Let's consider an article about the production of asphalt (asphalt concrete), equipment for it (factories and mini-factories) and manufacturing technology.
Let us immediately note that asphalt and asphalt concrete are different things. Asphalt is the Greek name for bitumen, a black rock tar that forms in shale and coal rocks. Asphalt concrete is any mixture of bitumen with crushed stone, gravel and/or sand, as well as various materials(more about them below).
Since asphalt concrete is most often referred to simply as asphalt in everyday life, in this article we will most often use the latter option as the name.
Production technology
GOST standards
GOST standards for bitumen and asphalt concrete mixtures are different. For the latter, this is GOST 9128, and for bitumen they differ based on the purpose of use:
- Petroleum construction bitumens – GOST 6617;
- Petroleum roofing bitumens – GOST 9548;
- Viscous petroleum road bitumens - GOST 22245.
Compound
Asphalt is used to construct road surfaces. It is a mixture that includes sand, fine and medium fractions of crushed stone, mineral powder and bitumen, which acts as a connecting link between the other components of the material.
85% of the asphalt material is gravel or crushed stone, 6% of the total volume is bitumen. The production of asphalt involves combining and mixing all the necessary components and immediately laying the road surface with this material.
The binding function of bitumen is carried out only in a hot state. If the asphalt was prepared but not laid immediately, then it is not suitable for further use, because it has lost its properties. As a result of this, asphalt cannot be compacted to the required state, as it becomes quite brittle.
Kinds
There are three types of artificial asphalt used for road surface construction. Moreover, each type of asphalt has its own purpose.
- Coarse grain. This asphalt is used in the process of arranging the lower layers of the road surface. To prepare this type of mixture, fine-fraction crushed stone (from 5 to 15 mm) and coarse-fraction crushed stone (from 20 to 40 mm) are used.
- Fine grain. This asphalt concrete is used during the laying of road surfaces of the carriageway. This asphalt is used as the top layer in the case of a two-layer coating. The composition of the mixture includes crushed stone of a fine fraction (from 5 to 15 mm).
- Sandy. This type of asphalt is used for paving sidewalks and walkways. The composition of the mixture includes mainly sand and a small amount of mineral powder, bitumen and crushed stone having a fine fraction (5mm).
Manufacturing technology
According to the method of production technology, three types of asphalt are distinguished:
- hot;
- warm;
- cold.
The difference between these methods lies in the level of temperature at which the mixed components are brought together. Heated or hot mix asphalt is produced by adding heated components to a warm or hot binder. In cold asphalt, only one of the heated components is used.
The technology for producing hot asphalt is as follows: 1) inert materials are dried or heated to 200°C; 2) at a temperature of 160°C, the components are mixed with the addition of bitumen and mineral powder; 3) storage of the finished asphalt mixture at a temperature of 150-180°C.
Necessary equipment
Asphalt concrete plants are used as equipment for the production of asphalt. They are mobile and stationary.
There are also ultramobile (sumermobile) asphalt concrete mini-plants, but they are called that not so much for their compactness, but rather for their even greater ease of transportation.
Typically, stationary asphalt plants (from about 80 tons per hour) are, of course, more productive than mobile ones (from about 3-80 tons per hour). However, their prices are completely different. You can buy a stationary asphalt concrete plant from 7,000,000 rubles. The lowest-productivity mobile mini-plant of 3-5 tons per hour will cost approximately 1,200,000 rubles.
Mobile plant of the Chinese manufacturer TIETUO, price from 1,200,000 rubles. 
Stationary, price from 7 million rubles.
An important point in the asphalt production business is the need to have front loader necessary for loading the necessary raw materials into the bunker of the plant. The cost of this loader starts from 2,000,000 rubles. That's why the best option in this case, there will be a rental of this type of special equipment. However, this will also increase the cost.
Mobile factory video:
How much money is needed
To start the production of an asphalt concrete mixture with a minimum capacity of 10 tons per hour, the following costs should be taken into account.
Capital investments:
- purchase of an asphalt concrete plant – 2,000,000 rubles;
- transportation costs – 100,000 rubles;
- purchase of raw materials – 500,000 rubles;
- other expenses – 200,000 rubles.
The amount of these investments is 2,800,000 rubles.
Estimated revenue and profit data:
- asphalt concrete production – 50 tons per shift;
- number of shifts – 30 per month;
- output – 1500 tons per month;
- wholesale price – 2300 rubles per 1 ton of asphalt;
- revenue – 3,450,000 rubles.
