Crushed-mastic asphalt concrete is an optimally selected composition of mineral materials, which are designed to provide the pavement structure with high water resistance, shear resistance and increased roughness.
What is the feature?
Such asphalt mixtures have a special structure, due to which paving is possible in thin layers. This reduces the specific consumption of material. The price of raw materials for the preparation of such asphalt concrete is higher in comparison with the production of traditional asphalt concrete, however, it is not inferior to it in profitability.
State Standards and Composition
At first glance, crushed stone and mastic asphalt concrete, which is manufactured according to GOST 31015-2002, could be attributed to the group of classic pavings created on the basis of oil and bitumen binders. However, it is not. Structural features and component composition of this mixture stands out among competitors.
The basis of the material is formed by a rigid framework of crushed stone, which explains the high resistance to plastic deformation. Inside contains a large amount of bitumen binder, which occupies the free space between the aggregates. This reduces residual porosity, which is 1% or less. This made it possible to obtain a durable coating, which during operation exhibits high resistance to climatic and intense transport influences.
Primary Use
Roads (GOST 31015-2002) are usually arranged using asphalt. One of the main areas of use of this material is also the device of the upper layers:
- road surfaces;
- city ββstreets;
- airfields;
- areas.
The composition can also be used for overhaul of the upper layers of coatings. Asphalt concrete is also used to create durable and high-quality areas and sites.
Basic properties
Crushed stone mastic asphalt contains the following ingredients:
- crushed stone;
- stabilizing additive;
- bitumen;
- mineral powder.
1st is contained in a volume of 70 to 80%. As for bitumen, its amount in relation to the total mass can reach the limit of 7.5%. If we compare with conventional asphalt mixtures, the described one is characterized by a high volume of oil bitumen and crushed stone.
To protect against delamination and maintain a homogeneous structure, the asphalt mix is ββbonded with stabilizing additives in the form of fibers. This is especially true when performing road works. Depending on which aggregate of which fraction is used in production, asphalt concrete can be systematized by composition.
If you have material with the marking 10 in front of you, this indicates that the grain size of the crushed stone should not be more than 10 mm. The most common brand is asphalt concrete with the marking 15. Here the standardized size of the aggregate grains is 15 mm. Crushed stone mastic asphalt concrete can be represented by the marking 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 brands is recommended for use in the manufacture of top layers of road surfaces up to 6 cm thick. Such compositions are used on highways, city streets of all categories in 1 to 5 climatic zones.
Specialist advice
When road construction work is underway for aerodrome coatings, the adhesion coefficient and compressive strength should be increased by 25%. The use of such concrete on high-speed roads, which are subjected to heavy traffic, allows to achieve many advantages. This is especially true when compared with traditional asphalt.
Additional properties
ShchMA, GOST of which was mentioned above, has high wear resistance, a long service life and a low noise level indicator when driving vehicles. 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 in this case does not depend on climatic conditions of operation. The service life will be three times higher compared to similar coatings used for the same purpose.
Main characteristics
Crushed stone mastic asphalt concrete () is tested according to state standards 12801-98. We agree with them, there are certain parameters that are subject to study, among them should be highlighted:
- ultimate compressive strength;
- shear resistance;
- crack resistance.
The compressive strength of 15 is 9 MPa, which is true at a temperature of 0 Β° C. Shear resistance is equivalent to 0.93. Considering the 15, you can pay attention also to crack resistance. For this brand, it is 4.3 MPa.
The true density of this material is 2.56 t / m 3 . The normalized thickness of the upper coating layer is 0.05 m. According to GOST, SCHMA 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?
Asphalt technology provides certain requirements for the materials used, among which are:
- crushed stone;
- bitumen;
- mineral powder;
- stabilizing constituent mixture.
As for crushed stone, its grain composition should consist of solid rocks. It is permissible to use crushed material from metallurgical slag. The mark must be equal to 1000 or higher. The shape of the grain should have a cuboid type. According to the total mass, the volume of grains of lamellar and needle shape should not exceed 15%.
Frost resistance of crushed stone should be equal to F50 or higher. According to abrasion, the value should correspond to the brand I-1. If you are wondering what the asphalt is made of, then you should know that bitumen is also the basis. Recommended oil bitumen, which comply with GOST 22245β90. Can be used and polymer-bitumen binders. In the latter case, the requirement for bitumen runoff performance should be provided.
