RU2623748C1 - Method for producing cold asphalt-concrete mixture based on asphalt granulate - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: method for producing cold asphalt-concrete mixture based on asphalt granulate, comprising sieving the asphalt granulate into fractions, applying the coatings of an asphalt binder consisting of a mineral powder and bitumen modified with spent motor oil in an amount of 15-25% by weight of bitumen on the heated particles of each asphalt granulate fraction separately by the method of granulating by balling, with the subsequent stirring of the cooled granules to obtain the final cold bituminous mixture comprising the mineral powder not more than 15% by weight of said mixture and said bitumen not more than 2% by weight of said mixture.

EFFECT: increasing strength and durability, preventing shrinkage, increasing the shelf life of the material without loss of performance properties, reducing the tendency to caking.

1 ex, 2 tbl

Description

The invention relates to road construction, and in particular to a technology for the preparation of asphalt mixtures for patching of the roadway, as well as the device of the bases and coatings of roads.

There is a method of processing old asphalt concrete, including crushing the removed asphalt concrete pavement and adding it directly to the mixer to stone materials having a higher temperature (220-260 ° C) compared to conventional technology (AP Lupanov. Processing of asphalt concrete at ABZ. M .: Econ-inform, 2012 .-- 210 p.). The addition of asphalt granulate (asphalt crumb) in this case is not more than 15-20% by weight of the asphalt mix.

The advantage of this technology is the ability to use standard asphalt mixing plants, retrofitted with a crushing plant and a line for feeding and dosing of asphalt granulate. However, the addition of granulate to the asphalt mix is very small, which cannot dramatically affect the reduction in the cost of the material. The opportunity to increase the dosage of asphalt crumb up to 50% is connected with equipping with an additional drying drum, where the heating of old asphalt concrete is carried out to relatively low temperatures of 120-140 ° С.

The material produced by this technology is a typical hot asphalt concrete, the use of which for repairing the roadway is possible only in the warm season with functioning asphalt concrete plants. The production of cold asphalt mixtures according to the considered technology is not possible.

A known method of producing cold asphalt, called Multi-Grade. The material made by this method is a compacted high-crushed asphalt mixture prepared on a gel-modified binder Multi-Grade (www.VPTechnologiesLLC.com). Asphalt concrete mixture is produced on standard equipment of asphalt concrete plants and includes the operations of heating the mineral part, the formation of the granulation composition of the mixture and mixing with a binder. The main difference between this material and typical asphalt concrete is the use of a gel-like binder Multigrade. It is prepared by chemical modification of viscous road bitumen using a special Multigrade additive, which “thickens” the consistency of bitumen and turns it into a gel with high thixotropy, for example, it increases the softening temperature of the source bitumen by 15-30 ° С. Gel-like bitumen forms up to 10-20 times thicker film of crushed stone binder on grains, which does not drain during the production and laying of the mixture, as well as during the operation of the coating.

The internal spatial structure created in bitumen by Multigrade additive prevents the diluent used in cold mixtures from evaporating completely from bitumen for a long time. As a result, the binder Multigrade remains plastic at low temperatures for a long time, possessing increased elasticity at high temperatures and high resistance to cracking. Due to the plasticity of the binder and the structure of the stone skeleton, temperature cracks practically do not form. And if they form at extremely low temperatures, then when warm weather sets in, they tend to heal themselves.

Thus obtained mixture has all the advantages of cold asphalt mixtures that distinguish them from hot mixtures:

- the possibility of using the material at low temperatures;

- the ability to sell material in construction stores;

- the ability to maintain the proper quality of the road surface in areas with harsh climates.

According to its structure and properties, the Multi-Grad asphalt concrete mix is similar to alkali grades, that is, it has the advantages of crushed stone mixtures. These include:

- high resistance to cracking due to ductility of the binder;

- sufficiently high strength characteristics, as well as increased shear stability, which prevents the formation of a rut.

