X Международная студенческая научная конференция Студенческий научный форум - 2018

A growing number of freight, number of vehicles and the loads on the road surface creates difficult conditions for the operation of roads, especially those built on the basis of binders and require specific countermeasures. One of the main problems that occurs because of high axial loads and high traffic density, is the deformation of asphalt concrete pavements of highways, which are built using simple, not modified bitumen.

To increase the reliability and durability of road surfaces is currently better to use modified bitumen, i.e. bitumen, modified with special polymers. Active use of modified bitumen due to their high performance.

The fact is that the modified bitumen has a higher temperature range, for example, the difference between the temperatures of brittleness and softening of modified bitumen is about 100 degrees, at that time, as a conventional bitumen – only about 60.

Asphalt concrete prepared with the use of modified bitumen have a high resistance to deformation due to the higher degree of elasticity of such bitumen. Also not to say that the modified bitumen slows down the aging process of asphalt. Studies of foreign experts show that the modified bitumen that was extracted from pavements after 10 years of operation, is not observed any significant changes in viscosity.

To improve the properties of bitumen, i.e., bitumen modification, as a rule, uses special artificial materials. Currently, because of the diversity of such materials, which are petrochemical industries, there is a large selection of used polymers for modifications.

CLASSIFICATION OF POLYMERS FOR BITUMEN MODIFICATION

Conventionally, such polymers can be classified into three groups, namely thermoplastics or plastomers, elastomers, and termoelektricheskie artificial substances.

THERMOPLASTICS

Thermoplastics consist of linear or low-branched polymers, razmyagchayuschiesya when heated. When cooled they again become hard. The addition of plastomers increases the viscosity and stiffness of bitumen at normal operating temperatures (from -30 °C to 60 °C). But plastomers do not affect the elasticity of modified bitumen. When heated bitumen, plastomers improved, there is a tendency to phase separation of bitumen and polymer, which means that bitumen is unstable to storage, so should be prepared immediately before use at the asphalt plant. As plastomers are most often used polyethylene and atactic (stereomicroscopy) polypropylene.

ELASTOMERS

Consist of elongated polymer chains with branches. They are sufficiently elastic in a wide temperature range, starting from negative end 200 degrees Celsius. With the addition of elastomers modified bitumen becomes more viscous, increasing its elasticity.

However, this modified bitumen is not sustainable during storage, to prevent separation between the artificial material and the bitumen requires constant stirring. Modified with elastomers bitumen is bitumen with elastic filler. As elastomers can apply or regenerated natural rubber and polybutadiene.

A THERMOELASTIC MATERIALS

Thermoelastic artificial materials have been used since 1965 the Most famous representative of the group of thermoelastic plastics is styrene-butadiene-styrene (SBS). This artificial material is biocopolymers composed of blocks of styrene and polybutadiene. This additive material to the bitumen is usually from 3 to 6% by weight. The required amount of added material depends on the dispersed state of the injected material: if the SBS is introduced into the bitumen in finely divided form, the flow rate decreases if in coarsely disperse form, that requires a large amount of modifier. Surfactant additives for bitumen

All the recommended surface-active additives improve the wetting of mineral materials with bitumen, resulting in facilitated and accelerated the processes of mixing, reduces the consumption of bitumen. In addition, a monomolecular layer of surfactant, adsorbiruemymi on mineral surface and provide durable adhesion of the film of bitumen to the mineral material. It should be noted that the bitumen contains a small amount anionactive compounds, primarily type asfaltenovyh acid, so the introduction of cationic substances can lead to the neutralization of active groups. Additions of surfactants introduced into the bitumen have an influence on the processes of irreversible changes under the action of air oxygen and high temperature. The aging process of bitumen under the influence of thermo-oxidative factors is reduced to the processes of emergence, development and destruction of the hard structural grid of asphaltenes.

Additives are substances of class amines slow down the aging of bitumen coagulation type. Therefore, these additives having a stabilizing effect, prevent the occurrence and development, spatial structural grid of asphaltenes and even slow down the aging of bitumen coagulation type.

