Cast asphalt concrete: technology, application

Cast asphalt concrete is a multipurpose material that is frequently utilized in building projects. It is well-known for being resilient and versatile, combining the best aspects of conventional asphalt with special characteristics to make it fit for a range of uses. A vital component of contemporary infrastructure is cast asphalt concrete, which is used to pave sidewalks, roadways, and even airport runways.

By heating the asphalt mixture to a high temperature, cast asphalt concrete’s technology makes the material more pliable and workable. This process guarantees a more even and seamless application, resulting in a surface that lasts longer. Although the procedure is simple, accuracy is needed to get the intended outcomes.

Cast asphalt concrete’s resilience to severe weather and large loads is one of its main advantages. Its superior resistance to moisture and temperature fluctuations lowers the possibility of cracks and potholes. Because of this, it is the best option for places with heavy traffic and erratic weather.

Apart from its durability, cast asphalt concrete also has a low environmental impact. Because it is recyclable and reusable, it supports environmentally friendly building methods. By selecting this material, builders promote environmentally beneficial initiatives while also ensuring the longevity of their projects.

Aspect	Description
Technology	Cast asphalt concrete is made by heating bitumen and mineral aggregates to a high temperature. The mixture is then poured into molds and compacted using rollers or vibratory machines to achieve a dense and durable surface.
Application	Cast asphalt concrete is commonly used for road surfaces, bridges, and airport runways due to its durability and ability to withstand heavy traffic and harsh weather conditions.

General information

Cast asphalt concrete mixtures are laid in the road structure without compaction at an operating temperature of 220 °C because of their high mobility, which allows them to be easily distributed over the surface. This material solidifies at lower temperatures, creating a long-lasting, waterproof, and crack-resistant layer (see the article’s video).

The following kinds of road surfaces are frequently constructed using cast-technology asphalt concretes:

• highways;
• city streets and squares;
• bridge structures;
• airfields;
• tunnels;
• indoor and outdoor parking lots;
• Also used to carry out patching of road structures.

Classification and main characteristics

The characteristics of cast composites vary from one another, as do the quantity and quality of the original mineral components, the manufacturing technology, and the phase composition of the asphalt concrete binder.

According to the TU for cast asphalt concrete, the following table shows the proportion of the content of asphalt mixture components and the range of their application:

Cast mixtures differ from traditional bitumen solutions in a few ways, including:

• increased content of oil-bitumen binder (11%) and mineral powder (25%);
• high viscosity;
• much higher production and laying temperature (220-250°C).

Cast asphalt concretes can have any of the following compositions, depending on the binder used:

1. Standard mixture, prepared using heat-resistant unmodified bitumen.
2. Polymeraseasfalto concrete — polymer-bitumen binder is used as the main component.
3. Gray asphalt concrete – composite material. The binders are: modified sulfur and road bitumen. The use of technical sulfur makes it possible to reduce the bitumen content in the solution and slightly reduce the preparation temperature.
4. Rubber asphalt concrete — crumb rubber is used as the main filler. The use of this material helps to increase the wear resistance of the coating, increases its durability, and in some cases, helps reduce the consumption of crushed stone.

Cast asphalt concrete benefits include:

• there is no need to compact the laid layers;
• increased corrosion resistance, wear resistance, water resistance;
• increased ductility, facilitating stress absorption;
• high adhesion to overlying or underlying layers.

In addition to the aforementioned benefits, cast asphalt mixtures have several noteworthy disadvantages:

• high price of the material compared to traditional asphalt concrete;
• low resistance to plastic deformations (comb, track, etc.) is observed when the temperature rises.;
• impossibility of laying by hand – installation of coatings only with the use of special equipment and tools;
• high vapor impermeability, which can lead to the formation of blisters on the surface of the layers being laid, especially when installing coatings on cement concrete bases.

However, cast asphalt concrete 50 mm can successfully withstand any transport loads for an extended period of time when the mixture composition is technologically selected correctly, based on many years of experience using the material.

Materials

The proposed design documentation may indicate variations in the composition of cast asphalt concrete, contingent upon the intended use, coating technology, and operating conditions.

The following materials represent the standard set of components:

• petroleum road bitumen;
• sand;
• crushed stone or gravel;
• mineral powder.
• black crushed stone.

Large aggregates — crushed stone

Robust, frost-resistant rocks or blast furnace metallurgical slags are used to produce crushed stone. Natural raw materials should have strengths between 100 and 120 MPa, while porous blast furnace slags should have strengths between 80 and 100 MPa. The excellent adherence of blast furnace slags to the binder makes up for the slightly lower requirements.

