Molded asphalt and features of its application. If we lay cast asphalt, then the skating rink is not needed at all Asphalt concrete what is cast concrete

Method for preparing cast asphalt concrete mix relates to the production of road building materials. technical task solved by the invention is to reduce the time of preparation of a cast asphalt concrete mixture, reduce energy consumption while ensuring heat resistance, maintaining the mobility of the mixture and improving environmental safety. The method consists in mixing preheated mineral stone materials, bitumen and sulfur to a homogeneous mass. According to the invention, sulfur can be in powder or liquid state. In this case, sulfur is mixed with mineral stone materials heated to a temperature of 160-180 o C in an amount of 3-6% by weight of mineral materials. After mixing the resulting mass to a homogeneous state, oil bitumen heated to 140-160 o C is introduced in an amount of 5-8% by weight of mineral materials, the components are mixed again. The resulting cast asphalt concrete is characterized by increased heat resistance, water resistance while maintaining mobility. At the same time, the preparation time of the mixture is reduced by 2 times. 1 z.p. f-ly, 1 tab.

The invention relates to the field of production of road building materials, in particular to the preparation of asphalt mixtures. A known method of preparing a cast asphalt mixture, including mixing components in the form of mineral materials heated to a temperature of 190-240 o C with bitumen heated to 160-180 o C. The prepared mixture has a temperature of 165-240 o C. The disadvantage of this method for the preparation of cast asphalt concrete mixtures is: - the use of oil deeply oxidized viscous road bitumens with a flash point of at least 240 o C, characterized at 25 o C by a needle penetration depth of 50-60 units, a softening temperature according to the KiSh method of at least 52 o C, the brittleness temperature is not higher than -12 o C. A known method of preparing a cast asphalt mixture, adopted as a prototype, according to which the preparation of the mixture is carried out by mixing bitumen heated to 145-150 o C in an amount of 4-6% with sulfur in the form of a finely dispersed sludge for sulfur purification in a ratio of 1:1 (in terms of sulfur) for 60-120 s, the resulting sulfur-bitumen binder is mixed with limestone mineral powder heated to 140-150 o C in a ratio of 1:1.5 for 30-60 s, and then the resulting the mixture is stirred with mineral material heated to 140-150 o C for 15-30 s. The disadvantages of this method of preparing cast asphalt mixtures are: - long time mixture preparation 105-210 s; - the need for pre-heating of the mineral powder to 140-150 o With the preparation of cast asphalt mixture; - high dustiness of finely dispersed sulfur sludge. The technical problem solved by the invention is to reduce the time of preparation of a cast asphalt concrete mixture while maintaining heat resistance, mobility of the mixture and improving environmental safety. To achieve this result, in the method for preparing a cast asphalt concrete mixture, which includes mixing heated mineral materials with heated bitumen and sulfur, first mineral stone materials heated to a temperature of 160-180 o C are mixed without preheating with mineral powder for 15-20 s, and then sulfur is introduced in a powder or liquid state in an amount of 3-6% by weight of mineral stone materials and mixed for 20-30 seconds, after which bitumen is introduced in an amount of 5-8% by weight of mineral materials and mixed for 20-30 with. The total preparation time of the mixture is 55-80 s. Sulfur added directly to mineral materials activates the surface mineral material, provides better adhesion of bitumen. According to the prototype method and according to the proposed method, a cast asphalt concrete mixture was prepared with the following composition, %: Granite crushed stone (fractions 5-15) - 14 Natural sand - 69 Mineral powder - 17 Bitumen, % by weight of mineral materials - 5 Sulfur (in powder form) ,% by weight of mineral materials - 5
The prototype method and the proposed method are implemented in the following examples. Example 1 (prototype). In heated to 145 o With bitumen was introduced in portions of cold fine sulfur in the amount of 5% by weight of mineral materials in a ratio of 1:1 (corresponding to the prototype in terms of sulfur) and stirred for 80 seconds. The resulting sulfur-bitumen binder was mixed with limestone mineral powder heated to 145 o C in a ratio of 1:1.5 for 40 s and final mixing with mineral material heated to 145 o C for 30 s. The total mixing time was 150 s. Example 2
Heated crushed stone and sand to a temperature of 170 o C was mixed with mineral powder for 10 s, after which sulfur was introduced into the mixer in an amount of 5% by weight of mineral materials and mixed for 15 s. Bitumen heated to a temperature of 140 o C was introduced into the resulting mixture in an amount of 5% by weight of mineral materials, mixing was carried out to a homogeneous mass for 15 seconds. The total mixing time was 40 s. Example 3
Heated crushed stone and sand to a temperature of 170 o C was mixed with mineral powder for 15 seconds, after which sulfur was introduced into the mixer in an amount of 5% by weight of mineral materials and mixed for 20 seconds. Bitumen heated to a temperature of 140 o C was introduced into the resulting mixture in an amount of 5% by weight of mineral materials, mixing was carried out until a homogeneous mass was carried out for 20 seconds. The total mixing time was 55 s. Example 4
Heated crushed stone and sand to a temperature of 170 o C was mixed with mineral powder for 20 seconds, after which sulfur was introduced into the mixer in an amount of 5% by weight of mineral materials and mixed for 30 seconds. Bitumen heated to a temperature of 140 o C was introduced into the resulting mixture in an amount of 5% by weight of mineral materials, mixing was carried out until a homogeneous mass was carried out for 30 seconds. The total mixing time was 80 s. Example 5
Crushed stone and sand heated to a temperature of 170 o C were mixed with mineral powder for 30 seconds, after which sulfur was introduced into the mixer in an amount of 5% by weight of mineral materials and mixed for 40 seconds. Bitumen heated to a temperature of 140 o C was introduced into the resulting mixture in an amount of 5% by weight of mineral materials, mixing was carried out until a homogeneous mass was carried out for 40 seconds. Total cooking time - 110 s. Were tested cast asphalt mixture prepared by a known method (prototype) and the proposed method, as well as samples of cast asphalt from these mixtures. The test results are shown in the table. It can be seen from the table that the cast asphalt mixtures, prepared within 55-80 s according to the proposed method, ensured the receipt of all technical indicators at the prototype level. Information sources
1. TU 400-24-15 8-89* "Mixed asphalt concrete and cast asphalt concrete. Specifications". 2. A. S. USSR 1474133, IPC C 04 B 26/26, publ. 04/23/1989, 3 p. (prototype).

