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15DETERMINATION OF ASPHALT CONCRETE COMPOSITION
Bakhromjon Adhamovich Bekzod Xomidjonovich Hojiakbar Solijon o'g'li Otakulov Kodirov Solijonov
Fergana Polytechnic Institute
ABSTRACT
The purpose of the work is to determine the composition of asphalt concrete for the device of the upper layer of the road surface.
Keywords: seals, tar concrete, polymer concrete, thermoplasticity, porosity, road-climatic zone, hot, cold, high density, high porosity, mineral zone, water resistance, water saturation, viscosity
Main parameters and indicators: 1. Depending on the type of mineral component, they are subdivided into crushed stone, gravel and sand.
2. The mixtures, depending on the viscosity of the bitumen used and the temperature during laying, are divided into:
- hot, prepared using viscous and liquid oil road bitumen and laid with a temperature of at least 120 DC;
- cold, prepared using liquid oil road bitumen and laid with a temperature of at least 5 ° C.
3. Hot and cold mixes-asphalt concrete
a) Hot mixes and asphalt concrete, depending on the largest size of mineral grains, are divided into:
- coarse-grained with a grain size of up to 40 mm;
- fine-grained with a grain size of up to 20 mm;
- sandy with a grain size of up to 5 mm.
Asphalt concrete from hot mixes, depending on the value of residual porosity, are divided into types:
high-density with a residual porosity of 1.0 to 2.5%; dense with residual porosity of St. 2.5 to 5.0%; porous with residual porosity of St. 5.0 to 10.0%; highly porous with residual porosity of St. 10.0 to 18.0%.
b) Cold mixtures are subdivided into fine-grained and sandy ones.
Asphalt concrete from hot mixes, depending on the value of residual porosity, are divided into types:
high-density with a residual porosity of 1.0 to 2.5%; dense with residual porosity of St. 2.5 to 5.0%;
porous with residual porosity of St. 5.0 to 10.0%; highly porous with residual porosity of St. 10.0 to 18.0%. Asphalt concrete from cold mixes must have a residual porosity of over 6.0 to 10.0%. 4. Crushed stone and gravel hot mixes, and dense asphalt concrete, depending on the content of crushed stone (gravel) in them, are divided into types: A. with the content of crushed stone of St. 50 to 60%; B. with the content of crushed stone of St. 40 to 50%; V. with the content of crushed stone of St. 30 to 40%.
Crushed stone and gravel cold mixtures and the corresponding asphalt concrete, depending on the content of crushed stone (gravel) in them, are divided into types Bx and Bx.
Hot and cold sand mixtures and the corresponding asphalt concrete, depending on the type of sand, are divided into types:
r and rx - on sands from crushing screenings, as well as on their mixtures with natural sand with a content of the latter not exceeding 30% by weight;
D and Dx - on natural sands or mixtures of natural sands with crushing screenings when the content of the latter is less than 70% by weight.
High-density hot mixes and the corresponding asphalt concrete contain over 50 to 70% crushed stone. Hot and cold sand mixtures and the corresponding asphalt concrete, depending on the type of sand, are divided into types:
r and rx - on sands from crushing screenings, as well as on their mixtures with natural sand with a content of the latter not exceeding 30% by weight;
D and Dx - on natural sands or mixtures of natural sands with crushing screenings when the content of the latter is less than 70% by weight.
