The calculation consists in the selection of a rational ratio between the materials making up the asphalt concrete mixture.
The method of calculation from curves of dense mixtures has become widespread. The greatest strength of asphalt concrete is achieved at the maximum density of the mineral skeleton, the optimal amount of bitumen and mineral powder.
There is a direct relationship between the grain size composition of a mineral material and its density. Optimal will be compositions containing grains of various sizes, the diameters of which are halved.
where d 1 - the largest grain diameter, set depending on the type of mixture;
d 2 - the smallest grain diameter corresponding to the dusty fraction and mineral powder (0.004 ... 0.005 mm).
Grain sizes as per previous level
(6.6.2)
The number of sizes is determined by the formula
(6.6.3)
Number of fractions NS one less than the number of sizes T
(6.6.4)
The ratio of adjacent fractions by weight
(6.6.5)
where TO is the coefficient of escape.
The value that shows how many times the amount of the next fraction is less than the previous one is called the escape coefficient. The most dense mixture is obtained with a slip coefficient of 0.8, but such a mixture is difficult to select, therefore, according to N.N. Ivanova, escape coefficient TO adopted from 0.7 to 0.9.
Knowing the size of the fractions, their number and the adopted escape coefficient (for example, 0.7), they make up equations of this type:
The sum of all fractions (by weight) is equal to 100%, that is:
at 1 + at 1 To + at 1 To 2 + at 1 To 3 +...+ at 1 To n -1 = 100 (6.6.6)
at 1 (1 + To + To 2 + To 3 +... + To n -1) = 100 (6.6.7)
The sum of the geometric progression and, therefore, the amount of the first fraction in the mixture is indicated in brackets.
(6.6.8)
Similarly, we determine the percentage of the first fraction at 1, for the escape coefficient To= 0.9. Knowing the amount of the first faction at 1, easy to identify at 2 , at 3 and so on.
On the basis of the data obtained, limit curves are plotted corresponding to the adopted runoff coefficients. Compositions calculated using a runoff coefficient of 0.9 contain an increased amount of mineral powder, and when To < 0,7 - уменьшенное количество минерального порошка.
The curve of the grain size composition of the calculated mixture should be located between the limiting curves (Fig. 6.6.1).
Rice. 6.6.1... Grain formulations:
A - fine-grained asphalt concrete mixture with continuous granulometry of types A, B, C; B - the mineral part of sand mixtures of types D and D
High performance indicators give mixtures with an increased content of crushed stone and a reduced content of mineral powder. Preference should be given to mixtures with a run factor of 0.70 ... 0.80.
If it is impossible to calculate a dense mineral mixture according to the limiting curves (the absence of coarse-grained sands and the impossibility of replacing them with seeding ones), the required density can be selected according to the principle of discontinuous granulometry. Mixtures with discontinuous granulometry are more shear resistant due to their rigid framework.
To determine the bitumen consumption, test samples are formed from a mixture with a deliberately low bitumen content, then the volume of voids in the mineral core is determined.
(6.6.9)
where g- the volumetric mass of the asphalt concrete sample;
B pr- bitumen content in the test mixture,%;
r m- average density of mineral material:
(6.6.10)
where u u,at n , at mp- content of crushed stone, sand, mineral powder in% by weight;
r u,r p , r mp- density of crushed stone, sand, mineral powder.
The calculation formula for determining the optimal bitumen content will have the form
(6.6.11)
where r b- density of bitumen;
j- the filling factor of the voids of the mineral mixture with bitumen, depending on the specified residual porosity
where By- porosity of the asphalt concrete mineral skeleton,% of the volume;
NS- the specified residual porosity of asphalt concrete at 20 ° C,% of the volume.
Cold asphalt concrete
The composition of cold asphalt concrete can be calculated according to typical compositions or according to the method used for calculating hot mixtures, with mandatory verification of the physical and mechanical properties in the laboratory. The amount of liquid bitumen is reduced by 10 ... 15% against the optimum in order to reduce caking.
A characteristic feature of cold asphalt concrete, which distinguishes it from hot, is the ability to remain in a loose state for a long time after preparation. This ability of cold asphalt concrete mixtures is explained by the presence of a thin bitumen film on mineral grains, as a result of which the microstructural bonds in the mixture are so weak that a small force leads to their destruction. Therefore, the prepared mixtures do not cake under the influence of their own weight during storage in stacks and transportation. Mixtures for a long time (up to 12 months) remain in a loose state. They can be relatively easily loaded onto vehicles and spread in a thin layer during road paving.
Grain compositions of cold asphalt concrete mixtures differ from those of hot mixtures in the direction of an increased content of mineral powder (up to 20%) - particles finer than 0.071 mm and a reduced content of crushed stone (up to 50%). An increased amount of mineral powder is caused by the use of liquid bitumen, which requires a larger amount of powder for structure formation, and when the content of crushed stone is more than 50%, the conditions for the formation of the coating deteriorate. The largest grain size in cold asphalt concrete is 20 mm. Coarser crushed stone worsens the conditions for the formation of the coating.
Crushed stone obtained by crushing rocky rocks and metallurgical slags is used as a large component for cold asphalt concrete. These materials must have a compressive strength of at least 80 MPa, and for grade II asphalt concrete - at least 60 MPa.
For the preparation of cold asphalt concrete, the same mineral powder and sand are used as for hot mixes.
Liquid bitumen must have a viscosity within 
which corresponds to the brands SG 70/130, MG 70/130. The viscosity and class of bitumen are selected taking into account the expected shelf life of the mixture in warehouses, the air temperature during storage and use, as well as the quality of mineral materials. Cold asphalt concrete mixtures are used for road surfaces with traffic intensities of up to 2000 vehicles per day.
Cast asphalt concrete
Cast asphalt concrete is a specially designed mixture of crushed stone, sand, mineral powder and viscous bitumen, prepared and laid hot without additional compaction. Cast asphalt differs from hot asphalt concrete by a high content of mineral powder and bitumen, a technology of preparation and a method of laying. Cast asphalt concrete is used as a road surface on highways, on the roadway of bridges, as well as for flooring in industrial buildings. Repairs using cast mixes can be performed at air temperatures down to -10 ° C. A feature of the work is the need for continuous mixing of the cast mixture during its transportation to the place of laying.