Claim

1. A method for preparing a cast asphalt concrete mixture, including mixing heated mineral stone materials with heated bitumen and sulfur, characterized in that, first, mineral stone materials heated to a temperature of 160-180 o C are mixed with sulfur in a powder or liquid state, in an amount of 3 -6% by weight of mineral stone materials, and after mixing, oil bitumen is introduced into the resulting mixture in an amount of 5-8% by weight of mineral stone materials. 2. The method according to p. 1, characterized in that oil bitumen is used, having at 25 o With a needle penetration depth of more than 60 units.

DRAWINGS

NF4A Reinstatement of USSR patent or patent Russian Federation for an invention

The scheme is this: necessary components mixed, prepared from hot or cold mix, poured and necessarily compacted. The latter procedure provides sufficient coating strength and resistance to deformation.

Cast is inherently a very viscous liquid, and there is no need to compact it.

Molded asphalt after cooling acquires its own operational density, which means cost savings and a significant acceleration of road construction. This feature of the material is due to its unusual and manufacturing method.

If for ordinary asphalt concrete the macrostructure, that is, the ratio and shape of sand or mineral powder, is the decisive factor, then for cast asphalt concrete it is the microstructure, which, in turn, is associated with the qualities of the asphalt binder bitumen.

The binder contains mineral powder and. Its share in the composition of cast AB is increased to 28%: 7.5–10% of bitumen itself, and 20–30% of powder. Such a high concentration determines the formation of a semi-frame structure of the final product.
The content of crushed stone - with a diameter of up to 5%, ranges from 0 to 50%.

This video will tell you about the features of cast asphalt concrete:

Types

Depending on the volume of the largest grains, cast AB is divided into 3 types:

1 – maximum diameter reaches 15 mm, and mass fraction stone reaches 45–55%. Such a composition is used both for the construction of new roads and for the repair of old ones.
2 – maximum size less - up to 20 mm, and the proportion of stone will be 20-25%. The range of applications is also wide.
3 - here the maximum diameter reaches 40 mm, and the share of crushed stone increases again - 45–65%. This composition is suitable for new construction.
4 - only a fraction with a grain size of less than 5 mm is used. This AB option is suitable for laying sidewalks, bike paths and more.
5 - the maximum grain diameter reaches 20 mm, the proportion of stone is 35–50%. At the same time, the volume of bitumen is a record great importance – 22–28%.

Another major difference is the feature of the technology. Cast AB is made at more than high temperature asphalt mixture and continuously mixed to the construction site with constant heating. Then the material is laid with special machines. It is not necessary to compact it; when cooled, the cast AB gains the required strength.

Despite the higher cost of the mixture, its use pays off, since such a coating lasts much longer.

Specifications and properties

The top surface of the road is subject to very high requirements, because in addition to the obvious strength and durability, "road clothes" must protect the lower layers from rain and snow. Therefore, the main qualities of cast asphalt concrete include low porosity and, accordingly, high density (t/m3).

For type 1 porosity mineral composition does not exceed 20%, for the rest - 22% by volume.
Water saturation (by volume) for types 1 and 2 is 1%, and for the rest, respectively, 5.7 and 0.5%. Since the material is not saturated with moisture, it can protect the underlying layers. In addition, the same quality explains the excellent coating of cast AB.
Good resistance to low temperatures increase and due to the production of crushed stone of a cubic shape from mountain metamorphic rocks. Its indicator corresponds to the class F 50.
The residual porosity of cast AB will be 2%.
The compressive strength is at least 1 for types 1, 2, 3 and 5 and at least 0.7 for type 4.
Density, which means specific gravity or volume of cast asphalt concrete depends mainly on the proportion of the stone fraction. Accordingly, with a different mass of crushed stone, the weight and volumetric weight of the material will fluctuate, and within significant limits. On average, the range will be 1.5–2.2 tons per 1 cubic meter. m.
In addition, each region has developed its own standards for the manufacture of AB, both cast and conventional. Therefore, you can accurately find out these parameters only from the specialists of the manufacturer.
To important characteristics also applies to durability. Cast AB is less prone to deformation: at +40 C, the indentation depth is 1–6, 1–4 mm and 1–10 for type 5.
Since the laying of cast AB is carried out at a higher temperature, the adhesion to the lower layers also turns out to be large. This means a kind of "sintering" with materials roll waterproofing. Thus, the water resistance of the entire structure is increased.
In cast AB, there is no effect of corrosion, moreover, the coating of the material is resistant to salts.