High-density hot mixes and the corresponding asphalt concrete contain over 50 to 70% crushed stone.Asphalt concrete design:
Analysis of the working conditions of the designed asphalt concrete in the structure
(transport loads, maximum slopes, geological and climatic conditions);
The choice of the method of production of work, depending on the weather and climatic
conditions and the area of construction;
Selection of raw materials;
Calculation of the composition of asphalt concrete:
a) calculation of the composition of the mineral part according to the curves of dense mixtures:
- the goal is to obtain a mineral composition with a minimum amount of voids. Formulations can be continuous or discontinuous.
b) determination of the optimal amount of bitumen: we determine empirically:
c) prepare mixtures with different amounts of bitumen
- crushed stone and sand are heated to 150 - 1700Q
- bitumen up to 130 - 1500QcMecb go 140 - 1600Q d) compacted at a pressure of 40 MPa. Preparation and testing of the control mixture:
-determine the physical and mechanical indicators and compare with the requirement of GOST.Technical requirements for road asphalt concrete from hot, dense mixtures: Depending on the quality indicators, a / b is divided into three grades (brands): Compressive strength:
- at 20-C - R20, MPa
- at 50-C - R50, MPa - characterizes the sound resistance
- at 0C -R0, MPa - characterizes fragility;
1. Coefficient of water resistance:
Kb = Rb / R20, where Rb is the ultimate strength of a water-saturated sample;
2. Coefficient of water resistance at long-term water saturation:
Kvd = Rvd, where Rvd is the strength of the sample after saturation, within 15 days;
3. Water saturation by volume, [1,4]%;
4. Porosity of the mineral backbone:
- for types A and B no more than 19%;
- for types C, D, D no more than 22%.
1. Residual porosity,% by volume [2-5]% - for dense a / b. Stages of asphalt concrete structure formation:
1. The period of active structure formation occurs at the moment of combining bitumen with mineral material.
2. The convergence of the structural elements of the mixture during its laying and compaction.
3. The period of stabilization of microstructural bonds in asphalt concrete during the operation of the pavement.Increase in viscosity of bitumen during cooling. Increasing the viscosity of bitumen due to the volatilization of light hydrocarbons, due to the stabilization of oriented bitumen molecules, or when a neoplasm appears in the contact zone.Reconsolidation under the influence of transport.At the stage of development of a road project, asphalt concrete of a certain type is selected, specifically for each structural layer of the road pavement.In the upper layers of road surfaces of all categories, only dense asphalt concrete is used.The lower layers of pavements on roads of categories I - II are made of porous asphalt concrete, and on roads of categories III -IV - of highly porous asphalt concrete.In the upper layers of the bases, both porous and highly porous asphalt concrete can be used.In stage-by-stage construction, the bottom layer of pavements is usually made of dense coarse-grained asphalt concrete.The type and type of dense asphalt concrete for the upper layers of pavements is assigned depending on the category of the road and the climatic conditions of the construction
area.In areas I, II and partially III road-climatic zones characterized by a cold and humid climate, it is advisable to use mixtures of type B with a crushed stone or gravel content of 40 - 50%, as well as types C, D and D, in which a closed pore structure is formed, which prevents the penetration of water into the coating. At the same time, in areas of the II road-climatic zone, it is recommended to use asphalt concrete with a residual porosity of no more than 5% of the volume.For the second road-climatic zone (GOST 9128-97):
Table 1
Indicator name Results trials Indicator name Requirements of GOST 9128-97 for type B grade II
Crushed stone grade by: -strength - abrasion - frost resistance Content of lamellar and needle-shaped grains,% 1000 And II F100 14.89 Not lower than 800 Not lower than AND II Not lower than F50 No more than 25
During the construction of the upper layer of coatings on the roads of the third category, it is possible to use hot mixes of types A, B, C, D and D of grade II, as well as cold asphalt concrete mixes of types Bx, Bx, Gx of grade I.
In accordance with the requirements of regulatory documents and the data of the assignment for the design of the asphalt concrete mixture, I chose type B asphalt from hot mixes of grade II, because:
- test results meet the requirements of GOST 9128 - 97
- For practical reasons, it is very important for the second climatic zone with its cold climate. It has a fairly high resistance to mechanical and atmospheric factors, therefore it is used for the device of the upper layer of two-layer coatings and during heavy traffic
- compared to type B, type A is multi-gravel a / b, and since crushed stone is more expensive than sand, type A is less economical. Type B is easier to design because type A is more demanding on the percentage of particles on sieves.
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