For the preparation of cast asphalt concrete, crushed stone (up to 40 mm in size), natural or crushed sand is used. Crushed stone, seeding and sand should be of high quality, as for normal hot asphalt concrete. Bitumen BND 40/60 is used as a binder. In accordance with TU 400-24-158-89, cast mixes are subdivided into five types (Table 6.6.11).
Table 6.6.11
Classification of cast asphalt concrete mixtures
The positive properties of cast asphalt concrete include durability, low cost of work on compaction, and water resistance. During road reconstruction, the existing poured asphalt pavement can be reused in full and almost without adding new materials.
Tar concrete
Tar concrete, depending on the viscosity of the tar and the temperature of the mixtures during laying, is divided into hot and cold. In terms of physical and mechanical properties, tar concrete is inferior to asphalt concrete, since it has less strength and heat resistance.
Tar concrete, depending on the type of stone material, is divided into crushed stone, gravel and sand. For the preparation of tar concrete, the same mineral materials are used as for asphalt concrete, the requirements for them are similar. As a binder, road coal tar is used: for hot tar concrete - D-6, for cold - D-4 and D-5. Tar is used both industrially and prepared directly at an asphalt concrete plant by oxidizing or mixing sand with a thinner (anthracene oil, coal tar, etc.).
The calculation of the composition of tar concrete can be performed in the same way as for asphalt concrete, while the main attention should be paid to careful selection of the amount of tar, since a small deviation in its content in the mixture significantly affects the properties of tar.
For the preparation of hot tar concrete, tar with a viscosity much lower than the viscosity of bitumen for the corresponding type of asphalt concrete is used. The reduced viscosity of the tar causes the weakening of internal structural bonds, which can be compensated for by an increase in the internal friction of the mineral part. To do this, it is necessary to use stone materials with grains of an angular shape and a rough surface, as well as to replace part or all of the natural sand with rounded grains for seeding. For the preparation of tar mixtures, crushed stone from more acidic rocks (quartz sandstones, quartz-rich granites, etc.) can be used.
Dense tar concrete is used for paving on roads of II ... IV categories. Due to sanitary and hygienic conditions, the device of the upper layers of tar concrete coatings is allowed only outside settlements. When preparing tar mixtures, special safety rules must be observed.
Tar concrete mixture is prepared in asphalt concrete plants with forced action mixers. Due to the lower viscosity of the tar, the enveloping of the grains of the mineral material with it proceeds better than with the use of bitumen, as a result of which the time for mixing the materials is reduced. For the same reason, the compaction of the mixtures during the coating is facilitated. The compaction coefficient, which is the ratio of the thickness of the layer of the laid mixture before compaction to the thickness of the compacted coating, can be equal to 1.3 ... 1.4.
When producing tar concrete mixture, it is necessary to strictly observe the established temperature regime, since tar is more sensitive to temperature changes than bitumen (Table 6.6.12).
Table 6.6.12
Temperature conditions for the preparation and laying of tar concrete
In terms of physical and mechanical properties, tar concrete is inferior to asphalt concrete: it has less strength, heat resistance. But at the same time it is characterized by increased wear resistance. Tar concrete pavement has an increased roughness, a higher coefficient of wheel adhesion to the road, increased traffic safety. This is due to the lower viscosity of tars, weaker cohesive forces of intermolecular interaction, and the presence of volatile components. Volatile substances in the composition of tar accelerate the formation of the structure of tar concrete in the coating, and also contribute to a more intensive change in its properties. Tar concrete is less plastic in comparison with asphalt concrete, which is also associated with the composition and structure of tar, which consist mainly of aromatic hydrocarbons, which form more rigid structural bonds in binders and at low temperatures are poorly deformed, as a result of which cracks form in the coatings.
Control over the manufacture of tar mix at the plant and during the installation of tar concrete, as well as test methods for tar are the same as for asphalt concrete.
The most used road building material in the 20th century - asphalt - is divided into many types, grades and types. The basis for the separation is not only and not so much the list of the initial components included in the asphalt concrete mixture, but the ratio of their mass fractions in the composition, as well as some characteristics of the components - in particular, the size of the fractions of sand and crushed stone, the degree of purification of the mineral powder and all the same sand.
Asphalt composition
Asphalt of any type and brand contains sand, crushed stone or gravel, mineral powder and bitumen. However, as far as crushed stone is concerned, it is not used in the preparation of some types of road surface - but if the asphalting of territories is carried out taking into account high traffic and strong short-term loads on the surface, then crushed stone (or gravel) is necessary - as a frame-forming protective element.
Mineral powder- an obligatory initial element for the preparation of asphalt of any brands and types. As a rule, the mass fraction of powder - and it is obtained by crushing rocks in which a high content of carbon compounds (in other words, from limestone and other organic fossilized deposits) - is determined based on the tasks and requirements for the viscosity of the material. A large percentage of mineral powders allows it to be used in such works as asphalting roads and sites: a viscous (that is, durable) material will successfully dampen the internal vibrations of bridge structures without cracking.
Most types and grades of asphalt use sand- the exception, as we said, is the types of road surface where the mass fraction is high gravel... The quality of sand is determined not only by the degree of its purification, but also by the method of production: the sand extracted by the open method, as a rule, needs to be thoroughly cleaned, but the artificial sand obtained by crushing rocks is considered ready “to work”.
Finally, bitumen is the cornerstone of the paving industry. A product of oil refining, bitumen is contained in a mixture of any brand in a very small amount - its mass fraction in most varieties hardly reaches 4-5 percent. Although widely used in applications such as asphalting areas with difficult terrain and road maintenance, cast asphalt boasts a bitumen content of 10 percent or more. Bitumen gives such a web a fair amount of elasticity after hardening and fluidity, which makes it easy to distribute the finished mixture over the site.
Grades and types of asphalt
Depending on the percentage in the composition of the listed components, there are three brands of asphalt... Technical characteristics, scope and composition of the mixture of various brands are described in GOST 9128-2009, which, among other things, takes into account the possibility of adding additional additives that increase frost resistance, hydrophobicity, flexibility or wear resistance of the coating.