The use of cast asphalt concrete will be discussed further.

Application environment

Molded asphalt concrete is successfully used in the construction of roads, bridges, tunnels and many other objects. At the same time, it is important to select the material corresponding to the conditions, since the indicators of the types are very different.
GOST recommends using cast asphalt concrete of types 1 and 2 in the construction of both lower and upper layers with an expected load of more than 3 thousand avt. per day. These are high-speed sections of the highway, highways, airfields and so on.

Also, type 1 and 2 material is allowed to be used for the construction of routes and at a lower load, although in this case the economic benefit will not be so obvious.

For the arrangement of pedestrian and bicycle paths, type 1 is not used. 2, 3 and 4 are used to form the top and bottom layers.
When building bridges and tunnels, as well as for any type of repair - for the formation of a leveling layer, for coating, for repairing potholes and other things, AB types 1, 2 and 5 are used.
The preference for cast AB is also due to its high roughness. This property ensures that the tires of a car or bicycle tire grip the road surface, which is especially important during rain or snowfall.
Due to the high waterproofing properties of cast AB, it is also used in a not quite typical way, for example, in the arrangement of roofs, even heated ones, as well as floors, in waterproofing tunnels and other things.

The technology of preparation, the device of cast asphalt concrete, the equipment for this and the composition will be discussed below.

Material manufacturing

For specifications The composition of the product is equally important, and the method of production, and even the method of laying. The finished product, the road surface, is the result of following the technology at all stages.

Compound

The composition and ingredients used for the production of cast ABs are somewhat different from the usual ones. In Russia, GOST regulates the requirements for the composition and materials in the manufacture.

Bitumen - it is allowed to use oil viscous bitumen of the BND 40/60 or 40/90 grade, but the use of improved types of bitumen enriched with polymeric additives is recommended. This is especially true of AB designed for bridge structures or high-load routes. For example - styrene-butadiene-styrene of recommended grades.
Crushed stone - material from igneous and metamorphic rocks is used with a total content of lamellar grains of not more than 20%.
The sand in the composition of cast AB is natural and crushed. In the production of AB for the top layer, its use is limited.
Mineral powder is selected according to the instructions of GOST R 52129-2003.
The composition may include various modifying additives: coloring pigments, dephlegmators, and so on.

Preparation of poured asphalt concrete

For the manufacture of cast AB, bitumens with a high degree viscosity, which means higher heating temperatures when mixing ingredients. However, excessive heating can lead to a change in properties, so they try to organize the cooking process in such a way as to limit themselves to the lowest possible heating.

So, bitumen is heated to a temperature not of 250 C, but of 160–180 C.
Mineral components are heated up to 190-240 C.
At the outlet, the temperature of the asphalt concrete mixture is 200–220 C. This value is still considered excessive.

It is better to use activated mineral powder: in this case, it is possible to achieve a mixture temperature of 170–190 C.

This manufacturing method eliminates on-site production, as temperature conditions you have to be tough here. Stages of production - according to general scheme, look like this:

delivery of components to bunkers;
transfer to the dryer drum - here the ingredients are mixed and heated to the desired temperature;
in the bituminous part, the binder is heated and transferred to the mixer along with the solid ingredients of the mixture. Dry mixing time - only dry parts of the material, is 15–20 s. Mixing together with bitumen takes 1.5-2 times more time than in the manufacture of conventional mixtures. Any asphalt mixing machines with forced-type mixers are suitable for preparation;
transportation is carried out only in special heated boilers and with continuous mixing during movement - cochers. The resulting mixture is similar in properties to a suspension and can delaminate. When transported without mixing, this danger increases markedly, and then the cast AB becomes unusable.

Laying

The delivered mixture is unloaded into special asphalt pavers. The machines carry out the laying of the mixture with a layer of the desired thickness - from 3 to 7.5 cm.

Before this, support bars are laid at the construction site to prevent the mixture from spreading. The bars are removed after the AB temperature drops to 60-70 C.

Thicken road layer not necessary. However, to increase the roughness, it is recommended to embed black gravel. To do this, use the lightest rollers.

You will learn how the poured asphalt concrete is laid in the video below:

Cost and popular manufacturers

Cast manufacturing road asphalt concrete somewhat more difficult than the usual hot, and even more so cold. In general, the share of production cast asphalt in Russia is only 9-10%, although there is an upward trend.

The leaders in this market are producers of concrete and oil products.

The first place is deservedly occupied by the first enterprise in Russia specializing in the manufacture of asphalt concrete - this is JSC Asphalt Concrete Plant No. 1 in St. Petersburg. All possible asphalts of any type are obtained here.
Surgutneftegaz specializes in the production and sale of oil. concrete production is a side effect for them. Although the company is in the top ten in terms of gross volume.
AOA Asphalt Concrete Plant No. 4 in Moscow offers everything, including cast.
State Unitary Enterprise "Bashkiravtodor" is a road construction company engaged in both the construction and repair of roads, and the production of the materials required for this.
JSC "Sverlovskavtodor" - at 45 asphalt concrete plants, enterprises produce all types and. The company carries out a full range of road works.

