Selection of the composition of the asphalt concrete mixture. An example of the selection of the composition of the asphalt concrete mixture. Bitumen ratio and mineral components

3.8. It is necessary to choose the composition of the fine-grained hot asphalt concrete mixture of type B brand II for a dense asphalt concrete intended for the device of the upper coating layer in the third road-climatic zone.

The following materials are available:

rubble granite fraction 5-20 mm;

crushed stone limestone fraction 5-20 mm;

sand River;

material from sefing crushing granite;

material from limestone fragments;

mineral powder non-activated;

bitumen of the oil brand BND 90/130 (by passport).

Characteristics of test materials listed.

Crushed stone granite: stamp for strength when crushing in the cylinder - 1000, brand of wear - I - I, brand for frost resistance - MRЗ25, true density - 2.70 g / cm 3;

limestone crushed stone: stamp for strength when crushing in the cylinder - 400, brand of wear - I-IV, stamp on frost resistance - MPZ15, true density - 2.76 g / cm 3;

sand River: The content of dust and clay particles - 1.8%, clays - 0.2% mass, true density - 2.68 g / cm 3;

material from seferences of crushing granite brand 1000:

material from seferences of crushing of limestone grade 400: the content of dust and clay particles - 12%, clay - 0.5% mass, the true density - 2.76 g / cm 3;

mineral powder Unactivated: porosity - 33% of the volume, swelling of samples from a mixture of powder with bitumen - 2% of the volume, the true density - 2.74 g / cm 3, the bitmary capacity indicator is 59 g, the humidity is 0.3% of the mass;

bitumen: the depth of penetration of the needle at 25 ° C - 94 × 0.1 mm, at 0 ° C - 31 × 0.1 mm, the softening temperature is 45 ° C, tensile at 25 ° C - 80 cm, at 0 ° C - 6 cm, the temperature of fragility according to Fraas - minus 18 ° C, the flash point is 240 ° C, the adhesion with the mineral part of the asphalt concrete mixture withstands, the penetration index is minus 1.

According to the results of the tests suitable for the preparation of mixtures of type B brand II, it can be considered crushed stone granite, the sand river, material from the sefs of crushing granite, mineral powder and the BND 90/130 bits of the BND brand.

Table 7.

Crushed limestone and material from seferences of crushing limestone do not meet the requirements of Table. 10i 11. GOST 9128-84in terms of strength.

The grain compositions of selected mineral materials are given in table. 7..

The calculation of the composition of the mineral part of the asphalt concrete mixture is beginning with the determination of such a ratio of masses of rubble, sand and mineral powder, in which the grain composition of the mixture of these materials satisfies the requirements of Table. 6. GOST 9128-84.

The calculation is the selection of rational relationship between the components of the asphalt concrete mixture with materials.

Wide distribution received a method for calculating the curves of dense mixtures. The greatest strength of the asphalt concrete is achieved at the maximum density of the mineral island, the optimal amount of bitumen and mineral powder.

There is direct dependence between the grain composition of mineral material and density. The optimal compositions containing grains of various sized, the diameters of which are reduced by two times.

where d. 1 - the largest diameter of the grain, mounted depending on the type of mixture;

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

Grain sizes, according to the previous level

(6.6.2)

The number of sizes are determined by the formula

(6.6.3)

Number of fractions p per unit less than the number of sizes t.

(6.6.4)

The ratio of neighboring fractions by mass

(6.6.5)

where TO - Razba coefficient.

The value indicating 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 range of 0.8, but it is difficult to choose such a mixture, therefore, at the proposal of N.N. Ivanova, Ranger Fatiff TO Adopted from 0.7 to 0.9.

It is largely dependent on the properties of the ingredients of the mixture and their ratio.

There are several types of asphalt concrete, the composition of which is noticeably different. In some cases, the composition and quality of the initial ingredients turns out to be related to the production method.

• So, for 1-3 climatic belts, dense and highly qualified ab are made of rubble, whose class of frost resistance is F50. Porous and highly porous - from stone class F 15 and F25.
• For zones 4 and 5, only high-detached hot asphalt is performed on the basis of rubble class F 50

We will talk about the role of sand as picked up asphalt concrete.

Sand

Available in any kind of AB, but in some - sand asphalt concrete, it acts as the only mineral part. Apply both natural - from quarries and the resulting by the screening during crushing. Requirements for material dictation GOST 8736.

• So, for dense and highly discovered sand with a class of strength of 800 and 1000. For porous - decreases to 400.
• The number of clay particles - in diameter less than 0.16 mm, is also adjustable: for dense - 0.5%. For porous - 1%.
• Increases the ability of AB to swelling and reduces frost resistance, so it is particularly followed by this factor.

Mineral powder

This part forms a binder with bitumen. Also, the powder fills the pores between large stone particles, which reduces the internal friction. Grain sizes are extremely small - 0, 074 mm. Get them from the dust collectors system.

In fact, the mineral powder is made from waste of cement enterprises and metallurgical - it is dust-carrying cement, ashlake mixtures, waste recycling of metallurgical slags. Grain composition, the amount of water-soluble compounds, water resistance and other adjusts GOST 16557.