Depending on the percentage of filler in the road-building mixture, it is divided into the following types:
- A - 50-60% of crushed stone;
- B - 40-50% crushed stone or gravel;
- B - 30-40% crushed stone or gravel;
- G - up to 30% of sand from crushing screenings;
- D - up to 70% of sand or mixture with crushing screenings.
Asphalt grade 1
A wide range of different types of coatings are produced under this brand - from dense to highly porous, with a significant content of crushed stone. Area of use- road construction and improvement: only porous materials are not at all suitable for the role of the actual coating, the upper layer of the roadbed. It is much better to use them for arranging bases, leveling the base for laying denser types of material.
Asphalt grade 2
The density range is roughly the same, but the content and percentage of sand and gravel can vary widely. This is the same "average" asphalt, with a very wide range of applications: and the construction of highways, and their repair, and the arrangement of territories for parking lots and squares cannot do without it.
Grade 3 asphalts
Grade 3 coatings are distinguished by the fact that crushed stone or gravel is not used in their manufacture - they are replaced by mineral powders and especially high-quality sand obtained by crushing hard rocks.
The ratio of sand and crushed stone (gravel)
The ratio of sand and gravel content is one of the most important indicators that determines the area of application of a particular type of coating. Depending on the prevalence of a particular material it is designated by letters from A to D: A - more than half consists of fine gravel or gravel, and D - about 70 percent consists of sand (however, sand is used mostly from crushed rocks).
The ratio of bitumen and minerals
No less important - after all, it is it that determines the strength characteristics of the roadway. The high content of mineral powders significantly increases its fragility. That's why sandy asphalt can only be used to a limited extent: landscaping of parks or sidewalks. But coatings with a high content of bitumen are a welcome guest at any work: especially if it is road construction in harsh climatic conditions, at subzero temperatures, if the speed of work is such that a day later, road equipment will go along the new road, and after the finished road is delivered - heavy vehicles will rush.
Master's degree
O.A. KISELEVA
CALCULATION OF THE COMPOSITION OF THE ASPHALT CONCRETE MIXTURE
For undergraduates studying in the direction of 270100
"Construction", guidelines for settlement and graphic work
in the discipline "Physical foundations of the design of new construction
materials "
Approved by the Editorial and Publishing Council of TSTU
Printed version of the electronic edition
Tambov
RIS TSTU
UDC 625.855.3 (076)
BBK 0311-033ya73-5
Compiled by: Ph.D., Assoc. OA Kiseleva
Reviewer: prof. V. I. Ledenev
Calculation of the composition of the asphalt concrete mixture: Method. / Comp .: O.A. Kiseleva. Tambov: TSTU, 2010 - 16 p.
Methodological instructions for the implementation of computational and graphic work in the discipline "Physical foundations of the design of new building materials" for undergraduates studying in the direction 270100 "Construction".
Approved by the Editorial and Publishing Council of the Tambov State Technical University
© GOU VPO "Tambov State
Technical University "(TSTU), 2010
INTRODUCTION
Methodical instructions are devoted to the selection of the composition of asphalt concrete.
To design the composition of asphalt concrete, you need to know the following:
- grain size composition of aggregates,
- a brand of bitumen,
- brand of asphalt concrete.
Calculation of the composition of asphalt concrete consists in choosing a rational ratio between the constituent materials, which ensures the optimal density of the mineral skeleton with the required amount of bitumen and the production of concrete with specified technical properties with a specific work technology.
METHODS FOR CALCULATING ASPHALT CONCRETE MIXTURE
The most widely used method of calculating the curves of dense mixtures. It states that the greatest strength of concrete is achieved under the condition of the maximum density of the mineral composition by calculating the granulometric composition and determining the content of the optimal amount of bitumen and mineral powder.
Calculation of the composition of asphalt concrete includes the following steps:
- calculation of the granulometric composition of the mineral mixture according to the principle of minimum voids,
- determining the optimum amount of bitumen,
- determination of the physical and mechanical properties of the calculated mixtures,
- making adjustments in the compositions obtained mixtures.
1.Calculation of the particle size distribution of the mineral mixture ... For this purpose, for small and large aggregates, according to the data on partial residues on sieves, residues A i are found,% equal to the sum of partial residues (a i) on a given sieve and on all sieves smaller than this one. The results obtained, taking into account the grade of asphalt concrete by aggregate size, are entered in Table 1.
2.Determine the amount of aggregate fractions. The calculation is performed according to the limiting curves corresponding to the selected run-off factors (Fig. 1). Curves with a run-off coefficient of less than 0.7 refer to the composition of the mineral part of the asphalt concrete mixture with an insignificant content of mineral powder. Compositions calculated with a run-off factor of 0.9 contain an increased amount of mineral powder.
For this purpose, depending on the grade of asphalt concrete, the required amount of sand is determined on a sieve with a mesh size of 1.25 or crushed stone on a sieve with a mesh size of 5 mm (for fine-grained asphalt concrete). For example, for coarse-grained asphalt concrete, the amount of sand particles finer than 1.25 mm ranges from 23 to 46%. We accept 40%. After that, we determine the coefficient for adjusting the grain size composition of the sand
Table 1
Granulometric composition of the mineral mixture
| Placeholder type | Leftovers | Sieve hole sizes | ||||||||
| 2,5 | 1,25 | 0,63 | 0,315 | 0,14 | 0,07 | |||||
| Crushed stone | and i | a 20 u | a 10 u | a 5 u | ||||||
| A i | A 20 u | A 10 u | A 5 u | |||||||
| Sand | and i | a 2.5 p | a 1.25 p | a 0.63 p | a 0.315 p | a 0.14 p | ||||
| A i | A 2.5 p | A 1.25 n | A 0.63 p | A 0.315 p | A 0.14 p | |||||
| Mineral powder | and i | a 0.63 m | a 0.315 m | a 0.14 m | a 0.07 m | |||||
| A i | A 0.63 m | A 0.315 m | A 0.14 m | A 0.07 m |
Determine the required amount of mineral powder on a sieve with a mesh size of 0.071. For coarse-grained asphalt concrete, the amount of particles finer than 0.071 mm ranges from 4 to 18%. We accept 10%. After that, we determine the coefficient for adjusting the grain size composition of the mineral powder 
.
Determine the coefficient for adjusting the grain composition of crushed stone (or sand) 
... And we clarify the grain composition of the aggregates (table 2).
