Guidelines of Selection, Operation and Maintenance of Bituminous Hot Mix Plant (First Revision)

IRC 90: Scope Summary & Key Specifications

• Scope: IRC 90 covers the specifications, operation, maintenance, and safety of Hot Mix Plants (HMP) used in road construction.

• Types Covered:

  • Continuous type Hot Mix Plant
  • Batch type Hot Mix Plant

• Capacity: Plants typically range from 60 to 90 TPH (Tonnes per hour).

• Key Components:

  • Cold bin feeder, cold elevator/conveyor
  • Dryer drum (counter flow or parallel flow)
  • Primary & secondary pollution control devices (e.g., baghouse filters)
  • Hot elevator, screening unit, hot bins
  • Weigh hopper, bitumen unit, mixing unit (pugmill)
  • Mineral filler system, control panel

• Running Charges Formula (per hour):

  [ \text{Total Running Charges} = H + I + J + K ]

  where:

  • (H) = Operating staff wages/hour
  • (I) = Servicing staff wages/hour
  • (J) = Material cost/hour (fuel, lubricants)
  • (K) = Cost of lubricating oil and fuel consumed/hour

• Hire Charges:

  [ \text{Hire Charges} = \text{Ownership Charges} + \text{Operational Charges} + \text{Running Charges} + \text{Overhead Charges} ]

  Overhead = 5% of total charges per hour.

• Maintenance & Safety: Detailed do's and don'ts are provided to ensure efficient and safe operation (see Annex-G).

• Output Example (Annex-H):

  Type of Pavement	Volume (cum/km)	Aggregate (Tonnes/km)
  75 mm BM	525	1155
  25 mm SDBC	175	385

This scope ensures standardized quality, safety, and efficiency for Hot Mix Plants in road construction projects.

flowchart LR
    A[Cold Bin Feeder] --> B[Cold Elevator]
    B --> C[Dryer Drum]
    C --> D[Hot Elevator]
    D --> E[Screening Unit]
    E --> F[Hot Bins]
    F

Capacity of Hot Mix Plant (IRC 90 based on IS 3066-1965 & IS 5890-2004)

Key Specification:

• Capacity is expressed in tonnes per hour (TPH).
• Specified for two moisture contents in aggregates:
  • At 6% moisture content (lower output)
  • At 2% moisture content (higher output)

Example:

• A 40/60 TPH plant means:
  • 40 TPH output at 6% moisture
  • 60 TPH output at 2% moisture

Batch Type Hot Mix Plant (Clause 3.2.2)

• Mix prepared in batches; each batch takes 45 to 60 seconds.
• Capacity = Number of batches/hour × Batch size (tonnes).
• Typical capacity up to 400 TPH internationally.

Sample Calculation for Output (Annex-H)

Density assumed = 2.2 tonne/cum

Running & Hire Charges Summary (Clause 1.4)

Maintenance Do's and Don'ts (Annex-G Highlights)

• Maintain proper belt alignment and lubrication.
• Pre-heat drum before feeding aggregates.
• Regular calibration of load cells.
• Avoid running plant above rated capacity.
• Safety: Proper earthing, no welding with power ON, no smoking near fuel.

flowchart TD
    A[Aggregates + Bitumen + Filler] --> B[Batch Mixer]
    B

Key Components of Hot Mix Plant (IRC 90 - Clause 5.6.3 and related):

• Cold Aggregate Feeder & Bucket Elevator: Feeds and elevates aggregates to dryer.
• Dryer Unit: Dries and heats aggregates.
• Burner: Provides heat for drying.
• Hot Elevator: Transports hot aggregates.
• Gradation Unit: Screens aggregates by size.
• Mixer Unit (Pugmill): Mixes aggregates and bitumen.
• Bitumen Unit: Heats and supplies bitumen.
• Mineral Filler System: Adds mineral filler to mix.
• Pollution Control Device (Bag House Filter): Controls dust emissions.
• Hot Mix Surge Silo: Stores hot mix before dispatch.
• Control Cabin: Central control for operations.

Operation Principles (Clause 5.6.3 & 6.3)

• Sequence: Start cold feed → Dry aggregates → Elevate hot aggregates → Screen and weigh → Mix with bitumen → Store/dispatch.
• Precautions: Monitor moisture, temperature, and dust; maintain burner efficiency.
• Maintenance: Daily checks, lubrication, filter cleaning.