The cost of the material varies markedly depending on the type and region of manufacture. On average, the price of cast asphalt concrete varies from 3700 to 4200 rubles. per ton or 5940–8800 r. per cubic meter

We will talk about laying technologies, patching with cast asphalt concrete below.

patching

The current repair of roads is still carried out in the warm season - it is much more economical. However, in the case emergency repairs are carried out regardless of weather conditions. The pothole is filled with hot asphalt mix of the required class and type.

At the first stage, the damaged area - a map, is marked and cleaned. Chop along the contour using a seam cutter, as well as a pneumatic or hydraulic jackhammer. They cut out the remnants of the coating inside the marked area, and then remove the resulting debris. At large volumes works use self-propelled road cutters mounted or trailed type.
Then the bottom and walls of the pothole are covered with liquid bitumen or bitumen emulsion - a kind of primer. It is carried out manually with a brush and a watering can, and for large volumes - with the help of an asphalt distributor, a repairer, and so on.
Cast AB is delivered to the place of repair only in special machines - cochers, in which a certain thermal regime and mixing regime are maintained.
To pour the mixture into the pothole, special devices are used. There is no need to seal.
To increase the roughness, the area is covered with a layer of black rubble and sunk with a hand roller.

Cast AB is one of the best materials for high-class road surface, designed for a fair load. And thanks to its excellent water resistance, it is also used in numerous waterproofing works.

The following video will tell you how minor patching is done using cast asphalt concrete:

(cast asphalt mix) - a composite road building material, which is a mixture of mineral materials (crushed stone, sand, mineral powder) and bituminous binder (heat-resistant bitumen or polymer-bitumen binder).

Refers to high-density asphalt concrete mixtures and in the form ready for laying is a hot viscous-flowing plastic mass of black color. Unlike conventional compacted hot mixes, poured asphalt is characterized by an excess of bituminous binder, which gives it high plasticity.

Cast asphalt concrete- a solid monolithic pavement made of cast asphalt concrete mix.

Cast asphalt mixes should not be confused with cast emulsion-mineral mixes (LEMS), which, in addition to a different composition, also have a different purpose (as a rule, they are used for thin-layer surface treatment asphalt pavement).

Purpose and scope of cast asphalt

The main purpose of cast asphalt mixes is the device upper layers road surface. In more rare cases, poured asphalt is used for the construction of the lower layers of the pavement, followed by laying on top of them a thin layer of crushed stone mastic asphalt (SMA) or another type of poured asphalt mix (this approach is common when asphalting bridge structures).

The main area of application of cast asphalt is bridge construction. This material is used to create the upper protective layers of the coating of bridge structures, also performing the function of waterproofing.

The second most important area of application for cast asphalt mixes is road construction. Molded asphalt can be used for asphalting roads of any technical category in all road and climatic zones of Ukraine (from A-1 to A-7), as well as for asphalting sidewalks, pedestrian and bicycle paths, interrail space of tram tracks.

The use of hot cast asphalt concrete mixes is of particular relevance when it is necessary to carry out patching of asphalt pavement in the cold season at low temperatures.

Despite the fact that the main area of application of cast asphalt mixes is bridge and road construction, given material quite often used in industrial and civil construction as waterproofing material, material for the device of hard coatings at production and storage sites, the device of screeds and floor coverings(with subsequent grinding and polishing of such a coating to a smooth state), creating a blind area.

Typical composition and production technology of poured asphalt

Molded asphalt differs from conventional compacted asphalt concrete mixtures by a higher content of bituminous binder (up to 11%) and mineral powder (up to 25%).

The mineral component of the cast asphalt mix includes crushed stone, sand and mineral powder. Crushed stone is used from dense rocks with the following characteristics:

The crushability grade must be at least 1000
Abrasion grade not less than I1
Frost resistance grade not lower than F50
The content of flaky and needle-shaped grains is not more than 15% by weight
The content of dust and clay particles is not more than 1% by weight

Sand is used natural, crushed or from screenings of crushing dense rocks. Mineral powder is used activated and non-activated from carbonate rocks (limestone or dolomite).

Thus, in terms of the mineral component (crushed stone, sand and mineral powder), cast asphalt is similar to conventional asphalt concrete mix, but its main difference is the binder component. When preparing cast asphalt concrete mixes, heat-resistant bitumen, polymer-bitumen binder or other bitumen binders with improved properties (bitumen-rubber binder, rubber-bitumen binder, etc.) are used.

Molded asphalt is produced at asphalt concrete plants in special asphalt mixing plants using a technology similar to the preparation of conventional asphalt mixtures. The temperature of the cast mixture at the outlet of the mixer depends on the type of binder and can vary from 190 °C to 240 °C.

Since the poured asphalt concrete mixture has a high content of bituminous binder and has a high temperature (190–240 °C) during discharge, this leads to delamination and a rapid loss of uniformity (manifested in the form of uneven settling of mineral particles). To prevent the process of delamination, maintain the homogeneity of the mixture and maintain a high operating temperature, during the transportation of cast asphalt to the object, its continuous mixing with simultaneous heating is required. Transportation of cast asphalt is carried out by specialized machines - “kochers” (another name is a thermos mixer).