Fiber stabilizing additives may not be included. 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 the asphalt is made of, then you should know that there is also sand in the composition. It should be taken from the screening crushing of solid rocks. The sand mark must be equal to 1000 or higher. The material must comply with GOST 8736β93. The volume of clay particles in it should not be more than 0.5%.
Mineral powder in the composition
Road construction works are carried out using asphalt concrete, in which there is mineral powder. Its characteristics are regulated by GOST 16557-78. It is made by crushing calcareous rocks or dolomite rocks. It is permissible to use mineral powder from screenings of volcanic rocks. The fraction of particles should not be more than 0.16 mm. If the composition contains a large amount of bitumen binder, this must certainly entail the presence of a stabilizing additive. Without this component, it is impossible to obtain a mixture with physico-mechanical properties that are prescribed by the standards.
Stabilizing component mixture
According to GOST, roads should be laid using asphalt 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 contribute to the retention of hot bitumen on the surface of gravel. This makes it possible to eliminate the stratification of the solution at high temperatures, which are characteristic of the laying process.
The properties and characteristics of crushed stone mastic asphalt concrete include stabilizing mixtures, namely:
- crumb rubber;
- polymer fibers;
- thermoplastic polymers;
- acrylic threads;
- asbestos fibers;
- mineral components;
- silicic acid based products;
- cellulose fibers.
Due to the fact that the 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 for a long time keeps bitumen on the surface of the coating and eliminates delamination of the composition.
Characteristics in accordance with state standards
Hot mixtures must be resistant to delamination, including during storage and transportation. Such resistance to delamination is provided by stabilizing additives, and an assessment of this quality must be carried out according to GOST 31015.
The runoff should not exceed 0.3% by weight. When the composition of the mixture is selected, it is recommended that the binder runoff index be equal to the limit of 0.1 to 0.2% by weight. As for the color of asphalt, 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 Β° C.
Coating Device Technology
Mixes asphalt concrete and crushed stone and mastic asphalt 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 Λ. In autumn, this indicator is + 10 Λ. The base must be dry and have a positive temperature.
The composition of the work includes some technological operations. At the first stage, preparatory work is carried out. Next, acceptance of the asphalt concrete mixture and its unloading into the paver hopper, if it is used, is carried out. Another mechanism may be used. The mixture is then laid by the paver and compacted by a roller.
If the work is carried out using hot asphalt concrete, they are delivered to the place of work by dump trucks with clean bodies that have a heating system. The mixture is covered with a waterproof awning. Laying should be carried out at a continuous pace, it must be coordinated with the plant's productivity. The pace of work is regulated by the relevant documentation and is prescribed in the project work.
For laying the mixture, pavers with an automatic system to ensure lateral slope and evenness of the coating should be used. To compact the coatings, road rollers are used, the mass of which reaches 18 tons. Preparations are carried out when the coatings are arranged. They include the installation of fences and traffic signs.
Before laying a layer of hot asphalt concrete, you need to make sure the evenness and quality of the underlying coating. The base should be cleaned of dust and dirt by treating with an organic binder based on bitumen emulsion. For this purpose, you can use liquid road bitumen.
Asphalt concrete is laid without cooled longitudinal joints to the width of the carriageway. The number of stackers working at the same time should be assigned taking into account the width of the sealing working bodies. The step between pavers working simultaneously in the neighborhood should not be higher than 30 m. In order to get a smooth surface of the coating, it is necessary to ensure a constant speed and continuity of paving. The first of these depends on the uniformity of the delivery of the mixture to the paver and usually varies from 2 to 4 m per minute.
The mixture should protrude from the car body during installation as evenly as possible. In order to achieve a layer of constant thickness and the required evenness, it is necessary to ensure uniform pressure of the material on the plate. At the beginning of the shift, when laying is resumed after a break, the transverse joint should be warmed up. The smoothing plate is installed on the previously laid coating. The screw chamber is then gradually filled with the mixture.
Finally
The color of the asphalt is regulated by state standards. But this is not the only characteristic that should be paid attention to when assessing the quality of asphalt concrete. If the composition was made in accordance with the rules, it will help to reduce noise during traffic, will serve a much longer period, and will be resistant to rutting.