The disadvantages of the asphalt mixture Multigrade should include:

- the disadvantages characteristic of mixtures of alkali, i.e. unnecessarily stringent requirements for the quality of the mixture components and their content;

- the need for selection of granulation composition;

- a fairly high cost of material due to the use of expensive Multi-Grade powder;

- the need to use additional technological operations for the preparation of bitumen Multigrade, which is obtained in a special mixer, into which road bitumen, Multigrade powder and bitumen thinner heated to 160-165 ° C are introduced. As a diluent, diesel fuel and kerosene are used in a total amount of 12-20% by weight of bitumen. The duration of the process is from 30 to 60 minutes;

- limited storage time of the asphalt concrete mixture due to the use of volatile petroleum products as a bitumen diluent, upon evaporation of which the material loses its plastic properties and exhibits a tendency to caking. In this regard, there is a need to store the finished asphalt mix in a sealed package;

- time-limited self-healing ability of asphalt concrete associated with the use of volatile components.

Closest to the claimed method is the "Method for producing cold asphalt mix" in accordance with RF patent No. 2560364 of 2015. Asphalt mix according to this method is obtained by rolling large particles of the mineral part of the mixture (gravel) with mineral powder in the presence of modified bitumen. As a bitumen modifier, mineral engine oil workings in the amount of 15-25% by weight of bitumen are used, and the content of mineral powder in the asphalt concrete mixture is 50% by weight of the mineral part of the mixture.

The cold asphalt mixture obtained in this way has strength characteristics that meet the requirements of GOST 9128-2009 for cold mixtures, has low water saturation due to the high content of mineral powder in the mixture. With such a content of mineral powder, the asphalt binder shell on crushed stone particles deform upon compaction, forming an almost monolithic system. At the same time, there is no need to select the granulation composition of the asphalt mixture, the requirements for which are standardized by GOST 9128-2009 for each type of mixture. The material does not show a tendency to caking, fits well in the cold state and can be stored for a long time without losing operational properties.

The main disadvantage of this material is its high cost, due to the high content of mineral powder in the mixture. When pelletizing by pelletizing, the content of bitumen in the "mineral powder - bitumen" system is usually 13-15%. When the content of mineral powder in the mixture is 50%, the bitumen content will be 6.5-7.5%, which is higher than in typical asphalt mixes. On the other hand, bitumen and mineral powder are the most expensive components of the asphalt mix, determining the cost of the material.

In addition, there is another significant drawback of the material obtained from the considered asphalt mix. Granular asphalt mix with the indicated mineral powder content is subject to significant shrinkage when compacted under the wheels of automobiles. During shrinkage, the level of material in the repaired well decreases, as a result of which the coating material is subjected to dynamic loads from a moving vehicle, leading to its rapid destruction. The increased content of mineral powder also leads to the formation of a material structure in which stone solid particles of the mixture "float" in the asphalt binder without contacting each other. This leads to stratification of the material, extrusion of the asphalt binder into the upper part of the pavement, its removal by the wheels of automobiles and the destruction of the repaired section of the roadway. In addition, granular material with a high asphalt binder content tends to agglomerate when stored in a stack under pressure at elevated air temperatures.

The tasks to which the invention is directed are to reduce the cost of the material, increase the strength and durability of cold asphalt concrete, prevent shrinkage of the road surface from traffic loads, increase the shelf life of the material without losing operational properties, and reduce the tendency to caking.

The problem is solved in that in a method for producing a cold asphalt mix based on asphalt crumbs, comprising sieving the asphalt crumbs into fractions, applying asphalt binders, consisting of mineral powder and bitumen, modified with used motor oil in an amount of 15-25% by weight of bitumen, on heated particles of each of the fractions of asphalt crumbs individually by pelletizing by pelletizing followed by stirring of the cooled granules to obtain a finished cold asphalt concrete a mixture containing mineral powder of not more than 15% by weight of the asphalt mix and said bitumen not more than 2% by weight of the asphalt mix.

The practical implementation of the proposed method is based on the production of a granular product containing a granule core and a structured asphalt binder shell. The use of pelletizing by pelletizing allows one to obtain the structure of an asphalt binder material with bitumen films, the thicknesses of which are measured by nanometers, and the material itself has increased strength characteristics. The introduction of bitumen engine oil residues in the amount of 15-25% by weight of bitumen allows to increase the ductility of the material and to ensure its ability to stack in the roadway in the cold state. However, the increased content of mineral powder and bitumen, firstly, sharply increases the cost of the material and makes it not competitive in comparison with other materials of a similar purpose. Secondly, neglect of the requirements for the granulation composition of the mixture leads to significant shrinkage of the coating material and the formation of a floating structure, prone to premature failure.

