Asphalt concrete mix composition: components, design

An indispensable component of contemporary infrastructure is asphalt concrete, or just asphalt. Roads, parking lots, airport runways, and other projects all use it. This adaptable material is made up of a few essential elements that come together to form a robust, long-lasting surface.

The three main components of asphalt concrete are bitumen, additives, and aggregates. The bulk of the mixture is composed of aggregates, which include things like crushed stone, gravel, and sand. The strength and bulk of the asphalt are derived from these materials. The binder that keeps the aggregates together and makes the mixture cohesive and durable is bitumen, a sticky, black material. To improve a particular feature of asphalt, like its resilience to cracking or its capacity to tolerate high temperatures, additives can be added.

Choosing the appropriate ratios of these elements to satisfy a project’s demands is part of designing an asphalt concrete mix. The mix design is heavily influenced by various factors, including the intended use of the surface, the expected load, and the climate. For the mix to provide the required performance, longevity, and economy, engineers must carefully balance it.

The first step in creating an asphalt mix design is evaluating the materials that will be utilized in-depth. In order to make sure the bitumen and aggregates fulfill quality requirements, this involves examining their characteristics. Following material selection, different mix designs are tested in order to determine the best combination. In order to do this, sample batches must be created and their performance assessed using a range of tests, including ones that gauge how resilient they are to deformation and wear and tear.

It is essential to comprehend the composition and design of asphalt concrete in order to create surfaces that are dependable and long-lasting. Through meticulous component selection and proportioning, engineers can create mixes that are tailored to the specific requirements of each project, guaranteeing long-lasting and secure infrastructure.

Component	Description
Aggregates	Stone, sand, and gravel that provide structure and strength.
Asphalt Binder	A sticky, black substance that holds the aggregates together.
Additives	Materials added to improve performance, like polymers and anti-stripping agents.
Design Process	Determining the right mix of components to meet project requirements.
Quality Control	Testing the mix to ensure it meets standards and performs well.

Properties and types of asphalt concrete

Bitumen serves as the primary binding agent in asphalt concrete mixtures. The qualities of the material are greatly influenced by its features.

Insufficient viscosity in hot weather will cause plastic deformations of the coating, while excessive viscosity in low temperatures can cause cracks. Determining the coating’s performance properties and the qualities of the materials used is the first step in choosing the composition of the asphalt concrete mixture.

Properties

Road concretes are classified into the following types based on the type of binders used and the operating environment:

1. Classic asphalt concrete mixtures are used for the construction of road surfaces of highways and various urban road and sidewalk surfaces;
2. Polymer asphalt concrete — these are concretes based on bitumen and other classic components with the addition of copolymers and plasticizers. They are used to equip the roadway of industrial enterprises, to construct road surfaces for bridges and airfields.
3. Stone mastic mixtures. The composition of the asphalt concrete mixture SMA differs from the presented types of concrete by the presence of a stabilizing fibrous additive (cellulose, etc.) in the structure of the solution.). It is used for the construction of highways with high throughput.

Mixtures, according to filler type, are:

• crushed stone;
• gravel;
• sand (without crushed stone and gravel).

They are separated into the following categories based on the laying temperature and viscosity of binders:

1. Hot, made on the basis of liquid and viscous bitumen, with a laying temperature of> 110 ° C.
2. Cold, prepared using liquid road bitumen, with a use temperature of at least 5 ° C.

The following list is based on the aggregate grains’ sizes:

1. coarse-grained (up to 40 mm);
2. fine-grained (up to 20 mm);
3. sand (up to 10 mm).

Based on the aggregate amount of crushed stone present, they are separated into the subsequent classifications:

1. A — 50%-60%;
2. B — 40%-50%;
3. C — 30%-40%.
4. G and D — without crushed stone (sandy).

Apart from these kinds, there are also high-density hot asphalt concrete mixtures, which are mixes that contain more than 50% crushed stone or gravel.

For asphalt concrete, the following grades are available (see table).

It is essential to have a thorough understanding of the composition of asphalt concrete in order to design the structure of the mixture in a technologically sound manner. Additionally, the economic component—that is, the cost of materials—and the viability of utilizing a specific grade of concrete for a given pavement and set of operating conditions determine the recipe for the asphalt concrete mixture.