Additional components

To improve the composition or giving some specific properties, various additives are introduced into the initial mixture. Share them for 2 main groups:

• components developed and manufactured specifically to improve properties - plasticizers, stabilizers, substances that prevent aging and so on;
• waste or secondary raw materials - sulfur, granulated rubber and so on. The cost of such additives is of course much less.

The selection and design of the composition of the road and airfield asphalt concrete are discussed below.

About selection of samples to assess the composition and quality of asphalt concrete will tell the video below:

Design

The composition of the coating device from the asphalt concrete is selected based on the destination: the street in a small town, the highway and the bicycle path require different asphalt. To get the best coating, but at the same time not to overcome the materials, the following selection principles use.

Basic principles

• The grain composition of the mineral ingredient, that is, stone, sand and powder, is basic to ensure the density and roughness of the coating. Most often use the principle of continuous granulometry, and only in the absence of large sand - the method of intermittent granulometry. Grain composition - particle diameters and their correct ratio, must fully correspond to that.

The mixture is selected in such a way that the curve is placed on the site between the limit values \u200b\u200band did not include fractures: the latter means that an excess one is observed or a lack of some fraction.

• Various types of asphalt can form a frame and frameless structure of the mineral component. In the first case, rubble enough so that the stones come into contact with each other and the finished product formed a clearly pronounced structure of the asphalt concrete. In the second case, stones and grains of large sand do not come into contact. A somewhat conventional boundary between the two structures is the content of rubble in the range of 40-45%. When selecting this nuance must be considered.
• The maximum strength guarantees crushed stone cuboid or tetrahedral form. Such a stone is the most wearless.
• Surface roughness reports 50-60% of rubble from hard-pointed rocks or sand from them. Such a stone retains the roughness of natural chip, and this is important to ensure the adequacy of the asphalt.
• In general, asphalt based on crushed sand is more shifted than based on the career due to the smooth surface of the latter. For the same reasons, durability and durability of material based on gravel, especially marine less.
• Excess grinding of the mining machine leads to an increase in porosity, and, it means that bitumen consumption. And such property has most industrial waste. To reduce the parameter, the mineral powder is activated - treated with surfactants and bitumen. Such a modification not only reduces the content of bitumen, but also increases the water and frost resistance.
• When selecting bitumen, it is necessary to focus not only on its absolute viscosity - the higher it is higher, the higher the density of the asphalt, but also on the weather conditions. Thus, in arid areas, the composition is selected, providing the minimum possible porosity. In cold mixtures, on the contrary, the bitumen is reduced by 10-15% to reduce the level of hellight.

Selection of composition

The selection procedure is generally the same:

• evaluation of the properties of mineral ingredients and bitumen. This refers not only absolute indicators, but their compliance of the ultimate goal;
• calculate such a ratio of stone, sand and powder so that this part of the asphalt acquires the highest possible density;
• lastly, the amount of bitumen is calculated: sufficient to provide the desired technical properties of the finished product on the basis of the selected materials.

First, theoretical calculations are carried out, and then laboratory tests. First of all, the residual porosity is checked, and then the correspondence of all other characteristics are supposed. Calculations and tests are carried out until a mixture is obtained that fully satisfying the task.

As with all sorts of complex building material, AB has no one-valued qualities - density, specific gravity, strength, and so on. Its parameters determine the composition and method of preparation.

On how the design of asphalt concrete composition in the United States, the next cognitive video will tell:

In Russia, the largest distribution was obtained by the search for the compositions of the mineral part of asphalt concrete mixtures on the limiting curves of grain compositions. A mixture of rubble, sand and mineral powder is chosen in such a way that the cereal curve is located in a zone limited by limit curves, and was smooth. The fractional composition of the mineral mixture is calculated depending on the content of selected components and their grain compositions by the following dependency:

j - number component;

n - the number of components in the mixture;

When selecting the grain composition of the asphalt concrete mixture, especially with the use of sand from crushing sections, it is necessary to take into account the grain-contained grain with a smallest of 0.071 mm., Which when heated in the drying drum is blew and settle in the dust collection system.

These dust particles can either be removed from the mixture, or dose to the mixing unit with mineral powder. The procedure for using dust capture is negotiated in the technological regulation on the preparation of asphalt concrete mixtures, taking into account the quality of the material and features of the asphalt mixing installation.

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

With the calculated amount of bitumen, the mixture is prepared, formulate samples from it and again determine the residual porosity of the asphalt concrete. If it will correspond to the required, the calculated amount of bitumen is based on the basis. Otherwise, the procedure for selecting a bitumen content based on approximation to the normalized pore volume in the compacted asphalt concrete is repeated.

From the asphalt concrete mixture with a predetermined content of bitumen, the standard method of samples is molded by a standard sealing method and determine the full range of indicators of physicomechanical properties provided for in GOST 9128-97. If the asphalt concrete for any indicators does not respond to the requirements of the standard, the composition of the mixture is changed.

With an insufficient value of the inner friction coefficient, the content of large fractions of rubble or crushed grains in the sandy part of the mixture should be increased.

