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1 System of regulatory documents in construction ENTERPRISE STANDARD The procedure for selecting and approving recipes for asphalt concrete mixtures STP Directorate of the Kemerovo Regional Road Fund PREFACE

2 1. DESIGNED TO stand alone non-profit organization“Kuzbassdorcertification” (candidate of technical sciences, associate professor O.P. Afinogenov, engineer V.B. Sadkov). 2. INTRODUCED by the Autonomous Non-Profit Organization “Kuzbassdorcertification”. 3. APPROVED and put into effect by the State Institution “Kemerovo Directorate of the Regional Road Fund”. 4. INTRODUCED FOR THE FIRST TIME. State Institution "Kemerovo dir. regional road fund", 2000 Enterprise standard The procedure for selecting and approving recipes for asphalt concrete mixtures Introduced for the first time Approved and put into effect by order of March 13, 2001, 31

3 1. SCOPE OF APPLICATION Date of introduction This standard establishes the basic requirements for the procedure for selecting recipes for asphalt concrete mixtures, the procedure for their coordination when performing road works under agreements with the State Institution “Kemerovo Directorate of the Regional Road Fund” (hereinafter the customer, State Institution “Kemerovo DODF”). 2. REGULATORY REFERENCES This standard uses references to the following regulatory documents: SNiP System of regulatory documents in construction. Basic provisions; SNiP Highways; SNiP *. Organization construction production; GOST Testing and quality control of products. Basic terms and definitions; GOST Mixtures of asphalt concrete for road, airfield and asphalt concrete; GOST Materials based on organic binders for road and airfield construction. Test methods; STP Preparation of road bitumens modified with atactic polypropylene. Model regulations; TU Road bitumens modified with atactic polypropylene. 3. DEFINITIONS 3.1. This standard uses terms and their definitions corresponding to GOST 9128, GOST 16504, SNiP, SNiP Asphalt concrete mixture is a rationally selected mixture of mineral materials (crushed stone [gravel] and sand with or without mineral powder) with bitumen, taken in certain proportions and mixed in heated state. Asphalt concrete is a compacted asphalt concrete mixture. Asphalt recipe concrete mixture a document that is part of the technological regulations, containing information characterizing the scope of application of the mixture, its composition and physical and mechanical properties, material consumption; approved and agreed upon in accordance with the established procedure. 4. GENERAL PROVISIONS

4 4.1. The Contractor does not have the right to carry out work using asphalt concrete mixtures at the facilities of the Kemerovo DODF State Institution without recipes for their production, agreed upon in the manner regulated by this standard. The recipe is drawn up for the construction season, for each mixture used at this facility. It is allowed to issue one recipe for several objects of the same type. In case of adjustment of the recipe based on the results of production control, when replacing materials, etc., the recipe is subject to re-approval in the manner prescribed in the section The recipe must comply with the requirements of project documentation, SNiP, GOST, and other regulatory documents ( VSN, OST, STP, etc.) The selection of the composition of the asphalt concrete mixture must be carried out by an organization that has a competent laboratory and guarantees the reliability of test results and the completeness of the controlled signs (characteristics) of the asphalt concrete mixture. A laboratory accredited for the relevant types of tests in a registered and (or ) duly recognized by the laboratory accreditation system, or having a certificate of official assessment of the state of measurements according to MI. The recipe for an asphalt concrete mixture is compiled on the basis of a specially made selection, the purpose of which is to provide the mixture with the specified properties. The selection (design) of the mixture consists of five stages: 1) establishing requirements to the mixture; 2) selection of materials and assessment of their suitability; 3) determination of a rational quantitative ratio of mixture components; 4) quality control of the composition; 5) economic assessment of the quality of the composition. The task for designing an asphalt concrete mixture is issued by the chief engineer of the contracting organization. The mixture can be selected by the contractor's road construction laboratory or an external laboratory. The assignment for designing the mixture must indicate: the type of asphalt concrete mixture (hot, cold, coarse-grained, fine-grained, sand); type of asphalt concrete (high-density, dense, porous, highly porous); type of mixture and brand of asphalt concrete; Desirable materials When designing asphalt concrete mixtures, one should strive to obtain the most economical composition. 5. DESIGNATION OF THE MAIN PARAMETERS OF THE MIXTURE 5.1. The main parameters and type of mixture (asphalt concrete) are assigned according to the design documentation. If deviations from the requirements of the regulatory documents in force at the time of selection of the mixture are found, it is necessary to agree on the parameters with the customer. Asphalt concrete mixtures must

5 apply in accordance with p SNiP, adj. A GOST and meet the requirements of GOST The customer has the right to establish higher rates of asphalt concrete mixture (asphalt concrete) than provided for by SNiP (with appropriate compensation for the contractor’s costs). For the installation of the bottom layer of coating, leveling layers, predominantly coarse-grained mixtures with a rough surface should be used (to ensure reliable adhesion to the top layer) and high shear resistance. On roads with heavy traffic, hot, high-density mixtures of type A should be used. To repair minor damage to asphalt concrete pavements, mixtures are used that are similar in properties to the mixtures of the coating layer being repaired. 6. SELECTION OF MIXTURE COMPONENTS 6.1. The materials used for the preparation of asphalt concrete mixtures must comply with the requirements of GOST. It is advisable to use crushed stone from igneous or metamorphic basic and carbonate rocks, which have better adhesion to petroleum bitumen. The shape of the crushed stone should be close to a cube and not have flat flaky grains. Gravel is a less desirable component because it has a smooth surface and weak rock inclusions. Increasing the amount of crushed stone increases the crack resistance and shear resistance of coatings. It is advisable to use sand consisting of particles different sizes. Uniform sand increases the porosity of the mineral part. Sand from crushing screenings increases the internal friction of the mineral part due to the content of acute-angled grains in it. River sand is not recommended for use. Mineral powders obtained by artificial grinding of limestone and dolomite should be used for asphalt concrete mixtures. The presence of very fine clay particles in the mineral powder increases the swelling of asphalt concrete when moistened and increases the bitumen capacity of the mixture. A large number of particles larger than 0.071 mm increases the consumption of mineral powder and complicates the process of preparing and laying the mixture. The properties of the binder largely determine the quality of asphalt concrete. Excessive viscosity of bitumen leads to the formation of cracks at low temperatures, and low viscosity leads to plastic deformation of coatings in hot weather. In accordance with the requirements of SNiP, in the conditions of the Kemerovo region it is necessary to use polymer-bitumen binders (modified bitumens). For modification, polymer-bitumen binders of the PBB and Kaudest-D brands are used, bitumen-rubber binders of the BKV brands; it is allowed to use atactic polypropylene of the APP-G/B brand on territorial roads (the binder must meet the requirements of the Technical Specifications for Preparation of Bitumen,

6 modified with atactic polypropylene, carried out using FSW. Polymer additives increase the elasticity of bitumen, its thermal stability over a wide temperature range, the strength and corrosion resistance of asphalt concrete. It should be borne in mind that with a lack or excess of bitumen, the mechanical strength of concrete decreases. With an increase in the amount of bitumen, the water resistance of asphalt concrete increases due to the more complete enveloping of stone materials with a bitumen film and filling of pores, and the heat resistance decreases. With a decrease in the amount of bitumen, the opposite phenomenon is observed: water saturation increases, water resistance decreases, and heat resistance increases, concrete becomes more rigid and brittle. 7. CALCULATION OF THE MIXTURE COMPOSITION 7.1. Designing the composition of an asphalt concrete mixture (asphalt concrete) can be carried out using any known method. It is recommended to use the SoyuzdorNII method, to which GOST is oriented. The basis of the method is the assumption that the strength of concrete is determined by its structure and is ensured by the creation of a dense mineral mixture with an optimal amount of bitumen. In the conditions of the Kemerovo region, it is advisable to strive for the use of a smaller amount of sand and mineral powder, which have a higher moisture capacity, i.e. .e. use mixtures of types A and B Calculation of asphalt concrete includes two stages: calculation of the granulometric (grain) composition of the mineral part of the mixture from a given set of materials according to the granulometric composition tables (Tables 2 and 3 GOST); experimental determination of the physical and mechanical properties of asphalt concrete, assessment of their compliance with GOST requirements, as well as selection optimal quantity bitumen by testing test samples with the same composition of stone materials and different bitumen contents. The criterion for determining the optimal amount of bitumen is the best correspondence between water saturation and mechanical strength for compression at a temperature of 20 C and 50 C of test samples that meet the requirements of GOST EXAMPLE OF CALCULATION OF THE COMPOSITION OF A FINE-GRAINED MIXTURE 8.1. Task: Calculate the composition of fine-grained hot asphalt concrete type B, grade II. Components: Crushed stone from the Mozzhukhinsky quarry, fractions 5-20 mm; Sand from the Yaya building materials plant;