Most modern asphalt concrete pavements have a so-called skeleton structure formed from the largest particles of the mineral part of the asphalt concrete mix that are in direct contact with each other (GN Kiryukhin. Designing the composition of asphalt concrete and its testing methods. Overview. Highways and bridges. M .: Informavtodor. Issue 6, 2005, 89 pp.). Smaller fractions of the mineral part fill the cavities between the large particles, which ensures the creation of a framework of stone material in the road surface, which ensures its strength and prevents shrinkage during operation.

In the prototype method, a carcass structure can be obtained by reducing the content of asphalt binder in the asphalt mix. Simultaneously with the transformation of the structure of the material in this way, its cost can be reduced. However, an insufficient amount of asphalt binder in the mixture without taking into account the granulation composition inevitably leads to an increase in water saturation and a decrease in the durability of the coating. In accordance with this, a decrease in the content of mineral powder in the mixture should be accompanied by control of the granulation composition, providing the necessary level of water saturation.

The use of asphalt crumb as a mineral part of the asphalt mix obtained from a material with granulation in accordance with the requirements of GOST allows us to solve the problem of ensuring the necessary water saturation of the coating. The asphalt crumb obtained by milling the roadway or grinding large pieces of asphalt concrete consists of agglomerates, including densely packed stone particles of different sizes. When heated to a temperature of 120 in a rotating drum, the agglomerates break up into their constituent particles, capable of creating a dense-packed asphalt concrete structure.

The asphalt crumb contains a fairly large amount of bitumen, which, when heated, almost completely restores the original properties (see the monograph by A.P. Lupanov) and reduces the need for bitumen in the production of the material by the proposed method. Thus, the use of asphalt crumb as the mineral part of the mixture allows to reduce the content of both bitumen and mineral powder in asphalt concrete, i.e. significantly affect the cost of the material while ensuring its properties that meet the requirements of GOST. At the same time, the environmental problem of recycling industrial waste, which is asphalt crumb, is being solved. It should be noted that the proposed method allows you to completely recycle the secondary material regardless of the size of the particles that make up it.

However, when pelletizing particles of asphalt crumb with asphalt binders, it is necessary to take into account the peculiarity of the pelletizing process by pelletizing. It consists in the fact that during the process small particles increase most rapidly in size. With a sufficiently large spread in particle sizes in the granulated mixture, a situation may arise when the bulk of the asphalt binder is distributed among the small particles, and large fractions remain without shells. To prevent this, before granulating the material, it is preliminarily fractionated by 2-3 fractions, depending on the properties of the initial asphalt crumb.

When developing a recipe for an asphalt concrete mix, it is necessary to keep in mind that asphalt crumb, like any production waste, has a wide range of parameters that determine the properties of the material. This is due to the fact that asphalt granulate is obtained by milling various sections of road surfaces made of various types of asphalt concrete having different operating periods, etc. This fact should be subject to mandatory consideration in the development of new material. To average the variation in the parameters of the final product, it is planned to introduce into the material the amount of mineral powder and bitumen more than necessary to meet the requirements of GOST 9128-2009. The restrictions on the content of these components indicated in the claims allow to obtain a final product that guarantees the satisfaction of GOST requirements. Nevertheless, it is desirable to carry out quality control of the initial chips and the selection of the recipe for the mixture for each batch of material.

An example of the method for producing cold asphalt mix on asphalt crumb.

 Granular cold asphalt mix was obtained by pelletizing particles of asphalt crumb with MP-1 mineral powder using BND 60/90 as a binder bitumen modified by working out engine oil in the amount of 15% by weight of bitumen. Two fractions of asphalt crumbs were used: small with particle sizes up to 15 mm and large with particles of 20-25 mm. The test results are presented in the table. The tests were carried out in the laboratory of Dorekspert LLC at Kapotnya-4 ABZ. There are test reports. The percentages of the components of the asphalt mixture are given in relation to its mass.