Materials

The following materials’ physical and chemical properties, as well as regulatory requirements, are taken into consideration when designing the composition of asphalt concrete:

• sand;
• gravel or crushed stone;
• mineral powder;
• bitumen.

Gravel or crushed stone

The binder’s strong adherence to the aggregate grains is crucial for reducing creep and enhancing the longevity of asphalt concrete pavements. Large gravel, dense metallurgical slags, or crushed stone produced by crushing rocks are utilized as large aggregates in asphalt concrete road mixtures.

Since acidic types of crushed stone don’t stick to bitumen well, metamorphic basic and mountain carbonate rocks (limestone, dolomite) are the most commonly used types. It is best to use crushed stone that is shaped like a cube and has as little flake (flat) grain content as possible in terms of weight.

The maximum amount of lamellar grains per grade should be:

There is also a strict limit on the quantity of dust and clay inclusions. They shouldn’t make up more than 1-2 percent of the aggregates.

Pavements are more resistant to cracks and experience less creep when there is a greater volume of crushed stone used.

Grain sizes of 10–40 mm are used in the manufacturing of crushed stone, taking into consideration the design characteristics of the pavements. Furthermore, the grain size in the upper layers should not exceed 0.6, and in the lower layers, it should not exceed the coefficient of 0.75 (optimal layer thickness in a dense state).

Tests are used to determine the quality and suitability of a particular type of large aggregate, accounting for the road’s classification and surface design.

Sand

Natural sand or crushed stone screenings are used to prepare asphalt concrete.

Using sand with varying grain sizes is a good idea because uniform fractions make the asphalt pavement more porous. Sand from rivers is not advised.

Hints: Because there are a lot of sharp-angled particles in the structure, crushed stone screenings aid in raising internal friction.

Grain size (fineness modulus) is used to differentiate between the following types of sand:

• Mk 2.5 – coarse-grained;
• Mk 2.0–2.5 – medium grain size;
• Mk 1.0–2.0 – fine-grained.

The swelling method should be used to determine the volume of clay particles, and the strength grade of fine aggregates should not be less than 1000.

Hints: Slag sands, sands from carbonate crushing screenings, and other sedimentary rocks with a strength value of 600–1000 can be used in grade II road concrete requirements.

The only way to use fine-grained sand is to enrich it with coarse-sand additives.

There is a restricted amount of clay and silty inclusions.

• for natural sand – 3%;
• artificial – 5%.

The necessary roughness of the asphalt pavement is ensured by the use of crushed natural sand and wear-resistant, high-strength crushed stone.

Mineral structuring powder

The density, heat resistance, and strength of asphalt concrete are all greatly impacted by the mineral powder, which functions as a ligature to structure bitumen and produce asphalt concrete binder alongside it. Crushing and grinding materials such as limestones, blast furnace slags, and dolomites results in finely ground mineral powder.

The hydrophilicity coefficient and the degree of grinding are significant features of this additive. When wet sifting, the mineral powder should freely flow through a special sieve with a 1.25 mm hole size if the grinding is done fine enough. The hydrophilicity coefficient shouldn’t have a value greater than 1.

It is acceptable to replace a mineral mixture with dust from mixing plant dust collectors when there is sufficient technical and financial justification.

Hints: The presence of tiny clay inclusions in mineral powder causes bitumen consumption to rise, mixture preparation and application to become more difficult, and the moistened asphalt concrete to swell more.

The binder’s structure is greatly impacted by the type and amount of powder mixed with the same brand of bitumen. The strength of the coating decreases when there is an excess of mineral powder, particularly at low temperatures.

Watch the video in this article to gain a better understanding of the different types of aggregates.

Road bitumen

Bitumen, a byproduct of oil refinement, serves as a binder when combined with the powder. Sand and crushed stone particles are fused together to form a single material. Additionally, it adds the necessary strength and water resistance to asphalt concrete by bridging the spaces between filler particles.

To reduce the seasonal degradation of road surfaces, asphalt concrete mixture manufacturers use varying types of materials under varying climate conditions. These materials vary in:

• viscosity;
• softening point;
• plasticity;
• brittleness.

Liquid and viscous bitumen can be distinguished based on their amorphous state.

The viscosity value, which is dependent on temperature and component composition, represents the mechanical and physical characteristics of bitumen. This indicator rises with a drop in temperature and falls with an increase. Bitumen becomes brittle and hardens in cold air temperatures.

