Crushed-stone-mastic asph alt concrete (ShMA): GOST, properties and characteristics

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Crushed-stone-mastic asph alt concrete is an optimally selected composition of mineral materials that are designed to provide pavement structures with high water resistance, shear resistance and increased roughness.

What's special?

Such asph alt mixes have a special structure, due to which laying is possible in thin layers. This allows you to reduce the specific consumption of material. The price of raw materials for the preparation of such asph alt concrete is higher compared to the production of traditional asph alt concrete, but it is not inferior to it in terms of profitability.

State standards and composition

Crushed-stone-mastic asph alt concrete, which is manufactured in accordance with GOST 31015-2002, at first glance, could be attributed to the group of classic road surfaces created on the basis of oil and bituminous binders. However, it is not. Structural features and component composition of thisblend stands out from the competition.

The basis of the material is formed by a rigid frame of crushed stone, which explains the high resistance to plastic deformation. Inside contains a large amount of bituminous binder, which occupies the free space between the aggregates. This reduces the residual porosity, which is 1% or less. This made it possible to obtain a durable coating, which during operation shows high resistance to climatic and intensive transport influences.

Main area of use

Highways (GOST 31015-2002) are usually built using asph alt concrete. One of the main areas of use of this material is also the device of the upper layers:

• road surfaces;
• city streets;
• airfields;
• squares.

The composition can also be used for overhaul of the upper layers of coatings. Asph alt concrete is also used to create durable and high-quality areas and sites.

Basic Features

Crushed-stone-mastic asph alt concrete contains the following ingredients:

• rubble;
• stabilizing additive;
• bitumen;
• mineral powder.

1 is contained in the volume from 70 to 80%. As for bitumen, its amount in relation to the total mass can reach a limit of 7.5%. When compared with conventionalasph alt concrete mixtures, described is characterized by a high volume of oil bitumen and crushed stone.

To protect against delamination and maintain a homogeneous structure, the asph alt mix is bound with stabilizing additives in the form of fibers. This is especially true for road works. Depending on the aggregate of which fraction is used in production, asph alt concrete can be systematized by composition.

If you have a material marked Shchma 10 in front of you, this indicates that the size of the crushed stone grains should not be more than 10 mm. The most common grade is asph alt concrete marked Shchma 15. Here, the normalized aggregate grain size is 15 mm. Crushed-stone-mastic asph alt concrete can be represented by marking ShMA 20. In this case, we are talking about a composition with a maximum grain size of up to 20 mm.

A mixture of the above grades is recommended for use in the manufacture of upper layers of road surfaces up to 6 cm thick. Such compounds are used on highways, city streets of all categories in 1 - 5 climatic zones.

Expert advice

When road construction work is underway for airfield pavement, the friction coefficient and compressive strength must be increased by 25%. The use of such concrete on high-speed roads that are subject to heavy traffic offers many advantages. This is especially true when compared to traditional asph alt pavement.

Additional properties

SCMA, GOST of which was mentionedhigher, has high wear resistance, long service life and low noise level when driving. The coating remains stable under mechanical stress, in addition, it is characterized by an increased coefficient of adhesion of tires to the road surface. Wear resistance does not depend on the climatic conditions of operation. The service life will be three times longer than similar coatings used for the same purposes.

Key Features

Crushed stone mastic asph alt (ShMA) is tested according to state standards 12801-98. They agree that there are certain parameters that are subject to study, among them should be highlighted:

• compressive strength;
• shear resistance;
• crack resistance.

The compressive strength of ShMA 15 is 9 MPa, which is true at a temperature of 0 ˚С. Shear resistance is equivalent to 0.93. Considering SMA 15, you can also pay attention to crack resistance. For this grade, it is 4.3 MPa.

The true density of this material is 2.56 t/m³. The normalized thickness of the top layer of the coating is 0.05 m. According to GOST, ShchMA has a mass of 0.128 t/m^{2. The cost of one square meter of coverage is approximately equal to 265 rubles.}

What are they made of?

Asph alt concrete technology provides for certain requirements for the materials used, among which arehighlight:

• rubble;
• bitumen;
• mineral powder;
• stabilizing compound.

As for crushed stone, its grain composition should consist of solid rocks. It is acceptable to use crushed material from metallurgical slags. The mark must be equal to 1000 or higher. The shape of the grain should be cubic. By total mass, the volume of lamellar and needle-shaped grains should not exceed 15%.

Frost resistance of crushed stone should be equal to F50 or higher. In terms of abrasion, the value should correspond to the I-1 brand. If you wondered what asph alt is made of, then you should know that the base also contains bitumen. Petroleum bitumens are recommended, which comply with GOST 22245–90. Polymer-bitumen binders can also be used. In the latter case, the requirement for bitumen runoff must be met.