7 Limestone mineral powder. Calculation procedure. Based on the limits of the required particle size distributions (Table 3 GOST) and based on the results of sifting the mineral materials used (Table 1), we determine the approximate percentage content of each material (crushed stone, sand, mineral powder). Table 1 Name of material, manufacturer or quarry Partial residues (number of grains, % by weight, less remaining on a sieve with mesh size, mm) .5 1.25 0.63 0.315 0.14 0.071 less Mozzhukhinsky quarry crushed stone, fr mm Yaisky sand KSM Mineral powder 5.3 33.7 30.2 23.6 3.7 3.5 1.0 18.5 17.0 7.5 12.4 24.6 8.8 4.2 6.0 1, 2 2.0 8.6 16.6 71.6 Crushed stone content X a 45 = 100 = 100 = 48.49% b 92.8 where a is the average value of total residues on a sieve with a diameter of 5 mm, required by table. 3 GOST; b fraction content larger than 5 mm in crushed stone. Mineral powder content a1 6 Z = 100 = 100 = 8.4% b 71.6 1 where a1 is the minimum permissible content of the fraction “less than 0.071 mm” in the composition of type B asphalt concrete (Table 3 GOST); b1 content of fractions finer than 0.071 mm in mineral powder. Taking into account the presence of grains in the sand with a particle size of more than 5 mm and finer than 0.071 mm, we reduce the above values ​​​​of the content of crushed stone and mineral powder in the mixture to the following values: crushed stone 42.0%, mineral powder 7.0%. Then the sand content in the mixture Fill out table 2. Y = 100 (x + z); Y = 100 (42 + 7) = 51%

8 Comparison of the data in column 10 with the data in column 11 indicates that the composition of the designed mineral part of the asphalt concrete mixture corresponds to the required compositions of dense mixtures. Table 2 Calculation table for determining the total residues of the designed mineral mixture Size of the sieve openings in mm Particle size distribution of the constituent materials in % crushed stone sand mineral powder Particle size distribution of materials in the designed mixture in % crushed sand mineral powder Partial residues of the designed mineral mixture in % Total residues of the designed mineral mixture in % Full passes Permissible limits of full passes according to GOST,3 2.2 2.2 2.2 97.7 14.2 14.2 16.4 83.2 1.0 12.6 0.5 13.1 29, 5 70.6 18.5 9.9 9.4 19.3 48.8 51.5 3.7 17.0 1.6 8.7 10.3 59.1 40.25 3.5 7.5 1 .5 3.8 5.3 64.4 36.63 12.4 1.2 6.3 0.1 6.4 70.8 29.315 24.6 2.0 12.5 0.1 12.6 83, 4 16.14 8.8 8.6 4.6 0.6 5.2 88.6 11.071 4.2 16.6 2.1 1.2 3.3 91.9 8, Less than 6.0 71.6 3.1 5.0 8, We determine the percentage of bitumen in accordance with the recommendations of GOST Appendix G, it is 5.0-6.5%. Based on this, we prepare three asphalt concrete mixtures with the same mineral composition and the calculated amount of bitumen (5.0-5.8-6.5%). Test samples are made from these compositions and tested for compression at temperatures of +20 and +50 C and for water saturation. The optimal amount of bitumen is taken to be the content at which the best performance of asphalt concrete was achieved. We produce control samples of the designed composition with the optimal amount of bitumen and subject them to full cycle tests. The test results are recorded in Table 3. Table 3 Indicators of asphalt concrete properties

9 Name of indicator GOST Requirements Actual indicators Name of indicator GOST Requirements Actual indicators Average density, 2.38 Water resistance at g/cm 3 long-term water saturation Porosity of the mineral part by volume, % Residual porosity, % 19 16.3 Adhesion of bitumen to the mineral part 2.5 5.0 3.4 Shear resistance index Water saturation, % 1.5 4.0 2.8 Crack resistance index Compressive strength at temperature, MPa Total specific effective activity of natural radionuclides, Bq/kg 0.75 0.87 Passes Passes C 2 .2 2.6 50 C 1.0 1.1 0 C 12.0 10.0 Water resistance 0.85 0.93 Indicators of shear resistance and crack resistance are determined if they are standardized in the design documentation for the construction of asphalt concrete pavement. We calculate the composition of the asphalt concrete mixture for one mixer batch. The initial data are the mass of the batch and the mesh sizes of the screens of the hot materials screen installed at the asphalt plant. For ABZ DS, the mass of the batch is 600 kg; sieves with cells of 5, 15, 35 mm are installed on the screen. The mass of material that must come from the hopper for batching is equal to (F1 F2) 600 D i =, 100 B where i is the number of the hopper from which material is collected for batching; F1 is the total residue on the underlying sieve in %, taken according to the data in table. 2; F2 is the total residue on the overlying sieve in %, taken according to the data in table. 2; 600 batch weight, kg; B percentage of bitumen in the mixture;

10 (100 48.8) 600 D 0 5 = = 289.8 kg; 100 1.06 (48.8 16.4) 600 D 5 15 = = 183.4 kg 100 1.06 (16.4 0) 600 D = = 92.8 kg.06 ; Since mineral powder is supplied through a separate supply line, it is necessary to subtract the mass of mineral powder from the mass of material shipped from bunker D0-5 "289, D 0 5 = = 289.6 39.6 = 250 kg; 100 1.06 Calculation results enter in table 4. Composition of the asphalt concrete mixture Binder or fractions of stone materials in accordance with Dosage per batch 600 kg hot bins ABZ 1 Fraction mm 92.8 2 Fraction 5-15 mm 183.4 3 Fraction 0-5 mm 250.0 4 Mineral powder 39.6 5 Bitumen 34.2 Table 4 We calculate the consumption of asphalt concrete mixture per 1000 m2 of pavement and the consumption of constituent materials per 100 tons of mixture, the results are entered in Table 5. V = H S G = 0.38 = 95.2 t, where V consumption asphalt concrete mixture, t; H layer thickness, m; S layer area, equal to 1000 m2; G average density of asphalt concrete, from Table 3, t/m 3. It must be taken into account that in some cases the customer agrees to pay the contractor for irreparable losses, as a rule this is 3% of the volume of asphalt concrete. V "W 100 = P (100 + C),

11 where V" consumption of inert stone materials, m 3; W percentage of this material in the mixture; P volumetric bulk mass of stone materials; C percentage of bitumen in the mixture. "V 1 = = 28.5 m 1.39 () " V 2 = = 33.0 m 1.46 () Material consumption 3 3 ; ; Table 5 Per 100 m of mixture Per 1000 m 2 of coating Name of material Bulk density, t/m 3 Content in the mixture in % T M 3 Crushed stone 1.5 Mozzhukhinsky quarry Sand Yaisky KSM 1, Mineral powder 7 6.6 Bitumen 6 5.7 Asphalt concrete mixture (t), with a layer thickness of 2 9. DESIGN OF MIXTURE RECIPES 9.1. A separate recipe is drawn up for each mixture, which must have an individual number consisting from the serial number in a given year and the last two digits of the year for which it was compiled (for example, 14-00). The serial numbers must correspond to the registration numbers according to the "Journal for determining the physical and mechanical properties of asphalt concrete mixtures when selecting compositions and periodically monitoring the quality of the produced asphalt concrete mixture "(Form D-7) Recipes are prepared on standard forms, according to the form given in the appendix. All entries must be clear and neat; crossing out text and blots are not allowed. Allowed the following options design: using personal computer; on a form by hand, in black or blue ink (paste). The second and third copies of the recipe may be photocopies. For examination and approval, 3 copies of the recipe approved by the chief engineer (technical director) of the organization are submitted (indicating the date of approval, surname, initials of the approver, name of the contractor. The signature is certified by a seal.

12 It is prohibited to submit photocopies of recipes where the signature and seal have been copied. The organization performing the examination and the customer have the right not to consider recipes drawn up in violation of p. The recipe indicates the structural element in which the mixture is used (top, bottom layer of coating, base), type, type and brand of mixture (asphalt concrete), object, for example: "... for the installation of a top layer of coating (hot, type A, grade I) on the Novosibirsk - Irkutsk highway, km 45-60" The recipe must contain: information about the materials used mineral materials, grain composition of the mixture (with and without division into component materials), binder; production recipe; indicators of properties of the mixture and asphalt concrete; data on material consumption. The norms for hard-to-remove losses taken into account in the recipe must be indicated. For installations of type DS-117, DS-158, the loss rate at the asphalt plant is 1.5%, the loss rate when laying the mixture is 1.5%. The recipe must be signed by the head of the laboratory that performed the selection. If the selection is made by a third-party organization, the recipe is signed by its technical director, and the signature is certified by a seal. 10. APPROVAL AND AGREEMENT OF THE RECIPE The recipe for the asphalt concrete mixture used at the facilities of the Kemerovo DODF State Institution must be approved by the chief engineer (technical director) of the contracting organization and agreed upon by the chief engineer of the customer (Kemerovo DODF State Institution). If contractor purchases a mixture from a third-party organization, it is obliged to ensure that the mixture complies with the recipe agreed upon by the Kemerovo DODF State Institution. Before the recipe is approved by the customer, it must undergo an examination at the Kuzbass Center for Road Research LLC. The examination must be carried out within no more than 5 working days. During the examination, the compliance of the recipe with the requirements of SNiP, GOST 9128, the correctness of its design and calculation of the composition of the mixture are assessed. The compliance of the physical-mechanical and other indicators of the mixture specified in the recipe with the actual values ​​is monitored during the technical supervision of the customer. The Contractor is responsible for the accuracy of the information presented in the recipe and the compliance of the mixtures used with the recipes. The customer is obliged to review the recipe submitted for approval within 5 days. If the recipe has gone through the approval procedure, one copy remains with the customer, one copy each is sent to the contractor and the organization exercising independent control. If approval is refused, the customer sends the recipe to the contractor. The refusal must be motivated. After appropriate adjustment, the recipe again goes through the approval procedure provided for by this standard. Grounds for refusal to approve a recipe: - the recipe has not passed the examination; - non-compliance with the requirements of regulatory documents and (or) the project;