With low clutch indicators for shift and compressive strength at 50 ° C, it should be increased (under permissible limits) the content of the mineral powder or apply a more viscous bitumen. At high strength values \u200b\u200bat 0 ° C, it is recommended to reduce the content of the mineral powder, reduce the viscosity of the bitumen, apply polymer-bitumen binder or use plasticizing additives.

With insufficient water resistance of the asphalt concrete, it is advisable to increase the content of mineral powder or bitumen, but within the limits that ensure the required values \u200b\u200bof residual porosity and porosity of the mineral part. To increase the water resistance, essentially used surfactants (surfactants), activators and activated mineral powders. The selection of the composition of the asphalt concrete mixture is considered complete if all indicators of physicomechanical properties obtained by testing asphalt-concrete samples will meet the requirements of the standard. However, in the framework of the standard requirements for the asphalt concrete, the composition of the mixture is recommended to be optimized in the direction of increasing the operational properties and the durability of the arranged structural layer of road clothing.

The optimization of the composition of the mixture intended for the device of the upper layers of road surfaces until recently was associated with an increase in the density of asphalt concrete. In this regard, in road construction, three methods were formed, used in the selection of grain compositions of dense mixtures. Initially, they were called as:

• - Experimental (German) method of selection of dense mixtures, consisting in the gradual filling of one material to others;
• - method of curves based on the selection of grain composition approaching the predetermined mathematically "ideal" curves of dense mixtures;
• - American method of standard mixtures based on appraded mixtures of concrete materials.

These methods were offered about 100 years ago and were further developed.

The essence of the experimental method of selection of dense mixtures is to gradually fill the pores of one material with larger grains of other smaller mineral material. Practically selection of the mixture is carried out in the following order.

To 100, the weight parts of the first material are added sequentially 10, 20, 30, etc., the weight parts of the second, determining after mixing and sealing the average density and choosing a mixture with a minimum amount of voids in the compacted state.

If it is necessary to make a mixture of three components, then to a dense mixture of two materials add gradually increasing portions of the third material and also choose the most dense mixture. Although this selection of the dense mineral island time-consuming and does not take into account the effects of the content of the liquid phase and the properties of the bitumen on the compaction of the mixture, nevertheless it is still used in experimental research.

In addition, the experimental method of selection of dense mixtures was based on the calculated methods for the preparation of dense concrete mixtures of bulk materials of various lampsiness and was further developed in the methods of planning the experiment. The principle of consistent filling of voids was used in the method of designing the optimal compositions of road asphalt concrete concrete, in which crushed stone, gravel and sand with any granulometry are used.

According to the authors of the work, the proposed estimated experimental technique allows you to optimally control the structure, composition, properties and cost of asphalt concrete. The role of variable structural control parameters uses:

• - coefficients of sliding grains of rubble, gravel and sand;
• - bulk concentration of mineral powder in asphalt binder;
• - the optimal criterion of the composition, expressed by the minimum total value of components per unit of products.

On the principle of consistent filling of voids in crushed, sand and mineral powder, an estimated composition of the mixture for asphalt concrete density based on liquid bitumens was calculated.

The content of components in the mixture was calculated based on the results of the preset value of the true and bulk density of mineral materials. The final composition was specified experimentally when varying the content of all components of the mixture by the method of mathematical planning experiment on the simplex. The composition of the mixture providing minimal porosity of the mineral island of asphalt concrete was considered optimal.

The second method of selection of the grain composition of asphalt concrete is based on the selection of dense mineral mixtures, the grain composition of which is approaching the perfect curves of Fuller, Count, Herman, Bolomey, Talbot Richard, Kitt-Pepfa and other authors. These curves in most cases are subsequent dependencies of the desired grain content in the mixture of their size. For example, the curve of the particle size composition of the dense mixture on the fuller is given by the following equation:

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

To normalize the grain composition of the asphalt concrete mixture in the modern American method of designing "SuperPave", granulometric curves of the maximum density, corresponding to the power dependence with the indicator of 0.45, are also taken.

Moreover, besides the control points that limit the range of grain content, the inner zone of the restriction is also given, which is located along the granulometric curve of the maximum density in the gap between the grains of 2.36 and 0.3 mm. It is believed that mixtures with a granulometric composition passing by the restrictive zone may have problems with sealing and shift stability, since they are more sensitive to the content of bitumen and become plastic in case of accidental overdose of organic binder.

It should be noted that GOST 9128-76 also prescribed a restrictive zone for curves of dense mixtures, located between the limit curves of continuous and intermittent granulometry. In fig. 1 This zone is shaded.

Fig. one. - The grain compositions of the mineral part of the fine-grained:

However, in 1986, when reproducing the standard, this restriction was canceled as insignificant. Moreover, in the works of the Leningrad branch of Somponia (A.O. Sal), it was shown that the so-called "semi-broker" compounds of mixtures in some cases preferably continuous due to lower porosity of the mineral part of the asphalt concrete, and intermittent - due to greater stability to bundle.