Typical Formula for Bitumen Content (% by weight):

[ \text{Bitumen Content} = \frac{\text{Weight of Bitumen}}{\text{Total Weight of Mix}} \times 100 ]

Typical Hot Mix Plant Flow (Mermaid.js):

flowchart TD
    A[Cold Aggregate Feeder] --> B[Cold Elevator]
    B --> C[Dryer Unit]
    C --> D[Hot Elevator]
    D --> E[Gradation Unit]
    E --> F[Weigh Hopper]
    F --> G[Bitumen Unit]
    G --> H[Mixer Unit]
    H --> I[Hot Mix Surge Silo]
    I --> J[Dispatch]

Advantages of Double Barrel Drum-Mix Type (Clause 5.6.3)

• Continuous operation
• High production rate
• Lower fuel consumption

Limitations

• Higher initial cost
• Complex maintenance

For detailed specs, refer IRC:90-2010 Clauses 5.6.3 to 6.3.8 and maintenance schedules (Clauses 8.1.1 onwards).

Pollution Control & Emission Management in Hot Mix Plants (IRC 90)

Key Devices & Types (Clause 5.2.14)

1. Primary Pollution Control Device: Dust collection system (Clause 5.6.2.5).
2. Secondary Pollution Control Devices:
   • Wet Scrubber
     • Open Spray Tower Type (Fig. 29): Dust-laden gas passes through water spray; slurry settles at bottom.
     • Venturi Type (Fig. 30): Gas passes through a venturi section wetted with high-pressure water spray; higher dust removal efficiency.
   • Bag House Filter: Fabric filter capturing fine dust particles (up to 5 microns).

Wet Scrubber Efficiency & Operation

• Removes dust particles ≥ 5 microns.
• Requires large water volume; slurry ponds needed.
• Slurry removal every 2-3 days for efficiency.

Diagram Summary (Venturi Wet Scrubber)

flowchart LR
    DG[Dirty Gases Inlet] --> VT(Venturi Section)
    VT --> CA[Clean Air Outlet]
    VT --> DS[Discharge for Slurry]

Additional Notes

• Venturi scrubber > Open spray tower in efficiency.
• Bag house filters are preferred for finer dust control.
• Refer Annex-C for emission limits and control specifics.

This concise summary aligns with IRC 90 clauses 4.1.13, 5.2.14, and 5.6.2.5 for effective emission management in hot mix plants.

Key Specifications & Formulas for Aggregate Handling & Feeding Systems (IRC 90)

1. Cold Aggregate Feeder (Clause 6.3.1 & 4.1.1)

• Bins: Minimum 4 bins with separators to prevent mixing.
• Bin Capacity: Sufficient for 30 mins operation.
• Flow Control: Graded scale on bin gates; gate opening controls tonnage/hr (calibration charts used).
• Arching Prevention: Vibrator on fine aggregate bin.
• Moisture Control: Avoid moisture in fines to prevent clogging.
• Variable Speed Motors: Control conveyor speed for aggregate proportioning.
• Discharge Gate Opening: ≥ 1.5 × max aggregate size to avoid belt damage.
• Grizzly: Optional over bins to prevent large stones clogging gates.
• Material Build-up: Check & clean rollers periodically.

2. Flow & Calibration

• Approximate Tonnage/hr (Q) through gate:
  [ Q = k \times A \times \sqrt{2gH} ] where,
  • (k) = discharge coefficient (from calibration),
  • (A) = gate opening area,
  • (g) = acceleration due to gravity,
  • (H) = head of aggregate above gate.

3. Maintenance Tips

• Leave bins with minimum material during rainy season.
• Regularly check & clear material build-up on rollers.

Summary Table: Aggregate Handling System Features

flowchart TD
    A[Aggregate Loading] --> B[Cold Aggregate Feeder Bins]
    B --> C{Bin Gates with Graded Scale}
    C --> D[Controlled Gate Opening]
    D --> E[Conveyor Belts with Variable Speed Motors]
    E -->

IRC 90: Operational Checklists & Safety Procedures Summary

1. Pre-Start Checklist (Clause 7.1)

Operators must verify and tick off the following before starting the plant:

• Daily maintenance done as per schedule.
• Oil levels in tanks, gearboxes, and air cleaner topped up with correct grade.
• Tension of belts and chains checked.
• All grease points lubricated.
• Safety guards and covers in place.
• Bitumen pipeline heated for smooth flow.
• Bucket elevator cleared of stones.
• Conveyor belts and rollers inspected.
• Fuel spray into dryer combustion chamber controlled.
• No water in bitumen tank.