13 - non-compliance with the requirements of this standard. 11. INSPECTION CONTROL OVER COMPLIANCE WITH MIXTURE RECIPES Inspection control over compliance with asphalt concrete mixture recipes is carried out by engineers of the customer's technical supervision service, an independent competent organization (on behalf of the customer), and the administration of the organization that produces the mixture or uses it. AGREED Chief Engineer KDODF A.S. Belokobylsky 200 M.P. I APPROVED Chief Engineer 200 M.P. RECIPE for asphalt concrete mixture for installation (type and brand type) (top/bottom/layer of coating, base) on a highway from PC (km) to PC (km) Name of material, 1. APPLIED MINERAL MATERIALS Partial residues (number of grains, % by mass remaining on a sieve with mesh size, mm)

14 manufacturer or quarry Name of material, 5 1.25 0.63 0.315 0.14 0.071 less than 2. GRAIN COMPOSITION OF ASPHALT CONCRETE MIXTURE 2.1. Divided into component materials Contents Partial residues (number of grains, % by weight, remaining on a sieve with mesh size, mm) in a/b.5 1.25 0.63 0.315 0.14 0.071 less mixture, e % 2.2. Without dividing into component materials Partial residues, % Total residues, % Passes, % Grain composition of the mineral part of the mixture according to GOST, % 3. BINDER, % in excess of 100% of the mineral part 3.1. Bitumen (brand, manufacturer) content in binder, % 3.2. Modifier (name, brand) content in binder, % 3.3. Solvent (name, brand,) content in the binder, % Binder or fractions of stone materials in accordance with the hot bunkers of the asphalt concrete plant 4. COMPOSITION OF ASPHALT CONCRETE MIXTURE Dosage per batch weighing, kg Binder or fractions of stone materials in accordance with the hot bunkers of the asphalt concrete plant Dosage per batch weighing, kg Name of indicators 5. INDICATORS OF ASPHALT CONCRETE PROPERTIES According to GOST Actually Name of indicators According to GOST Actually

15 1. Average density, g/cm 3 6. Water resistance during long-term water saturation 2. Porosity of the mineral part, % by volume 3. Water saturation, % by volume 4. Ultimate compressive strength (MPa) at: 20 C 50 C 0 C 5 Water resistance 7. Adhesion of bitumen to the mineral part of the asphalt concrete mixture 8*. Shear resistance index 9*. Crack resistance index 10. Total specific effective activity of natural radionuclides Passes the test * These indicators are determined if they are standardized by the design documentation for the construction of the coating 6. CONSUMPTION OF MATERIALS Bulk density, t/m 3 T Content Name of material in the mixture, % M 3 Per 100 tons of mixture Bq/kg Per 1000 m 2, coating Asphalt concrete mixture (t), with a layer thickness of 4 cm When changing the layer thickness by 0.5 cm, add The table is compiled taking into account the rate of losses % on asphalt concrete and % when laying the mixture. Head of the line that carried out the selection Agreed by KuzTsDI

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GOST 9128-2013 INTERSTATE STANDARD FOR ASPHALT CONCRETE MIXTURES, POLYMERSAPHALT CONCRETE, ASPHALT CONCRETE, POLYMERSAPHALT CONCRETE FOR HIGHWAYS AND AIRPORTS Technical specifications Asphaltic concrete

In Russia, the most widespread selection of the composition of the mineral part of asphalt concrete mixtures is based on the limiting curves of grain compositions. The mixture of crushed stone, sand and mineral powder is selected in such a way that the grain composition curve is located in the area limited by the limit curves and is as smooth as possible. The fractional composition of the mineral mixture is calculated depending on the content of the selected components and their grain compositions according to the following relationship:

j - component number;

n is the number of components in the mixture;

When selecting the grain composition of an asphalt concrete mixture, especially using sand from crushing screenings, it is necessary to take into account the grains contained in the mineral material smaller than 0.071 mm, which, when heated in the drying drum, are blown out and deposited in the dust collection system.

These dust particles can either be removed from the mixture or dosed into the mixing plant along with the mineral powder. The procedure for using dust collection is specified in the technological regulations for the preparation of asphalt concrete mixtures, taking into account the quality of the material and the characteristics of the asphalt mixing plant.

Next, in accordance with GOST 12801-98, the average and true density of asphalt concrete and the mineral part is determined and, based on their values, the residual porosity and porosity of the mineral part are calculated. If the residual porosity does not correspond to the standardized value, then the new content of bitumen B (% by weight) is calculated according to the following relationship:

With the calculated amount of bitumen, the mixture is again prepared, samples are formed from it, and the residual porosity of the asphalt concrete is again determined. If it corresponds to the required one, then the calculated amount of bitumen is taken as the basis. Otherwise, the procedure for selecting the bitumen content, based on approximation to the standardized pore volume in compacted asphalt concrete, is repeated.

A series of samples is formed from an asphalt concrete mixture with a given bitumen content using a standard compaction method and determined full complex indicators of physical and mechanical properties, provided for by GOST 9128-97. If the asphalt concrete does not meet the requirements of the standard for any indicators, then the composition of the mixture is changed.

If the coefficient of internal friction is insufficient, the content of large fractions of crushed stone or crushed grains in the sandy part of the mixture should be increased.

If shear adhesion and compressive strength at 50°C are low, the content of mineral powder should be increased (within acceptable limits) or a more viscous bitumen should be used. At high strength values ​​at 0°C, it is recommended to reduce the content of mineral powder, reduce the viscosity of bitumen, use a polymer-bitumen binder or use plasticizing additives.

If the water resistance of asphalt concrete is insufficient, it is advisable to increase the content of mineral powder or bitumen, but within limits that provide the required values ​​of residual porosity and porosity of the mineral part. To increase water resistance, it is effective to use surfactants (surfactants), activators and activated mineral powders. The selection of the composition of the asphalt concrete mixture is considered complete if all indicators of physical and mechanical properties obtained during testing of asphalt concrete samples meet the requirements of the standard. However, within the framework of standard requirements for asphalt concrete, it is recommended to optimize the composition of the mixture in the direction of increasing the performance properties and durability of the constructed structural layer of road pavement.

Until recently, optimization of the composition of the mixture intended for the construction of top layers of road surfaces was associated with an increase in the density of asphalt concrete. In this regard, in road construction Three methods have been formed that are used in the selection of grain compositions of dense mixtures. They were originally called:

• - experimental (German) method of selecting dense mixtures, which consists in gradually filling one material with another;
• - curve method, based on the selection of a grain composition that approaches predetermined mathematically “ideal” curves of dense mixtures;
• - American method of standard mixtures, based on proven compositions of mixtures from specific materials.

These methods were proposed about 100 years ago and received further development.

The essence of the experimental method for selecting dense mixtures is to gradually fill the pores of one material with larger grains with another smaller mineral material. In practice, mixture selection is carried out in the following order.

To 100 parts by weight of the first material, add sequentially 10, 20, 30, etc., parts by weight of the second, determining after mixing and compacting the average density and choosing a mixture with a minimum number of voids in the compacted state.

If it is necessary to make a mixture of three components, then a third material is added to a dense mixture of two materials in gradually increasing portions and the most dense mixture is also selected. Although this selection of a dense mineral framework is labor-intensive and does not take into account the influence of the liquid phase content and the properties of bitumen on the compaction of the mixture, it is nevertheless still used in experimental research work.

In addition, the experimental method for selecting dense mixtures was used as the basis for calculation methods for preparing dense concrete mixtures from bulk materials of various sizes and was further developed in experimental planning methods. The principle of sequential filling of voids is used in the methodology for designing optimal compositions of road asphalt concrete, which use crushed stone, gravel and sand with any granulometry.

According to the authors of the work, the proposed computational and experimental methodology allows for optimal control of the structure, composition, properties and cost of asphalt concrete. The following are used as variable structural control parameters:

• - coefficients of separation of grains of crushed stone, gravel and sand;
• - volume concentration of mineral powder in asphalt binder;
• - criterion for optimal composition, expressed by the minimum total cost of components per unit of production.

Based on the principle of sequential filling of voids in crushed stone, sand and mineral powder, the approximate composition of the mixture for high-density asphalt concrete based on liquid bitumen was calculated.

The content of components in the mixture was calculated based on the results of pre-established true and bulk density mineral materials. The final composition was refined experimentally by jointly varying the content of all components of the mixture using the method of mathematical planning of a simplex experiment. The composition of the mixture, which ensures minimal porosity of the mineral core of asphalt concrete, was considered optimal.

The second method for selecting the grain composition of asphalt concrete is based on the selection of dense mineral mixtures, the grain composition of which approaches the ideal curves of Fuller, Graf, Herman, Bolomey, Talbot-Richard, Kitt-Peff and other authors. In most cases, these curves are represented as power-law dependences of the required grain content in the mixture on their size. For example, the Fuller particle size distribution curve of a dense mixture is given by the following equation:

D is the largest grain size in the mixture, mm.

To standardize the grain composition of an asphalt concrete mixture, in the modern American design method “Superpave”, granulometric curves of maximum density are also adopted, corresponding to a power law with an exponent of 0.45.

Moreover, in addition to the control points that limit the range of grain content, there is also an internal limitation zone, which is located along the granulometric curve of maximum density in the interval between grains of size 2.36 and 0.3 mm. It is believed that mixtures with a grain size distribution running along the boundary zone may have problems with compaction and shear stability, since they are more sensitive to bitumen content and become plastic when accidentally overdosing organic binder.