In addition to transportation, the Kocher can be used as a mobile unit for the preparation of cast asphalt mixtures intended for patching roads. The process of preparing such a mixture can be carried out using new materials, as well as with the addition of recycled asphalt concrete (crushed asphalt) or from semi-finished products. The use of crushed asphalt in the preparation of cast asphalt for patching is one of the ways to reduce its high cost.

Classification of cast asphalt mixtures

By appointment

I type- it is used for the construction of the top layer of the road surface on motorways and roads of category I–III, the carriageway of bridges, overpasses, overpasses and parking lots. Type I cast asphalt mix is produced at a specialized asphalt mixing plant, transported to the site in a thermos-mixer, laid by a special paver (caterpillar, wheel or wheel-rail finisher) or manually without compaction. The largest grain size of stone filler (crushed stone) is 15 mm. The content of grains larger than 5 mm is 45–55% by weight.
II type (vibrated asphalt mix)- designed for coating highways I-III technical categories, airfields, bridges, flyovers, overpasses. Type II cast asphalt mix is produced in a conventional asphalt mixing plant, transported by dump trucks with a protective tarpaulin, laid by a conventional asphalt paver with vibrocompaction (hence the name "vibrocast"). The largest grain size of crushed stone is 20 mm. The content of grains larger than 5 mm is 35–50% by weight.
Type III (vibrated asphalt mix)- used for the construction of the upper layer of the base in the construction of roads of I-III technical categories, as well as airfields. Type III cast asphalt mixture is produced at a standard asphalt mixing plant, transported to the site in dump trucks, and laid with a conventional asphalt paver with vibration compaction. The largest grain size of crushed stone is 40 mm. The content of grains larger than 5 mm is 45–65% by weight.
IV type- it is used for asphalting sidewalks, indoor floors, screeds and roof waterproofing. The largest grain size of crushed stone is 5 mm.
V type- used for patching asphalt concrete pavement, waterproofing of coatings and asphalting of inter-rail space in tram tracks. The largest grain size of crushed stone is 20 mm. The content of grains larger than 5 mm is 35–50% by weight. When choosing materials for cooking cast mixtures Type V requirements for raw materials may be lower, since the properties of poured asphalt concrete should not significantly exceed the properties of the repaired asphalt pavement. Transportation and laying of poured asphalt type V is carried out with the help of a coher.

vibrocast asphalt mix- cast asphalt II-III type. There are disagreements regarding these types of poured asphalt in the professional and scientific environment, because formally they cannot be defined as cast asphalt, since they are transported to the asphalting facility by ordinary dump trucks, are laid with standard asphalt pavers with vibration compaction, and, moreover, require compaction with rollers, which does not happen. in the case of a cast mixture of types I, IV and V.

By type of binder

Cast asphalt mix- standard cast asphalt mixture prepared with heat-resistant unmodified road bitumen.
Cast polymer asphalt mix- cast asphalt concrete mixture in which polymer-bitumen binder (PBV) is used as a binder component.
Cast sulfur asphalt mix- a cast mixture in which a complex binder is used as a binder, consisting of bitumen and modified technical sulfur. The use of sulfur makes it possible to reduce the consumption of bitumen and lower the temperature of the preparation of a cast asphalt mixture.
Cast rubber asphalt mix- cast asphalt concrete mixture in which a rubber-bitumen composite binder is used as a binder. Use in poured asphalt concrete crumb rubber increases the durability of the road surface, improves its frictional properties, and, in some cases, reduces the consumption of crushed stone.

Advantages and disadvantages of poured asphalt

Asphalted pavements created using cast mixtures are characterized by a small layer thickness, high density and roughness. In addition, compared to traditional compacted asphalt mixes and crushed-stone-mastic asphalt, poured asphalt has a number of other advantages, namely:

High plasticity and mobility of the cast mixture.
Low porosity and water resistance.
The best, in comparison with conventional asphalt mix, waterproofing properties.
high corrosion resistance, crack and wear resistance.
High strength pavement comparable to traditional asphalt concrete.
High elasticity of the coating and the ability to withstand large deformation stretching.
Durability (resistance to aging and accumulation of fatigue damage).
Rutting resistance and high wear resistance of studded tires.
Resistant to strong temperature changes.
No need to compact the laid mixture.
Possibility to carry out repair work at negative temperatures.

The main disadvantages of cast asphalt mixtures and cast asphalt concrete include:

Low adhesion of the asphalt pavement (due to the high content of bituminous binder), which leads to the need for additional work associated with the distribution and embedding (pressing) of black crushed stone into the laid layer of poured asphalt.
The high cost of the mixture associated with the use of expensive components.
The high cost of asphalting, associated with the need for preparatory work and the involvement of special equipment (cochers, finishers, crushed stone distributors, etc.).

Asphalt paving technology using poured asphalt

1. Transportation of poured asphalt

Transportation of the cast asphalt mix to the work site is carried out by "kochers" (special machines equipped with a system for mixing, heating and controlling the temperature of the mixture). The need to use cochers for transporting poured asphalt (I, IV and V types) is due to the fact that without forced mixing and heating, the mixture begins to delaminate and lose plasticity. Type II-III cast asphalt mixtures are resistant to delamination and can be delivered by conventional dump trucks.