Main consumers
The main consumers of asphalt products are:
- organizations that are responsible for the condition of federal and municipal roads;
- companies that specialize in repairing these roads;
- business representatives responsible for the condition of parking lots, sidewalks and access roads located on the territory of these roads.
As you know, the production of asphalt is directly related to its laying. Therefore, the acquisition required kit equipment designed for asphalting roads allows for business expansion. At the same time, it becomes possible to sell asphalt products to contractors who lay them, as well as independently carry out the entire complex of road robots.
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Asphalt concrete mixtures |
Price with shipping(rub/t) |
Price without delivery(rub/t) |
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Sand type L4 |
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Sand type PDII, sand at PG screenings |
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Sand type PD3, PDo3 |
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Fine-grained type A, grade 1, MA1 |
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Fine-grained type B, grade 1, MB1 |
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Fine-grained type B, grade 2, MB2 |
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Coarse-grained dense KB1 |
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Coarse-grained porous KP1 |
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ShchMA 15, 20 on PBB |
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Shchma 15, 20 on binder BITREK |
The DorTransSnab company produces and sells high-quality asphalt at a low price and other bulk construction materials. Our company has its own fleet of road construction equipment and its own asphalt production, so we carry out all work quickly and efficiently.
From us you can buy asphalt either with delivery or through pick-up, the cost of which will allow you to save significantly during construction.
The asphalt concrete mixture is an optimally selected composition containing mineral materials, mineral powder and bitumen. Asphalt concrete is a compacted asphalt concrete mixture. The classification of such materials is carried out according to various parameters.
Depending on what mineral component is included in the material, sand, gravel and crushed stone mixtures are distinguished.
Depending on the viscosity of the bitumen included in the composition and the required temperature for laying asphalt, the mixtures can be hot or cold. Hot ones contain liquid and viscous bitumen, they are laid at a temperature of more than 120 degrees, and cold ones contain only liquid bitumen, the laying temperature must be at least 5 degrees.
Also, this kind of materials can be distinguished by grain size: sandy (less than 0.5 cm), fine-grained (less than 2 cm), coarse-grained (up to 4 cm). Cold mixtures are sandy and fine-grained.
Another important characteristic of such materials is residual porosity. According to this parameter, highly porous, porous, dense and high-density types are distinguished.
The letter designation used A (maximum content), B, C (minimum) corresponds to the content of crushed stone or gravel in hot mixes and dense asphalt concrete. For cold mixtures of this type, the designations Bx and Bx are used. For hot and cold sand mixtures - G and Gx (up to 30% sand), D and Dx (up to 70%).
Also, asphalt concrete mixtures are marked depending on their physical and mechanical properties and the materials used (MI, MII, MIII).
The use of the material is determined by its type and brand. Thus, a coarse-grained porous mixture of grade I is used to form the lower layers of pavement for highways, city streets, etc. Sandy highly porous mixture of grade I - for constructing sidewalks, laying curbs, etc.
What is asphalt concrete?
Asphalt concrete is a modified concrete that is formed after mixing and heating sand, crushed stone, mineral fillers, and bitumen binder.
Today, no road construction can be completed without the use of asphalt concrete mixtures. Excellent hygienic qualities, strength, durability, ease of rolling, and relatively low cost make this product the most popular in construction markets. The variety of requirements for asphalt pavement has led to the development of various laying methods and the qualitative and quantitative composition of mixtures.
Based on temperature, asphalt concrete mixtures are divided into hot and cold. Based on the size of mineral grains, they are divided into coarse-grained, fine-grained and sandy. Based on residual porosity, asphalt concrete can be high-density, dense, porous, or highly porous.
In many cases, we add various substances to the basic composition of asphalt concrete that provide frost resistance, sound insulation, surface roughness, increased strength and hardness. For this we use different materials: rubber, latex, rubber, sulfur, ash.
We produce high-quality asphalt concrete mixtures (asphalt) for the construction and repair of road (asphalt) surfaces on the streets of Moscow and the Moscow region. Each type of asphalt mixture has its own specifics. Some materials contain large fractions, others contain small fractions. In asphalt mixtures we use various bitumen and binder components, and mineral powders. In addition, production is carried out using various technologies.
Each asphalt mixture has its own characteristics. We provide our customers with a full range of services for selecting a suitable asphalt mixture for road construction or repair.
