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12ASSESSMENT OF THE QUALITY OF SOURCE MATERIALS FOR ASPHALT
CONCRETE
Bakhromjon Adhamovich Bekzod Xomidjonovich Hojiakbar Solijon o'g'li Otakulov Kodirov Solijonov
Fergana Polytechnic Institute
ABSTRACT
The purpose of the work is to assess the qualities of raw materials for asphalt concrete.
Keywords: aggregate, grain shape, igneous, metamorphic, sedimentary rocks, frost resistance, wear resistance, mineral powder, carbenes, carboids, asphaltenes
Coarse aggregate (crushed stone): For the preparation of crushed stone, strong frost-resistant igneous, metamorphic and sedimentary rocks, as well as strong and frost-resistant slow-cooled metallurgical slags are used.
The compressive strength of rocks should be at least 100 ... 120 MPa, and sedimentary carbonate rocks of metallurgical slags - at least 80 ... 100 MPa.
The indicator of wear resistance in a shelf drum for crushed stone from rocks is not more than 25 ... 35%, and for slags - not more than 35%. Wear grades are: I 1, I2, I3, I4.Crushed stone for asphalt concrete mixtures must be clean, (according to GOST 8267, clause 4.71, table 9), the content of clay and dusty particles in excess of 1% is not allowed (since in accordance with GOST 25100 granite crushed stone is an igneous rock) The shape of crushed stone grains must be approximated to tetrahedral and cuboid, and the surface to is rough, which increases internal friction and adhesion of the binder. The content of lamellar (flaky) and needle-shaped grains in crushed stone and gravel should be,% by weight, not more than:
15 - for mixtures of type A and high-density;
25 - for mixtures of types B, Bx;
35 - for mixtures of types B, Bx.
Crushed stone for a / b mixtures must withstand without destruction at least 50 cycles of alternating freezing and thawing, and for the lower layer of the coating - at least 25 cycles. Hence the frost resistance brands: F20, F25, F50.
Initial data:
Granite crushed stone
- density - 2.7 g / cm3
- grade for crushing strength in the cylinder - 1000
- wear grade in a shelf drum - II
- frost resistance grade -F100
- grain composition:
table 2
Indicator name Sieve hole diameters, mm
0 5 0 < 5
Total balance,% 7 8 1 00
Full sifting,% 4 1 3 0
- content of lamellar and needle-shaped grains,%:
fr. 5 - 10 mm - 16%
fr. 10 - 20 mm - 14%
Content of lamellar and needle-shaped grains:
(16 * 41 + 14 * 51) / (41 + 51) = 14.89% (<25%).
Conclusion: according to all the above indicators, limestone crushed stone can be used for the design of a hot asphalt concrete mixture of type B, grade II.
Fine aggregate (sand): For the preparation of asphalt concrete mixtures, natural and crushed sands are used, and screenings of products from crushing rocks and gravel. The sand must be clean and contain no more than 3% of dusty clay particles by mass.
Natural sand is an inorganic bulk material with a grain size of up to 5 mm, formed as a result of natural destruction of rocky rocks and obtained during the development of sand and sand and gravel deposits without the use of special processing equipment.
Crushed sand is obtained by crushing rocks or crystalline metallurgical slags. Depending on the strength of the original rock, crushed sand is divided into two grades: 800 and 400. For the first of them, rocks with a compressive strength of at least 80 MPa are used, and the second is at least 40 MPa.
Sand from crushing screenings is an inorganic bulk material with a particle size of up to 5 mm, obtained from rock crushing screenings in the production of crushed stone and from ores of ferrous and non-ferrous metals and metal minerals and other industries.
The granulometric composition of the sand should provide a mixture with other mineral materials with the highest density. For these reasons, coarse and medium-grained sands are used for the preparation of asphalt concrete.
Initial data:
Quartz sand
- density - 2.62 g / cm3
- content of contaminants - 1.5%
- grain composition:
table 3
Indicator name Sieve hole diameters, mm
.5 .25 .63 0 .315 0 .16 < 0.16
Total balance,% 0 0 0 8 5 9 8 1 00
Full sifting,% 00 0 0 4 2 8 8 0
- sand fineness modulus (Mc) without grains larger than 5 mm according to the formula:
- where A2.5, A1.25, A063, A0315, A016 - total residues on a sieve with round holes 2.5 mm in diameter and on sieves with meshes No. 1.25; 063; 0315, 016%.
- Mk = (20 + 40 + 60 + 85 + 98) / 100 = 3.0
- Conclusion: the group of sand by the size modulus is coarse sand of the II class (in accordance with GOST 8736-93 Sand for construction roads. TU). In this case, when there is coarse or medium sand, the mineral backbone of the asphalt concrete mixture is selected according to the principle of continuous granulometry. In terms of the content of dusty and clay particles, the sand meets the requirements of GOST and is suitable for the preparation of asphalt concrete.