As follows from the data in table 1, samples of material obtained by rolling asphalt crumb meet the requirements of GOST for cold asphalt mixtures for all indicators except one. Such an indicator is the saturation of asphalt concrete, the value of which is less than the lower limit of the requirements of GOST. Limitations on this value of water saturation according to Professor Hart (see http://www.drive-class.ru/arhiv/drive.php? Id = 226) are determined by the following considerations.

It is known that the coefficients of thermal expansion of the stone material that makes up the asphalt concrete frame and bitumen are different. As a result of this, at elevated air temperatures, part of the bitumen is squeezed onto the surface of the road surface and carried away on the wheels of a passing vehicle. The content of the binder decreases, which is accompanied by a decrease in the ductility of the material, the formation of cracks and premature destruction of the coating.

In the developed material, such a mechanism of coating destruction is excluded due to the fact that bitumen in the structure of asphalt concrete is in a structured state, i.e. in the form of the thinnest films, the thicknesses of which are measured by nanometers. On the other hand, the low value of the water saturation of the material prevents leakage of moisture into the structure of the pavement, which is especially dangerous during the off-season when alternating positive and negative temperatures. With this in mind, the value of water saturation of asphalt below the requirements of GOST for the developed product is rather a positive factor and cannot limit its use.

The most significant group of indicators of the material are its strength indicators both in dry and in water-saturated state. As can be seen from the table, the values of these indicators significantly exceed the requirements of GOST in all tested batches of material. It follows that this group of indicators cannot be a criterion for evaluating the effectiveness of the final product in determining its optimal composition. As such a criterion, the criterion of material durability would be quite logical. However, this indicator is not standardized by the requirements of GOST, apparently, due to the complexity of the necessary tests.

Therefore, the optimal composition of the asphalt mix according to the results of the tests performed is made taking into account technological and economic factors. From the standpoint of technology, it is advisable to obtain a material with stable performance indicators, independent or weakly dependent on the initial properties of asphalt crumb. Obviously, with an increase in the content of mineral powder and bitumen in the mixture, this dependence will decrease, rather weakly affecting the strength indices.

The test results shown in table 1 show that all tested mixtures satisfy the requirements of GOST 9128-2009. Each of these mixtures can be used for its own purpose, separately from mixtures of a different formulation and fractional composition of the crumbs. However, practice shows that when repairing deep holes it is advisable to use material of larger fractions, in contrast to minor damage to the pavement, when the use of coarse-grained material becomes impossible without additional deepening of the roadbed defect.

However, the use of material from large fractions of crumbs is associated with increased water saturation in comparison with finely divided material. Reducing the water saturation of a coarse product is possible in two ways:

- an increase in the content of mineral powder and bitumen in the granular material;

- the addition of small granules (less than 15 mm) in coarse material filling the gaps between large particles of material.

The first method is associated with a significant increase in the cost of the product, and therefore the second method is more preferable. This raises the problem of determining the optimal content of fractions in the finished asphalt mixture. Table 2 shows the test results of cold mixtures with different fractions.

In table 2, the following notation is used:

- K - asphalt crumb;

- MP - mineral powder;

- B - bitumen, modified 15% of the engine oil;

- CF - a large fraction of crumbs;

- MF - a fine fraction of crumbs.

As follows from the data of table 2, an increase in the content of mineral powder and bitumen leads to an increase in the strength of asphalt concrete, and an increase in the content of bitumen reduces the water saturation of the material. However, from the standpoint of the economy, an increase in the content of these components in the mixture leads to an increase in the cost of the material. Based on these considerations, it was assumed that the content of mineral powder should be no more than 15%, and modified bitumen should be no more than 2% by weight of the asphalt mix. These restrictions will allow you to get a material with fairly stable properties and cost at the cost level of typical asphalt mixtures.

Claims (1)

A method of producing a cold asphalt mix based on asphalt crumbs, comprising sieving the asphalt crumbs into fractions, applying asphalt binders, consisting of mineral powder and bitumen, modified with spent motor oil in an amount of 15-25% by weight of bitumen, to the heated particles of each of the fractions of asphalt crumb separately by pelletizing by pelletizing followed by stirring of the cooled granules to obtain a finished cold asphalt mixture containing mineral powder n more than 15% by weight of said mixture and said bitumen is not more than 2% by weight of said mixture.