Anionactive surfactant-type iron Soaps, on the contrary, increases the viscosity of bitumen of all types of structures.

Additions of surfactants different shift the upper bound of the interval elastic-plastic state bitumen: supplements class of amines and diamines in the direction of lower temperatures, and additives such as an iron wash - in the direction of higher temperatures.

During the period of active structure-obrazovaniya asphalt a small amount of surfactant, reducing the surface tension of the mineral material, dramatically increases the adhesion of bitumen to mineral material improves the conditions of wetting and facilitates mixing, and thus naturally reduces the consumption of bitumen.

In the period of formation of macrostructure of asphalt, surfactants contribute to a more rapid sealing of asphalt and a period of stabilization of the structure during operation there is a further orientation of the surfactant molecules, generating a water and frost-resistant material.

Synthetic rubbers (elastomeric polymers) used to create bitumi modified bitumen gives flexibility at low temperatures.

ADVANTAGES

SBS coatings are characterized by good adhesion and high resistance to significant temperature changes. In addition, the modified bitumen with SBS additives is cold-resistant, flexible and easily follows the shape of the surface, which fits. The heat resistance of the modified bitumen is slightly worse than that of bitumen with additives AMS, however, when using a high quality modifier SBS she, however, can reach values of 100 degrees.

SBS is the most common modifier for bitumen. Thus, the modified bitumen with additives, SBS has a polymeric matrix that represents a three-dimensional grid formed by the interaction of blocks of polystyrene and formed polystyrene domains. Inside this grid in the form of minor variances is distributed in the bitumen, which is characterized by a high content of special aromatic compounds.

APPLICATION

For this reason, SBS can be used either in powder form or in granules. In the first option, you can get a quality mix simple mixers. But in the case of using a granular styrene-butadiene-styrene you need a device which frays a polymer with bitumen.

HOMOGENIZER

Such a device is a homogenizer. The thermal resistance of the heterogeneous mixture and such nesovershennoletnih bitumen may in some cases be higher, but in any case, the flexibility in the cold and will deteriorate over time such modified bitumen this parameter will be the same as simple.

FLEXIBILITY

As the practice and experience, flexibility may be an indirect parameter of quality of SBS modified bitumen. High quality materials, which are modifiers, SBS (for example, the products of the company shell), achieve flexibility at temperatures down to minus 30 degrees Celsius. At the same time, materials with flexibility at temperatures below minus 20 degrees differ an insufficient concentration of polymer, or they use incompatible with the modifier of the bitumen. In practice, this modified bitumen is very quickly destroyed.

METHODS OF PRODUCING MODIFIED BITUMEN

Traditionally, there are two primary methods for obtaining modified bitumen:

1) the production of bitumen-polymer dispersions in a special colloidal mills (mixers with a large shearing force);

2) introduction of polymers into the bitumen by chemical means, by slowly rotating mixer with a small shear force.

In the first case for the normal stabilization of the polymer-bitumen mixture using sulfur and its various compounds.

So, between modifier and sulfur are reactions that give rise to new chemical compounds, which remain distributed in the modified bitumen due to its lattice structure. In the latter case, the polymer is, for example, styrene-butadiene-styrene is pre-processed so that almost dissolves in the bitumen.

A significant drawback of using colloidal mills for the production of modified biomasses that resulted in the bitumen after processing will appear in polymers with a lower molecular weight than he had in the beginning. This is due to the factor that appears in colloidal mills shear effort cause changes in the molecular structure of the used polymer. Mixer with a small shear stress provide an opportunity to obtain higher values of softening and greater ductility of the obtained modified bitumen.

With the active use of polymers not normally compatible with the chemical system of bitumen (for example, natural rubber, polyethylene), need special installation for the production of modified biomonitoramento on the asphalt-concrete factories that the material can immediately be used for the production of asphalt before the beginning of the phase separation.

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