According to the compaction method, asphalt concrete is divided into: rolled, compacted, vibrated and cast. Cast asphalt is characterized by plasticity, wear resistance, water resistance, corrosion resistance and other high performance characteristics. They use cast asphalt heated to 160-180 degrees, as a result of which the material takes on a consistency that makes it easier to lay on the surface and does not require additional compaction.
Depending on the degree of saturation of asphalt concrete with structure-forming components, basal, pore and contact structures are formed in it, which determine the quality of the coating.
Asphalt production
Our plant is equipped with high-precision equipment manufactured by Teltomat T-160. The plant takes into account all development trends in the production of asphalt and asphalt concrete mixtures. Teltomat T-160 asphalt plants fully comply with the requirements. Compared to similar asphalt plants, Teltomat T-160 plants reduce energy consumption and meet environmental standards. The combined filter purifies exhaust gases by 99.98%. The asphalt plant laboratory controls the quality of the asphalt produced.
Asphalt (from the Greek α'σφαλτος - mountain tar) is a mixture of bitumen (60...75% in natural and 13...60% in artificial) with minerals: limestone, sandstone, etc. Can be used together with sand, gravel, crushed stone for installation of road and other surfaces.
Asphalt can be of both natural and artificial origin. Natural asphalt is formed from heavy fractions of oil or their residues as a result of the evaporation of its light components and oxidation under the influence of hypergenesis. Artificial asphalt (asphalt concrete mixture, ABS) is construction material, obtained after compacting a mixture of crushed stone, sand, mineral powder and bitumen.
Historically, roads were paved with stone, but since the middle of the 19th century. In France, Switzerland, the United States and a number of other countries, bitumen-mineral mixtures are beginning to be used for road surfaces. As operating experience has shown, asphalt turned out to be the most suitable material for constructing road surfaces. Its main advantages are high speed construction, lower cost and excellent evenness of the resulting coatings. Today, asphalt concrete pavements remain the most common in the construction of roads, bridges, tunnels and other structures.
Asphalt concrete mixtures are made from components in a given proportion and degree of homogeneity in asphalt mixing plants (ASU). To obtain a high-quality mixture, it is necessary to choose the right ingredients, their physical properties and the intensity of their mixing, accurately determine the proportion. If all requirements are met, a homogeneous ABS with properties that meet GOST is obtained.
There are different operating principles of automated control systems. Currently, the best known are cyclic (batch) mixing systems and continuous (drum) ones. Cyclic technology is more widely used in Europe, while continuous automated control systems are more popular in the USA, Australia, Canada and Latin America. This division occurred due to the different lengths of roads in Europe and America. According to statistics, in 2006 the volume of production of asphalt concrete mixtures in the USA exceeded 500 million tons, while in Germany about 56 million tons were produced, in all of Europe - about 350 million tons. The gap in the level between European countries and the USA. At the dawn of the era of asphalt pavements, cyclic plants were also used in the States, but during the period of the road boom and a sharp increase in the demand for asphalt, the question arose of reducing the cost of its production and increasing the productivity of automated control systems. The solution was the introduction of continuous technology for the production of mixtures, which made it possible to significantly reduce production costs and increase the volume of mixture production from one installation.
Let's look at the principles on which these technologies are built and their advantages.
The main component of a classic cyclic asphalt concrete plant (ACBP) is an inert supply system that pre-doses cold inert materials, such as crushed stone and sand, which are fed via an inclined conveyor into a drying drum, where they are heated to a given temperature by gas flows. The heated inerts are fed to the hot inerts elevator and then to a vibrating screen, which disperses the material flow into different fractions according to the number and size of the sieve cells. In the asphalt plants of some manufacturers, for example LINTEC GmbH & Co. KG, they use drum screens rather than vibrating screens, which reduces the cost of installation. Such screens were once used in domestic asphalt plants, but modern automated control systems are equipped with vibrating screens, as they provide more accurate separation of fractions. In drum screens, it is possible to redistribute small fractions into larger ones at maximum loads and with increased flakiness of crushed stone, which can get stuck in the sieves and block the passage of small fractions, which is confirmed by the experience of operating automated control systems of this type in Russia. Beneath the screen there are hot inert bunkers, each containing its own fraction. According to the composition of the mixture specified in the control program, the required amount of material is dosed in turn from each bunker with a separate fraction into the weigh hopper. A weigh hopper for bitumen and a hopper for mineral powder and dust are installed separately. Bitumen is dosed from a bitumen storage facility, and mineral powder and dust are dosed from appropriate silos. Dosing is carried out using dynamic weighing of all components of the mixture. The dosed components are fed into the mixing chamber, where they are mixed. The average duration of the total dosing and mixing cycle is 45 s, i.e. 80 cycles per hour. This is how the rated performance of cyclic asphalt plants is determined - the useful volume of the mixing chamber is multiplied by 80 cycles. For example, with a mixer of 2 t x 80 cycles we get 160 t/h.