Table 2
Estimated composition of aggregates
| Placeholder type | Leftovers | Sieve hole sizes | ||||||||
| 2,5 | 1,25 | 0,63 | 0,315 | 0,14 | 0,07 | |||||
| Crushed stone | and i | K sh × a 20 sh | K u × a 10 u | K u × a 5 u | ||||||
| A i | ||||||||||
| Sand | and i | K p × a 2.5 p | K p × a 1.25 p | K p × a 0.63 p | K p × a 0.315 p | K × n 0.14 and n | ||||
| A i | ||||||||||
| Mineral powder | and i | K m × a 0.63 m | K m × a 0.315 m | K m × a 0.14 m | K m × a 0.07 m | |||||
| A i | ||||||||||
| ∑A |
 |
 |
Based on the data obtained, a particle size distribution curve for a specific calculated mixture is plotted, which should be located between the limiting runoff curves. We clarify the number of filler components by fractions, taking into account the type of asphalt concrete according to table 3.
Table 3
Optimal particle size distribution of the mineral mixture
| Mix type | Content of grains of mineral material,%, finer than a given size, mm | Approximate consumption of bitumen,% by weight | |||||||||
| 2,5 | 1,25 | 0,63 | 0,315 | 0,14 | 0,071 | ||||||
| Continuous granolumetry mixtures | |||||||||||
| Medium-grained types: A B C | 95-100 95-100 95-100 | 78-85 85-91 91-96 | 60-70 70-80 81-90 | 35-50 50-65 65-80 | 26-40 40-55 55-70 | 17-28 28-39 39-53 | 12-20 20-29 29-40 | 9-15 14-22 20-28 | 6-10 9-15 12-19 | 4-8 6-10 8-12 | 5-6,5 5-6,5 6,5-7 |
| Fine-grained types: A B C | 95-100 95-100 95-100 | 63-75 75-85 85-93 | 35-50 50-65 65-80 | 26-40 40-55 57-70 | 17-28 29-39 39-53 | 12-20 20-29 29-40 | 9-15 14-22 20-28 | 6-10 9-15 12-19 | 4-8 6-10 8-12 | 5-6,5 5,5-7 6-7,5 | |
| Sand types: D D | 95-100 95-100 | 75-88 80-95 | 45-67 53-86 | 28-60 37-75 | 18-35 27-55 | 11-23 17-55 | 8-14 10-16 | 7,5-9 7-9 | |||
| Discontinuous mixtures | |||||||||||
| Medium-type: AB | 95-100 95-100 | 78-85 85-91 | 60-70 70-80 | 35-50 50-65 | 35-50 50-65 | 35-50 50-65 | 35-50 50-65 | 17-28 28-40 | 8-14 14-22 | 4-8 6-10 | 5-6,5 5-6,5 |
Proposition 3
3.Determine the bitumen consumption. It is promising to calculate the amount of bitumen in the mixture according to the method developed by KHADI and based on the bitumen capacity of mineral components. The calculation is carried out in two stages: determination of the bitumen capacity of each fraction of the mineral part of the mixture and the calculation of the bitumen content. To determine the bitumen capacity, dried materials are scattered into fractions less than 0.071, 0.071-0.14, 0.14-0.315, 0.315-0.63, 0.63-1.25, 1.25-3, 3-5, 5-10 mm, etc. to the largest crushed stone. The bituminous capacity of each fraction is presented in table 4. Determine the bitumen content for each fraction (table 5).
Table 4
Bituminous capacity of filler
| Fraction size, mm | Bituminous capacity,% | |||
| Granite material | Diorite material | Dense, durable limestone material | Pure rounded quartz sand and gravel | |
| 20-40 | 3,9 | 3,3 | 2,9 | – |
| 10-20 | 4,7 | 3,5 | – | |
| 5-10 | 5,4 | 4,5 | 4,1 | 2,8 |
| 2,5-5 | 5,6 | 5,6 | 4,6 | 3,3 |
| 1,25-2,5 | 5,7 | 5,9 | 5,3 | 3,8 |
| 0,63-1,25 | 5,9 | 6,0 | 4,6 | |
| 0,315-0,63 | 6,4 | 7,9 | 7,0 | 4,8 |
| 0,14-0,315 | 7,4 | 7,3 | 6,1 | |
| 0,071-0,14 | 8,4 | 9,4 | ||
| 0,071 | 16,5 |
Table 5
Determination of bitumen content
Table 6
Physical and mechanical characteristics of asphalt concrete
| Indicators | Mixing rates for the top layer | Mix rates for the bottom layer | |
| I mark | II mark | ||
| Porosity of the mineral framework,% by volume for mixtures of types: A (multi-crushed stone, crushed stone 50-65%) B (medium-crushed stone, crushed stone 35-50%) C (low-crushed stone, crushed stone 20-35%) D (sandy from crushed sand with a fraction content 1.25-5 mm> 33%) D (sandy from natural sand) | 15-19 15-19 18-22 – – | 15-19 15-19 18-22 18-22 | 16-22 |
| Residual porosity,% by volume | 3-5 | 3-5 | 5-10 |
| Water saturation,% by volume for mixtures: A B and D C and E | 2-5 2-3,5 1,5-3 | 2-5 2-3,5 1,5-3 | 3-8 |
| Swelling,% by volume, no more | 0,5 | 1,5 | |
| Compressive strength, kgf / cm 2 for mixtures of types at temperatures of 20-50 0 C: A B and D C and E at a temperature of 0 0 C | – | – | |
| Water resistance coefficient, not less | 0,9 | 0,85 | – |
| Water resistance coefficient at long-term water saturation, not less | 0,8 | 0,75 | – |
The optimal bitumen content in the mixture is determined by the following formula
where K is a coefficient depending on the grade of bitumen (with BND 60/90 - 1.05; BND 90/130 - 1; BND 130/200 - 0.95; BND 200/300 - 0.9); B i - bitumen capacity of fraction i; Р i is the content of fraction i in the mixture in parts from the whole.
4. From table 6 we write out the physical and mechanical indicators characteristic of this asphalt concrete.
EXAMPLE OF CALCULATION
Select the composition of fine-grained asphalt concrete of type A. Fillers: crushed granite, quartz sand, mineral powder obtained by crushing diorite.
