What Are the Most Common Sizes of Aggregate Used in Hot Asphalt Mix?

Hot asphalt mix is a crucial component of road construction, providing a durable and smooth surface for vehicles to traverse. The selection of aggregates plays a vital role in the quality and performance of this hot mix. There are various sizes of aggregate that can be used, with each size serving a specific purpose in the overall pavement design. The appropriate NMAS to be used depends on the intended use and pavement design, taking into consideration factors such as traffic load, climate conditions, and the desired level of performance. By selecting the right aggregate sizes, engineers and contractors can ensure that the hot asphalt mix produced will meet the required specifications and provide a long-lasting and reliable road surface.

How Thick Is Asphalt Compared to Aggregate Size?

The thickness of asphalt compared to aggregate size is an important factor in achieving good paving results. In order to ensure a durable and long-lasting pavement, it’s recommended that the lift thickness of a dense-graded asphalt mix should be 2½ to 3 times the maximum aggregate size. This means that if the maximum aggregate size in the mix is 1 inch, the lift thickness should be between 2½ to 3 inches.

This guideline is based on practical experience and engineering principles. By having a sufficient thickness of asphalt, the mix is able to adequately support traffic loads and resist deformation. It also allows for proper compaction, which is crucial for achieving a uniform and smooth surface.

The choice of aggregate size in the asphalt mix is also important. Common aggregate sizes used in hot asphalt mixes include ½ inch, ¾ inch, and 1 inch. These sizes are often referred to as maximum aggregate size (MAS), which is the largest sieve size that allows all the aggregate particles to pass through. The nominal aggregate size (NAS) refers to the sieve size that divides the aggregate particles into two equal parts by weight. In general, the NAS is slightly smaller than the MAS.

The smaller aggregate particles fill the voids between the larger particles, resulting in a strong and interlocking structure. This helps to improve the overall strength and stability of the pavement.

By following these guidelines, it’s possible to achieve a durable and high-quality asphalt pavement that can withstand the traffic loads and environmental conditions.

A well-structured aggregate gradation ensures that the hot mix asphalt will have the desired engineering properties, such as sufficient stability, durability, and resistance to moisture damage. Achieving the correct percentage of different sizes of aggregate is crucial for the overall quality and performance of the asphalt mix.

What Is Aggregate Gradation for Hot Mix Asphalt?

The most common sizes of aggregate used in hot asphalt mix are known as coarse and fine aggregates. Coarse aggregates typically consist of crushed stone or gravel, while fine aggregates are made up of sand or fine particles. The aggregate gradation in hot mix asphalt is carefully calculated to ensure optimum performance.

The gradation of the aggregate affects numerous properties of the asphalt mix, including it’s stability, void content, and resistance to rutting and cracking.

This means that the mix should contain a range of particle sizes, including larger stones for stability and smaller particles to fill the voids between them. The overall distribution of particle sizes is determined by the specific requirements of the project and the type of pavement being constructed.

This combination allows for a balanced mix that provides good workability during construction and long-term performance under traffic loads.

Well-graded aggregates with a mix of angular and rounded particles can improve the interlocking between the particles, resulting in a stronger and more durable pavement.

Importance of Aggregate Gradation in Hot Mix Asphalt

  • Uniform aggregate gradation ensures better load distribution in hot mix asphalt.
  • Proper gradation improves the stability and durability of the asphalt pavement.
  • An optimal aggregate gradation reduces rutting and cracking of the asphalt surface.
  • Effective gradation enhances the performance and longevity of the pavement structure.
  • A well-graded aggregate mix provides better resistance to moisture damage.
  • Appropriate gradation improves the workability and compaction of the hot mix asphalt during construction.
  • Optimum particle distribution helps achieve the desired density and void content in the asphalt mixture.
  • Uniform gradation contributes to better adhesion between aggregates and asphalt binder.
  • Properly graded aggregate promotes improved frictional resistance and skid resistance on the road surface.
  • An optimal gradation minimizes the potential for segregation and segregation-related issues in the asphalt mix.


The gradation of asphalt plays a crucial role in determining the overall performance of a pavement. It can be classified into different types based on aggregate morphology or air voids of the mixture. Continuous and gap gradation are distinguished by the arrangement of aggregates, while dense, open, and semi-open gradation are based on the amount of air voids present. Despite the various classifications, the primary objective of aggregate gradation design remains the same – to adhere strictly to the requirements of pavement performance.

What Is the Gradation of Asphalt?

The gradation of asphalt refers to the distribution of aggregate particles in the asphalt mixture. It’s an important factor that directly affects the performance and durability of the pavement. In continuous gradation, the aggregate particles are uniformly distributed throughout the mixture, creating a dense and compact structure. This type of gradation is commonly used for high-traffic roads where strength and durability are crucial.

On the other hand, gap gradation consists of a mixture with varying sizes of aggregate particles. This design creates voids between the particles, allowing for better drainage and flexibility. Gap gradation is often used for low-volume roads or in areas with high freeze-thaw cycles, where the pavement needs to withstand drastic temperature changes and water infiltration.