It should be noted that GOST 9128-76 also prescribed for grain composition curves of dense mixtures a restrictive zone located between the limit curves of continuous and discontinuous granulometry. In Fig. 1 this area is shaded.

Rice. 1. - Grain compositions of the fine-grained mineral part:

However, in 1986, when the standard was reissued, this restriction was canceled as unimportant. Moreover, in the works of the Leningrad branch of Soyuzdornia (A.O. Sal) it was shown that the so-called “semi-discontinuous” mixture compositions passing through the shaded zone are in some cases preferable to continuous ones due to the lower porosity of the mineral part of asphalt concrete, and intermittent ones - due to greater resistance to delamination.

The basis of the domestic method for constructing curves of the granulometric composition of dense mixtures was the well-known research of V.V. Okhotin, in which it was shown that the most dense mixture can be obtained provided that the diameter of the particles making up the material decreases in the proportion of 1:16, and their weight amounts - as 1:0.43. However, given the tendency for mixtures formulated with this ratio of coarse and fine fractions to segregate, it has been proposed to add intermediate fractions. At the same time, the weight amount of a fraction with a diameter 16 times smaller will not change at all if you fill the voids not just with these fractions, but, for example, with fractions with a grain diameter 4 times smaller.

If, when filled with fractions with a grain diameter 16 times smaller, their weight content was equal to 0.43, then when filled with fractions with a grain diameter 4 times smaller, their content should be equal to k = 0.67. If you introduce another intermediate fraction with a diameter that decreases by 2 times, then the ratio of fractions should be k = 0.81. Thus, the weight number of fractions, which will always decrease by the same amount, can be expressed mathematically as a series of geometric progression:

Y1 - amount of the first fraction;

k - run-off coefficient;

n is the number of fractions in the mixture.

From the resulting progression, the quantitative value of the first fraction is derived:

Thus, the runoff coefficient is usually called the weight ratio of fractions whose particle sizes are related as 1:2, i.e., as the ratio of the nearest cell sizes in a standard set of sieves.

Although theoretically the densest mixtures are calculated using a runoff coefficient of 0.81, in practice mixtures with discontinuous grain composition have proven to be denser.

This is explained by the fact that the presented theoretical calculations for the preparation of dense mixtures based on the runoff coefficient do not take into account the separation of large grains of the material by smaller grains. In this regard, P.V. Sakharov noted that positive results in terms of increasing the density of the mixture are obtained only with a stepwise (intermittent) selection of fractions.

If the ratio of the sizes of the mixed fractions is less than 1:2 or 1:3, then the small particles do not fill the gap between the large grains, but push them apart.

The granulometric composition curves of the mineral part of asphalt concrete with different runoff coefficients are shown in Fig. 2.

Rice. 2. - Granulometric composition of the mineral part of asphalt concrete mixtures with different runoff coefficients:

Later, the ratio of the diameters of particles of adjacent fractions was clarified, excluding the separation of large grains in a multi-fractional mineral mixture. According to P.I. Bozhenov, in order to exclude the separation of large grains by small ones, the ratio of the diameter of the fine fraction to the diameter of the large fraction should be no more than 0.225 (i.e., as 1: 4.44). Taking into account the compositions of mineral mixtures tested in practice, N.N. Ivanov proposed using granulometric composition curves with a runoff coefficient ranging from 0.65 to 0.90 to select mixtures.

The granulometric compositions of dense asphalt concrete mixtures, focused on workability, were standardized in the USSR from 1932 to 1967. In accordance with these standards, asphalt concrete mixtures contained a limited amount of crushed stone (26-45%) and an increased amount of mineral powder (8-23%). Experience with the use of such mixtures has shown that waves, shears and other plastic deformations are formed in coatings, especially on roads with heavy and intense traffic. At the same time, the surface roughness of the coatings was also insufficient to provide high adhesion to the wheels of cars, based on traffic safety conditions.

Fundamental changes to the standard for asphalt concrete mixtures were made in 1967. GOST 9128-67 included new mixture compositions for frame asphalt concrete with a high crushed stone content (up to 65%), which began to be included in road projects with high traffic intensity. The amount of mineral powder and bitumen in asphalt concrete mixtures was also reduced, which was justified by the need to switch from plastic to more rigid mixtures.

The compositions of the mineral part of many crushed stone mixtures were calculated using the equation of a cubic parabola tied to four control grain sizes: 20; 5; 1.25 and 0.071 mm.

When researching and implementing frame asphalt concrete great importance was given to increase the roughness of the coatings. Methods for constructing asphalt concrete pavements with a rough surface are reflected in the recommendations developed in the early 60s of the last century and were initially implemented at the Glavdorstroy facilities of the USSR Ministry of Transport. According to the developers, the creation of roughness should have been preceded by the formation of a spatial framework in asphalt concrete. In practice, this was achieved by reducing the amount of mineral powder in the mixture, increasing the content of large crushed grains, and completely compacting the mixture, in which the grains of crushed stone and large sand fractions come into contact with each other. The production of asphalt concrete with a frame structure and a rough surface was ensured with a content of 50-65% by weight of grains larger than 5 (3) mm. in fine-grained mixtures of type A and 33-55% of grains are larger than 1.25 mm. in sand mixtures of type G with a limited content of mineral powder (4-8% in fine-grained mixtures and 8-14% in sand mixtures).

Recommendations for ensuring the shear resistance of asphalt concrete pavements as a result of the use of frame asphalt concrete by increasing the internal friction of the mineral framework are also present in foreign publications.

For example, road companies from the UK, when constructing asphalt concrete pavements in tropical and subtropical countries, specifically use grain compositions selected according to the cubic parabola equation.

The stability of coatings made from such mixtures is ensured mainly as a result of the mechanical wedging of angular-shaped particles, which must be either durable crushed stone or crushed gravel. The use of uncrushed gravel in such mixtures is not permitted.

The resistance of coatings to shear deformations can be increased by increasing the size of crushed stone. The US standard ASTM D 3515-96 provided for asphalt concrete mixtures differentiated into nine grades depending on the maximum grain size from 1.18 to 50 mm.

The higher the grade, the larger the crushed stone and the lower the content of mineral powder in the mixture. Curves of grain compositions, constructed along a cubic parabola, provide, when compacting the coating, a rigid frame of large grains, which provides the main resistance to transport loads.

In most cases, the mineral part of the asphalt concrete mixture is selected from coarse-grained, medium-grained and fine-grained components. If the true density of the constituent mineral materials differs significantly from each other, then it is recommended to calculate their content in the mixture by volume.

The grain compositions of the mineral part of asphalt concrete mixtures, tested in practice, are standardized in all technical developed countries taking into account the scope of their application. These compositions, as a rule, are consistent with each other.

In general, it is generally accepted that the most developed element in designing the composition of asphalt concrete is the selection of the granulometric composition of the mineral part either according to optimal density curves or according to the principle of sequential filling of pores. The situation is more complicated with the choice of bitumen binder of the required quality and with the justification of its optimal content in the mixture. There is still no consensus on the reliability of calculation methods for determining the bitumen content in an asphalt concrete mixture.

Current experimental methods for selecting binder content suggest different methods manufacturing and testing of asphalt concrete samples in the laboratory and, most importantly, do not allow one to reliably predict the durability and operational condition of road surfaces depending on operating conditions.

P.V. Sakharov proposed designing the composition of asphalt concrete based on a pre-selected composition of asphalt binder. The quantitative ratio of bitumen and mineral powder in the asphalt binder was selected experimentally depending on the plastic deformation rate (by the water resistance method) and on the tensile strength of the eight-piece samples. The thermal stability of the asphalt binder was also taken into account by comparing strength indicators at temperatures of 30, 15 and 0°C. Based on experimental data, it was recommended to adhere to the ratio of bitumen to mineral powder by weight (B/MP) in the range from 0.5 to 0.2.

As a result, the asphalt concrete compositions were characterized by an increased content of mineral powder. In further studies I.A. Rybiev showed that rational values ​​of B/MP can be equal to 0.8 and even higher. Based on the law of strength of optimal structures (the alignment rule), a method for designing the composition of asphalt concrete according to the given operational conditions of the road surface was recommended. It was stated that the optimal structure of asphalt concrete is achieved when bitumen is converted into a film state.

At the same time, it was shown that the optimal bitumen content in the mixture depends not only on the quantitative and qualitative ratio of the components, but also on technological factors and compaction modes.

Therefore, scientific substantiation of the required performance indicators of asphalt concrete and rational methods for achieving them continues to be the main task associated with increasing the durability of road surfaces.

There are several calculation methods for determining the bitumen content in an asphalt concrete mixture, both by the thickness of the bitumen film on the surface of mineral grains and by the number of voids in the compacted mineral mixture.

The first attempts to use them in the design of asphalt concrete mixtures often ended in failure, which forced the improvement of calculation methods for determining the bitumen content in the mixture. N.N. Ivanov proposed taking into account the better compactability of the hot asphalt concrete mixture and a certain reserve for the thermal expansion of bitumen, if the calculation of the bitumen content is carried out based on the porosity of the compacted mineral mixture:

B - amount of bitumen,%;

P - porosity of the compacted mineral mixture, %;

c6 - true density of bitumen, g/cm. cubic;

c - average density of the compacted dry mixture, g/cm. cubic;

0.85 is the coefficient of reduction in the amount of bitumen due to better compaction of the mixture with bitumen and the expansion coefficient of bitumen, which is taken equal to 0.0017.