The domestic method for constructing curves of the particle size distribution of dense mixtures was the famous studies of V.V. The hunter, in which it was shown that the most dense mixture can be obtained provided if the diameter of the particles constituting the material will decrease in the proportion of 1:16, and the weights of their quantities are as 1: 0.43. However, given the tendency to segregation of mixtures, composed with this ratio of large and small fractions, was proposed to add intermediate fractions. In this case, the weight of the fraction with a diameter, 16 times smaller, will not change at all, if the emptiness is not simply filled with these fractions, but, for example, fractions with a grain diameter of 4 times smaller.

If when filling with fractions 16 times with a smaller diameter, their weight content was 0.43, then when filling with fractions with a diameter of grains, 4 times smaller, their content should be equal to \u003d 0.67. If you enter another intermediate fraction with a diameter that decreased by 2 times, the ratio of fractions should be K \u003d 0.81. Thus, the weight number of fractions that will decrease on the same value all the time, it can be expressed mathematically as a series of geometric progression:

Y1 - the number of the first fraction;

to - the escape coefficient;

n is the number of fractions in the mixture.

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

Thus, the escape ratio is made to call the weight ratio of fractions, the dimensions of the particles of which are treated as 1: 2, i.e., as the ratio of the nearest sizes of cells in the standard set of SIT.

Although theoretically, the most dense mixtures are calculated by the outfit ratio of 0.81, mixtures with intermittent grain composition were more dense.

This is explained by the fact that the theoretical calculations of the compilation of dense mixtures on the outfit ratio do not take into account the sliding of large grains of the material with smaller grains. In this regard, P.V. Sakharov noted that positive results from the point of view of increasing the density of the mixture are obtained only with a step (intermittent) selection of fractions.

If the ratio of the size of the mixed fractions is less than 1: 2 or 1: 3, then small particles do not fill the gap between large grains, and spread them.

The curves of the particle size composition of the mineral part of the asphalt concrete with various rebel coefficients are shown in Fig. 2.

Fig. 2. - Granulometric composition of the mineral part of the asphalt concrete mixtures with various Raceba coefficients:

Later, the ratio of the diameters of the particles of adjacent fractions, excluding the sliding of large grains in many fractional mineral mixtures, was specified. According to P.I. Bozhenova to eliminate the sliding of large grains with small, the ratio of the diameter of the shallow fraction to the diameter of the large fraction should be no more than 0.225 (i.e., as 1: 4.44). Given the composition of mineral mixtures proven in practice, N.N. Ivanov proposed to be used to seize mixtures a granulometric composition curve with a rank factor ranging from 0.65 to 0.90.

Granulometric compositions of dense asphalt concrete mixtures, focused on convenientness, were normalized in the USSR from 1932 to 1967. In accordance with these norms, the asphalt concrete mixtures contained a limited amount of rubble (26-45%) and an increased amount of mineral powder (8-23%). The experience of using such mixtures has shown that in coatings, especially on roads with severe and intensive movement, waves, shifts and other plastic deformations are formed. At the same time, the roughness of the surface of the coating was also insufficient to provide high adhesion with the wheels of cars, based on traffic safety conditions.

The fundamental changes in the standard for asphalt mixtures were made in 1967. GOST 9128-67 included new compounds of mixtures for framework asphalt concrete concrete (up to 65%), which began to provide in projects with high traffic intensity. The asphalt concrete mixtures also reduced the amount of mineral powder and bitumen, which justified the need to move from plastic to tougher mixtures.

The compositions of the mineral part Many crushed wall mixtures were calculated using a cubic parabolic equation tied to four control dimensions of grains: 20; 5; 1.25 and 0.071 mm.

In the study and implementation of the frame asphalt concrete, great importance was attached to the increase in coating roughness. The methods of the device of asphalt concrete coatings with a rough surface were reflected in the recommendations developed in the early 60s of the last century and received the initial introduction at the facilities of the Glavdorstroy Ministry of Transport of the USSR. According to developers, the creation of roughness should be preceded by the formation of a spatial frame in the asphalt concrete. Almost this was achieved by a decrease in the amount of mineral powder in a mixture, an increase in the content of large crushed grains, a complete seal of the mixture, in which grains of rubble and large sand fractions come into contact with each other. Obtaining an asphalt concrete with a frame structure and a rough surface was provided 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% grains are larger than 1.25 mm. In the sandy mixtures of type r with a limited content of mineral powder (4-8% in fine-grained mixtures and 8-14% in sandy).

Recommendations for ensuring the effectability of asphalt concrete coatings as a result of the use of frame asphalt concrete, by increasing the internal friction of the mineral island and are also present in foreign publications.

For example, road firms from the UK during the construction of asphalt concrete coatings in tropical and subtropical countries specially apply grain compositions, selected by the equation of the cubic parabola.

The stability of coating from such mixtures is mainly due to the mechanical sugar of particles of angular shape, which must be either durable rubble or crushed gravel. Apply unfinished gravel in such mixtures is not allowed.

The resistance of the coating shift deformations can be increased by increasing rubble size. In the USATM D 3515-96 standard, asphalt concrete mixes were provided, differentiated by nine grades, depending on the maximum grain size of 1.18 to 50 mm.

