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37ASPHALT CONCRETE PREPARATION TECHNOLOGY
Bakhromjon Adhamovich Bekzod Xomidjonovich Hojiakbar Solijon o'g'li Otakulov Kodirov Solijonov
Fergana Polytechnic Institute
ABSTRACT
Purpose of work studying the technological process of preparing asphalt concrete Keywords: hot, cold, asphalt mixer, dustless technology, dosing
Asphalt mixtures (hot and cold) are produced at stationary or mobile asphalt-concrete plants (ACP). Stationary asphalt plants are built where there is a constant demand for asphalt mixtures - in cities, at major transport hubs. Mobile asphalt plants are created during construction or reconstruction of highways.
Remoteness of the plant from the location of hot or warm mixture is determined by the duration of its transportation, which should not exceed 1.5 hours. A practical radius of 60 ... 80 km is the radius of service of roads under construction with one asphalt plant. The transportation distance of the cold asphalt concrete mix has no limitations and is determined by the technical and economic calculations.
The choice of the site for an asphalt mixing plant is determined by the shortest distance of the transportation of ready mix and source materials, the availability of rail and water ways and other conditions. The best place for the location of the concrete mixing plant should be selected on the basis of technical and economic research. The modern level of technology allows to fully mechanize the production of asphalt concrete mixtures at the asphalt plant.
Mineral materials arriving to the plant are unloaded on special platforms, which should have a hard surface. It is recommended to arrange covered warehouses or sheds for storing 10 ... 15 - day stocks of crushed stone smaller than 20 mm and sand. Stone material for the production of mineral powder after drying in a rotating drum is ground in ball or tube mills. Mineral powder is stored in enclosed bunker-type rooms or in silos. For mechanization of warehousing operations usually apply auto-loaders, belt conveyors, transport trestles and other machines and mechanisms. Asphalt concrete mixture is prepared, as a rule, by one of the following methods: in batch-type forced mixing asphalt mixers with preliminary drying, heating and dosing of mineral materials. Because of the most widespread use of this technology, it is called the traditional technology;
1. in compulsory asphalt mixers in which dosed cold wet mineral materials are mixed with hot bitumen, and then they go into the drying drum, where they are heated to a predetermined temperature. This technology is called dust-free technology;
2. in asphalt mixers of free mixing drum type, in which the dosed mineral materials are dried, heated and mixed with bitumen. Such technology is called turbulent. In our country asphalt concrete mixtures are made mainly by traditional technology in mixers of periodic action.
The technological scheme of the asphalt concrete plant
1) Dust collector.
2) Cyclone unit.
3) Control cabin.
4) Bitumen heater.
5) Bunkers for ready mix.
6) Mixer.
7) Mineral powder unit
8) Sorting device.
9) Drying drum.
10) Feeder aggregate bunkers.
Cold wet sand and crushed stone are fed from the warehouse in the bunker feed unit 10 with the help of forklifts. From the bunkers of the feeder unit cold and wet sand and gravel are continuously fed by feeders in certain proportions to collecting belt conveyor located in the lower part of the feeder unit. From the prefabricated conveyor material enters the inclined belt conveyor, which loads cold and wet sand and crushed stone into the drum of the drying unit 9. In the drum the sand and crushed stone are dried and heated to working temperature. Heating of the material is due to combustion of liquid or gaseous fuel in the furnaces of drying aggregates. Gases and dust, generated by combustion of fuel and drying of the material, go to the dust collection device, consisting of cyclone unit 2, where the dust is deposited. The fine dust, not precipitated, is captured by the wet dust collector 1 and removed as sludge.
Sand and gravel heated to a working temperature are fed from the drying drum to the elevator, which feeds them to the sorting device of the mixing unit 8. Sorting device divides the materials into fractions according to the size of the grains and delivers them to the hoppers for hot material. From these hoppers, sand and crushed stone of different fractions are fed into batchers, and from there into the mixer 6.
Mineral powder comes from the mineral powder unit 7, which includes equipment for storing and transporting this material. With the help of a dispenser mounted on the mineral powder aggregate, the specified content of the powder in the mixture is provided. From the dispenser the powder is fed into the mixer by an auger. Bitumen heated in the storage up to a liquid state, is fed by a heating and pumping unit into the bitumen heater 4, where it is dehydrated and heated to a working temperature. Bitumen from the heater asphalt is delivered to the mixing unit, dosed and injected into the mixer.
All the components fed into the mixer are mixed. Then the finished product is unloaded into dump trucks or sent with the help of lifters to the hoppers for the finished mixture 5.
Asphalt mixing plants are controlled from the cabin 3.
Asphalt-mixing plants of this type include DS-158 with 50 tons/hour capacity and DS-842 with 200 tons/hour capacity.
Asphalt mixers operating under such technological scheme, serve reliably and give high quality of products.
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