An asphalt plant with a horizontal skip is essentially a trolley moving along guide rail supports, which delivers the mixture from the mixer to the desired mixture storage bin and is driven by a winch mechanism with a drive. The asphalt storage is divided into different compartments - bunkers, where mixtures with different recipes can be stored. The hot exhaust gases from the drying drum are purified in a bag filter, where dust is deposited using fabric bags (sleeves). The settled dust is usually either removed from the asphalt plant or fed into a dust silo, from which it is dosed into the mineral powder hopper in the required proportion with the mineral powder. Bitumen is stored in tanks, which can be horizontal, vertical or mobile. The process of dosing, mixing and loading the mixture into dump trucks is controlled by operators from the control center. Most modern asphalt plants have a microprocessor control system installed, which makes work easier, but at the same time, there are often no manual controls, and this does not allow work to continue in the event of a computer system failure.
Many continuous type asphalt asphalt units are similar to cyclic type asphalt asphalt units. Also, dosing of cold inerts is carried out from cold dispensers, the difference of which is that they act as dispensers, and not preliminary dispensers, as in cyclic asphalt dispensers. In cyclic asphalt plants, the dosing of components comes from hot inert hoppers into the weigh hopper, and from the pre-dosers there is only a preliminary supply of material. The dosing error of pre-dosers can reach 10% or more, which is not significant for this type of asphalt plant, since there is weight control. At the same time, in continuous asphalt plants, cold dosers are precisely the dosing device and provide high dosing accuracy with an error of ±0.1%. This is achieved through modern microprocessor control, frequency controlled drives, tachometers on the drive shafts with feedback and a weigh bridge installed in the inclined conveyor. Cold inerts are accurately dosed from hoppers and fed onto an inclined conveyor equipped with an oversized screen that screens out oversized crushed stone. The flow of material after the screen enters the weighing bridge, which dynamically weighs the total volume of inert materials and adjusts the operation of the dispensers through the system feedback with control program. The suspended material enters the drying and mixing drum, where, as in a cyclic asphalt plant, it is dried by a flow of heated gas from the burner flame. After drying, the heated material is mixed in the same unit with mineral powder, own dust, bitumen and other components. The resulting mixture is discharged from the drying and mixing drum. Traditionally, round silos with a scraper conveyor are used to store the mixture. Systems of this type can provide storage of 9 pcs. x 300 t = 2700 t or more.
The continuous asphalt plant also includes bitumen storage, mineral powder and own dust silos. There is a bag filter with the same fabric bags and a dust evacuation system either into a silo, or back into a drum, or into a dump truck for removal.
The development of continuous-type asphalt mixing plants can be divided into three stages - these are direct-flow type drum mixers, when the flow of material and hot gas went in one direction, which was not as efficient as in the second generation - counter-flow drums. The third stage in the development of continuous asphalt plants was the development of drum-mixing units with a built-in burner and a Double Barrel drum (“double drum”) by Astec Inc.
In direct-flow drums, the flow of hot gas runs parallel to the inert materials. With such heating, gas can pass through holes in the curtain of material and not transfer heat to the inerts. The temperature of the exhaust gases is high, which leads to premature wear of the fabric filters. The material enters the combustion zone of the flame, due to which the fuel does not burn completely and moist inert materials are sintered. Mineral powder and bitumen are carried away by the gas flow into the bag filter, and as a result the filters become dirty. Characteristic low quality stirring the mixture.
In counterflow drums, material is fed from the opposite side of the drum and moves towards the hot gas. The problem of caking and entrainment of inerts and bitumen has been eliminated. Mixing times have been increased and the quality of the mixtures has improved. It is also possible to add up to 50% reclaimed asphalt pavement (RAP) with low hydrocarbon emissions since the RAP is fed after the burner flame. Operational efficiency has increased - fuel consumption has decreased and productivity has increased. A modification of this type is a two-drum system, when one drum dries the material in countercurrent, and the heated inerts are fed into the second drum, intended only for mixing. Such asphalt plants also provide more time mixing and best quality mixtures.