It should be noted that calculations of the volumetric content of components in compacted asphalt concrete, including the volume of air pores or residual porosity, are performed in any design method in the form of phase volume normalization. As an example in Fig. Figure 3 shows the volumetric composition of asphalt concrete type A in the form of a pie chart.

Rice. 3. - Normalization of the volume of phases in asphalt concrete:

According to this diagram, the bitumen content (% by volume) is equal to the difference between the porosity of the mineral matrix and the residual porosity of the compacted asphalt concrete. Thus, M. Durieu recommended a method for calculating the bitumen content in a hot asphalt concrete mixture based on the saturation modulus. The saturation module of asphalt concrete with binder was established based on experimental and production data and characterizes the percentage of binder in a mineral mixture having a specific surface of 1 m2/kg.

This methodology is adopted to determine the minimum bitumen binder content depending on the grain composition of the mineral part in the LCPC asphalt mixture design method. developed by the Central Laboratory of Bridges and Roads of France. The weight content of bitumen using this method is determined by the formula:

k is the saturation module of asphalt concrete with binder.

• S - partial residue on a sieve with holes measuring 0.315 mm, %;
• s - partial residue on a sieve with holes measuring 0.08 mm, %;

The method for calculating the bitumen content based on the thickness of the bitumen film was significantly improved by I.V. Korolev. Based on experimental data, he differentiated the specific surface area of ​​grains of standard fractions depending on the nature of the rock. The influence of the nature of the stone material, grain size and bitumen viscosity on optimal thickness bitumen film in asphalt concrete mixture.

The next step is a differentiated assessment of the bitumen capacity of mineral particles smaller than 0.071 mm. As a result of a statistical forecast of the grain compositions of mineral powder and the bitumen capacity of fractions ranging in size from 1 to 71 microns, a technique was developed at MADI (GTU) that allows one to obtain calculated data that satisfactorily coincides with the experimental bitumen content in the asphalt concrete mixture.

Another approach to assigning bitumen content in asphalt concrete is based on the relationship between the porosity of the mineral matrix and the grain composition of the mineral part. Based on the study of experimental mixtures of particles of various sizes, Japanese specialists proposed mathematical model porosity of mineral matrix (VMA). The values ​​of the coefficients of the established correlation dependence were determined for crushed stone-mastic asphalt concrete, which was compacted in a rotary compactor (gyrator) at 300 revolutions of the mold. An algorithm for calculating bitumen content, based on the correlation of the pore characteristics of asphalt concrete with the grain composition of the mixture, was proposed in the work. Based on the results of processing a data array obtained from testing various types of dense asphalt concrete, the following correlation dependencies were established for calculating the optimal bitumen content:

K - granulometry parameter.

Dcr - minimum size grains of the coarse fraction, the finer grains of which contain 69.1% by weight of the mixture, mm;

D0 is the grain size of the middle fraction, smaller than which 38.1% by weight of the mixture is contained, mm;

Dfine is the maximum grain size of the fine fraction, the finer of which contains 19.1% by weight of the mixture, mm.

However, in any case, the calculated dosages of bitumen should be adjusted when preparing control batches depending on the test results of molded asphalt concrete samples.

When selecting the composition of asphalt concrete mixtures, the following statement by Prof. N.N. Ivanova: “No more bitumen should be taken than is determined by obtaining a sufficiently strong and stable mixture, but bitumen should be taken as much as possible, and in no case less.” Experimental methods for selecting asphalt concrete mixtures usually involve preparing standard samples using specified compaction methods and testing them in laboratory conditions. For each method, appropriate criteria have been developed that establish, to one degree or another, a relationship between the results of laboratory tests of compacted samples and the performance characteristics of asphalt concrete under operating conditions.

In most cases, these criteria are defined and standardized by national standards for asphalt concrete.

The following schemes for mechanical testing of asphalt concrete samples are common, shown in Fig. 4.

Rice. 4. - Schemes for testing cylindrical samples when designing the composition of asphalt concrete:

a - according to Duriez;

b - according to Marshall;

c - according to Khvim;

g - according to Hubbard-Field.

Analysis of various experimental methods design of asphalt concrete compositions indicates the similarity in the approaches to assigning a formulation and the difference both in the methods of testing samples and in the criteria for the properties being assessed.

The similarity of methods for designing an asphalt concrete mixture is based on the selection of such a volumetric ratio of components that ensures the specified values ​​of residual porosity and standardized indicators of the mechanical properties of asphalt concrete.

In Russia, when designing asphalt concrete, standard cylindrical samples are tested for uniaxial compression (according to the Duriez scheme), which are molded in the laboratory according to GOST 12801-98, depending on the crushed stone content in the mixture, either with a static load of 40 MPa, or by vibration with subsequent additional compaction with a load of 20 MPa. In foreign practice, the most widely used method for designing asphalt concrete mixtures is the Marshall method.

In the USA, until recently, methods for designing asphalt concrete mixtures according to Marshall, Hubbard-Field and Hvim have been used. but recently, a number of states are introducing the “Superpave” design system.

When developing new methods for designing asphalt concrete mixtures abroad, much attention was paid to improving methods for compacting samples. Currently, Marshall mix designs provide three levels of sample compaction: 35, 50, and 75 blows per side, respectively, for light, medium, and heavy vehicle traffic conditions. The United States Army Corps of Engineers, through extensive research, refined Marshall testing and extended it to the design of mixture designs for airfield pavements.

Designing an asphalt concrete mixture using the Marshall method assumes that:

• - the compliance of the initial mineral materials and bitumen with the requirements of technical specifications has been previously established;
• - the granulometric composition of the mixture of mineral materials has been selected to meet the design requirements;
• - the values ​​of the true density of viscous bitumen and mineral materials were determined by appropriate test methods;
• - sufficient quantity stone material is dried and divided into fractions in order to prepare laboratory batches of mixtures with different binder contents.

For Marshall tests, standard cylindrical samples with a height of 6.35 cm and a diameter of 10.2 cm are made and compacted by impacts of a falling weight. Mixtures are prepared with different bitumen contents, usually differing from one another by 0.5%. It is recommended to prepare at least two mixtures with a bitumen content above the “optimal” value and two mixtures with a bitumen content below the “optimal” value.

To more accurately assign bitumen content for laboratory testing, it is recommended to first establish an approximate “optimal” bitumen content.

By “optimal” we mean the bitumen content in the mixture that provides maximum Marshall stability of the molded samples. Approximately for selection you need to have 22 south of stone materials and about 4 liters. bitumen

The results of asphalt concrete testing using the Marshall method are shown in Fig. 5.

Based on the results of testing asphalt concrete samples using the Marshall method, the following conclusions are usually reached:

• - The stability value increases with increasing binder content up to a certain maximum, after which the stability value decreases;
• - The value of conditional plasticity of asphalt concrete increases with increasing binder content;
• - The density versus bitumen content curve is similar to the stability curve, but its maximum is more often observed at a slightly higher bitumen content;
• - The residual porosity of asphalt concrete decreases with increasing bitumen content, approaching asymptotically to the minimum value;
• - The percentage of pores filled with bitumen increases with increasing bitumen content.

Rice. 5. - Results (a, b, c, d) of testing asphalt concrete using the Marshall method:

It is recommended that the optimum bitumen content be determined as the average of four values ​​established according to the graphs for the corresponding design requirements. An asphalt concrete mixture with an optimal bitumen content must meet all the requirements specified in the technical specifications. When making the final choice of the composition of the asphalt concrete mixture, technical and economic indicators can also be taken into account. It is usually recommended to select a mixture that has the highest Marshall stability.

However, it should be borne in mind that mixtures with excessively high Marshall stability values ​​and low ductility are undesirable, since coatings from such mixtures will be excessively rigid and may crack when driven by heavy vehicles, especially with weak bases and high deflections of the coating. Often in Western Europe and in the USA, the Marshall method of designing asphalt concrete mixtures has been criticized. It is noted that the Marshall impact compaction of samples does not model the compaction of the mixture in the pavement, and the Marshall stability does not allow for a satisfactory assessment of the shear strength of asphalt concrete.

The Khvim method is also criticized, the disadvantages of which include rather cumbersome and expensive testing equipment.

In addition, some important volumetric metric parameters of asphalt concrete related to its durability are not properly disclosed in this method. According to American engineers, the Hvim method for selecting bitumen content is subjective and can lead to the fragility of asphalt concrete due to the appointment of a low binder content in the mixture.

The LCPC method (France) is based on the fact that hot mix asphalt must be designed and compacted during construction to maximum density.

Therefore, special studies were carried out on the calculated compaction work, which was determined as 16 passes of a roller with pneumatic tires, with an axle load of 3 tf at a tire pressure of 6 bar. On a full-scale laboratory bench when compacting a hot asphalt concrete mixture, a standard layer thickness equal to 5 maximum sizes of mineral grains was justified. For appropriate compaction of laboratory samples, the rotation angle on the laboratory compactor (gyrator) was standardized to 1° and the vertical pressure on the compacted mixture was 600 kPa. In this case, the standard number of rotations of the gyrator should be a value equal to the thickness of the layer of the compacted mixture, expressed in millimeters.

In the American method of the “Superpave” design system, it is customary to compact samples from an asphalt concrete mixture also in a gyrator, but at a rotation angle of 1.25°. The work on compacting asphalt concrete samples is standardized depending on the calculated value of the total transport load on the pavement for which the mixture is being designed. A diagram of the compaction of samples from an asphalt concrete mixture in a rotary compaction device is shown in Fig. 6.