Fibrous stabilizing additives may not be added to the composition. All bitumen used must have sufficient adhesion to crushed stone. Otherwise, it is necessary to introduce a cationic type adhesive additive. If you want to know what asph alt is made of, then you should know that sand is also included in the composition. It must be taken from screenings crushing hard rocks. Sand grade must be 1000 or higher. The material must comply with GOST 8736–93. The volume of clay particles in it should not exceed 0.5%.

Mineral powder in the composition

Road construction works are carried out using asph alt concrete, which contains mineralpowder. Its characteristics are regulated by GOST 16557-78. It is made by crushing calcareous rocks or dolomite rocks. It is acceptable to use mineral powder from screenings of volcanic rocks. The particle fraction should not exceed 0.16 mm. If the composition contains a large amount of bituminous binder, this must necessarily entail the presence of a stabilizing additive. Without this component, it is impossible to obtain a mixture with physical and mechanical properties that are prescribed by the standards.

Stabilizing compound

According to GOST, roads must be laid using asph alt concrete, which contains a stabilizing component. Its properties and appearance are of great importance for improving the quality of the final material, its transportation, preparation and installation. Additives are structuring fibrous. They allow you to maintain uniformity and help keep hot bitumen on the surface of crushed stone. This makes it possible to eliminate the separation of the solution at high temperatures, which are characteristic of the laying process.

Properties and characteristics of crushed-stone-mastic asph alt concrete provide for the presence of stabilizing mixtures in the composition, namely:

• rubber crumb;
• polymer fibers;
• thermoplastic polymers;
• acrylic threads;
• asbestos fibers;
• mineral components;
• silicic acid products;
• cellulose fibers.

BecauseThe cost of production is quite low, and cellulose and fiber are used in the form of fibers, as well as special granules based on them, the material keeps bitumen on the surface of the coating for a long time and eliminates delamination of the composition.

Specification according to government standards

Hot mixes must be resistant to delamination, including during storage and transportation. Such resistance to delamination is provided by stabilizing additives, and this quality must be assessed in accordance with GOST 31015.

The drip rate should not exceed 0.3% by weight. When selecting the composition of the mixture, it is recommended that the flow rate of the binder be equal to the limit from 0.1 to 0.2% by weight. As for the color of the asph alt, the mixture should have a uniform shiny black color, it should be characterized by uniformity, which is evaluated according to GOST 12801. The variation of the indicator should not be more than 0.18% at a temperature of 50 ˚С.

Cover device technology

Asph alt mixes and crushed-stone-mastic asph alt concrete should be laid in dry weather. If work is carried out in the spring, then the ambient temperature should not be lower than + 5 ˚С. In autumn, this figure is + 10 ˚С. The substrate must be dry and have a positive temperature.

The scope of work includes some technological operations. At their first stage, preparatory work is carried out. Next, the asph alt concrete mixture is received and unloaded into the bunker of the asph alt paver,if it is applied. Other mechanisms may also be used. The mixture is then spread by a paver and compacted by a roller.

If the work is carried out using hot asph alt concrete, they are delivered to the work site by dump trucks with clean bodies that have a heating system. The mixture is covered with a waterproof tent. Laying must be carried out at a continuous pace, it must be coordinated with the productivity of the plant. The pace of work is regulated by the relevant documentation and is prescribed in the project for the production of work.

Pavers with automatic cross-slope and leveling systems should be used for paving the mix. For compaction of coatings, road rollers are used, the mass of which reaches 18 tons. Preparatory work is carried out during the installation of coatings. They include the installation of fences and road signs.

Before laying a layer of hot asph alt concrete, you need to make sure that the underlying surface is even and quality. The base should be cleaned of dust and dirt, treated with an organic binder based on a bitumen emulsion. For this purpose, liquid road bitumen can be used.

Asph alt concrete is being laid without cooled longitudinal joints to the width of the carriageway. The number of simultaneously working pavers should be assigned taking into account the width of the compacting working bodies. The spacing between asph alt pavers working simultaneously in the neighborhood should not be higher than 30 m.laying continuity. The first of these depends on the uniformity of the mixture delivery to the paver and usually varies from 2 to 4 m per minute.

The mixture should come out of the car body during installation as evenly as possible. In order to achieve a layer of constant thickness and the desired evenness, uniform pressure of the material on the plate should be ensured. At the beginning of the shift, when laying is resumed after a break, the transverse joint should be warmed up. The smoothing plate is then installed on the previously laid coating. The screw chamber then gradually fills with the mixture.

In closing

Asph alt color is regulated by state standards. But this is not the only characteristic that should be paid attention to when assessing the quality of asph alt concrete. If the composition was made according to the rules, then it will help reduce traffic noise, last a much longer time, and be resistant to rutting.