Asphalt concrete mixes: all their types, varieties and

In road construction, asphalt concrete is the most common material.

It differs from the usual analogue in that it uses petroleum products as a binder:

• asphalt,
• bitumen,
• tar, not cement.

In addition, the preparation and curing of the material occurs without the participation of water (hydration).

Astringents

Translated from the Greek word "asphaltos" means "mountain pitch."

What is asphalt

This material can be natural or artificial.

1. The natural analog is transformed from oil as a result of volatilization of its light fractions and further oxidation under the action of hypergenesis. Initially, the oil becomes viscous and thick malta, then hard, easily melted asphalt. When compacted, it turns into asphalt.

This substance is common in places of close bedding to the surface or oil-bearing formations on it. It is contained in caverns and cracks of limestone, dolomite, etc. The content of a substance in a rock is 2/20% by mass.

1. Artificial asphalt is a composite of bitumen (13/60%) and finely ground mineral aggregates, most often limestone. The instruction warns that, unlike the natural counterpart, such asphalt contains a few percent of paraffin, and the volume of petroleum oils in it is greater.

Note! Asphalt is indispensable for road and construction work. It is used, as a rule, mixed with sand, gravel or gravel. Such material is called "asphalt mastic."

Bitum and Goodron

1. Natural bitumen - it is a solid or viscous liquid consisting of a composite of carbohydrates, as well as their derivatives. It turns out in the course of polymerization (oxidizing) oil. Natural bitumen occurs in areas of oil reservoirs, forming lenses in sedimentary rocks, and occasionally asphalt "lakes".
2. Artificial bitumen get by refining crude oil. There are three known technologies for its production.

Residual material is obtained from tar by deep extraction of petroleum oil from it. The oxidized analogue is produced by oxidizing tar in special installations when air is blown through. Cracking bitumen is the product of processing of oil cracking residues.

1. Gudron is the residue of the selection of oils from fuel oil. This is the main raw material for the production of petroleum bitumen. It is also used as a binder for road works.

Types of asphalt mixes

Road asphalt mixes according to GOST consist of:

• mineral fillers;
• organic binder.

According to the type of production, the components used and the method of laying, asphalt concrete mixtures are divided into many categories.

According to the type of aggregates, asphalt concrete is divided according to State Committee No 9128/2009 into the following types:

• gravel;
• crushed stone;
• sandy.

GOST 9128 97 into aerodrome and road asphalt mixtures divides them according to the level of viscosity of bitumen, as well as acceptable indicators of laying temperature.

1. In hot solutions, heated viscous and liquid petroleum bitumen act as a binder. Laying them should be carried out at a concrete temperature of at least +120 degrees.
2. Cold counterparts include liquid types of oil bitumen. Laying can be done at temperatures ranging from +5 degrees.

Asphalt concrete has typical differences in the fractionality of aggregates. They are listed in the bottom table.

In this case, cold varieties of material are only fine-grained or sandy.

Hot mixes are divided into categories based on the level of their residual porosity. This indicator means the percentage of the number of pores in the applied coating. This is demonstrated by the table below.

Cold varieties of mixtures have a residual porosity of 6 to 10%.

According to the mass content of gravel or crushed stone, hot mixtures are divided into the following types:

• type A - 50/60%;
• type B - 40/50%;
• type B - 30/40%.

Cold counterparts on gravel or rubble are divided according to this indicator into types Bh and Bx.

According to the type of sand used, hot and cold asphalt concretes are divided into the following categories.

1. Type G or Gh. Crushing screenings or its mixture with natural sand (not more than 30 percent) is used.
2. Type D or Dx. Natural sand or its mixture with screening crushing is used (less than 70 percent).

Based on the raw materials used, as well as physicomechanical qualities, hot road airfield asphalt concrete mixes and asphalt concrete are divided into brands presented in the table.

Cold mixtures are divided into the following categories:

• Types Bh and Bx - for brands М-I and М-II;
• Type Gh - on the marks M-I and M-II;
• Type Dx may be M-II.

Selection of the composition and production of material

At the moment, several techniques have been developed for the selection of the composition of asphalt mixes. Any of them contains measures for compacting hot material, determining the porosity of the coating and includes testing the concrete to determine its characteristics.

Note! The fundamental factor here is the design of the mixture. It makes it possible to comply with all requirements and standards applicable to the quality of concrete. The main goal of the design is to find the optimal characteristics of the road surface and ensure the durability of its service.