Rice. 6. - Scheme of compaction of samples from asphalt concrete mixture in a rotary compaction device:

The MTQ (Ministry of Transport of Quebec, Canada) asphalt mix design method adopts the Superpave rotary compactor instead of the LCPC gyrator. The calculated number of rotations during compaction is accepted for mixtures with a maximum grain size of 10 mm. equal to 80, and for mixtures with a particle size of 14 mm. - 100 revolutions of rotation. The estimated content of air holes in the sample should be in the range from 4 to 7%. The nominal pore volume is typically 5%. The effective volume of bitumen is established for each type of mixture, as in the LCPC method.

It is noteworthy that when designing asphalt concrete mixtures from the same materials using the Marshall method, the LCPC method (France), the Superpave design system method (USA) and the MTQ method (Canada), approximately the same results were obtained.

Despite the fact that each of the four methods provided for different conditions for compacting the samples:

• - Marshall - 75 blows from both sides;
• - “Superpave” - 100 revolutions of rotation in the gyrator at an angle of 1.25°;
• - MTQ - 80 revolutions of rotation in the gyrator at an angle of 1.25°;
• - LCPC - 60 revolutions of rotation of the effective compactor at an angle of 1°C, quite comparable results were obtained for the optimal bitumen content.

Therefore, the authors of the work came to the conclusion that it is important not to have the “correct” method of compacting laboratory samples, but to have a system for the influence of the compacting force on the structure of asphalt concrete in the sample and on its performance in the coating.

It should be noted that rotational methods for compacting asphalt concrete samples are also not without drawbacks. Noticeable abrasion of the stone material was established during the compaction of the hot asphalt concrete mixture in the gyrator.

Therefore, in the case of using stone materials characterized by wear in the Los Angeles drum of more than 30%, the normalized number of revolutions of the mixture compactor when obtaining samples of crushed stone-mastic asphalt concrete is set to 75 instead of 100.

The composition of the asphalt concrete mixture is selected according to instructions drawn up on the basis of the highway design. The assignment specifies the type, type and grade of the asphalt concrete mixture, as well as the structural layer of the road pavement for which it is intended. The selection of the composition of an asphalt concrete mixture includes testing and, based on its results, the selection of component materials, and then the establishment of a rational relationship between them, ensuring the production of asphalt concrete with properties that meet the requirements of the standard. Mineral materials and bitumen are tested in accordance with current standards, and after carrying out the entire set of tests, the suitability of the materials for an asphalt concrete mixture of a given type and grade is established, guided by the provisions of GOST. The choice of a rational relationship between the constituent materials begins with the calculation of the grain composition. The mineral part of coarse and fine-grained asphalt concrete mixtures in the presence of coarse or medium sand, as well as crushing screenings, is recommended to be selected according to continuous grain compositions, in the presence of fine natural sand - according to intermittent compositions, where the frame of crushed stone or gravel is filled with a mixture that practically does not contain grains of size 5-0.63 mm.

The mineral part of hot and warm sand and all types of cold asphalt concrete mixtures is selected only according to continuous grain compositions. For the convenience of calculations, it is advisable to use curves limit values grain compositions built in accordance with the requirements of GOST (Fig.). A mixture of crushed stone (gravel), sand and mineral powder is selected in such a way that the grain composition curve is located in the area limited by the limit curves and is as smooth as possible. When selecting the grain composition of mixtures based on crushed sand and crushed gravel, as well as on materials from rock crushing screenings, which are characterized by a high content of fine grains (finer than 0.071 mm), it is necessary to take into account the amount of the latter in the total content of mineral powder. When using materials from screenings of crushing igneous rocks complete replacement mineral powder, their finely dispersed part, is allowed in mixtures for dense hot asphalt concrete grades III, as well as in mixtures for porous and highly porous asphalt concrete grades I and II. In mixtures for hot, warm and cold asphalt concrete grades I and II, only partial replacement mineral powder; at the same time, the mass of grains finer than 0.071 mm included in the mixture must contain at least 50% limestone mineral powder that meets the requirements of GOST

When using materials from crushing screenings of carbonate rocks in the composition of hot and warm mixtures for dense asphalt concrete grades II and III, as well as cold mixtures of grades I and II and mixtures for porous and highly porous asphalt concrete grades I and II, mineral powder can be omitted if the content grains finer than 0.071 mm in screenings ensure compliance of grain compositions with GOST requirements, and the properties of grains finer than 0.315 mm in screenings meet GOST requirements for mineral powder. Rice. Continuous grain compositions of the mineral part of hot and warm fine-grained (a) and sand (b) mixtures for dense asphalt concrete used in upper layers coatings

When using polymineral gravel crushing products in asphalt concrete in road-climatic zones IV-V, it is also allowed not to introduce mineral powder into asphalt concrete mixtures of grade II if the mass of grains finer than 0.071 mm contains at least 40% calcium and magnesium carbonates (CaCO3 + MgCO3). As a result of selecting the grain composition, the percentage ratio by weight between the mineral components of asphalt concrete is established: crushed stone (gravel), sand and mineral powder. The bitumen content in the mixture is pre-selected in accordance with the recommendations of Appendix 1 of GOST and taking into account the standard requirements for the residual porosity of asphalt concrete for a specific climatic region. Thus, in road climatic zones IV-V, the use of asphalt concrete with higher residual porosity than in I-II is allowed, therefore the bitumen content in asphalt concrete for these zones is prescribed closer to the lower recommended limits, and in I-II - to the upper.

In the laboratory, three samples are prepared from an asphalt concrete mixture with a pre-selected amount of bitumen and the following are determined: the average density of asphalt concrete, the average and true density of the mineral part, the porosity of the mineral part and the residual porosity of asphalt concrete according to GOST. If the residual porosity does not correspond to the selected one, then the required content is calculated from the obtained characteristics bitumen B (%) according to the formula: B where V°pop is the porosity of the mineral part, % volume; Vpor - selected residual porosity, % volume, is accepted in accordance with GOST for a given road-climatic zone; gb - true density of bitumen, g/cm 3; gb = 1 g/cm 3; r°m - average density of the mineral part, g/cm3.

Having calculated the required amount of bitumen, the mixture is prepared again, three samples are formed from it and the residual porosity of the asphalt concrete is determined. If the residual porosity coincides with the selected one, then the calculated amount of bitumen is accepted. An asphalt concrete mixture of selected composition is prepared in the laboratory: coarse-grained kg, fine-grained kg and sand mixture kg. Samples are made from the mixture and their compliance with the physical and mechanical properties of GOST is determined. If asphalt concrete of the selected composition does not meet the requirements of the standard for some indicators, for example, strength at 50 ° C, then it is recommended to increase (within acceptable limits) the content of mineral powder or use more viscous bitumen; if strength values ​​at 0°C are unsatisfactory, the content of mineral powder should be reduced, the viscosity of bitumen should be reduced, or a polymer additive should be added.

If the water resistance of asphalt concrete is insufficient, it is advisable to increase the content of either mineral powder or bitumen; however, the residual porosity and the porosity of the mineral matrix must remain within the limits provided for by the above-mentioned standard. To increase water resistance, surfactants and activated mineral powders are most effective. When assigning bitumen content to cold asphalt concrete mixtures, additional measures should be taken to ensure that the mixture does not caking during storage. To do this, after determining the required amount of bitumen, samples are prepared for caking testing. If the caking indicator exceeds the GOST requirements, then the bitumen content is reduced by 0.5% and the test is repeated. The amount of bitumen should be reduced until satisfactory caking results are obtained, however, it is necessary to ensure that the residual porosity of cold asphalt concrete does not exceed the requirements of GOST. After adjusting the composition of the asphalt concrete mixture, the selected mixture should be tested again. The selection of the composition of the asphalt concrete mixture can be considered complete if all indicators of the properties of asphalt concrete samples meet the requirements of the above-mentioned GOST.

An example of selecting the composition of an asphalt concrete mixture. It is necessary to select the composition of a fine-grained hot asphalt concrete mixture of type B, grade II, for dense asphalt concrete intended for the installation of a top layer of pavement in the III road climate zone. The following materials are available: - crushed granite stone fraction 5-20 mm; - crushed limestone fraction 5-20 mm; - river sand; - material from granite crushing screenings; - material from limestone crushing screenings; - non-activated mineral powder; - oil grade bitumen BND 90/130 (according to the passport). The characteristics of the tested materials are given below. Crushed granite: grade for strength when crushed in a cylinder, grade for wear - I-I, grade for frost resistance - Mrz 25, true density - 2.70 g/cm 3; crushed limestone: grade for strength when crushed in a cylinder - 400, grade for wear - I-IV, grade for frost resistance - Mrz 15, true density - 2.76 g/cm 3; river sand: content of dust and clay particles - 1.8%, clay - 0.2% of mass, true density - 2.68 g/cm 3; material from granite crushing screenings grade 1000:

The content of dust and clay particles is 5%, clay is 0.4% of the mass, the true density is 2.70 g/cm 3; material from screenings of crushing limestone grade 400: content of dust and clay particles - 12%, clay - 0.5% of mass, true density - 2.76 g/cm 3; non-activated mineral powder: porosity - 33% of the volume, swelling of samples from a mixture of powder with bitumen - 2% of the volume, true density - 2.74 g/cm 3, bitumen capacity - 59 g, humidity - 0.3% of the mass; bitumen: needle penetration depth at 25°C - 94×0.1 mm, at 0°C - 31×0.1 mm, softening temperature - 45°C, elongation at 25°C - 80 cm, at 0°C - 6 cm, Fraas brittleness temperature - minus 18°C, flash point - 240°C, withstands adhesion to the mineral part of the asphalt concrete mixture, penetration index - minus 1. According to test results, crushed granite stone can be considered suitable for preparing mixtures of type B, grade II, river sand, material from granite crushing screenings, mineral powder and bitumen grade BND 90/130.