Counterflow drying and mixing drums are still the most common type of units for drying and mixing in continuous asphalt plants. Mixing in these asphalt plants occurs under the influence of gravity - the drum, rotating, lifts the mixture with blades, which falls at a certain moment. When falling, mixing occurs. This type of mixing is often called gravitational.
Fundamentally new system drying and mixing was developed and patented by the brilliant engineer Don Brock. D. Brock created his own company, Astec Inc. and began production of asphalt plants with the patented Double Barrel system. In a short period of time, Astec Inc. has grown to the level of an absolute leader among asphalt producers. The genius of the Double Barrel design is that it was possible to combine the advantages of continuous and cyclic technology - low cost of producing the mixture and high-quality forced mixing, as in a cyclic asphalt plant.
The mixture is fed into the Double Barrel drum and heated in countercurrent. At the end of the drying drum, the heated mixture is discharged through the windows into the mixing drum, dressed on top of the drying drum. Mixing blades are welded onto the rotating drying drum, which mix the ingredients that are static, as in a cyclic asphalt plant. The mixing time is 90 s and is designed to produce SMA without reducing productivity and with the possibility of adding RAP up to 50%. The main advantages of Double Barrel are the lowest fuel consumption in the industry, high-quality mixed, homogeneous mixtures, ease of operation and low costs, high productivity in the production of mixtures of all types.
Now let’s look at the fundamental differences between cyclic and continuous asphalt protection and the advisability of their use in certain conditions.
The main difference between these technologies is the dosing and mixing system. In a continuous asphalt plant there is no tower and dosing immediately comes from cold dispensers, the mixture flows in a continuous stream. In a cyclic asphalt plant, the material is screened into fractions and components are dosed by weight, portions, and the mixture is produced in portions.
Cyclic ABZ make it easier and faster to change the mixture recipe; in theory, each batch can have a different recipe. Such asphalt plants are most in demand in the production of asphalt in cities and metropolitan areas, when asphalt is produced for several paving complexes. At the same time, cyclic asphalt stations are less mobile due to the tower. The tower is large in size, and to reduce it the size of the hot inert bunkers is reduced. As a result, the mobile cyclic asphalt plant operates in screening mode - hot inert bunkers are often either overfilled with one fraction or empty, which leads to either a violation of the recipe or downtime and the discharge of excess heated fractions, mainly larger ones. The owner of the asphalt plant loses the volume of asphalt production and money for the useless heating of dumped crushed stone. When producing SMA, productivity can drop by 40% of the nameplate due to the addition of a dry mixing cycle and an increase in cycle time.
The advantage of continuous asphalt plants is their simplicity of design. They are easier to transport, erect in a new location and maintain. Such an asphalt plant can be put into operation within 3 days and produce asphalt. The cost is lower than that of a cyclic one of the same productivity, and the actual output of asphalt per shift is higher. A special feature is that in the realities of Russia, the fractional composition of purchased crushed stone in quarries may not comply with GOST, and since this type of asphalt plant does not have a screen that separates the inert material into fractions, sometimes violations occur in the mixture recipe and the composition of the inert may change. A simple solution to this problem is to install a separate screen for the preliminary preparation of inert materials, fortunately, it is offered on the market great amount both stationary and mobile solutions. Installing a screen allows you to control the composition of inerts before they are heated, and not after money has already been spent on heating. Moreover, even with the additional equipment of a screen, the continuous asphalt plant is competitive in price. When working in cities and the need to produce asphalt concrete mixtures of different recipes during one shift, asphalt concrete mixtures are equipped with silos long-term storage allowing the mixture to be stored for up to 4 days. For example, one of the asphalt manufacturers in the USA, which has 6 silos complete with an asphalt plant, changed the recipe 50 times per shift. This is done simply - a new recipe is set and after 40...60 s the mixture is fed into another silo, where the new mixture is accumulated. If you have operating experience, the transition is simple and quick. The accuracy of dosing of inert, mineral filler, bitumen and other ingredients meets the standard, which is confirmed by operating experience around the world and in Russia as well. The quality of the resulting mixtures, including ShchMA, is at a high level.
Each technology has its own characteristics and advantages. When choosing an asphalt plant, once again weigh the pros and cons based on how you plan to work. Realities modern Russia once again confirmed that if you have a mobile asphalt plant, you have the opportunity to quickly respond to the situation and participate in contracts not only in your region.
