Asphalt mixes: the main varieties, especially the

In this article we will talk about what are the most popular building materials used for road paving. In addition, we will look at how asphalt concrete mixes are produced according to GOST and what requirements are imposed on this type of product.

Material Features

Asphalt concrete is a kind of building materials of artificial origin used for the device of the roadbed and other large-size coatings. The production process involves the manufacture, and subsequent compaction of a special mixture, selected in accordance with the requirements set out in GOST 9128.

Asphalt mix today is made of the following components:

• mineral materials (fine-grained crushed stone, quartz sand, and also fine-dispersed mineral powder for asphalt concrete mixes);
• astringent organic base (bitumen).

Important: In the last century, instead of bitumen or with bitumen, tar was used as a binding base. Subsequently, due to the high cost, low strength and unprofitability of use, the tar was excluded from the composition of asphalt concrete mixtures.

Making a mixture involves the thorough mixing of all components with bringing the composition to high temperatures.

Classification of mixtures

Depending on which mineral powder is applied, the following modifications of the mixtures differ:

• gravel;
• crushed stone;
• sandy.

Attitude to one or another modification determines the characteristics of the use of asphalt.

So, for example, gravel and crushed stone modifications, as a rule, are used when constructing a roadbed, covering squares, sidewalks, etc. At the same time, sand modifications are used in the manufacture of floor foundations at large industrial facilities.

Important: The specific weight of the asphalt concrete mix, depending on the weight of the components, is on average 1.8-2.2 tons per 1 m ?.

In accordance with the fraction of applied aggregate, the asphalt mix can be of the following types:

• coarse-grained (with a particle size of not more than 40 mm);
• fine-grained (with a particle size of not more than 20 mm);
• sandy (with a particle size of not more than 10 mm).

According to the content of crushed stone or gravel, dense hot asphalt concrete is divided into the following types:

• "A" with the content of aggregate 50-60% of the total;
• "B" with a filler content of 40-50%;
• "B" with a filler content of 30-40%.

Cold асфальтобетоны также содержат мелкозернистый заполнитель и представлены на рынке типами Бх и Вх, где добавочная буква «х» является температурной характеристикой готового материала.

Sandy asphalt concrete, both hot and cold, is divided into the following categories according to the type of aggregate used:

• Materials produced using sand obtained from crushing screenings are denoted as G and Gh (aggregate content up to 30% of the total volume);
• Materials produced using natural sand or its mixture with screening crushing are denoted as D and Dx (content - up to 70%).

Based on the physicomechanical indicators of the finished materials and on the composition of the components used, asphalt concrete mixtures are assigned the appropriate marks. Depending on the assigned brand and on the thickness of the coating, the consumption of the asphalt-concrete mixture per 1 m2 is determined.

Brand cold modifications:

• MI, MII - Bh and Bx;
• MI, MII - GC;
• MII - Dk.

Brand of highly porous and porous modifications - MI, MII;

Brand of high-density and dense hot modifications:

• MI, MII - A;
• MI, MII, MIII - B and T;
• MII, MIII - B and D.

As already mentioned, asphalt mixes are made using a binder, which, together with the aggregate, is heated to operating temperatures.

In accordance with this feature, the finished mixtures are divided into the following modifications:

• Cold - manufactured using liquid petroleum bitumen. The working temperature of the finished material is + 5 ° C and above.
• Hot - manufactured using predominantly viscous petroleum bitumen. The working temperature of the material at which laying is possible is + 120 ° C;

Important: In the manufacture of cold mixtures, only fine-grained or sandy aggregate is used.

In the production of road material, there is a residual porosity of the asphalt mix. This phenomenon is inherent in both hot and cold modifications and is calculated as a percentage, based on the ratio of the number of pores to the volume of the material after compaction.

In accordance with this parameter, the finished material is divided into the following categories:

• high-density asphalt concrete (residual porosity 1.0-2.5%);
• dense (2.5-5.0%);
• porous (5.0-10.0%);
• highly porous (10.0-18.0%).

After compaction, cold mixtures are characterized by a residual porosity of not more than 10.0%.

ABZ and currently relevant production technologies

After we have decided on the general characteristics and classification of asphalt mixes, let us examine the instructions for their production.

The production of asphalt mixes is carried out industrially at specialized enterprises of asphalt concrete plants (ABZ). Consider briefly what is the modern ABZ.

Equipment for the production of asphalt concrete

Modern ABZ can be mobile (mobile) or stationary. But, despite the configuration, they are equipped with all the devices necessary for the autonomous execution of all technological operations.

Among the technological operations carried out at modern ABZ, we note the following:

• Operations during which acceptance, storage and supply of stone aggregate to the hoppers are performed.
• Operations in the process of which acceptance, storage, heating and supply of the binder component (bitumen) to the dispenser is performed;
• Operations during which reception, storage and supply of mineral powder aggregates to the dispenser are performed;
• The operation of receiving, storing, heating and supplying the surface active substances (surfactant) to the dispenser;
• Complex operations focused on the preparation of mixtures (dosing of components, pre-drying of mineral aggregates, screening (sorting) of heated rubble or gravel, dosing of the binder component (bitumen), mixing the components in the mixer and their subsequent unloading as a ready-mixed mixture)
• Operations during which the storage, short-term storage and shipment of the finished product is performed.