Crushed limestone and material from limestone crushing screenings do not meet the requirements of Table. 10 and 11 GOST for strength indicators. The grain compositions of the selected mineral materials are given in Table. Calculation of the composition of the mineral part of the asphalt concrete mixture begins with determining such a ratio of the masses of crushed stone, sand and mineral powder at which the grain composition of the mixture of these materials satisfies the requirements of Table. 6 GOST Table

Calculation of the amount of crushed stone In accordance with GOST and Fig. 2, and the content of crushed stone particles larger than 5 mm in type B asphalt concrete mixture is 35-50%. For this case, we accept the crushed stone content Sh = 48%. Since crushed stone contains 95% of grains larger than 5 mm, crushed stone will be required = The resulting value is entered in the table. 7 and calculate the content of each fraction in the crushed stone mixture (take 50% of the amount of each crushed stone fraction). Calculation of the amount of mineral powder In accordance with GOST and Fig. 2, and the content of particles finer than 0.071 mm in the mineral part of the asphalt concrete mixture of type B should be in the range of 6-12%. For calculation, we take the particle content, for example, closer to the lower limit of the requirements, i.e. 7%. If the number of these particles in the mineral powder is 74%, then the content of the mineral powder in the MP mixture =

However, for our conditions, 8% mineral powder should be taken, since sand and material from granite crushing screenings already contain a small amount of particles smaller than 0.071 mm. The data obtained are entered into Table 7 and the content of mineral powder of each fraction is calculated (take 8%). Calculation of the amount of sand The amount of sand P in the mixture will be: P = 100 - (Sh + MP) = (50 + 8) = 42% Since in this example two types of sand were used (river and materials from granite crushing screenings), it is necessary to determine the amount each of them separately. The relationship between river sand Pr and material from granite crushing screenings can be established by the content of grains finer than 1.25 mm, which, according to GOST and Fig. 2, and in type B asphalt concrete mixture it should be 28-39%. We accept 34%; of which 8%, as calculated above, is the share of mineral powder. Then the share of sand remains 34-8 = 26% of grains finer than 1.25 mm. Considering that the mass fraction of such grains in river sand is 73%, and in the material from granite crushing screenings - 49%, we draw up a proportion to determine the mass fraction of river sand in the mineral part of the asphalt concrete mixture:

For calculation we take Pr = 22%; then the amount of material from granite crushing screenings will be = 20%. Having calculated, similarly to crushed stone and mineral powder, the amount of each fraction in sand and material from granite crushing screenings, we record the obtained data in table. 7. By summing up the number of particles smaller than a given size in each vertical column, we obtain the overall grain composition of the mixture of mineral materials. Comparison of the resulting composition with the requirements of GOST shows that it satisfies them. Similarly, we calculate the mineral part of an asphalt concrete mixture of discontinuous grain composition. Determination of bitumen content Crushed stone, sand, material from granite crushing screenings and mineral powder are mixed with 6% bitumen. This amount of bitumen is the average value recommended in adj. 1. GOST for all road climatic zones. Three samples with a diameter and height of 71.4 mm are prepared from the resulting mixture.

Since the asphalt concrete mixture contains 50% crushed stone, the mixture is compacted using a combined method: vibrating on a vibrating platform for 3 minutes under a load of 0.03 MPa (0.3 kgf/cm 2) and additional compaction on a press for 3 minutes under a load of 20 MPa (200 kgf/cm 2). After an hour, the average density is determined ( volumetric mass) of asphalt concrete (samples), the true density of the mineral part of asphalt concrete r° and, based on these data, calculate the average density and porosity of the mineral part of the samples. Knowing the true density of all materials and choosing the residual porosity of asphalt concrete Vpor = 4% according to GOST, the approximate amount of bitumen is calculated. The average density of test asphalt concrete samples with a bitumen content of 6.0% (over 100% of the mineral part) is 2.35 g/cm3. In this case

G/cm 3 ; Three samples are made from a control mixture with 6.2% bitumen and the residual porosity is determined. If it is within 4.0 ± 0.5% (as was customary for fine-grained asphalt concrete from type B mixtures), then a new mixture is prepared with the same amount of bitumen, 15 samples are formed and tested in accordance with GOST requirements (three sample for each type of test). If the properties of samples prepared from the selected mixture deviate from GOST requirements, then it is necessary to adjust the composition of the mixture and test it again.

The grain compositions of the mineral part of mixtures and asphalt concretes must correspond to those indicated in the table. Indicators of the physical and mechanical properties of asphalt concrete used in specific road and climatic zones must correspond to those indicated in the table.

Components, formulation and properties The suitability of a powder for use in cast asphalt concrete can be objectively assessed only by testing the asphalt concrete samples produced with it. Taking into account this important circumstance makes it possible to use in some types of cast asphalt concrete even such powders that are of little use at first glance, such as loess powder, ground marl, gypsum stone or gypsum, filter press waste from the sugar industry, waste from soda factories, ferrochrome slag, etc. Sand plays important technological and economic role in the production of cast asphalt concrete mixtures. When choosing sand, preference is given to natural sand. The denser and larger the grain, the more mobile and dense the mineral mixture and the less bitumen it requires. Unlike mineral powder, most natural sea, river and lake quartz sands in chemical reaction does not interact with bitumen. For most cast mixtures, we can recommend sands that meet the requirements of the standard and table.

Components, formulation and properties For mixtures of types I and II, the use of crushing screenings containing an increased amount of dust particles is not recommended in order to avoid deterioration in the mobility of the mixtures and an increase in bitumen consumption. It is advisable to use crushed sand only as an additive to natural rounded sand in the preparation of mixtures of types I and II. in their pure form they can only be used in mixtures of types III, IV and V. Almost all properties of cast asphalt concrete are significantly improved when a 3-5 mm fraction of hard-to-polish rocks is added to the mixture. The ratio of the 3-5 mm fraction and the 5-10 fraction in the mixture should be taken as 2:1 or 1.5:1. Crushed stone (gravel) for crushed stone (gravel) cast mixtures must meet the requirements and table. 3. It is not recommended to use crushed stone obtained by crushing weak (breakability grade below 600) and porous rocks. Porous crushed stone quickly absorbs bitumen, and to ensure the necessary mobility of the mixture, the bitumen content has to be increased.

Components, formulation and properties In mixtures for the top layer, it is necessary to use crushed stone from dense and difficult to polish rocks, cubic in shape with a maximum size of up to 15 (20) mm. Moreover, for mixtures of type I crushed stone, fractions of 3-15 with a grain ratio of 3-5, 5-10 and mm in size as 2.5: 1.5: 1.0 are recommended. For type V mixtures, the maximum grain size can reach 20 mm, and for III - 40 mm. In the latter case, the strength of the original rock can be reduced by %.

Components, formulation and properties Without much damage to asphalt concrete from mixtures of types II, III and V, but with great benefits for production, the requirement for crushability of crushed stone grains can be reduced. Crushing of grains in these asphalt concrete mixtures is unlikely, since the formation of the structure into a monolith occurs under the influence of gravity or vibration and without the participation of heavy rollers. In cast mixtures of type II, III and V, gravel can be successfully used. Due to the rounded shape and ultra-acidic nature of the surface of the grains, the mixture has increased mobility with less bitumen consumption. Bitumen determines the phase composition of the asphalt binder in asphalt concrete, is subject to the greatest changes compared to other components of the mixture and affects the heat resistance of the coating. Therefore, they focus mainly on viscous grades having the properties indicated in table. 4.

Components, formulation and properties If bitumen does not have the complex of specified properties, it is improved by adding natural bitumen, bituminous rocks, elastomers, etc. Very effective additives include natural bitumen, which are well compatible with petroleum bitumen and are easy to use. Natural bitumens were formed from oil in the upper layers of the earth's crust as a result of the loss of light and medium fractions - natural deasphalting of oil, as well as the processes of interaction of its components with oxygen or sulfur. On the territory of our country, natural bitumen is found in various bituminous rocks and is rarely found in its pure form. Components, formulation and properties Bitumen deposits occur in the form of layers, lenses, veins and on the surface. The largest amount of bitumen is contained in reservoir and lens deposits. Vein deposits are rare in our country. A significant amount of natural bitumen is found in surface deposits. In terms of their chemical composition, these bitumens are similar to petroleum bitumens. Natural bitumens are hard, viscous and liquid. Hard bitumen (asphaltite). Density of asphaltites kg/m3, softening temperature °C. On average, asphaltite contains 25% oils, 20% resins and 55% asphaltenes. Asphaltites have increased adhesive properties due to the high content of natural surfactants in their composition - asphaltogenic acids and their anhydrides. Asphaltites are resistant to aging when exposed to solar radiation and atmospheric oxygen.