2. Safety Procedures (Clause 9.1 & 9.2)

• Work Site Safety (9.1):

  • Train and medically fit staff.
  • Use PPE: helmets, gloves, goggles, safety belts.
  • Maintain clean, illuminated platforms and pathways.
  • Firefighting equipment and first aid box available.
  • Emergency siren and stop switch installed.
  • Prohibit smoking near fuel/bitumen storage.

• Plant & Equipment Safety (9.2):

  • Operate only safe, well-maintained equipment.
  • Operator must be familiar with controls.
  • No servicing while running.
  • Avoid loose electrical connections.
  • Engine off and immobilized when unattended.
  • Follow proper shutdown: neutral controls, idle engine, then stop.
  • Prevent leaks, overheating, and backfire.
  • Store fuel/lubricants safely.

3. Recommended Safety Flowchart

flowchart TD
    A[Start Pre-Start Checklist] --> B{All Checks OK?}
    B -- Yes --> C[Start Plant]
    B -- No --> D[Rectify Issues]
    D --> A
    C --> E[Operate Plant with Safety Procedures]
    E --> F{Emergency?}
    F -- Yes --> G[Use Emergency Stop Switch]
    F -- No --> H[Continue Operation]
    H --> I[Shutdown Procedure]
    I --> J[End]

4. Reference Table: Key Safety Items

IRC 90: Plant and Equipment Requirements - Key Points

1. Hot Mix Plant Types & Capacities (Annex-E)

• Capacity range: 3 TPH to 650 TPH
• Types: Batch, Continuous; Static, Portable, Mobile; Conventional or Tower Layout; Parallel/Counter/Double Barrel flow.
• Selection based on volume, completion time, site area, emission norms, fuel efficiency, and use of reclaimed bitumen pavement (RBP).

2. Emission Factors & Control (Annex-C)

• Control efficiencies:
  • Baghouse: 99-99.7% PM10 removal
  • Cyclones: 50-75%
  • Venturi scrubber: 90-99.5%

3. Output Dependency (Annex-D)

• Moisture in aggregates drastically reduces output (e.g., 2% moisture = 100% output; 10% moisture ≈ 34% output).
• Dust content effect: 40% dust = 100% output; 70% dust = 82% output.
• Altitude reduces output (e.g., 0 ft = 100%, 10,000 ft = 69%).

4. Maintenance Do's and Don'ts (Annex-G)

• Regular greasing, oil checks, belt alignment.
• Avoid running plant over capacity.
• Safety: proper earthing, no welding with power ON, avoid fuel leaks.
• Calibration of load cells monthly.

5. Cost Calculation (Annex-F)

• Salvage value = 15% of equipment cost.
• Storage = 1% of investment/year.
• Repair/Maintenance = 150% of investment/year.
• Overhead = 5% of wages + servicing.
• Hire charges

Key Specifications for Burner Operation (IRC 90 - Clause 4.1.3.1)

• Fuel Type: Light diesel oil or furnace oil (India-specific).
• Burner Components:

• Fuel Tank & Pipeline: Tank near burner, bottom at same elevation; pipelines clean, minimal bends, adequate diameter.

Insulation of Drum (Clause 10.4 & 2.5)

• Maintain temperature difference ≈ 60°C between inner and outer shell.
• Use glass wool insulation or aluminium painting on drum shell.
• Benefits:
  • Increase plant output by 2.5%
  • Decrease fuel consumption by 4%

Altitude Derating (Clause 3.5)

• Plant output derated by 3.5% per 300 m rise above sea level.

Burner Air-Fuel Control Logic (Simplified)

flowchart TD
    FuelSupply --> ControlValve --> Nozzle
    Blower --> AirDamper --> CombustionChamber
    FlameDetector -->|Flame OK| ControlPanel
    ControlPanel -->|Adjust| AirDamper
    ControlPanel -->|Adjust| ControlValve
    AutomaticTempController --> ControlPanel

Summary: Efficient burner operation requires proper fuel atomization (pre-heating, pressure control), air

Calibration & Output Analysis of Hot Mix Plants (IRC: 90, Annex-J & related clauses)

1. Calibration of Load Cell (Drum Mix Plant)

• Slinger Conveyor Speed (m/s):
  [ v = \frac{L \times N}{60} ]
  where,
  (L) = length of slinger conveyor (m),
  (N) = RPM of slinger conveyor.

• Theoretical TPH (Tonnes per hour):
  [ \text{TPH}_{theoretical} = \text{Weight (kg)} \times v \times \frac{3600}{1000} ]

• Load Cell Constant:
  [ \text{Constant} = \frac{\text{Actual TPH}}{\text{Theoretical TPH}} ]

• Calibration is done at 3-4 control settings covering expected production range.

