RU2056387C1 - Method for preparation of asphalt-concrete mix - Google Patents

Abstract

FIELD: road building. SUBSTANCE: method involves individual mixing of mineral material of coarse and fine fractions with bitumen followed by mixing the resulting compositions. Coarse fractions in the form of broken stone, sand and siftings are mixed with bitumen in asphalt mixer. Fine fractions of powder-like mineral material are mixed with bitumen in a high-speed mixer with speed gradient equal to 3000-5000 I/s. Bitumen for mixing coarse and small fractions should be of the same grade while bitumen for mixing of mineral powder shall amount to 80-90% of the total weight of bitumen in the asphalt-concrete mix. Compressive strength of produced asphalt-concrete at 50 C is 1.57-1.75 Mpa, same at 20 C is 4.99-5.25 MPa, coefficient of prolonged water resistance is 1.00-1.04; bending strength at 10 C is 8.85-9.20 MPa, reference Marshall rigidity is 272-292 kg/mm. EFFECT: higher efficiency. 2 cl, 1 tbl

Description

 The invention relates to road construction, in particular to a technology for the preparation of asphalt mixtures used as a material for paving.

A known method of preparing an asphalt mixture, including obtaining an asphalt binder by mixing mineral powder with viscous bitumen in an asphalt mixer, followed by mixing the asphalt binder with coarse and fine aggregates [1]
Another known process for preparing bituminous mixtures comprising forming asfaltovyazhuschego in a vibratory mixer, it was held for 3-4 minutes at 140-150 ^C and then stirring it with large and small aggregates [2]
Closest to the invention is a method of preparing an asphalt mixture by separately mixing the mineral aggregate fine fraction (0-5 mm) with liquid bitumen and coarse fraction (5-15 mm) with viscous bitumen, followed by mixing the resulting compositions with each other [3]
The disadvantages of asphalt mixtures obtained by known methods using asphalt mixers are the incomplete bitumen coating of particles of fine sand aggregate and coarse aggregate aggregate, as well as the formation of floccules of aggregated finely divided mineral powder fractions coated with a bitumen film that do not break down even with prolonged mixing. As a result, the mineral powder does not fulfill its main function as a filler of bitumen, and a uniform distribution of bitumen in the mineral powder is not achieved, which does not allow to obtain a homogeneous asphalt mix. This leads to overuse of bitumen and the deterioration of physical and mechanical properties and a decrease in the durability of asphalt concrete pavements. Another disadvantage of the prototype is the complexity of the technology associated with the use of two grades of bitumen.

 The invention is aimed at improving the quality of the asphalt mixture, providing improved operational properties: water resistance, strength and durability of the coating.

 To achieve this result in a method for preparing an asphalt concrete mixture, comprising mixing preheated bitumen with heated coarse mineral material, mixing fine coarse mineral material with heated bitumen, and then mixing the resulting compositions together, heated coarse mineral material, pre-mixed crushed stone, sowing and sand mixed with heated bitumen in an asphalt mixer, and fine mineral material in the form of a mineral powder mix they are mixed with heated bitumen separately in a high-speed mixer with a shear rate gradient of 3000-5000 1 / s, and the resulting asphalt-binder mixture is added to the mixture of bitumen with gravel sowings and sand. At the same time, for the preparation of the asphalt mix at all stages of mixing the mineral material of coarse and fine fractions with bitumen, one brand of bitumen is used. In addition, bitumen for mixing with mineral powder is taken in an amount of 80-90% of the total mass of bitumen in the asphalt mix.

 The use of a high-speed mixer, characterized by a speed gradient of 3000-5000 1 / s, which is determined by the ratio of the linear speed of the ends of the mixer blades to the gap between the walls of the chamber and the edges of the blades, will provide a more mobile asphalt binder. When mixed in a high-speed mixer, the mineral powder flocs formed at the first stage of the mixing process are rapidly destroyed and almost every solid particle is covered with a bitumen film, forming a homogeneous coagulation structure.

 As a result of large shear stresses arising in the material, in the zones between the edges of the blades and the walls of the chamber in the surface layers of particles of mineral powder, as well as in adjacent films of bitumen, chemical bonds break and free radicals form. In this case, complex chemical reactions occur in the contact zones and new stable compounds are formed, which increase the strength and water resistance of asphalt concrete pavements. A decrease in the velocity gradient of less than 3000 1 / s (velocity of 10 m / s, clearance of 3 mm) leads to a decrease in the mechanochemical effect. At the same time, the necessary destruction of the mineral powder flocs into smaller particles is not ensured, the enveloping effect of the mineral powder particles by the binder decreases, which leads to a decrease in the quality of the asphalt mix. An increase in the velocity gradient of more than 5000 1 / s (speed of 15 m / s, clearance of 3 mm) is impractical, since it leads to excessive wear of the mixer blades and an increase in power consumption.

 A decrease in the amount of bitumen less than 80% for the preparation of asphalt binder and a corresponding increase in its content in the composition with coarse aggregate leads to an increase in the thickness of the film of bitumen on aggregate grains, and this leads to a decrease in the strength of asphalt concrete.

