A dry mix concrete plant operates by precisely weighing and combining dry materials (aggregates, sand, cement) before introducing water during transit. The process involves material storage, automated weighing, dry mixing in a transit mixer, and controlled water addition en route to the construction site. Key components include storage bins, conveyors, weighing systems, and a central control system to coordinate operations. Unlike wet mix plants, dry mix plants reduce waste and allow longer transport times since mixing occurs during delivery. The modular design enables efficient batch production tailored to project requirements.
Key Points Explained:
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Material Storage and Handling
- Raw materials (aggregates, sand, cement) are stored in designated bins or silos.
- Conveyors or bucket elevators transport materials to weighing hoppers.
- Systems like radial stackers or screw conveyors ensure continuous material flow.
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Precision Weighing
- Each material is weighed separately using load cells for accuracy.
- The small concrete batch plant typically uses a cumulative weighing system where materials are added sequentially to a central hopper.
- Tolerance levels are maintained within ±1% for cement and ±2% for aggregates.
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Dry Mixing Process
- Weighed dry materials are discharged into a transit mixer truck.
- No water is added at the plant; mixing begins during transportation.
- The drum rotation (10–15 RPM) ensures homogeneous blending before water introduction.
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Water Addition and Final Mixing
- Water is added en route via the truck’s onboard water tank, controlled by the driver or automated systems.
- Mixing continues for 70–100 revolutions to achieve optimal slump (typically 50–100 mm).
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Control System Coordination
- A PLC-based system automates batching sequences, reducing human error.
- Monitors material levels, mixer speed, and discharge timing.
- Generates batch reports for quality control and traceability.
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Advantages Over Wet Mix Plants
- Longer shelf life: Dry mix can be transported farther without setting.
- Reduced waste: Unused dry materials can be returned to storage.
- Flexibility: Water content can be adjusted based on site conditions.
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Discharge and Delivery
- Mixed concrete is discharged directly at the construction site.
- Transit mixers can typically carry 6–12 m³ per batch.
This process highlights how dry mix plants balance efficiency with adaptability, making them ideal for projects requiring just-in-time delivery or remote locations. The absence of on-site wet mixing also reduces cleanup and maintenance costs.
Summary Table:
| Key Component | Function |
|---|---|
| Material Storage | Holds aggregates, sand, and cement in designated bins/silos. |
| Precision Weighing | Uses load cells for accurate measurement (±1% cement, ±2% aggregates). |
| Dry Mixing | Materials blended in transit mixer without water. |
| Water Addition | Added en route via truck’s tank, controlled for optimal slump. |
| Control System | PLC automates batching, monitors mixer speed, and generates batch reports. |
| Advantages | Longer transport time, reduced waste, adjustable water content. |
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