IN Lately The state of the road network in the regions of Russia began to attract the attention of the authorities. In 2013, large-scale government projects were launched, the goal of which is- construction of highways and restoration of existing highways, asphalting of routes and landscaping of adjacent areas. Create new ones transport arteries planned according to European standards, and Special attention will focus on the quality of the asphalt mixture. The production of asphalt concrete, which has become a profitable field of activity, began to attract more and more business representatives working in the field of road construction. How does the complex process of making asphalt take place?
Components of asphalt mixture
Naturally occurring asphalt It is formed from heavy residues of evaporated oil and is a black, refractory substance. Artificially created asphalt is a mixture of solid and loose mineral filler (crushed stone, gravel, sand, sandstone, limestone) and viscous binding elements (various bitumen, tar). To be used as a road surface, it is compacted using a special roller, turning it into asphalt concrete - a durable stone material that can withstand heavy loads. Mineral components, the particles of which vary greatly in size (gravel, sand), are required to fill all holes and cavities, and limestone and sandstone are used to improve enveloping properties. Some European manufacturers add to asphalt for greater strength. different kinds rubber, and also offer customers coatings in different colors, which are used for decorative purposes.
Types of asphalt
Maintaining the required proportions of asphalt mixture ingredients is one of the most important tasks in the production of the material. Too high a percentage of viscous or hard components will cause the new coating to crack under the influence of water, loads and temperature changes. Depending on the conditions under which the roadway will be used, the “recipe” of asphalt concrete may undergo significant changes. The easiest type of asphalt to produce is called sand. and is made from sand and bitumen. Adding crushed stone and mineral powder to this mixture will give the so-called crushed stone asphalt. The most complex asphalt in composition is gravel., it is made from bitumen, crushed stone, gravel and various mineral elements.
Depending on the temperature at which the bitumen that is part of the asphalt mixture melts, several types of asphalt are distinguished according to the laying temperature:
- hot(contains viscous bitumen, installation requires a temperature of at least 120 °C, the main area of application is road construction of new routes);
- warm(contains low-viscosity bitumen, compacts at a temperature of about 40-80 ° C);
- cold(containing special liquid bitumen, requiring an ambient temperature of at least 10 °C, the most common use is road repair, filling holes and potholes in an existing road surface).
Asphalt plants
Depending on the production mechanism, asphalt production plants are divided into cyclic and continuous.
Cyclic asphalt plants are located near large cities, where small batches of various types of asphalt are required every now and then. The technology for producing asphalt concrete at a cyclic plant implies the ability to change the type of material produced dozens of times per shift without sacrificing its quality. The cycle plant has the usual set of devices for receiving solid elements, areas for storing finished asphalt concrete and asphalt mixing plants. The specific additional equipment includes a tower and a screening-crushing-sorting vibrating sieve, which is used for screening stone materials. The use of a screen provides high quality produced asphalt, since all bulk materials are completely separated into fractions before entering the mixture. The disadvantages of a cyclic plant include the relatively small amount of product produced, as well as the stationary nature of the plant itself, due to the presence of a screen and a tower.
Continuous Asphalt Batching Plants equipped only with the most necessary equipment, which makes them convenient for transportation from place to place. The process of producing asphalt mixtures in continuous plants goes on without stopping - the ingredients are constantly fed into the heating bunker, from where the finished asphalt is moved to silos that can keep the material hot for 4 days. The disadvantage of continuous plants is the absence of a screening apparatus. Often, solid mineral elements purchased for the production of asphalt concrete do not meet standards and contain foreign inclusions, which, without the screening procedure, fall directly into the finished asphalt, deteriorating its properties.
Stages of asphalt production
The asphalt concrete production process can be divided into four stages:
- checking the quality of the ingredients of the future mixture- crushed stone, gravel, mineral elements, bitumen, etc. This stage is especially important for obtaining high-quality and wear-resistant asphalt that does not contain foreign inclusions;
- hard materials processing, ideally including passing sand through a sieve and crushing crushed stone into fractions using a crushing apparatus;
- receipt of materials into the heating hopper. Under the influence of high temperatures, moisture is removed from sand and crushed stone, which can significantly deteriorate the strength of the material. At the same time, the bitumen is heated to 160 °C);
- combination of ingredients in one container, equipped with spatulas for mixing. High-quality mixing is necessary to destroy air voids in newly created asphalt concrete - at the stage of laying asphalt, it is no longer possible to get rid of air bubbles that make the road surface vulnerable to the influence of water;
- loading hot mixture into storage container (silo), where it is maintained for several days heat. Asphalt used for highway construction or repair must be hot - this is the technology of road construction.