The higher the brand, the larger the crushed stone and the lower the content of the mineral powder in the composition of the mixture. Curves grain compositions built on cubic parabole provide a hard frame of large grains during sealing coating, which has the main resistance to transport loads.

In most cases, the mineral part of the asphalt concrete mixture is selected from the coarse, mediterranean and fine-grained components. If the true density of the components of mineral materials differs significantly among themselves, the content of them in the mixture is recommended to calculate in volume.

Tested in practice, the grain compositions of the mineral part of the asphalt concrete mixtures are standardized in all technically developed countries, taking into account the field of their application. These compositions are usually consistent with each other.

In general, it is believed that the most developed element of the design of the composition of the asphalt concrete is the selection of the granulometric composition of the mineral part or by the optimal density curve, or on the principle of consistent pore fill. It is more difficult to deal with the choice of bitumen binders of necessary quality and with the rationale for its optimal content in the mixture. Until now, there is no single opinion on the reliability of the calculated methods for the purpose of the content of bitumen in the asphalt concrete mixture.

The current experimental methods of selection of the binding content involve different methods of manufacturing and testing asphalt-concrete samples in the laboratory and, most importantly, it is enough to reliably predict the durability and operational condition of the road surfaces depending on the operating conditions.

P.V. Sakharov offered to design the composition of the asphalt concrete at a pre-selected composition of the asphalt binder. The quantitative ratio of bitumen and mineral powder in the asphalt binder was selected experimentally depending on the plastic deformation indicator (by water removal) and on the tensile strength of the eight samples. The thermal stability of the asphalt binder with comparison of strength indicators at temperatures 30, 15 and 0 ° C was also taken into account. Based on the experimental data, it was recommended to adhere to the values \u200b\u200bof the ratio of bitumen to the mineral powder by mass (b / mp) in the range from 0.5 to 0.2.

As a result, the composition of the asphalt concrete was characterized by an increased content of mineral powder. In further research I.A. Fishkeva It was shown that the rational values \u200b\u200bof b / mp can be equal to 0.8 and even higher. Based on the strength of the strength of the optimal structures (the rule of the crust), the method of designing the composition of the asphalt concrete on the specified operating conditions of the road surface was recommended. It was stated that the optimal structure of the asphalt concrete is achieved when the bitumen is translated into a film state.

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

Therefore, the scientific substantiation of the required operational indicators of asphalt concrete and rational ways to achieve them continue to remain the main task associated with increasing the durability of road surfaces.

There are several calculated ways to prescribe bitumen content in the asphalt concrete mixture both by the thickness of the bitumen film on the surface of mineral grains and by the amount of voids in the compacted mineral mixture.

The first attempts of their use when designing asphalt concrete mixtures often ended in failure, which forced to improve the calculated methods for determining the content of bitumen in the mixture. N.N. Ivanov proposed to take into account the best sealability of the hot asphalt mixture and some stock on the temperature expansion of the bitumen if the calculation of the bitumen content is carried out on the porosity of the compacted mineral mixture:

B - the number of bitumen,%;

P - porosity of a compacted mineral mixture,%;

c6 - True bitumen density, g / cm. cube;

c is the average density of a compacted dry mixture, g / cm. cube;

0.85 - the coefficient of reducing the number of bitumen due to the best sealing of the mixture with bitumen and the bitumen expansion coefficient, which is taken equal to 0.0017.

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

Fig. 3. - Normalization of the phase volume in the asphalt concrete:

In accordance with this diagram, the content of bitumen (% by volume) is equal to the difference between the porosity of the mineral island and the residual porosity of the compacted asphalt concrete. So, M. Düyrie recommended a methodology for calculating the content of bitumen in a hot asphalt concrete mixture in the saturation module. The saturation module of the asphalt concrete binding substance was established according to experimental and production data and characterizes the percentage of binder in a mineral mixture having a specific surface of 1 mq / kg.

This technique is adopted to determine the minimum content of bitumen binder depending on the grain composition of the mineral part in the design method of the asphalt concrete mixture of LCPC. Developed by the central laboratory of bridges and roads of France. The weight content of the bitumen on this method is determined by the formula:

k is a module of saturation of asphalt concrete binder.

• S - Private residue on sieve with holes of 0.315 mm.,%;
• s is a private residue on sieve with holes of 0.08 mm.,%;

The method of calculating the content of bitumen in the thickness of the bitumen film significantly improved I.V. Queen. Based on the experimental data, they produced differentiation of the specific surface of the grains of standard fractions, depending on the nature of the rock. The influence of the nature of the stone material, the size of grains and viscosity of bitumen on the optimal thickness of the bituminous film in the asphalt mixture was shown.

The next step is the differentiated assessment of the bituminosity of mineral particles with smaller than 0.071 mm. As a result of the statistical prediction of the grain compositions of the mineral powder and bitmaking fractions of fractions from 1 to 71 μm in MADI (GTU), a technique was developed that allows us to obtain calculated data that satisfactorily coincide with the experimental content of bitumen in the asphalt concrete mixture.