Components, formulation and properties Positive results were obtained by introducing crushed polyethylene into the cast mixture, as well as finely ground rubber powder (TIRP) in an amount of 1.5% by weight of mineral materials. As an additive that increases the thermal stability of cast asphalt concrete, it is recommended to use degassed sulfur in lump, granular (granule size up to 6 mm) or liquid form. Sulfur is introduced into the mixer on hot mineral materials, i.e. before feeding bitumen. The amount of sulfur is prescribed within 0.25-0.65 of the bitumen content. In this case, the amount of bitumen with sulfur is 0.4-0.6 of the content of mineral powder.

Components, formulation and properties To summarize the above, you need to keep in mind that most of the listed “know-how” require overcoming serious technical and technological problems, as well as additional financial costs, which not all organizations can solve. By increasing production costs, they do not always contribute to improving the technological properties of mixtures and performance characteristics coatings, as well as human health and the environment. It is recommended to select the mixture recipe using a special method. The calculation of the component content begins after determining the grain (granulometric) composition of all mineral materials and constructing a sieving curve. The curve must fit within the recommended limits for a particular type of mixture 53 Components, formulation and properties If the sieving curve does not fit within the recommended limits, adjust the content of individual grains by changing their quantity in the mineral mixture. When calculating the amount of mineral powder, it is necessary to make an adjustment for the content of dust from sand and crushed stone in the mineral mixture. Next, guided by the numerical values ​​of the phase composition of the asphalt binder (B/MP) and its quantity (B+MP) for the corresponding type of cast mixture, a dose of bitumen (polymer bitumen or other bitumen binder) is introduced and the property indicators are determined. The main indicators of the properties of cast mixture and asphalt concrete samples, for the given values ​​of which the composition is selected, are for types: I and V - mobility, depth of stamp indentation and water saturation; II - mobility, compressive strength at +50 °C and depth of indentation of the stamp; III - mobility and water saturation; IV - water saturation and compressive strength at +50 °C.

Components, formulation and properties The tensile strength in bending and the elastic modulus at 0 °C are optionally determined, as well as the crack resistance coefficient as the ratio of the values ​​of these indicators. If the properties of the mixture and asphalt concrete fully comply with the required ones (table), the selection is considered successful. Table - Physical and mechanical properties of cast asphalt concrete

Asphalt concrete mixture is a building material obtained artificially. According to the production technology, a rational selection of the main components is carried out, and then the material is compacted with vibrators. Performance Requirements asphalt concrete composition included in GOST 9128.

What ingredients are used in the mixture?

The asphalt concrete solution contains the following ingredients:

• components of mineral origin, such as natural or crushed sand, crushed stone (gravel), fine powder admixtures (if necessary);
• binders of organic origin, such as bitumen.

Initially, tar was used instead of bitumen. However, it was abandoned due to its harmful effects on human health and the environment. To mix the components, the asphalt concrete mixture is heated. The purpose of asphalt concrete is laying roads for airfields and highways, arranging industrial floors. According to the principle of laying, asphalt concrete is:

• compacted;
• cast, it is characterized by high fluidity and a high content of binder material, therefore it allows masonry to be carried out without compaction.

The composition of asphalt concrete is:

• crushed stone;
• gravel;
• sandy.

Viscosity of bitumen and Maximum temperature masonry determines the following types of mixtures:

• hot, laid at 120 °C with binders in the form of viscous-liquid road bitumen;
• cold, laid up to 5 °C, where liquid bitumen materials of petroleum origin act as a binder;
• warm for masonry up to 70 °C based on viscous-liquid bitumen.

However, the latter type has not been found as a separate species since 1999. Types of hot asphalt concrete based on residual percentage porosity:

• high-density - 1-2.5%;
• highly porous - 10-18%;
• dense - 2.5-5%;
• porous - 5-10%.

In cold solutions this value is 6-10%. According to the maximum particle size of the mineral component used, the asphalt concrete sheet can be:

• coarse-grained with particle size up to 4 cm;
• fine-grained with particles up to 2 cm;
• sandy with a size of up to 5 cm.

• type A, in which the composition of the mineral stone is 50-60%;
• type B with stone content 40-50%;
• type B, including 30-40% filler.

What algorithms exist for designing the component composition of asphalt concrete?

To select the composition of the asphalt concrete solution, a rational ratio of components is selected. The resulting compositions have a given density and technical properties. There are four design algorithms:

1. Method of Professor P.V. Sakharov
2. Modulo saturation method provided by Professor Durieu M.
3. Design algorithm for the required operating conditions of the coating, obtained through the research of Professor I. A. Rybyev.
4. Selection based on density curves, developed by Professor N.I. Ivanov with the assistance of SoyuzDorNII.

An example of the optimal selection of asphalt concrete mixture ingredients

As an example of asphalt concrete components, it is proposed to consider the problem: a fine-grained hot mixture of type B of the second grade is needed to create a dense top ball of the road in the third climatic zone. The following ingredients are available:

• granite and limestone crushed stone with a grain size of 0.5-2 cm;
• river sand;
• screening after grinding granite chips;
• screenings after crushing limestone;
• non-activated mineral powder;
• bitumen material BND 90/130.

The first stage involves testing and comparing the characteristics of the ingredients presented above. Based on the results of testing samples with different ratios of components, it was concluded that river sand, granite dust, mineral powder, and bitumen material are suitable for producing type B and second grade asphalt concrete mixtures.

Limestone and dust from the crushed limestone component did not meet GOST standards for strength parameters. At the second stage, crushed stone is calculated. Its content with a particle size greater than 0.5 cm is 35-50%. The optimal content in mixtures is 48%. The material contains 95% of particles of the specified size, so the formula looks like:

In this way, the amount of crushed stone in the mixture for the fractional composition is calculated.

At the third stage, the composition of the mineral powder is determined. Calculations begin with deriving the mass proportions of crushed stone, sand and mineral powder with a fractional composition, according to GOST. Consequently, the content of grains smaller than 0.0071 cm in the asphalt concrete mineral material should be in the range of 6-12%. For calculations, 7% is taken. When the content of elements with a particle size of 0.0071 cm is 74% in a powder mineral, the calculation formula looks like this:

Due to the presence of particles less than 0.0071 cm from granite screenings in the mixture, the minpowder fraction is taken equal to 8%. At the fourth stage, the amount of sand is calculated. Its general content is:

Sand = 100 - (Crushed stone minpowder) = 100 - (50 8) = 42%.

The example uses river and granite sand screening. Therefore, the proportions of each are determined separately. The percentage of the river component and granite screenings is established by their fraction with a particle size of less than 0.125 cm. For an asphalt concrete mixture, the grains should be in an amount of 28-39%. The average 34% is taken, 8% of which is calculated as the proportion of minpowder. Therefore, sand needs 34-8 = 26% for particles with a particle size of less than 0.125 cm. Since the mass fraction of these grains in river sand material is 73%, granite dust is 49%, the proportion for type B asphalt concrete mixtures is:

We round the resulting value to 22%, therefore, the content of screenings from granite chips is 42 - 22 = 20%. A similar calculation is carried out for each fraction of sand and screenings. The data is summarized in a table and values ​​with dimensions less than those specified for each individual ingredient are summed up, then compared with the requirements of GOST.

At the fifth stage, the content of the bitumen component is calculated. According to the conditions, crushed stone, sand, screenings of crushed granite, mineral powder are mixed with 6% of the binding ingredient, which corresponds to the average value required in the regulatory document. Three samples of the mixture are prepared with a height of 7.14 cm and an appropriate diameter. Next, compaction is carried out using a combined method:

• three minutes on a vibration platform at a pressure of 0.03 MPa;
• three-minute compaction on a vibropress at a pressure of 20 MPa.

After two days, the average density is determined, that is, the mass in terms of the volume of asphalt concrete, the real density of the mineral component of the mixture r°. Based on the data obtained, in addition to density, the porosity of the mineral component of the tested samples is calculated.

The approximate amount of bitumen binder is determined by the actual density of all ingredients, taking into account the residual porosity of asphalt concrete V pores = 4%. At the same time, the average density of asphalt concrete samples with a bitumen content of 6% per 100% minerals is 2.35 g/cm3. Therefore, the calculation formulas look like:

Next, three more asphalt concrete samples with a bitumen content of 6.2% are prepared to determine the residual porosity. If its value is 4.0 ± 0.5%, additional 15 samples of such a mixture are prepared and tested in accordance with GOST 9128-84.

If a discrepancy with the requirements of the regulatory document is detected, the mixture is adjusted and subsequently tested, as indicated above.

The calculation consists of selecting a rational ratio between the materials that make up the asphalt concrete mixture.

The method of calculation using curves of dense mixtures has become widespread. The greatest strength of asphalt concrete is achieved with the maximum density of the mineral core, the optimal amount of bitumen and mineral powder.

Between grain composition mineral material and density there is a direct relationship. Formulations containing grains will be optimal. various sizes, the diameters of which are halved.

Where d 1 - largest grain diameter, set depending on the type of mixture;

d 2 - the smallest grain diameter corresponding to the dust fraction and mineral powder (0.004...0.005 mm).

Grain sizes according to previous level

(6.6.2)

The number of sizes is determined by the formula

(6.6.3)

Number of factions P per unit less number sizes T

(6.6.4)

Ratio of adjacent fractions by mass

(6.6.5)

Where TO- escape coefficient.

The value showing how many times the amount of the subsequent fraction is less than the previous one is called the escape coefficient. The most dense mixture is obtained with a runoff coefficient of 0.8, but such a mixture is difficult to select, therefore, according to the suggestion of N.N. Ivanova, escape coefficient TO accepted from 0.7 to 0.9.