The calculation of the total balances is presented in table 7.
Table 7
Private balances
| Placeholder type | Leftovers | Sieve hole sizes | |||||||||
| 2,5 | 1,25 | 0,63 | 0,315 | 0,14 | 0,071 | ||||||
| Crushed stone | and i | ||||||||||
| A i | |||||||||||
| Sand | and i | ||||||||||
| A i | |||||||||||
| Mineral powder | and i | ||||||||||
| A i |
Since the crushed stone is fine-grained, it is sieved through a sieve with a mesh size of 5 mm, and larger fractions are removed.
Determine the amount of aggregate by fractions. For fine-grained asphalt concrete, the amount of crushed stone particles finer than 5 mm is in the range from 84 to 70%. We accept the required content of crushed stone larger than 5 mm 25%. We determine the coefficient for adjusting the grain size composition of crushed stone K u = 25 * 100 / (100-28) = 34.7.
The required amount of mineral powder on a sieve with a mesh size of 0.071 is in the range from 10 to 25%. We accept 15%. The coefficient for adjusting the grain size composition of the mineral powder is K m = 15 * 100/74 = 27.7.
Determine the coefficient for adjusting the grain size composition of sand K p = 100-35-28 = 37.
We clarify the grain size composition of the aggregates, taking into account the brand of asphalt concrete by the aggregate size (table 8).
Table 8
Grain composition of aggregates
| Placeholder type | Leftovers | Sieve hole sizes | ||||||||
| 2,5 | 1,25 | 0,63 | 0,315 | 0,14 | 0,071 | |||||
| Crushed stone | and i | 28*0,35=9,8 | ||||||||
| A i | 9,8 | |||||||||
| Sand | and i | 16*0,37=5,9 | 22*0,37=8,2 | 20*0,37=7,4 | 30*0,37=11,1 | 12*0,37=4,4 | ||||
| A i | 31,1 | 22,9 | 15,5 | 4,4 | ||||||
| Mineral powder | and i | 7*0,28=2 | 10*0,28=2,8 | 9*0,28= 2,5 | 74*0,28=20,7 | |||||
| A i | 23,2 | 20,7 | ||||||||
| ∑A | 74,8 | 59,1 | 50,9 | 41,5 | 27,6 | 20,7 |
We check the correctness of the choice of the grain composition of the mineral mixture. To do this, we build a graph of the granulometric composition and plot it on the slope curves (Fig. 5). It can be seen from the figure that the graph is included in the admissible area. The calculation is correct.
Knowing the bitumen capacity of individual fractions, we determine the bitumen consumption (table 9).
Determine the estimated content of bitumen grade BND 90/130 B = 1 * 6.71 = 6.71%. We check the bitumen content according to table. 3. Since the amount of bitumen, according to the calculation, is more than the normative 5-6.5%, we take B = 6.71%.
We write out the physical and mechanical indicators characteristic of this asphalt concrete:
- porosity of the mineral skeleton -18-22%,
- residual porosity - 3-5%,
- water saturation - 1.5-3%,
- swelling - 0.5%,
- ultimate compressive strength - 10 kgf / cm 2,
- coefficient of water resistance - 0.9,
 |
- coefficient of water resistance with long-term water saturation - 0.8.
Table 9
Determination of bitumen content
| Fraction size | Private balances (in fractions of a unit) | Bituminous capacity,% (from table 4) | Total bitumen capacity,% | ||||
| Crushed stone | Sand | Mineral powder | Crushed stone | Sand | Mineral powder | ||
| 2,5-5 | 0,098 | 4,6 | 0,45 | ||||
| 1,25-2,5 | 0,059 | 3,8 | 0,22 | ||||
| 0,63-1,25 | 0,082 | 4,6 | 0,38 | ||||
| 0,315-0,63 | 0,074 | 0,02 | 4,8 | 7,9 | 0,36+0,16 | ||
| 0,14-0,315 | 0,111 | 0,028 | 6,1 | 9,0 | 0,68+0,25 | ||
| 0,071-0,14 | 0,044 | 0,025 | 19,0 | 0,31+0,48 | |||
| 0,071 | 0,207 | 16,5 | 3,42 | ||||
| Bitumen content = ∑ | 6,71 |
BIBLIOGRAPHY
1. Glushko I.M. Road construction materials. Textbook for automotive and road institutes / Glushko I.M., Korolev I.V., Borshch I.M. and others .. - M. 1983.
2. Gorelyshev N.V. Materials and products for road construction. Directory. / Gorelyshev N.V., Guryachkov I.L., Pinus E.R. and others - M .: Transport, 1986. - 288 p.
3. Korchagina O.A. Calculation of the composition of concrete mixtures: Method. decree / Korchagina O.A., Odnolko V.G. - Tambov: TSTU, 1996 .-- 28 p.