- Mineral powder: Mineral powder is obtained by grinding limestones, dolomites and other carbonate rocks with a strength of at least 20 MPa and a content of pollutants and clay impurities of no more than 5%.
- In some cases, powdery industrial waste is used as a mineral powder - dust from cement plants, ash from thermal power plants.
- Mineral powder increases the strength of asphalt concrete, but increases its fragility, therefore, the content of mineral powder in the mixture should be minimal, sufficient only to give a / b standard strength and density.
- Mineral Powder Functions:
- - fills the voids of the sand-crushed stone frame and increases the density of the mineral part;
- - converts petroleum bitumen into asphalt binder.For mineral powders there is GOST 52129-2003 "Powders", according to which mineral powders are classified:
- MP - 1 - powders from non-activated and activated carbonate rocks, and from bitumen rocks;
- MP-2 - powders from non-carbonate rocks, solid and powdery rocks of industrial production.
- Technical requirements:
- The fineness of grinding should be such that, when wet sieving, it passes through a sieve 1.25 - 100%;
- 0.315 - 90 - 95%;
- 0.071 - 70 - 80%;
- Porosity is not more than 35%;
- Swelling of samples from a mixture of powder with bitumen is not more than 2.5%;
- Humidity no more than 1%.
- These requirements are only for MP - 1.
- Initial data:
- Limestone mineral powder
- - porosity - 25%
- - density - 2.6 g / cm3
- - humidity - 0.5%
- - grain composition:
table 4
Indicator name Sieve hole diameters, mm
.25 .63 0 .315 0 .16 0 .071 < 0.071
Total balance,% 0 7 1 9 2 5 1 00
Full sifting,% 00 6 9 3 8 1 7 5 0
table 5
Indicator name Result Requirements of
s GOST R 52129-2003 for
tests grade MP-1
Porosity,% 25 35
Density, g / cm3 2,6 -
Humidity, % 0,8 Not more than 1.0
Grain composition:
smaller than 1.25 100 Not less than 100
mm 93 Not less than 90
finer than 0.315 mm 75 From 70 to 80
finer than 0.071 mm
Conclusion: The mineral powder in terms of physical and mechanical properties complies with GOST R 52129-2003 and is suitable for the preparation of asphalt concrete.
Bitumen: Bitumens are organic binders consisting of high molecular hydrocarbons: naphthenic, methane and aromatic, as well as oxygen, sulfur and nitrogenous derivatives.
The group composition of bitumen:
1. Oils - molecular weight 300 - 500 a.u., <1, content in bitumen 40 - 60%.
2. Resins - molecular weight 500 - 1000 a. u., 1, content in bitumen 20-40%.
Asphaltenes - molecular weight 1000 - 5000 a. u., >1, content in bitumen 10-25%.
4. Carbenes, carboids insoluble in benzene.
5. Asphaltogenic acids - >1, their content determines the intensity of adhesion of binders to stone materials.
6 . Paraffins - worsen the properties of bitumen, making it brittle.
For preparation of asphalt concrete mixtures oil road viscous and oil road liquid bitumens are used. For hot and warm asphalt concrete mixtures of I and II grades should be used only BND grade bitumen, and for hot and warm asphalt concrete mixtures of III and IV grades as well as for asphalt concrete mixtures designed for making the foundations and the lower layers of coatings, together with BND grade bitumen can also be used of BN appropriate viscosity.
BND grade bitumens have a wider temperature range of plasticity and higher heat resistance compared to BN grade bitumens, have better low-temperature properties and adhesion to the surface of mineral materials, but are less resistant to aging.
Viscosity grade of bitumen and grade of liquid bitumen is selected depending on the type of asphalt concrete, climatic conditions of the construction area and road category, and for the cold asphalt concrete - taking into account the conditions and periods of storage of the mixture in the warehouse. The grade is determined by the following indicators:
- needle penetration depth (at 0oC, at 25oC);
- the softening temperature of the ring and the ball, oC;
- extensibility, cm. (at 0oC, at 25oC);
- brittle point, oC;
- flash point, oC;
- penetration index;
- Water-soluble compounds content, %;
- Change of softening point after heating, oC.
Conclusion: According to the chosen type of asphalt concrete (hot dense asphalt concrete, grade II, type B), II road and climatic zone, III road category, using the table "Recommended scope of various asphalt concretes for the upper layer of the road surface considering the road category and climatic conditions" viscous bitumen grade BND 90/130 has been selected.
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