Sequence of mixture preparation. Preparation of asphalt concrete mixture consists of the following operations: preparation of mineral materials, preparation of bitumen, dosing of components, mixing of mineral materials with bitumen and unloading of the finished mixture into the bodies of dump trucks or storage bins.
The preparation of mineral materials includes their supply to drying units, and, if necessary, sorting into fractions or enrichment with additives of other material and activation. This includes drying the material and heating it to the required temperature. Crushed stone, gravel and sand must be completely dried and have a temperature 5 - 10 o C higher than bitumen before entering the mixer. Their temperature drops by 5 - 7 o C when moving by a hot elevator from the drying drum to the dispensers. Therefore, the temperature of mineral materials should be 180 - 200 o C for hot asphalt concrete. Mineral powder is usually served without heating.
The productivity of asphalt concrete plants largely depends on the operation of drying units. The drying unit includes a drying drum with a firebox and nozzles, as well as a fuel supply tank. Drying and heating of the material is carried out continuously by hot gases from fuel combustion, moving towards the direction of movement of crushed stone and sand. The drying speed of the material, and therefore the performance of the drying drum, depends on the moisture content of the sand and crushed stone.
Before entering the drying unit, crushed stone and sand are dosed using feed units; their final dosing is carried out by the mass of individual fractions before being fed into the mixer. The dosing accuracy for crushed stone, sand and mineral powder must be at least ±3%, and for bitumen ±1.5%. In continuous asphalt mixing plants, the constituent materials are dosed by continuous volumetric dosers. After drying and heating, all materials are fed into the mixing unit, which has a screen, a multi-fraction dispenser for crushed stone, sand, mineral powder and binder, as well as a mixer and other mechanisms and bunkers.
The materials are weighed on a totalizing weighing device and loaded into a twin-shaft paddle mixer, into which bitumen is fed from a dosing device. Bitumen is supplied by spraying under pressure up to 2 MPa. In this case, there is a uniform distribution and enveloping of the surface of the mineral particles with a film of bitumen; moreover, this supply reduces the duration of mixing.
The duration of mixing of a mixture weighing about 700 kg is 20.30 s for coarse-grained mixtures, 45.60 s for medium- and fine-grained mixtures and 60.75 s for sandy mixtures. Mixing time is reduced by 15.20% when using surfactants or activated mineral powders. With a low bitumen content or a high content of mineral powder, the mixing time increases. The mixture should be well mixed and homogeneous in mass. The quality of the finished mixture is also influenced by the order in which the components are mixed. Using traditional technology, all components are mixed simultaneously.
The temperature of the finished asphalt concrete mixture used in a hot state should be within 140-170°C, and when using surfactants - 120-140°C. The mass of one batch is 600.700 kg. It takes up to 15 minutes to load a heavy-duty dump truck. Therefore, in order to reduce vehicle downtime during loading, storage bins are installed near the mixers, into which the mixture flows directly from the mixers, and from there it is unloaded into the body of a dump truck. It takes 2.3 minutes to load the machine.
The asphalt concrete mixture is delivered to the highway by dump trucks, the bodies of which must be thoroughly cleaned and lubricated with a thin layer of oil, oil or soap solution before loading the mixture. In the spring and autumn, car bodies are covered with special shields or mats to prevent the mixture from cooling. For each vehicle shipped with an asphalt concrete mixture, an accompanying passport is issued, which indicates the weight, temperature of the mixture and time of dispatch from the plant.
The asphalt concrete mixture is laid into the pavement using asphalt pavers in dry and warm weather. According to the current instructions, hot mix asphalt concrete must be laid in the spring at an air temperature not lower than - f5°C, and in the fall - not lower
10°C, and the surface of the underlying base layer or coating must be clean and dry. Otherwise, the required adhesion between the layers will not be provided.
To ensure proper adhesion between structural layers, the underlying surface is treated with bitumen or bitumen emulsions and suspensions. The binder consumption is 0.4.0.6 l/m^. Traffic on the section of road prepared in this way must be stopped.
Immediately after laying out, the asphalt concrete mixture is compacted with light rollers, and then with heavy ones. As a result of compaction of the mixture, its density increases, its layer acquires water resistance, and upon cooling, strength. Under-compacted asphalt pavements can cause premature failure. Thus, the durability and most important properties of asphalt concrete pavements depend on the degree of compaction. Mixtures with activated mineral powders or surfactants have increased compactability, so the maximum compaction load for such mixtures is significantly lower than for asphalt concrete with non-activated mineral powders. Pneumatic rubber and vibrating rollers give very good compaction results. It is necessary that the pavement be completely compacted during construction. The degree of compaction is judged by the ratio of the density of asphalt concrete compacted by rollers and a press under a pressure of 40 MPa. This ratio, called the compaction coefficient, should be 0.98 to 0.99.