2. Preparatory work

When arranging road surfaces from poured asphalt concrete important role plays careful preparation the underlying base on which the cast mixture will be laid. If the underlying layer is not sufficiently even, it is leveled by cold milling or by using an asphalt leveling layer (with a difference in grades of up to 6 cm, a fine-grained asphalt concrete mixture is used, more than 6 cm - a coarse-grained one).

After milling or leveling, the underlying coating is treated with a bituminous emulsion. Priming of the underlying layer may not be performed if no more than 10 days have passed between the installation of the lower layer (including leveling) and the laying of poured asphalt. Priming is also not required when the bottom layer is made of poured asphalt mix.

Before the poured asphalt mix is laid, a wooden or metal formwork is arranged on both sides of the asphalt strip with a height equal to the thickness of the layer being laid. If poured asphalt is being laid by a wheel-rail paver, then the formwork is not installed, since in this case the rails themselves play the role of formwork. Molded asphalt mixes of type II-III do not require the installation of formwork, since they are laid by conventional asphalt pavers using the vibrocasting method.

3. Laying poured asphalt

Coatings made of cast asphalt concrete mixtures are installed in dry weather, in spring at an ambient temperature of at least 5 °C, in autumn - at least 10 °C. It is allowed to perform asphalting and negative temperature air, but not lower than -10 °С. In this case, the poured asphalt mixture must have a temperature of at least 240 °C and the laying must be carried out in calm weather (or light wind) on a dry and clean surface. Surface drying can be done using infrared heaters.

Depending on the type of poured asphalt mix, paving can be done by wheeled, caterpillar or wheel-rail finishers (for poured asphalt types I, IV and V) or conventional pavers (for poured asphalt types II–III). Places not accessible for mechanical laying of the cast mixture are asphalted manually.

4. Compaction of poured asphalt

Molded asphalt mix I, IV and V type does not require compaction, because it has a fluid consistency and gains density in the process of cooling. The cast asphalt concrete mix of type II–III is compacted by the asphalt paver's vibrating tamper at the stage of laying and by light rollers at the stage of pressing the black crushed stone.

5. Pressing (embedding) black gravel

Since one of the main disadvantages of cast asphalt concrete pavement is the low coefficient of adhesion with tires vehicles, then to increase its roughness, an additional procedure for the distribution and pressing of crushed stone is performed immediately after the poured asphalt is laid. By the time of pressing, the black crushed stone must have a temperature of at least 100 °С, and the surface of the laid cast mixture must not cool below 140–180 °С. The distribution of the black gravel mixture can be done manually or with the help of a crushed stone distributor.

Pressing black gravel- a technological operation to give the coating of cast asphalt concrete of type I and V the required frictional characteristics by distributing and embedding hot black crushed stone into it. As a material for processing, black crushed stone of a fraction of 5 (3)–10 mm or 10–15 mm is used.

black rubble- an artificial road building material obtained by mixing crushed granite, gravel or limestone with a viscous or liquid organic binder (petroleum road bitumen, bitumen emulsion or tar).

A Brief History of Molded Asphalt

On the post-Soviet space The first attempts to use cast asphalt date back to the 19th century. Already in 1865, in St. Petersburg, cast mixtures based on natural bitumen were first used in asphalting the terraces of the Winter Palace. After 5 years (in 1870) with the help of the same cast mixture, Malaya Sadovaya Street was asphalted and a pavement was created on the embankment of the Fontanka River. Later, with the use of cast mixtures, asphalting of roads began in Kyiv, Kharkov, Odessa, Zhitomir and other cities of the Russian Empire.

The use of poured asphalt in Moscow began in 1874, when the first plant in Russia for the production of asphalt mastic was built near the city of Syzran. The process of preparing and laying cast mixtures has been significantly simplified since the production of petroleum bitumen was launched in the city of Grozny in 1914. However, precisely because of the intensive development bitumen production compacted asphalt mix has become more and more widespread as a simpler and more cheap material for paving, and interest in the use of a cast mixture is beginning to fall.

Since the beginning of the 1970s, asphalt paving with the use of poured asphalt has returned to the USSR, which was largely facilitated by the positive operating experience (ability to withstand heavy traffic, wear resistance and corrosion resistance) of cast asphalt concrete pavement on the roads of West and East Germany, Hungary and Romania.

By the end of the 1970s, the casting technology began to decline again due to a shortage of materials (heat-resistant bitumen and fine crushed stone), low construction rates, high cost of imported equipment (because no own equipment was produced yet) and other problems. These difficulties led to the fact that the USSR began to develop its own direction of injection molding technology, based on the use of the vibrocasting method and the use of more rigid cast mixtures.

In European countries, cast asphalt has been widely used since the middle of the 20th century. In the United States, cast asphalt prepared using petroleum bitumen was first used in 1876. The most widespread injection molding technology has received in Germany, where there is a large number of modern factories producing equipment for the preparation, transportation and laying of cast mixtures.

Today in the world there are many organizations whose activities are related to the development of standards, technical documentation, new formulations and compositions for poured asphalt, the largest of which are:

IMAA (International Mastic Asphalt Association) - International Mastic Asphalt Association.
EMAA (European Mastic Asphalt Association) - European Mastic Asphalt Association.