In addition to aggregate morphology, asphalt mixture gradation can also be categorized into three types based on the air voids content: dense, open, and semi-open gradation. Dense gradation refers to a mixture with minimal air voids, providing high stability and resistance to deformation. Open gradation, as the name suggests, allows for more air voids, enhancing drainage characteristics. Semi-open gradation falls in between, providing a balance between stability and drainage.

Regardless of the specific type of gradation design chosen, the most important principle to follow is to meet the requirements of pavement performance. This means that the gradation should be selected based on factors such as traffic volume, climate conditions, and desired pavement characteristics. By carefully considering these factors, engineers can design asphalt mixtures with optimal gradation that will ensure long-lasting and high-performing pavements.

When it comes to asphalt thickness, there are different factors to consider. While a 4-inch thickness may be sufficient for some driveways, going for a thicker option can provide additional strength and stability. Opting for a 5 or 6-inch full-depth asphalt ensures that your driveway can withstand various climate conditions and heavy loads. Alternatively, some contractors choose to use a base of 6 to 8 inches of compacted aggregate or gravel, followed by 3 inches of asphalt pavement.

How Thick Does Asphalt Have to Be?

When it comes to determining the thickness of asphalt, it’s essential to consider various factors such as climate and load requirements. While a 4-inch thickness may be sufficient for certain driveways, opting for a thicker layer of 5 or even 6 inches of full-depth asphalt can provide you with a stronger and more stable surface. This is particularly important in regions with harsh weather conditions or areas that experience heavy traffic loads.

Alternatively, some contractors choose to incorporate a base layer of compacted aggregate or gravel beneath the asphalt pavement. This option involves using 6 to 8 inches of compacted aggregate as a solid foundation, followed by a top layer of 3 inches of asphalt. By employing this method, the base layer helps to distribute the weight of the traffic more evenly, enhancing the overall durability and longevity of the asphalt pavement.

The use of compacted aggregate as a base layer offers additional benefits, such as improved drainage and enhanced load-bearing capacity. It helps to prevent water from accumulating on the surface, reducing the risk of damage caused by water infiltration. Additionally, the compacted aggregate serves as a stabilizing element, offering increased resistance to shifting and settling of the pavement.

The Benefits and Drawbacks of Incorporating a Base Layer of Compacted Aggregate Beneath Asphalt Pavement

  • Improved stability and durability of the asphalt pavement
  • Reduces the likelihood of cracks and potholes
  • Enhanced load-bearing capacity
  • Allows for heavier traffic volumes
  • Helps to prevent water damage and drainage issues
  • Contributes to a smoother and more comfortable driving surface
  • Cost-effective solution for long-term pavement maintenance
  • Provides a solid foundation for the asphalt layer
  • Offers better compaction and compaction uniformity
  • Reduces the potential for settling and shifting of the pavement
  • Can extend the lifespan of the asphalt pavement
  • Improves the overall performance and longevity of the pavement
  • May require additional time and resources for installation
  • Can increase the initial construction costs
  • Requires careful engineering and preparation
  • May pose challenges for certain geographic areas with specific soil conditions
  • Difficult to repair or replace once installed
  • May result in increased noise levels

Coarse aggregates play a crucial role in the composition of concrete, offering strength and stability to the final product. Generally ranging between 3/8 and 1.5 inches in diameter, these particles are larger than 0.19 inch, providing the necessary bulk for construction purposes. Among coarse aggregates, gravels have emerged as the predominant choice, while crushed stone also contributes significantly to the mix.

What Is Considered Coarse Aggregate?

Coarse aggregates, also known as stone particles, are an essential component in concrete production. These aggregates are typically larger than 0.19 inch, and their diameter ranges between 3/8 and 1.5 inches.

Gravel, a popular coarse aggregate, is formed by naturally occurring rock fragments. This material is often composed of a mixture of various rock types, such as limestone, granite, or basalt. Gravels versatile nature makes it a suitable choice for various applications in the construction industry, including road construction, foundation work, and concrete production. It’s specific composition and size distribution contribute to it’s overall strength and stability in concrete mixtures.

This aggregate is produced by crushing large rocks, such as granite, limestone, or trap rock, into smaller fragments. Crushed stone offers several advantages, including uniformity in size and shape, increased strength, and enhanced drainage properties. It’s durable nature makes it suitable for various construction projects, including roadways, driveways, and sidewalks.

Both gravel and crushed stone play crucial roles in concrete production. They provide stability and strength while reducing voids and improving workability. These coarse aggregates effectively interlock with the cement paste, creating a strong matrix that withstands structural loads and environmental forces. Properly selecting and proportioning coarse aggregate sizes is vital to achieving the desired characteristics and performance of hot asphalt mix.

Testing and Quality Control of Coarse Aggregate: This Topic Would Discuss the Various Tests and Quality Control Measures That Are Conducted on Coarse Aggregate to Ensure It’s Conformity to Specifications. It Would Include Tests Such as Sieve Analysis, Specific Gravity, and Absorption Capacity.

  • Sieve Analysis
  • Specific Gravity
  • Absorption Capacity


There are five standard nominal maximum aggregate sizes, ranging from 37.5mm (1½ inch) to 9.5mm (3/8 inch). These sizes are carefully selected to ensure the optimal performance and durability of the asphalt mix.

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