Another approach to the purpose of the content of bitumen in the asphalt concrete is based on the dependence between the porosity of the mineral island and the grain composition of the mineral part. Based on the study of experimental mixtures from particles of various majority, Japanese specialists proposed a mathematical model of the porosity of the mineral island (VMA). The values \u200b\u200bof the coefficients of the established correlation dependence were determined for a crushed stone-mastic asphalt concrete, which was compacted in the rotational seal (hyporator) at 300 mold revolutions. The algorithm for calculating the content of bitumen based on the correlation of the pore characteristics of the asphalt concrete with the grain composition of the mixture was proposed in operation. According to the results of the processing of the data array obtained by testing dense asphalt concrete, the following correlations are established to calculate the optimal content of the bitumen:

K - Granureometry parameter.

DKR is the minimum grain size of a large fraction, which contains 69.1% by weight of the mixture, mm.;

D0 - the size of the grains of the middle fraction, the smaller of which contains 38.1% by weight of the mixture, mm.;

DMELK is the maximum grain size of a shallow fraction, the smoother of which contains 19.1% by weight of the mixture, mm.

However, in any case, the calculated bitumen dosages should be adjusted in the preparation of control injuries depending on the results of the test samples of the asphalt concrete.

When selecting the compositions of asphalt concrete mixtures, the following statement of prof is relevant. N.N. Ivanova: "bitumen should be taken no more than it is due to the production of a sufficiently strong and stable mixture, but the bitumen must be taken possible more, and in no case maybe less." Experimental methods of selection of asphalt concrete mixtures usually suggest the preparation of standard samples given by the specified methods of sealing and testing them in laboratory conditions. For each method, appropriate criteria are developed that establish a link between the results of laboratory tests of compacted samples and the operational characteristics of the asphalt concrete under operating conditions.

In most cases, ZGI criteria are defined and standardized by national standards on asphalt concrete.

The following schemes of mechanical tests of the asphalt concrete samples are distributed, presented in Fig. four.

Fig. four. - Test schemes of cylindrical samples when designing the composition of the asphalt concrete:

a - in Dultsu;

b - by Marshall;

in - by kvimim;

mr. Hubbard Field.

An analysis of the various experimental methods for the design of the composition of the asphalt concrete indicates the similarity in approaches when prescription and the difference in the test methods and in the criteria of the estimated properties.

The similarity methods for the design of the asphalt concrete mixture is based on the selection of such a volumetric ratio of components in which the predetermined values \u200b\u200bof residual porosity are ensured and the normalized indicators of the mechanical properties of the asphalt concrete.

In Russia, in the design of the asphalt concrete, there are tests of standard cylindrical samples on a uniaxial compression (according to Dageza scheme), which are molded in the laboratory according to GOST 12801-98, depending on the content of rubble in a mixture or a static load of 40 MPa, or a vibration method with subsequent additional load seal 20 MPa. In overseas practice, the method of designing asphalt concrete mixtures in Marshall was the greatest distribution.

In the US, until recently, the methods of designing asphalt concrete mixtures in Marshall, Hubbardo-Filth and Quimea are applied. But recently, the SuperPave design system is introduced in a number of states.

When developing new methods for the design of asphalt concrete mixtures abroad, much attention was paid to improving the methods of sealing samples. Currently, when designing mixtures in Marshall, three levels of sample seal are provided: 35, 50 and 75 of the strikes on each side, respectively, for the conditions of the lung, medium and intensive movement of vehicles. The United States engineering troops, conducting extensive studies, improved the tests according to the Marshall method and distributed it to the design of mixtures for airfield coatings.

The design of the asphalt concrete mixture according to the Marshall method assumes that:

• - preliminarily established the initial mineral materials and bitumens of the requirements of technical specifications;
• - selected granulometric composition of a mixture of mineral materials satisfying project requirements;
• - the values \u200b\u200bof the true density of viscous bitumen and mineral materials are determined by the corresponding test methods;
• - A sufficient amount of stone material was dried and divided into fractions to prepare laboratory mixtures with different binder content.

For tests according to the Marshall method, standard cylindrical samples are made of 6.35 cm high. And a diameter of 10.2 cm. When sealing the incident cargo. The mixtures are prepared with different content of bitumen, usually different from another 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.

In order to more accurately assign the content of the bitumen to conduct laboratory tests, it is recommended to initially set the approximate "optimal" bitumen content.

Under the "optimal" implies the content of bitumen in the mixture, which ensures maximum stability by the Marshall molded samples. Approximately for the selection, it is necessary to have 22 south of stone materials and about 4 liters. bitumen.

The test results of the asphalt concrete according to the Marshall method are shown in Fig. five.

Based on the test results of the samples of asphalt concrete according to the Marshall method, usually come to the following conclusions:

• - the value of stability increases with an increase in the content of the binder to a certain maximum, after which the resistance value is reduced;
• - the value of the conditional plasticity of the asphalt concrete increases with increasing the content of the binder;
• - the dependence of the density density on the content of the bitumen is similar to the stability curve, however, for it, the maximum is more often observed with a somewhat higher content of bitumen;
• - the residual porosity of the asphalt concrete is reduced by increasing the content of the bitumen, approaching asymptotically to the minimum value;
• - The percentage of pore pores is increased with increasing bitumen content.