To effectively carry out the above list of works, ABZ are equipped with the following list of technological equipment:

• Devices for receiving, storing and supplying stone materials to mixer bins;
• Devices for receiving storage and supply of mineral powder to the mixer (material is supplied by means of a pneumatic system);
• Devices for receiving, storing, heating and pumping bitumen into the mixer;
• Devices for receiving, storing, heating and pumping surfactants into the mixer;
• Crushing and screening plants, intended for grinding the aggregate and screening the desired fraction;
• Mixers in which all components are mixed to the desired consistency;
• Equipment for the shipment of the finished product (elevator or skip) and storage bins.

Modern ABZ, in accordance with the type of location of access roads, are divided into on-site (roadside) and railway modifications.

When choosing production equipment, it is necessary to take into account the performance parameters, which are directly dependent on the number of mixing plants. So, in stationary plants, from two to six mixers are used, while on mobile counterparts, whose price is more affordable, the number of installations does not exceed two units.

Considering the fact that ABZs are subdivided according to the principle of action into modifications of periodic and continuous action, we consider production technologies characteristic for each category.

Production technologies of continuous and cyclic cooking

The technology of continuous preparation of asphalt concrete involves the following production steps:

• Acceptance and storage of mineral materials in special bunkers equipped with dispensers. At the same stage crushed stone and sand are dosed taking into account technological standards and the degree of moisture of materials.
• Acceptance and dosing of mineral aggregate in powder form.
• Further, the required amount of materials from the dispensers is transported to the dryer drum, where the components of the future mixture are heated and intensively mixed, as a result, excess moisture is discharged outside.
• Heating and subsequent dosing of bitumen. The heated material is sent to the mixer, where the rest of the previously dried materials go.
• The most important stage in which all components are mixed to a uniform consistency.
• Shipment of the finished material in the storage bin with the subsequent shipment of products to the vehicle.

Important: Continuous technology does not involve the sorting and dosing of hot mineral aggregates. Therefore, it is necessary to take a responsible approach to the dosage of these components with your own hands still in a cold state.

The cyclic technology of asphalt concrete preparation is a classical technique and involves careful screening and dosing of mineral aggregates in a heated state. As a result, the mixtures prepared on such equipment are more consistent with the technological requirements.

In addition, the product prepared according to the classical technology is considered more homogeneous, since all the aggregates are mixed both in the dry state and after the addition of the binder component.

So, we looked at the basic features of asphalt concrete and have a general idea of ​​the production of this material. Finally, we describe the factors that have a negative impact on the properties of asphalt concrete, and look at ways to minimize the damage.

Asphalt segregation and control

The practice of building a pavement indicates that the quality of asphalt concrete largely depends on the temperature and the uniformity of the particle size distribution of the mixture being laid.

In identifying the causes of the destruction of the roadway, it was found that the most important factor influencing these parameters is the segregation of the asphalt concrete mix.

Segregation (stratification) in relation to asphalt concrete can be temperature or fractional. The phenomenon of segregation inevitably arises in the process of transporting the finished mixture from the production plant to the site where construction is underway.

During transportation of the material, it cools down in areas of contact with the vehicle body. In addition, the mixture cools from above because, most often, is transported in the open state. During the course of these processes, heavy fractions of the mixture precipitate at the bottom of the body.

As a result, the mixture is stratified by temperature and fractional parameters, therefore, when laying the canvas, the optimal strength parameters can not be guaranteed.

Important: If you do not take care of the suspension of segregation processes, repair of the road surface during normal operation will have to be carried out at least once in 2-3 years.

An effective solution to this problem is the asphalt mix handler. If earlier the technological chain consisted of a dump truck, from which the mixture was shipped directly to the paver, and the handler itself, then to prevent segregation, an additional link is introduced - the loader.

Through this technique, the mixture from the dump truck is reloaded into the asphalt paver. In the process of reloading, the material is brought to the optimum working consistency and to the working temperature throughout the volume.

Of course, the use of additional special equipment turns into an increase in the cost of the finished result, but the strength of the fabric put into operation will increase by several times.

A modern material handler is equipped with a special roomy bunker, capable of providing a continuous process of asphalt concrete supply, which allows reducing the time required for laying the coating.

Conclusion

Теперь мы знаем о том, какой вес 1м3 асфальтобетонной смеси и о том, что представляет собой этот строительный материал. Кроме того, мы рассмотрели особенности промышленного производства в соответствии с ГОСТ на асфальтобетонные смеси и обозначили факторы, оказывающие негативное воздействие на прочностные параметры готового продукта (читайте также статью «Типы асфальтобетонных смесей и особенности их производства»).

Do you have any questions? You can find more useful information by watching the video in this article.