Crushed stone for cast mixtures should have an acute-angled shape (cube, tetrahedron, etc.). The content of flat (flaky) grains is limited to 15%.

Some guidance: no more than 1% of the filler’s total volume should contain clay or dust particles.

Small aggregate — sand

One method of obtaining sand for making cast asphalt concrete is to crush rocks or crystalline blast furnace slag. There are two types of crushed sand: grades 400 and 800, depending on the source material.

Rocks with a strength of at least 40 MPa are used in the production of the first type, and rocks with a strength of more than 80 MPa are used in the second. These sands are classified as medium- and coarse-grained by fraction.

Some tips: the small aggregates used in the solution preparation process need to have consistent (equal) grain sizes in order to guarantee the homogeneity of the asphalt concrete mixture.

Sand and crushed screenings characteristics must match the table values (see photo), depending on the kind, brand, and type of asphalt.

Mineral powder

One of the primary structural elements of asphalt concrete is this substance.

Converting petroleum bitumen from a bulk to a film state is the primary function of the powder as a filler. hence strengthening the hot cast mixture’s structure and increasing its viscosity.

Mineral structuring powder works as a single binding material in the solution to create a high-quality dispersed system with road bitumen. Blast furnace slags, bituminous limestones, and calcareous or dolomite rocks are ground to create mineral powder.

The hydrophilicity (swelling) coefficient of the powder additive, which is typically 1.25 mm or more, determines the joint work of bitumen and powder. The bitumen solution and powder should not swell by more than 2.5 percent.

Certain local materials, such as powdered industrial waste (fuel ash, fly ash, waste from sugar production, etc.), may be used as a powder additive in certain circumstances. Since these materials differ in quality, it is necessary to conduct experiments to ascertain the impact and quantity of each additive for each unique kind of mixture.

Bitumen

The type of asphalt concrete, the category of the road, and the climate in effect in specific construction areas are taken into consideration when choosing the class and grade of liquid or viscous bitumen.

GOST 22245-90 states that road bitumens should be used in the creation of cast hot mixes. Additional technical details are shown in the table below.

Blackened crushed stone

Black crushed stone is applied to the surface of cast asphalt concrete to improve adhesion of vehicle wheels to the road surface and to increase wear resistance.

This material is made by combining crushed stone from sedimentary or volcanic rocks with an organic binder and hot impregnation in a special installation.

Continuous or periodic mixing units are used to blacken crushed stone. The technological characteristics of a specific kind of road are taken into consideration when choosing the type of binder.

The crushed stone is dried and heated, and the binder is heated at the same time as part of the preparation technology. The table shows the recommended preparation temperature.

The type of organic binder and the processing conditions determine the process temperature regime. The lower temperature limit (table) is used in warm, dry weather (above 10°C), and the upper temperature limit (table) is used in below-freezing weather.

The information in the table below is used to determine how much organic binder is needed to process crushed stone.

An asphalt and aggregate mixture is poured hot and spread to create a smooth, resilient surface in cast asphalt concrete, a flexible and long-lasting material used in road construction and repairs. For busy cities and highways, its short setting time and resilience to high traffic make it perfect. In order to ensure a smooth and durable finish, cast asphalt concrete technology involves heating the mixture to a high temperature prior to application. Its versatility and dependability in a range of infrastructure projects are demonstrated by the fact that it is used not only on roadways but also on parking lots, industrial floors, and airport runways.

Cast asphalt concrete is a flexible and long-lasting solution for a range of building requirements. Because of its special qualities, it can be used for a lot of things, like industrial flooring and road surfaces. Cast asphalt concrete is made with technology that guarantees its strength and durability, enabling it to withstand severe weather and traffic.

Cast asphalt concrete application calls for meticulous preparation and exact execution. The mixture can be easily poured and spread, resulting in a smooth and even surface, by heating it to high temperatures. This technique saves a lot of time for a variety of projects because it doesn’t require as much compaction.

Cast asphalt concrete is not only environmentally friendly but also very practical. Its production frequently uses recyclable materials, supporting green building techniques. Because of this feature, it’s a desirable option for contemporary builders who want to reduce their environmental effect.

All things considered, cast asphalt concrete is a material that is highly dependable and effective in the construction sector. For many projects, its durability, application simplicity, and environmental advantages make it a wise choice. Through comprehension and application of this technology, builders can produce long-lasting, high-quality results.

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