Fig. five. - Results (A, B, B, D) Tests of asphalt concrete according to the Marshall method:

The optimal content of the bitumen is recommended to be defined as the average of the four values \u200b\u200bset by schedules for the relevant design requirements. The asphalt concrete mixture with the optimal content of bitumen should satisfy all the requirements for technical specifications. In the final selection of the composition of the asphalt mixture, technical and economic indicators may also be taken into account. It is usually recommended to choose a mixture with the highest marshall stability.

However, it should be borne in mind that mixtures with excessively high values \u200b\u200bof Marshall and low plasticity are undesirable, as coatings from such mixtures will be overly rigid and can crack when driving heavy vehicles, especially with fragile bases and high coating deflection. Often in Western Europe and in the United States, the method of designing an asphalt concrete mixture in Marshall is criticized. It is noted that the shock sealing of samples in Marshall does not model the sealing of the mixture in the coating, and the stability of Marshall does not allow to satisfactorily assess the strength of the asphalt concrete during the shift.

The method of CVIMA is also criticized, the disadvantages of which include pretty bulky and expensive test equipment.

In addition, some important volume of the metric indicators of asphalt concrete associated with its durability in this method are not properly disclosed. According to American engineers, the method of choosing the content of bitumen by CVIMU is subjective and can lead to the briefness of the asphalt concrete due to the purpose of the low content of the binder in the mixture.

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

Therefore, special studies of the calculation of the seal were carried out, which was determined as 16 passes of a roller rink with pneumatic tires, with a load on the axis of 3 vehicles at a pressure of a tire 6 bar. On a full-scale laboratory stand, a standard layer thickness equal to 5 maximum sizes of mineral grains was substantiated in the compaction of the hot asphalt concrete mixture. For the appropriate sealing of laboratory samples, the angle of rotation on the laboratory seal (the hyporator) equal to 1 ° was standardized, and the vertical pressure on the sealing mixture of 600 kPa. At the same time, the standard number of rotations of the hyporator should be a value equal to the thickness of the layer of a sealing mixture, expressed in millimeters.

In the American method of designing the "SuperPave" design system, it was customary to convene samples from the asphalt of a concrete mix also in the hyporator, but at an angle of rotation of 1.25 °. Work on the sealing of samples of asphalt concrete is normalized depending on the calculated value of the total transport load on the coating, for the device of which the mixture is designed. The sealing pattern of the samples from the asphalt concrete mixture in the device of the rotational seal is shown in Fig. 6.

Fig. 6. - Scheme of sealing samples from asphalt concrete mixture in the rotational seal device:

In the design method of the MTQ asphalt concrete mixture (Quebec, Canada's Ministry of Transport) is borrowed by the SUPERPAVE rotational seal instead of the LCPC hypoator. The calculated number of rotations during the seal is taken for mixtures with a maximum grain size of 10 mm. equal to 80, and for mixtures of 14 mm. - 100 revolutions of rotation. The calculated maintenance of air holes in the sample must be from 4 to 7%. The nominal pore volume is usually 5%. The effective volume of bitumen is set for mixtures of each type, as in the LCPC method.

It is noteworthy that when designing asphalt concrete mixes from the same materials according to the Marshall method, the LCPC method (France), the SuperPave design system (USA) method and the MTQ (Canada method) method were obtained about the same results.

Despite the fact that each of the four methods provided for various conditions of sample seals:

• - Marshall - 75 blows from two sides;
• - "SuperPave" - \u200b\u200b100 rotation revolutions in the hyporator at an angle of 1.25 °;
• - MTQ - 80 rotation revolutions in the hyporator at an angle of 1.25 °;
• - LCPC - 60 revolutions of rotation of an effective seal at an angle of 1 ° C were obtained quite comparable results on the optimal content of bitumen.

Therefore, the authors of the work came to the conclusion that it was not important to have a "right" method of sealing laboratory samples, but to have a system of influence of the sealing effort on the structure of the asphalt concrete in the sample and on the performance of it in the coating.

It should be noted that the rotational methods of compaction of asphalt concrete samples are also not devastable. A noticeable abrasion of the stone material was established when the hot asphalt mixture is sealing in the hyporator.

Therefore, in the case of the use of stone materials characterized by wear in the Los Angeles drum, more than 30%, the normalized number of rotation of the mixture seal when producing samples of a rubbed-mastic asphalt concrete are prescribed 75 instead of 100.

The asphalt concrete mixture is a building material obtained by artificially. According to the production technology, the rational selection of the main components is carried out, and then the material seal is sealing with vibrators. Requirements for the characteristics of the asphalt concrete composition are included in GOST 9128.

What ingredients are used in the mixture?

Ingredients are present in the asphalt concrete solution:

• components of mineral origin, such as natural or crushed sand, crushed stone (gravel), impurities of fine powder (as needed);
• binding ingredients of organic origin, such as bitumen.