During the production of asphalt concrete mixtures, systematic quality control is ensured at all stages. At the first stages, the quality of the starting materials is carefully checked and their compliance with the requirements of current GOSTs is established. Factory laboratory workers monitor the accuracy of dosing and maintain the quality of materials.
Description of equipment for preparing asphalt concrete mixtures. Asphalt concrete mixtures are prepared in special plants (APP), which can be stationary or temporary. Typically, stationary asphalt concrete plants are set up to meet the needs of urban road construction, and for the construction of suburban roads common use temporary plants are being built, operating for 1.5 years. Asphalt mixing plants are typically located near railroad tracks or near a road under construction to reduce the amount of material handling and transport works. One asphalt plant serves roads under construction within a radius of 60.70 km.
In recent years, both in the USSR and abroad, high-performance mobile and easily relocatable asphalt plants with a range of 5.10 km have been created. Installations are sets of units that take from Vehicle materials, dose them, dry and heat them, prepare and dispense the mixture into vehicles. All units are mounted on pneumatic trailers and are transferred from transport position during working hours due to the presence of lifting equipment. As a rule, warehouses and bitumen storage facilities are relocated when the mobile asphalt plant is significantly removed.
Asphalt concrete plants are equipped with equipment that allows you to mechanize and automate everything technological processes preparation of asphalt concrete mixtures. In road construction, asphalt plants with equipment with a capacity of 25,200 t/h are used. In the coming years, it is planned to produce DS-129-5 asphalt mixing machines with a capacity of up to 400 t/h.
The main units at the asphalt plant are asphalt mixers, which are divided into three groups: batch mixers with free mixing type D-138 and G-1m; batch mixers with forced mixing; continuous mixers.
Mixers of the first group were widely used 10.15 years ago. They are simple in design and maintenance. Currently, they are used mainly for the preparation of coarse mixtures. Their productivity is low - 10.15 t/h, the weight of one batch is 3.5 tons.
Currently, batch mixers with forced mixing are used to prepare asphalt concrete mixtures: D-508-2A with a capacity of 25 t/h, DS-117-2E - 25 t/h, D-617-2-50 t/h, D- 645-2-100 t/h, dS-84-2-200 t/h.
Continuous mixers include D-645-3 with D-647 mixer with a capacity of 100 t/h. The composition of the asphalt concrete plant includes: warehouses for stone materials with equipment for their additional processing; mineral powder warehouse; workshop for the preparation of mineral powder; bitumen facilities, including bitumen storage, bitumen supply boilers, bitumen pipelines and bitumen pumps; equipment and mechanisms for moving and supplying stone materials; equipment for drying and heating mineral materials to the required temperature; equipment for dosing and mixing all components. In addition, the asphalt plant includes: equipment for energy, water, air and steam supply, as well as a laboratory for quality control of the materials used and the finished mixture, a warehouse for small parts and tools, service and household premises.
Crushed stone, gravel, sand and other stone materials are stored in piles 8.10 m high in open areas. At the same time, make sure that these materials do not mix.
It is advisable to store stone materials under shelters to avoid excessive moisture.
Stone materials, depending on the adopted technology for preparing the asphalt concrete mixture, are supplied to drying plants by belt conveyors, mechanical loaders, etc.
Mineral powder is supplied to factories in finished form, and can also be prepared at asphalt plants. Dried limestone or dolomite is ground in ball or tube mills to the required fineness. During the grinding process, you can introduce activating additives and obtain activated mineral powders; store the mineral powder in closed rooms or silos that prevent moisture from entering. Mineral powder is fed into dispensers and mixers using belt or screw conveyors, as well as pneumatic transport.
The bitumen storage facility is usually located near railway access tracks, and, if there is a waterway, at the pier. They try to place bitumen melting boilers closer to the bitumen storage facility, but in this case they may be far from the mixers, which leads to the need to install separate supply boilers at the mixing units. Bitumen can be heated by: steam coils, flame tubes and electric heating elements. Electric heating is the most hygienic and progressive, as it makes it possible to automatically regulate and maintain the set temperature. Bitumen is supplied to the mixers by bitumen pumps through heated pipelines.
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