 An increase in the content of bitumen in asphalt binder in excess of 90% and a corresponding decrease in its content in the composition with coarse aggregate leads to incomplete enveloping of the aggregate grains with bitumen, which leads to a decrease in the strength and water resistance of asphalt concrete pavements.

To implement the proposed method in the manufacture of mixtures, the following materials and equipment were used:
Coarse aggregate, granite, fractions 5-15 mm
Fine aggregate sand and seeding granite fractions of 0.071-5 mm
Fine aggregate mineral powder, lime flour, 0-0.71 mm
Bitumen viscous BND 90/130 brands
Asphalt mixer two-shaft DS-158
Single-shaft high-speed batch mixer of the design of the All-Russian Research Institute of Construction Polymer Model SS _to P-70.

 The preparation of the asphalt mixture according to the invention is as follows. Coarse-grained heated aggregates (crushed stone), fine-grained (seeders; sand) are mixed with each other, and then with heated bitumen in a low-speed, twin-shaft asphalt mixer. At the same time, an asphalt binder is prepared, mineral powder is mixed with heated viscous bitumen in a high-speed mixer with a shear rate gradient of 3000-5000 T / s, determined by the ratio of the linear velocity at the edges of the blades, m / s, to the gap between the chamber and the blades of the high-speed mixer, mm. Then, the obtained asphalt binder is fed into the asphalt mixer into a mixture of bitumen with coarse and fine aggregates and mixing is continued until a homogeneous asphalt mix is obtained.

 According to the proposed method.

 Asphalt mixture was prepared in three stages of mixing the components.

PRI me R 1. Obtaining a mixture of coarse aggregate with bitumen. Heated to 140 ^C. boundary coarse aggregate 5-15 mm crushed stone fraction in an amount of 35 wt. pre-mixed with sand and bran fractions 0,071-5 mm in an amount of 53% Asphalt was mixed in with the heated to ¹⁴⁰ ° C viscous bitumen in an amount of 0.87 wt. mineral part for 15 s.

 PRI me R 2. Preparation of asphalt binder.

Heated to 140 ^about With viscous bitumen in the amount of 4.93 wt. the mineral part, which is 85% of the total amount of bitumen for the preparation of the asphalt mix, was mixed with fine aggregate with a mineral powder of a fraction of 0-0.071 mm, taken in an amount of 12 wt. in a high-speed mixer with a gradient of 3000-5000 1 / s (with linear velocity values along the edges of the mixer blades equal to V _l 10 m / s and a gap of b 3 mm and, accordingly, V _{l of} 15 m / s b 3 mm) for 30 s.

 PRI me R 3. Mixing two compositions of asphalt binder with a mixture of coarse aggregate with bitumen.

 The obtained asphalt binder was discharged from the high-speed mixer, introduced into the asphalt mixer with a mixture of coarse aggregate and bitumen, and mixed for 20 s.

 By a known prototype method.

 An asphalt mix was prepared in a two-shaft paddle asphalt mixer at all stages of mixing the compositions.

PRI me R 1. Heated to 160 ^about With a large aggregate mineral material fraction of 5-15 mm in the amount of 55 wt. mixed with viscous bitumen heated to 160 ^about With in the amount of 2.5 wt. mineral material in an asphalt mixer with a speed gradient of 300-600 1 / s for 15 s.

PRI me R 2. Then separately mixed in an asphalt mixer heated to 120 ^about With a fine aggregate fraction 0-5 mm in the amount of 45 wt. with heated to 100 ^about liquid bitumen in an amount of 7.5 wt. mineral material for 30 s.

 PRI me R 3. The resulting mixtures 1 and 2 were mixed in an asphalt mixer for 30 s.

 From the obtained asphalt mixtures according to the proposed method and the prototype method, samples were made and comparative tests were carried out to determine the quality indicators. The test results are shown in the table.

 The table shows that the application of the proposed method using a high-speed mixer at the stage of preparation of the binder in comparison with the prototype method provides a significant improvement in the physico-mechanical properties of asphalt concrete. Achieved is an increase in strength by 4-6% water resistance with long-term saturation by 11 fatigue strengths by 30% conditional hardness by 169% and a decrease in water saturation by 47%. In addition, in the proposed method, the use of one brand at all stages of mixing allows to simplify the process, and increased the amount of bitumen 80-90% in the asphalt binder provides the best mixing of all compositions and obtaining a homogeneous structure of the asphalt mix.

Claims (3)

 1. METHOD FOR PREPARING ASPHALT-CONCRETE MIX, including mixing heated bitumen with heated mineral material of a large fraction, mixing heated bitumen with heated mineral material of a fine fraction and final mixing of the resulting composition with each other, characterized in that a mixture of crushed stone and sand is used as a large fraction of the mineral material and seeding, which is mixed with heated bitumen in an asphalt mixer, and the heated mineral material of a fine fraction - the mineral powder is mixed in heated bitumen in a high-speed mixer with a shear rate gradient of 3000 - 5000 1 / s, the resulting asphalt binder is fed to an asphalt mixer, where the final mixing of the compositions is performed.  2. The method according to claim 1, characterized in that the mineral material of small and large fractions is mixed with bitumen of the same brand.  3. The method according to claims 1 and 2, characterized in that the mineral powder is mixed with 80 - 90% of bitumen from its total weight in the asphalt mix.

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