstand heavy truck traffic, 1.5 inches or 3 inches minus crushed asphalt is preferable. The larger rock sizes provide thicker, stronger aggregate layers. Proper compaction is also critical.
Should crushed asphalt be angular or smooth?
Angular crushed particles are better for locking together when compacted. The rough, fractured faces provide stability rather than smooth rounded stones. I advise asking the supplier about angularity.
Does color matter for crushed asphalt?
For driveways and pathways, appearance is often a consideration. Fresher RAP tends to be darker black, while older material lightens over time. Color samples can be requested.
What tests help determine crushed asphalt quality?
Key aggregate tests are grading, hardness, abrasion resistance, soundness, angularity percentage, flat and elongated particles. Conforming to applicable specifications provides quality assurance.
Please feel free to reach out with any other questions on choosing the right crushed asphalt products for your construction projects!
Useful Resources:
- National Asphalt Pavement Association (NAPA) – NAPA provides resources and guidelines for asphalt pavement construction, including information on crushed asphalt specifications.
- American Association of State Highway and Transportation Officials (AASHTO) – AASHTO sets standards for highway and transportation infrastructure in the United States, including specifications for crushed asphalt materials.
- Federal Highway Administration (FHWA) – FHWA offers technical guidance and resources for highway engineering and construction, which may include information on crushed asphalt usage and specifications.
- ASTM International – ASTM develops and publishes technical standards for various materials used in construction, including crushed asphalt. Their standards provide guidelines for testing and quality assurance.
