Hot Mix Asphalt Plant Process Flow

Hot mix asphalt plants are the core equipment for producing hot mix asphalt mixtures. The workflow encompasses raw material preparation, heating and mixing, finished product storage and transportation, and must strictly adhere to process specifications to ensure mixture quality.

1. Raw Material Preparation and Inspection
- Aggregates
Source: Includes crushed stone, sand, mineral powder, etc., and must meet design gradation requirements.
Inspection: Check particle size, mud content, crushing value, etc. Unqualified materials must be screened or discarded.
Storage: Store in enclosed silos according to specifications, preventing rain and mixing.
- Asphalt
Type: Select base asphalt, modified asphalt, or emulsified asphalt according to project requirements.
Inspection: Test penetration, softening point, ductility, and other performance indicators to ensure compliance with specifications.
Storage: Heat to 160-180℃ and maintain temperature to prevent aging.
- Filler (Mineral Powder)
Inspection: Control fineness and moisture content to ensure good flowability.
Storage: Store in sealed containers to prevent moisture absorption and clumping.
 

2. Aggregate Heating and Drying
- Cold Aggregate Supply:
Aggregates of different specifications are fed into the drying drum according to a preset ratio via a belt conveyor under the cold aggregate silo.
- Drying and Heating
Equipment: Drum-type drying drum equipped with a burner (oil or gas).
Process: The aggregate tumbles inside the drum, making full contact with the hot airflow (temperature approximately 160-200℃), removing moisture and heating to 160-190℃.
Key Points:
Control the burner flame to avoid localized overheating that could cause the aggregate to scorch.
Monitor the outlet temperature to ensure uniform aggregate temperature.
- Hot Aggregate Screening:
The heated aggregate is screened by a vibrating screen to separate it into different specifications (e.g., 0-5mm, 5-10mm, 10-15mm, etc.). Unqualified aggregate is returned to the drying drum for reheating.
 

3. Asphalt Heating and Metering
- Asphalt Heating:
Asphalt is heated to 150-170℃ (modified asphalt requires higher temperatures) using a heat transfer oil or electric heating system.
Maintain asphalt fluidity to avoid localized overheating that could lead to performance degradation.
- Metering System
Aggregate metering: Weighed according to the design ratio using an electronic scale, with an error controlled within ±0.5%.
Asphalt metering: Metered using a flow meter or weighing system, with an error controlled within ±0.3%.
Filler metering: Mineral powder added according to the ratio via a screw conveyor.
 

4. Mixing Process
- Mixing Tank
Heated aggregates, asphalt, and mineral powder are sequentially added to the mixing tank of hot mix asphalt plant (usually a twin-shaft forced mixer).
Mixing time: 45-60 seconds, ensuring uniform mixing without whitening or segregation.
- Temperature Control
Mixed asphalt discharge temperature: 140-165℃ for ordinary asphalt mixtures, 160-180℃ for modified asphalt mixtures. Excessive temperature will cause asphalt aging, while insufficient temperature will affect compaction.
 

5. Finished Product Storage and Transportation
- Finished Product Silo
The mixed mixture is transported to the finished product silo via conveyor belt or elevator. Storage time should not exceed 6 hours to prevent hardening due to temperature drop.
- Transportation:
Use dump trucks for transportation. Apply a release agent to the inner walls of the truck bed to prevent material adhesion.
Cover with insulating tarpaulins to reduce temperature loss and ensure the arrival temperature meets construction requirements (generally not lower than 130℃).
 

6. Environmental Protection and Safety Measures:
- Dust Control:
Install baghouse dust collectors or wet scrubbing systems to collect dust generated by the drying drum and screening machine, and recycle or discharge in compliance with standards.
- Exhaust Gas Treatment:
Burners are equipped with low-NOx combustion technology to reduce NOx emissions; asphalt fumes are treated by activated carbon adsorption or combustion.
- Safety Protection:
Operators wear protective clothing, dust masks, and safety helmets.
Equipment is equipped with an emergency stop button and explosion-proof devices. Electrical wiring and mechanical components are inspected regularly.
 

7. Quality Control and Testing:
- Process Monitoring:
Real-time monitoring of aggregate temperature, asphalt temperature, mixture temperature, and mixing time.
Regular sampling and testing of mixture gradation, asphalt-aggregate ratio, marshall stability, and other indicators.
- Finished Product Inspection:
Samples of each batch of asphalt mixture must be retained for rutting tests, freeze-thaw splitting tests, etc., to ensure performance meets design requirements.
 

8. Equipment Maintenance and Cleaning:
- Daily Maintenance:
Clean accumulated material from the inner wall of the drying drum; inspect burner nozzles and belt conveyor for wear.
Lubricate the mixing cylinder bearings and transmission components; replace worn mixing blades.
- Shutdown Cleaning:
After daily production, clean the mixing cylinder and conveying pipelines with diesel fuel to prevent asphalt hardening and blockage.
 

By strictly following the above process procedures, hot mix asphalt plants can efficiently produce consistently high-quality mixtures, providing reliable support for road construction.