Table P 1
Job data
| Option | Asphalt concrete type | Asphalt concrete type | Type of asphalt concrete by production method | Appointment of asphalt concrete | Bitumen grade BND |
| coarse-grained | A | hot | Top cover | 60/90 | |
| medium-grained | B | warm | Bottom cover | 90/130 | |
| fine-grained | V | hot | Top cover | 130/200 | |
| sandy | G | cold | Bottom cover | 200/300 | |
| coarse-grained | B | warm | Top cover | 60/90 | |
| medium-grained | V | cold | Bottom cover | 130/200 | |
| fine-grained | A | warm | Bottom cover | 90/130 | |
| sandy | D | hot | Top cover | 60/90 | |
| coarse-grained | V | hot | Bottom cover | 90/130 | |
| medium-grained | A | warm | Top cover | 60/90 | |
| fine-grained | B | cold | Bottom cover | 200/300 | |
| coarse-grained | A | warm | Bottom cover | 90/130 | |
| medium-grained | B | hot | Top cover | 60/90 | |
| fine-grained | V | cold | Top cover | 130/200 | |
| sandy | G | warm | Bottom cover | 90/130 | |
| coarse-grained | B | cold | Top cover | 200/300 | |
| medium-grained | V | hot | Bottom cover | 90/130 | |
| fine-grained | A | warm | Bottom cover | 60/90 | |
| sandy | D | cold | Top cover | 130/200 | |
| coarse-grained | V | cold | Top cover | 200/300 | |
| medium-grained | A | warm | Bottom cover | 90/130 | |
| fine-grained | B | hot | Top cover | 60/90 | |
| sandy | D | warm | Bottom cover | 90/130 | |
| coarse-grained | A | hot | Bottom cover | 60/90 | |
| medium-grained | B | cold | Top cover | 130/200 |
Table P 2
Job data
| Option | Granulometry | Filler material | ||
| rubble | sand | mineral powder | ||
| Continuous | granite | quartz | diorite | |
| Continuous | diorite | quartz | diorite | |
| Continuous | gravel | limestone | granite | |
| Continuous | – | limestone | limestone | |
| Intermittent | diorite | limestone | granite | |
| Continuous | granite | quartz | limestone | |
| Continuous | gravel | quartz | diorite | |
| Continuous | – | limestone | diorite | |
| Continuous | gravel | quartz | limestone | |
| Continuous | diorite | limestone | limestone | |
| Continuous | granite | quartz | granite | |
| Intermittent | diorite | quartz | limestone | |
| Continuous | gravel | limestone | limestone | |
| Continuous | granite | limestone | limestone | |
| Continuous | – | quartz | diorite | |
| Continuous | gravel | quartz | granite | |
| Continuous | granite | limestone | diorite | |
| Continuous | diorite | limestone | diorite | |
| Continuous | – | quartz | granite | |
| Intermittent | granite | limestone | granite | |
| Continuous | gravel | quartz | diorite | |
| Continuous | diorite | quartz | granite | |
| Continuous | – | quartz | limestone | |
| Continuous | gravel | limestone | diorite | |
| Intermittent | diorite | quartz | granite |
3.8. 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 device of the top layer of the coating in the III road-climatic zone.
The following materials are available:
granite crushed stone, fraction 5-20 mm;
limestone crushed stone, fraction 5-20 mm;
river sand;
material from screenings of crushing granite;
material from limestone crushing screenings;
non-activated mineral powder;
bitumen of oil grade BND 90/130 (according to the passport).
The characteristics of the tested materials are given below.
Granite crushed stone: grade for crushing strength in the cylinder - 1000, grade for wear - I-I, grade for frost resistance - Мрз25, true density - 2.70 g / cm 3;
limestone crushed stone: grade for crushing strength in the cylinder - 400, grade for wear - I-IV, grade for frost resistance - Мрз15, true density - 2.76 g / cm 3;
river sand: content of silt and clay particles - 1.8%, clay - 0.2% of the mass, true density - 2.68 g / cm 3;
material from screenings of crushing of granite grade 1000:
material from screenings of crushing of limestone grade 400: content of silt and clay particles - 12%, clay - 0.5% by weight, true density - 2.76 g / cm 3;
non-activated mineral powder: porosity - 33% by volume, swelling of samples from a mixture of powder with bitumen - 2% by volume, true density - 2.74 g / cm 3, bitumen capacity index - 59 g, moisture - 0.3% by weight;
bitumen: penetration depth of the needle at 25 ° С - 94 × 0.1 mm, at 0 ° С - 31 × 0.1 mm, softening temperature - 45 ° С, extensibility at 25 ° С - 80 cm, at 0 ° С - 6 cm, Fraas brittle temperature - minus 18 ° С, flash point - 240 ° С, adhesion to the mineral part of the asphalt concrete mixture withstands, penetration index - minus 1.
According to the test results, granite crushed stone, river sand, material from granite crushing screenings, mineral powder and bitumen of BND 90/130 grade can be considered suitable for the preparation of mixtures of type B grade II.
Table 7
|
Mineral material |
Mass fraction,%, grains finer than a given size, mm |
|||||||||
|
Initial data |
||||||||||
|
Granite crushed stone | ||||||||||
|
River sand | ||||||||||
|
Materials from screenings of crushing of granite | ||||||||||
|
Mineral powder | ||||||||||
|
Estimated data |
||||||||||
|
Granite crushed stone (50%) | ||||||||||
|
River sand (22%) | ||||||||||
|
Materials from screenings of crushing granite (20%) | ||||||||||
|
Mineral powder (8%) | ||||||||||
|
Requirements GOST 9128-84 for mixtures of type B | ||||||||||
Limestone crushed stone and material from limestone crushing screenings do not meet the requirements of Table. 10 and 11 GOST 9128-84 in terms of strength.
Grain compositions of selected mineral materials are given in tab. 7.
The calculation of the composition of the mineral part of the asphalt concrete mixture begins with the determination of such a ratio of the masses of crushed stone, sand and mineral powder, at which the grain size composition of the mixture of these materials meets the requirements of Table. 6 GOST 9128-84.
The composition of the asphalt concrete mixture is selected according to the assignment drawn up on the basis of the road design. The assignment specifies the type, type and brand of the asphalt concrete mixture, as well as the structural layer of the pavement for which it is intended. The selection of the composition of the asphalt concrete mixture includes testing and, according to its results, the selection of the constituent materials, and then the establishment of a rational ratio between them, which ensures 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 the entire set of tests, the suitability of 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 ratio between the constituent materials begins with the calculation of the grain size 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 discontinuous compositions, where the crushed stone or gravel framework is filled with a mixture that practically does not contain grains of size 5-0.63 mm.
The mineral part of hot and warm sandy 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 the curves of the limiting values of grain composition, constructed in accordance with the requirements of GOST (Fig). The mixture of crushed stone (gravel), sand and mineral powder is selected in such a way that the curve of the grain size composition is located in the zone bounded by the limiting curves and is as smooth as possible. When selecting the grain size composition of mixtures on crushed sands and crushed gravel, as well as on materials from crushing screenings of rocks, 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 the mineral powder. When using materials from the screenings of crushing of igneous rocks, complete replacement of the mineral powder with their finely dispersed part is allowed in mixtures for dense hot asphalt concrete of grade III, as well as in mixtures for porous and highly porous asphalt concrete of grades I and II. In mixtures for hot, warm and cold asphalt concrete grades I and II, only partial replacement of the mineral powder is allowed; at the same time, the mass of grains finer than 0.071 mm included in the mixture must contain at least 50% of limestone mineral powder that meets the requirements of GOST
When using materials from the screenings of crushing 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, the mineral powder can be omitted if the content grains finer than 0.071 mm in the screenings ensures that the grain composition meets the requirements of GOST, and the properties of grains finer than 0.315 mm in the screenings meet the requirements of GOST for mineral powder. Rice. Continuous grain size compositions of the mineral part of hot and warm fine-grained (a) and sandy (b) mixtures for dense asphalt concrete used in the upper layers of pavements.