Asphalting in Kyiv using cast polymer-asphalt concrete mixtures

Asphalt paving and asphalt repair services in Kyiv using cast asphalt mixtures of the Asphalt ALIT Selenizza, Asphalt ALIT ME brands and other cast mixtures. The Unidorstroy road construction company carries out the installation of high-quality and durable asphalt road surfaces in Kyiv and the Kyiv region.

Molded asphalt concrete is one of the types of asphalt concrete, which is a road-building material obtained in the process of solidification of a cast asphalt concrete mixture.

General information

Cast asphalt mix is a mixture with minimum porosity, consisting of mineral grains of sand, crushed stone, mineral powder, and petroleum bitumen with or without polymer additives, which is used as a binder.

Molded asphalt concretes differ from traditional ones in that bitumen from 7.5% to 10% of the total volume is added to their mixture, as well as polymers modified with various additives, such as mineral powders, which can be from 20% to 30% in volume. The total volume of such a binder is 28% or more.

The paving of the asphalt mix is carried out by pouring technology, which does not use any compaction technique such as vibration. The temperature of the concrete mix during laying must be at least 190°C. Depending on the temperature and magnitude of the load, as well as on the duration of the load, cast asphalt concrete behaves like an elastic material.

Classification of cast asphalt concrete

The main method of classifying asphalt concretes is to classify them according to the size of the largest particle of mineral material. Asphalt concrete can also be classified by the purpose of its application, as well as by the laying method.

Classification of asphalt concrete by largest size grains of the mineral part:

20 mm- this type of concrete contains from 30% to 50% of fractions larger than 5 mm, the recommended layer thickness of such concrete is from 40 to 50 mm, such asphalt concrete is used for new construction, as well as for major and patching roads;
15 mm- this type of concrete contains from 15% to 30% of fractions larger than 5 mm, the recommended layer thickness of such concrete is from 30 to 45 mm, such asphalt concrete is used for new construction, for major and patching roads, as well as for the construction of sidewalks ;
10 mm- this type of concrete contains from 0% to 15% of fractions larger than 5 mm, the recommended layer thickness of such concrete is from 20 to 35 mm, such asphalt concrete is used for the construction of sidewalks and bicycle paths.

Properties of poured asphalt concrete

Advantages of cast asphalt concrete

Molded asphalt concrete is a low-combustible substance that does not spread flames. It also has a low coefficient of thermal conductivity, in comparison with ordinary concrete, asphalt concrete has this coefficient 2 times less.

Also, asphalt concrete is a soundproofing and vapor barrier material; with a layer of such concrete of 35 mm, noise reduction is observed up to 14 dB.

In addition to cast asphalt concrete, there are also traditional compacted asphalt concrete. But poured asphalt concrete has some advantages that give it an advantage over traditional ones, such as water resistance and durability. In addition, the values of both parameters can be increased by several times by adding road bitumen modified with thermoplastic elastomers to the composition of the cast asphalt concrete mixture.

Disadvantages of poured asphalt concrete

The disadvantages of cast asphalt concrete include:

high cost of the mixture;
special equipment is needed in order to deliver and lay asphalt concrete;
low resistance to plastic rutting, especially when the composition of the concrete mix was poorly selected or violated in the laboratory technological processes production;
low crack resistance winter period, this is especially noticeable when unmodified bitumen is used in the composition of cast asphalt concrete, which often has an increased temperature fragility according to Fraas.

water resistance - which is several times higher than that of traditional compacted asphalt concrete;
high degree of adhesion of the surfaces of the layers, especially to the underlying layers - given property improves at high temperature of laying of asphalt concrete mix;
increased durability or as it is also called fatigue crack resistance - this property allows you to resist different kind loads in a fairly wide range of frequencies and vibration amplitudes throughout the entire life cycle of the asphalt concrete surface;
low susceptibility to vibrations, as well as the ability to dampen them;
resistance to corrosion;
antibacterial resistance and environmental friendliness.

Transportation of cast asphalt occurs with the help of a special device - Kocher. Kocher is a kind of tank or reservoir capable of maintaining the desired state of the mixture and its constant mixing. The mixture is then spread evenly in the required place with the help of a road paver. The road is able to take the load after 12 hours.

Although the technology of production and laying of asphalt concrete itself reduces the number of workers involved, the use of a large amount of bitumen and mineral powder still leads to an increase in the cost of the mixture. In addition, the use of special equipment during laying significantly increases the cost of poured asphalt. Therefore, while in Russia, the use of cast asphalt is not very common.

26. Cemento concrete pavement most often reinforced by laying one or more layers of asphalt concrete. However, to reduce the likelihood of cracking, it may consist of several layers with a total thickness of 9-18 cm or be a single layer. Before laying the asphalt concrete mixture, the seams in the cement concrete pavement are cleaned, filled with bitumen and cement mortar, sprinkled with sand, and to prevent adhesion of the layers, the seams are covered with polyethylene film, paper impregnated with bitumen to a width of 0.5-0.8 m on each side of the seam.

Rice. 24. Scheme of widening of the cement concrete pavement:

1 - new concrete coating widening; 2 - old concrete pavement; 3 - fittings. All dimensions are in meters

Another option for reinforcing cement concrete pavements to reduce cracking is to lay a 4-8 cm thick layer of asphalt concrete over pre-laid polypropylene film or nonwovens.