Blend design

1. The selection of the composition begins with the selection of the characteristics of the components of the mixture and the establishment of their compliance with the standards that are spelled out in the technical documentation.
2. Next, we determine the optimal proportions of the components that will guarantee the production of a coating with the desired qualities.
3. The final design stage is the evaluation of the selection options and the production of a test batch of asphalt concrete at the plant.

There are 2 approaches concerning the design of asphalt concrete.

The first method is the selection of the composition of the mixture with a constant granulometry of fillers. 

1. It guarantees the increased mechanical qualities of the roadway, due to the fine fraction of gravel / rubble of their larger grains due to the wedging.
2. The coating, made of material prepared with continuous granolumimetry filler, has a high level of roughness and resistance to shear.
3. Characteristics of concrete do not change if there are deviations in the dosing of its components. The material is easily laid, distributed and compacted during the pavement arrangement.

1. For asphalt mixes of this type, crushed stone or gravel of hard rock (for example, granite) with more than 50% grain surface is needed.
2. It is important to use bitumen resistant to aging (including the replacement of the phase and group composition). It should also have good adhesion to stone materials, because open concrete porosity is typical for such concrete.

Note! The second method of selection of the composition of the mixture uses the principle of dense concrete. When using it, a large filler having a rounded particle shape and intermittent granulometry will be used.

1. In the course of compaction of such a mixture, a coating is obtained that has a closed porosity, which has a greater water resistance and frost resistance.
2. Such a material is more prone to uneven distribution in the medium of grains of coarse aggregate of bitumen and mineral components.
3. The physico-mechanical qualities of such concrete are greatly influenced by deviations from the normative dosing of the binder and mineral powder.
4. For dense asphalt concretes, a low level of roughness is typical.

Kneading batch

Asphalt materials in short produce so.

1. First of all, the raw material for the mixture is selected and its quality is determined.
2. Then the volume of the necessary components for the ordered quantity of the mixture is determined.
3. Knowing the quality and volume of asphalt concrete, the experts determine what the price of the order will be.
4. Then the raw material is loaded into a special bunker, in which it is predisposed.
5. There, mineral materials are dried and heated to the standard temperature.
6. Then they are sorted by fractionation and fed to the exact weigher.
7. At the same time, the binder is heated to a temperature, the value of which depends on the type of asphalt-concrete mix. Then the bitumen is weighed and dosed.
8. At the final stage of production, the components of the material are fed into the mixer.

Men at work

1. Based on the purpose of the coating (industrial floor, road), asphalt workers lay their hands in one or two layers. The basis for it is crushed stone / gravel or concrete.
2. The bottom layer (4/5 cm thick) is made of a medium or coarse fraction having a residual porosity of 5/10%. The outer layer (thickness 3/4 cm) is laid of fine or medium-grained asphalt with a residual porosity of 3/5%.
3. If the loads are heavy (the runway of the airfield) or an intensive movement of vehicles is expected, the coating is placed in 3/4 layers, which have a total thickness of 11/15 cm.

1. In any case, road works should begin with cleaning the base of dirt and dust with machines with brushes and irrigation systems installed. Then, the irregularities of the base are straightened, and it is processed with bitumen mastic.
2. The material is produced in asphalt mixers on stationary lines of factories or in mobile installations. It is transported to the place of laying dump trucks, then loaded into the bunker machine stacker. It distributes, levels, and seals the coating for the first time.
3. Finally, the concrete is compacted road road rollers.

Pavement arrangement

1. First set side stones that separate the pavement and the road.
2. Further the basis - asphalt concrete with a filler from crushed stone, slag, brick fight keeps within. Asphalt chips are often used (“old” asphalt concrete).
3. Based on the type of soil, the base of the pavement can be from 10 to 15 cm thick.
4. After laying the mixture, it is carefully leveled, and then compacted by self-propelled and manual rollers.
5. Next is rasklintsovka small stones and slag.
6. The pavement itself (usually on sandy filler) has a thickness of 3/4 cm. An exception is the entrance part of the road, which leads to neighborhoods and courtyards. It should be 5 cm thick.

Conclusion

Asphalt concrete has no alternative for road construction, runways of airfields, and often industrial floors, pavements. This material is reliable, durable and inexpensive. There are many brands and varieties of it. Therefore, the design of the coating must be approached very carefully.

The video in this article contains much more useful.