Initially, instead of bitumen was used to targe. However, it was abandoned due to the harmful effect on human health and the environment.To mix the components, the asphalt concrete mixture is heated. Appointment of asphalt concrete - laying of roads of airfields and roads, arrangement of industrial floors. According to the principle of masonry asphalt concrete:

• compacted;
• cast, differs by high fluidity and large content of the binder material, therefore allows you to lead the masonry without a seal.

According to the composition of the asphalt concrete:

• rubbed;
• gravel;
• sandy.

Bitumen viscosity and maximum masonry temperature determine such varieties of mixtures:

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

However, the last type, as a separate species, is not found since 1999. Types of hot asphalt concrete largest percentage porosity:

• highlighted - 1-2.5%;
• high-faceted - 10-18%;
• dense - 2.5-5%;
• porous - 5-10%.

In cold solutions, this value is 6-10%. At the maximum size of the particles of the mineral component of the asphalt concrete canvas can be:

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

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

What are the algorithms for the design of the component composition of asphalt concreteins?

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

1. Method of Professor Sakharov P. V.
2. Method for the module of saturation provided by Professor Dage M.
3. Design algorithm for the required conditions of operation of the coating obtained by the research of Professor Fishseva I. A.
4. Selection of density curves developed by Professor Ivanov N. I. With the assistance of Somponia.

An example of an optimal selection of the ingredients of the asphalt concrete mixture

As an example of asphalt components, it is proposed to consider the task: you need a fine-grained hot mixture of a second grade type to create a dense top of the road in the third climatic zone. Ingredients are available:

• granite and limestone crushed stone graininess 0.5-2 cm;
• river sand;
• dropping after grinding granite crumbs;
• dropping after chopping limestone;
• non-activated minport store;
• bitumen material BND 90/130.

At the first stage, testing and comparison of the characteristics presented above ingredients are tested. According to the results of testing of samples with different components ratio, conclusions are made that to obtain asphalt concrete mixtures B type and second grade suitable, river sand, granite dust, mini position, bituminous material.

Limestone and dust of the crushed limestone component did not respond to the provisions of the GOST on the strength parameters. In the second stage, crushed stone is calculated. Its content with a large size of more than 0.5 cm is equal to 35-50%. Optimal in mixtures is the content of 48%. The material contains 95% of the particles, indicated, so the formula has the form:

In this way, the amount of rubbine in the mixture for a fractional composition is calculated.

In the third stage, the composition of the mineral powder is determined. Calculations begin with the removal of mass proportions of rubbank, sand and minipping with a fractional composition, according to GOST. Consequently, the grain content of less than 0.0071 cm in a minmaterial asphalt concrete should lie in the range of 6-12%. 7% takes for calculations. With the content of elements of the size of 0.0071 cm 74% in the mineral powder, the calculation formula looks like this:

Due to the presence in the particle mixture, less than 0.0071 cm made of granite checks, the Martipograph fraction takes 8%. At the fourth stage, the amount of sand is calculated. The total content is:

Sand \u003d 100 - (crushed stone of the minport) \u003d 100 - (50 8) \u003d 42%.

The example uses a river and granite sand dropout. Therefore, each proportions are determined separately. The percentage of the river component and the granite dropout is established by their fraction of less than 0.125 cm. For the asphalt concrete mixture of grain should be in an amount of 28-39%. Average 34% is taken, 8% of which are calculated as a minor apartment. Consequently, the sand is needed 34-8 \u003d 26% for particles of particles of less than 0.125 cm. Since the mass portion of these grains in the river sand material is 73%, granite dust - 49%, the proportion for asphalt-concrete mixtures B type has the form:

Rounded the resulting value up to 22%, therefore, the content of discovering from the granite crumb is 42 - 22 \u003d 20%. Such a calculation is carried out for each sand fraction and dropout. The data is booked in the table and are summarized with dimensions less than those specified for each individual ingredient, then compared with the requirements of the GOST.

The fifth stage calculates the content of the bitumen component. According to conditions, crushed stone, sand, chopped granite, the deposits are mixed with 6% of the binder ingredient, which corresponds to the average value required in the regulatory document. Three samples of a mixture with a height of 7.14 cm and the corresponding diameter are prepared. Next, a compaction is made by the combined method:

• three minutes on the vibrationboard at a pressure of 0.03 MPa;
• three-minute seal on vibropress at a pressure of 20 MPa.

After two days, the average density is determined, that is, the mass in the values \u200b\u200bof the asphalt concrete volume, the real density of the mineral component of the mixture R °. According to the data obtained, in addition to density, the porosity of the mineral component of the tested samples is calculated.

An approximate amount of bitumen binding is determined by the actual density of all ingredients, taking into account the residual porosity of the asphalt concrete V \u003d 4%. At the same time, the average density of the asphalt concrete samples with a bitumen content of 6% per 100% minerals is 2.35 g / cm3. Therefore, the calculation formulas are:

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

When a non-compliance with the requirements of the regulatory document is detected, the mixture is adjusted and its subsequent tests, as described above.