When using polymineral gravel crushing products in asphalt concrete in IV-V road-climatic zones, 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% of calcium and magnesium carbonates (CaCO3 + MgCO3). As a result of the selection of the grain composition, the percentage by weight is established between the mineral components of asphalt concrete: crushed stone (gravel), sand and mineral powder. The bitumen content in the mixture is selected in advance in accordance with the recommendations of Appendix 1 of GOST and taking into account the requirements of the standard for the value of the residual porosity of asphalt concrete for a specific climatic region. So in IV-V road-climatic zones, the use of asphalt concrete with a higher residual porosity than in I-II is allowed, therefore the bitumen content in asphalt concrete for these zones is assigned closer to the lower recommended limits, and in I-II - to the upper ones.
In the laboratory, three samples are prepared from an asphalt concrete mixture with a preselected amount of bitumen and determine: the average density of the asphalt concrete, the average and true density of the mineral part, the porosity of the mineral part and the residual porosity of the 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 - porosity of the mineral part,% of the volume; Vpore - the selected residual porosity,% of the volume, is taken 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 is the average density of the mineral part, g / cm 3.
Having calculated the required amount of bitumen, the mixture is again prepared, three samples are formed from it, and the residual porosity of the asphalt concrete is determined. If the residual porosity matches the selected one, then the calculated amount of bitumen is accepted. The asphalt concrete mixture of the selected composition is prepared in the laboratory: coarse-grained kg, fine-grained kg and sandy mixture kg. Samples are made from the mixture and the compliance of their physical and mechanical properties with GOST is determined. If asphalt concrete of the selected composition does not meet the requirements of the standard for some indicators, for example, for strength at 50 ° C, then it is recommended to increase (within acceptable limits) the content of mineral powder or apply more viscous bitumen; in case of unsatisfactory strength values at 0 ° C, the content of the mineral powder should be reduced, the viscosity of the bitumen should be reduced or a polymer additive should be added.
In case of insufficient water resistance of asphalt concrete, it is advisable to increase the content of either mineral powder or bitumen; while the residual porosity and the porosity of the mineral framework must remain within the limits stipulated by the above-mentioned standard. Surfactants and activated mineral powders are most effective for increasing water resistance. When assigning the bitumen content for cold asphalt concrete mixtures, additional measures should be taken to prevent the mixture from caking during storage. For this, after determining the required amount of bitumen, samples are prepared for testing for caking. If the caking index exceeds the requirements of GOST, 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 the indicators of the properties of asphalt concrete samples meet the requirements of the aforementioned GOST.
An example of the selection of the composition of the asphalt concrete mixture It is necessary to select the composition of the fine-grained hot asphalt concrete mixture of type B, grade II for dense asphalt concrete intended for the construction of the top layer of the coating in the III road-climatic zone. The following materials are available: - granite crushed stone, fraction 5-20 mm; - limestone crushed stone, fraction 5-20 mm; - river sand; - material from granite crushing screenings; - material from limestone crushing screenings; - non-activated mineral powder; - bitumen of oil grade BND 90/130 (according to the passport). The characteristics of the tested materials are given below. Granite crushed stone: grade for strength when crushing in a cylinder, grade for wear - I-I, grade for frost resistance - Mrz 25, true density - 2.70 g / cm 3; limestone crushed stone: grade for crushing strength 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 silt and clay particles - 1.8%, clay - 0.2% of the mass, true density - 2.68 g / cm 3; material from screenings of crushing of granite grade 1000:
Content of silt and clay particles - 5%, clay - 0.4% by weight, true density - 2.70 g / cm 3; material from screenings of crushing of limestone grade 400: content of silt and clay particles - 12%, clay - 0.5% by weight, 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, moisture - 0.3% by weight; bitumen: penetration depth of the needle at 25 ° С - 94 × 0.1 mm, at 0 ° С - 31 × 0.1 mm, softening temperature - 45 ° С, extensibility at 25 ° С - 80 cm, at 0 ° С - 6 cm, Fraas brittle temperature - minus 18 ° С, flash point - 240 ° С, adhesion to the mineral part of the asphalt concrete mixture withstands, penetration index - minus 1. According to the test results, granite crushed stone can be considered suitable for preparing mixtures of type B grade II, river sand, material from granite crushing screenings, mineral powder and bitumen of the BND 90/130 brand.
Limestone crushed stone and material from limestone crushing screenings do not meet the requirements of Table. 10 and 11 GOST in terms of strength. Grain compositions of the selected mineral materials are given in table. The calculation of the composition of the mineral part of the asphalt concrete mixture begins with the determination of such a ratio of the masses of crushed stone, sand and mineral powder, at which the grain size composition of the mixture of these materials meets 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 asphalt concrete mix of type B is 35-50%. For this case, we take the crushed stone content Ш = 48%. Since grains larger than 5 mm are contained in crushed stone 95%, crushed stone will be required Ш = The obtained value is entered in the table. 7 and calculate the content in the mixture of crushed stone of each fraction (take 50% of the amount of each fraction of crushed stone). 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 within 6-12%. For the calculation, we take the content of particles, for example, closer to the lower limit of the requirements, i.e. 7%. If the amount of these particles in the mineral powder is 74%, then the content of the mineral powder in the mixture is MP =
However, for our conditions, 8% of the mineral powder should be taken, since there is already a small amount of particles finer than 0.071 mm in the sand and material from the granite crushing screenings. The data obtained are entered in table 7 and the content of the mineral powder of each fraction is calculated (take 8%). Calculation of the amount of sand each of them separately. The ratio between river sand Pr and material from the screening of granite crushing can be established by the content of grains in them finer than 1.25 mm, which, according to GOST and Fig. 2, and in the asphalt concrete mixture of type B 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 the 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 make up the proportion to determine the mass fraction of river sand in the mineral part of the asphalt concrete mixture:
For the calculation we take Pr = 22%; then the amount of material from the screening of crushing of granite will be = 20%. Having calculated, similarly to crushed stone and mineral powder, the amount of each fraction in the sand and material, from the screenings of crushing granite, we write the data obtained in table. 7. Summing up the number of particles finer than a given size in each vertical column, we obtain the total grain size 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 the asphalt concrete mixture of discontinuous grain composition. Determination of bitumen content Crushed stone, sand, granite crushing screenings and mineral powder are mixed with 6% bitumen. This amount of bitumen is the average of the recommended in the app. 1. GOST for all road and climatic zones. Three samples with a diameter and height of 71.4 mm are prepared from the resulting mixture.