Abroad, they increase strength and eliminate surface defects by laying reinforced or unreinforced concrete (or fiber-reinforced concrete) different thickness. layer reinforce metal mesh with cells 10 × 30 cm in size and 7-8 cm thick. Reinforced concrete coatings have the advantage that they can be of small thickness.

When widening the pavement with cement concrete pavement (similar to the pavement on the Moscow Ring Road), it is advisable to cover the existing and widened carriageways with a layer of reinforcement from continuously reinforced concrete of a minimum thickness (about 10 cm). With high-quality performance of work, the service life of continuously reinforced coatings exceeds 45 years with negligible repair and maintenance costs. Such designs are most effective in heavy traffic, the bulk of which are heavy trucks. It is most expedient to use these structures on the approaches and bypasses of large cities and on roads of higher categories.

If the materials of the old coating and the reinforcement layer have different moduli of elasticity, first determine by calculating the tensile strength in bending the equivalent thickness of the plate from materials of different modulus, reduced to the thickness of the material with the highest modulus of elasticity, and then determine the required thickness of the reinforcement

h eq - thickness of a homogeneous plate, cm;

E st.p - - the modulus of elasticity of the material of the old coating, equivalent in bending stiffness to the old coating and the reinforcement layer, MPa;

hst.p - thickness of the old coating, cm;

E granite slab price us - the modulus of elasticity of the material used for reinforcement, MPa;

h Graphical operator panel with touch control sp270: operator panel sp270. mc - reinforcement thickness, cm.

To reinforce pavements with cement concrete pavement, it is recommended to use polymer asphalt concrete - it has increased strength, elasticity and heat resistance in a wide range of operating temperatures. The use of polymer asphalt concrete increases the crack resistance of the reinforcement layer above the transverse seams of the old cement concrete pavement.

For the preparation of polymer-asphalt-concrete mixtures, polymer-bitumen binders (PBV) based on divinylstyrene thermoplastic elastomer (DST) of the appropriate grades are used. Depending on the viscosity, PBBs are divided into the following grades: PBB 40/60, PBB 60/90, PBB 90/130, PBB 130/200, PBB 200/300.

Polymer-asphalt-concrete mixtures and their grain composition must meet the requirements of GOST 9128-84 for asphalt concrete mixtures of the corresponding grades.

Control tests of the quality of polymer asphalt concrete in the coating are carried out by water saturation, swelling, porosity of the mineral core and residual porosity, as well as by the compaction coefficient.

Reinforcement layers must ensure the strength and evenness of the pavement for a given service life under the influence of automotive loads and climatic factors.

27. The thickness of the reinforcement layer of continuously reinforced concrete is determined by calculation. When reinforcing pavement with cement concrete pavement, the thickness of the reinforcement layer of continuously reinforced concrete can be 10-12 cm. The reinforcement layer of continuously reinforced concrete is laid directly on the old cement concrete pavement without insulating and leveling layers (Fig. 25).

Rice. 25. Schematic diagrams of pavements with continuously reinforced pavements:

1 - new concrete coating; 2 - old continuously reinforced concrete pavement; 3 - sand-cement mixture; 4 - sand; 5 - black crushed stone; 6 - lean concrete; 7- heat insulator (styrofoam, polystyrene, etc.)

For reinforcing coatings, reinforcement of a periodic profile should be used. The diameter of the reinforcement is selected taking into account the minimum crack opening and the accepted construction technology. Reinforcement of coatings can be carried out with flat welded or knitted meshes, welded frames, individual reinforcing bars. Continuous reinforcement is placed at a distance of 1/3-1/2 h us (h us is the thickness of the reinforcement layer) from the surface of the reinforcement layer. Reinforcing cages are placed symmetrically about the neutral axis of the reinforcement layer.

Transverse seams (compression and expansion) on the reinforcement layer are not satisfactory. Longitudinal seams, depending on the amount of transverse reinforcement, are arranged after 3.75 m as false or after 7.5 m as tongue and groove (Fig. 26).

Rice. 26. Designs of longitudinal seams:

a - a seam of the type of false; b - seam according to the type of tongue; one - concrete slab coatings; 2 - reinforcing mesh; 3 - bituminous mastic

The length of the overlap must be at least: in the longitudinal direction - 30-35 d; in the transverse direction 25 d (where d is the diameter of the rods), and in all cases not less than 250 mm. The transverse joints of adjacent meshes should be spaced apart with a step of at least 50 cm. The following types of reinforcing steels are used to reinforce the reinforcement layer: rod hot-rolled periodic profile of class A-II with a diameter of 10 to 20 mm, class A-III with a diameter of 6 to 20 mm; rod, reinforced with a drawing of a periodic profile of class A-II in diameter from 10 to 20 mm, class A-III in diameter from 6 to 20 mm.

The calculation of the strength of the reinforcement layer of continuously reinforced concrete is carried out in accordance with the current regulatory documents.

Reinforcing cages of the reinforcement layer have reinforcement outlets from anchors (trench or pile types), subsequently mated with a continuously reinforced coating.

28. see questions 26,27 Strengthening pavements with cement concrete pavements can be performed in the following ways:

installation of reinforcement layers from asphalt concrete mixtures over the old cement concrete pavement without disturbing its continuity;

the same, with preliminary crushing of the old cement concrete pavement into small blocks and careful compaction of the base material thus obtained;

installation of a reinforcement layer of continuously reinforced concrete over the old cement concrete pavement.

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