The following grades of viscous road bitumen are available: BND 130/200, BND 90/130, BND 60/90, and BND 40/60. These binder grades can be identified by their high plasticity and strong adhesion to fillers.

The viscous product serves as the primary raw material for the synthesis of liquid bitumen using a variety of solvents. It is also utilized in the preparation of hot, cold, and warm asphalt concrete mixtures.

Winter is when liquid bitumen is most in demand. It has unique thinners and additives that evaporate as the asphalt concrete hardens, returning the bitumen to its typical viscous state.

Basic principles of designing the structure of the road surface

In order to meet the technical standards and requirements of GOST 9128-13, the composition of the asphalt concrete mixture is designed by calculating the optimal ratio of components. This ensures that the indicators of the main characteristics of a given type of asphalt concrete and the corresponding brand will be met.

Numerous techniques for creating compositions of asphalt concrete have been developed and are in use.

The most popular technique in modern construction is creating the limit curves of the mineral part of road concrete’s grain structure (see photo), which is done by following these guidelines:

1. In order to ensure the strength, cost-effectiveness and durability of the coating, its mineral component must have sufficient density, which is ensured by a certain content of grains of large and small fractions in the total composition of fillers.
2. The structure of the grain part is limited to the maximum curves of the permissible amount of a given grain fraction.
3. The minimum bitumen content must correspond to the physical and mechanical properties of asphalt concrete of the necessary brand, taking into account the technical requirements of GOST 9128-13. The optimal volume of the component is set experimentally on the basis of tables and graphs of tests.

The following steps make up the composition’s design:

• determination of the characteristics and quality of the initial components, assessment of their correspondence for a given brand;
• calculation of the mineral part of the selected materials;
• determination of the rational amount of bitumen;
• Specification of the composition of the mixture according to a detailed study of its physical and mechanical qualities.

A realistic and precise technical task is a prerequisite for composition design.

The construction, design, and operational data listed below are required in order to create the technical specifications:

• design design of the road pavement indicating the thickness of the layers of all coatings;
• technical category of the road;
• characteristics of the traffic mode of road transport on the designed road section;
• expected changes in road and climatic conditions during the construction and operation of the facility.
• balanced characteristics of all available source materials.

It’s essential to comprehend the composition and design of asphalt concrete mixes to produce long-lasting and effective road surfaces. Each of the main constituents—aggregates, binder, and additives—contributes significantly to the mix’s performance. The mix is guaranteed to fulfill precise standards for strength, flexibility, and resistance to different stresses when these materials are chosen and proportioned appropriately.

The majority of the mix is made up of aggregates, which give it stability and structure. The cohesive properties of the mix are derived from the binder, which is usually bitumen, which functions as the glue holding the aggregates together. Certain qualities can be improved with additives, such as increased flexibility in extremely hot or cold conditions or improved resistance to moisture damage.

In order to satisfy the needs of the intended application, these components must be carefully balanced when designing an asphalt concrete mix. To maximize performance attributes like load-bearing capacity, durability, and skid resistance, testing and adjustments are part of this process. In order to make sure the mix will function well under anticipated traffic and environmental conditions, engineers use established procedures and standards.

In the end, the precision of the design process as well as the caliber of the materials determine how well an asphalt concrete mix performs. It is possible to design road surfaces that are secure, durable, and reasonably priced by carefully considering these factors. Better transportation networks and infrastructure are made possible by this knowledge.

Often referred to as asphalt, asphalt concrete is a mixture that is mainly made up of aggregates, such as crushed stone, sand, or gravel, and a binder, typically bitumen, which holds everything together. The mix’s design and composition are essential to guaranteeing the pavement’s strength, flexibility, and longevity. Through the manipulation of component ratios, engineers are able to design asphalt mixtures that are specifically suited for use on high-traffic routes like airport runways. Comprehending the constituents and principles of asphalt concrete design facilitates the creation of superior pavements that exhibit enhanced durability and functionality.

Video on the topic

Asphalt concrete mixture coarse-grained porous M porous asphalt concrete.

Influence and consideration of dispersion of the granulometric composition of mineral components in design

WEBINAR. Innovations in ROAD CONSTRUCTION in 2025

The role of bitumen binder in ensuring the required durability of asphalt concrete

Selection of asphalt concrete composition

Org. aspects of the road industry"s transition to new standards for designing asphalt-bet compositions. mixtures