Since the crushed stone in the asphalt concrete mixture contains 50%, the mixture is compacted by a combined method: vibration 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 h, the average density (bulk density) of the asphalt concrete (samples), the true density of the mineral part of the asphalt concrete r ° are determined, and on the basis of these data the average density and porosity of the mineral part of the samples are calculated. 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 / cm 3. In this case
G / cm 3; Three samples were made from the control mixture with 6.2% bitumen and the residual porosity was determined. If it is within 4.0 ± 0.5% (as was customary for fine-grained asphalt concrete from mixes of type B), then prepare a new mix with the same amount of bitumen, mold 15 samples and test them in accordance with the requirements of GOST (three sample for each type of test). If the indicators of the properties of the samples prepared from the selected mixture deviate from the requirements of GOST, then it is necessary to adjust the composition of the mixture and test it again.
Grain compositions of the mineral part of mixtures and asphalt concrete must correspond to those indicated in the table. The indices 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 An objective assessment of the suitability of a powder for use in asphalt concrete is possible only by the results of tests of asphalt concrete samples made on it. Taking into account this important circumstance makes it possible to use in some types of cast asphalt concrete even such at first glance as unsuitable powders, such as loess, ground marl, gypsum stone or gypsum, filter press waste from the sugar industry, waste from soda plants, ferrochrome slag, etc. Sand plays an important technological and economic role in the production of asphalt concrete mix. When choosing sand, preference is given to natural sand. The denser and coarser the grain, the more mobile and denser the mineral mixture and the less bitumen it requires. Unlike mineral powder, most natural sea, river and lake quartz sands do not chemically react with bitumen. For most cast mixes, we can recommend sands that meet the requirements of the standard and table.
Components, formulation and properties For mixtures of types I and II, it is not recommended to use crushing screenings containing an increased amount of dusty particles, in order to avoid deterioration of the mobility of mixtures and an increase in bitumen consumption. It is advisable to use crushed sands only as an additive to natural rounded sand in the manufacture of mixtures of types I and II. in their pure form, they can only be used in mixtures of types III, IV and V. Practically all properties of cast asphalt concrete are significantly improved when a 3-5 mm fraction from hard-to-polish rocks is added to the seed mixture. The ratio of fraction 3-5 mm and fraction 5-10 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 (grade of crushing capacity below 600) and porous rocks. Porous crushed stone quickly absorbs bitumen, and in order to ensure the necessary mobility of the mixture, the bitumen content must be increased.
Components, formulation and properties In mixtures for the top layer, it is required to use crushed stone from dense and difficult to polish rocks, cubic shape with a maximum size of up to 15 (20) mm. Moreover, for mixtures of type I, crushed stone is recommended fractions 3-15 with a grain ratio of 3-5, 5-10 and mm as 2.5: 1.5: 1.0. For mixtures of type V, the maximum grain size can be up to 20 mm, and for type III - 40 mm. In the latter case, the strength of the original rock can be reduced by%.
Components, formulation and properties Without any special damage to asphalt concrete from mixtures of II, III and V types, but with great profit for production, the requirement for crushability of crushed stone grains can be reduced. The crushing of grains in these asphalt 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 types II, III and V, gravel can be successfully used. Due to the rounded shape and ultra-acidic nature of the grain surface, 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 in comparison with other components of the mixture and affects the heat resistance of the pavement. Therefore, they are guided mainly by viscous grades having the properties indicated in table. 4.
Components, formulation and properties If bitumen does not have a complex of these properties, it is improved by adding natural bitumen, bituminous rocks, elastomers, etc. Very effective additives include natural bitumen, which is well compatible with petroleum and easy to use. Natural bitumen was 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 bitumens are found in various bituminous rocks and are rarely found in 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 found in stratal and lenticular 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 ones. Natural bitumens are solid, viscous and liquid. Hard bitumens (asphaltites). Density of asphaltites kg / m 3, softening temperature ° С. 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 with the introduction of 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 heat resistance of cast asphalt concrete, it is recommended to use degassed sulfur in lumpy, granular (granule size up to 6 mm) or liquid form. Sulfur is introduced into the mixer for hot mineral materials, i. E. before feeding bitumen. The amount of sulfur is assigned in the range of 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 the mineral powder.
Components, recipes and properties Summarizing what has been said, it should be borne in mind that most of the listed "know-how" requires overcoming serious technical and technological problems, as well as additional financial costs, which can not be solved by all organizations. Increasing the production cost, they do not always improve the technological properties of the mixtures and the performance of the coating, as well as the health of people and the environment. It is recommended to select the recipe for mixtures using a special method. The calculation of the content of the components begins after determining the grain size (granulometric) composition of all mineral materials and constructing a sieving curve. The curve must fit within the recommended limits for a specific 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 amount in the mineral mixture. When calculating the amount of mineral powder, it is necessary to make a correction for the content of dust from sand and gravel in the mineral mixture. Further, guided by the numerical values of the phase composition of the asphalt binder (B / MP) and its amount (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 samples of cast mix and asphalt concrete, for the given values of which the composition is selected, are for types: I and V - mobility, depth of indentation of the stamp and water saturation; II - mobility, compressive strength at +50 ° C and indentation depth of the stamp; III - mobility and water saturation; IV - water saturation and compressive strength at +50 ° С.
Components, formulation and properties Optionally, the flexural tensile strength and elastic modulus at 0 ° C, as well as the fracture toughness coefficient, are determined as a ratio of the values of the indicated indicators. With full compliance of the properties of the mixture and asphalt concrete with the required ones (table), the selection is considered to be successfully completed. Table - Physical and mechanical properties of cast asphalt concrete