2. Calibration of Bitumen Flow Rate

• Run plant at 100% load with bitumen % (e.g., 3%).

• Collect output for 30 seconds; measure actual weight.

• Theoretical weight:
  [ W_{theoretical} = \text{TPH} \times \frac{1000}{3600} \times 30 \times \frac{% \text{Bitumen}}{100} ]

• Adjust pump speed if actual < theoretical.

3. Output Analysis Sample (Annex-H)

4. Key Specifications & Checks

• Cold bin feeders: Minimum 4.

• Regular calibration recommended monthly.

• Maintain proper belt alignment, greasing, and safety checks (Annex-G).

Summary Diagram: Calibration Flow

flowchart TD
    A[Start Calibration] --> B[Check Factory Settings]
    B --> C[Static Calibration with Standard Weight]
    C --> D[Calculate Theoretical TPH]
    D --> E[Run Dynamic Calibration]
    E --> F[Collect Output Weight]
    F -->

IRC 90: Information to be Furnished by Purchaser (Annex-A Summary)

When enquiring for a Hot Mix Plant (HMP), the purchaser should provide:

1. Site Conditions:

   • Available space for plant installation
   • Altitude above mean sea level
   • Temperature and climate details
   • Special operating conditions

2. Type of Hot Mix Plant:

   • Drum mix coater, embedded burner, batch type, double barrel, etc.

3. Type of Flow:

   • Counter flow or parallel flow

4. Preparation Methodology:

   • Continuous or batch type

5. Mobility:

   • Stationary or mobile plant

6. Essential & Optional Units:

   • Cold bin feeder (min. 4 nos.)
   • Aggregate oversize rejection screen
   • Cold elevator/feed conveyor
   • Automatic weighing system
   • Dryer cum mixing drum
   • Pollution control devices (bag house filter, wet scrubber)
   • Bitumen unit, mixing unit (pugmill)
   • Mineral filler/dust collection
   • Control panel, hot mix surge silo (optional)

Key Tables & Formulas for Running Charges (Clause 1.4)

Sample Output Calculation (Annex-H)

flowchart TD
    A[Purchaser] --> B[Provide Site Conditions]
    A --> C[Specify Plant Type & Flow]
    A --> D[Specify Mobility & Units]
    B --> E[Manufacturer Offers

IRC 90: Information to be Supplied by Manufacturer (Clause 11.3 & Annex-B)

The manufacturer must provide the purchaser with detailed information to aid in plant selection and operation:

Key Information to be Supplied by Manufacturer:

• Model and type of Hot Mix Plant offered.
• Description of plant units and their capacities.
• Special features of the plant.
• Dryer drum flights: Type and number.
• Electric motor capacities for each unit.
• DG set capacity required.
• Dimensions and weight of units (for transport).
• After-sales service location.
• Spare parts catalogue, operation & maintenance manuals.
• List of fast-moving components.
• Details of previously supplied plants (year-wise).
• Training facilities provision.

Summary Table (from Annex-B):

Additional Notes:

• Refer to Annex-A for purchaser’s info requirements.
• Calibration inputs for Hot Mix Plants are in Annex-J.
• Maintenance do's and don'ts are in Annex-G.
• Sample output calculations are in Annex-H.

flowchart LR
    A[Manufacturer] --> B[Provide Plant Info]
    B --> C[Model & Type]
    B --> D[Plant Description & Capacity]
    B --> E[Motor & DG Set Capacity]
    B --> F[Dimensions & Weight]
    B --> G[After Sales Service]
    B --> H[Spare Parts & Manuals]
    B --> I[Training & Past Supply Details]

This ensures clear communication and proper plant selection per IRC 90 standards.

Hot Mix Plant Emission & Control — IRC 90 Key Points

1. Pollution Control Devices:

• Primary pollution control: Dust collection system (cyclones, scrubbers).
• Secondary pollution control: Bag house filter system (Clause 4.1.13.3).
• Exhaust control system: To reduce particulate emissions from dryer and mixer.

2. Components related to Emission Control:

3. Typical Emission Control Measures:

• Use of bag house filters to capture fine dust.
• Proper sealing of conveyors and transfer points.
• Regular maintenance to prevent fugitive dust.

4. Sample Formula for Output (Annex-H):
Output (tons/hr) = (Volume of mix produced per batch × Bulk density) / Cycle time

5. Operational Precautions (Clause 5.6 & 6.3):

• Maintain burner efficiency to reduce smoke.
• Control moisture in aggregates to minimize dust.
• Ensure proper insulation of drum to reduce heat loss and emissions.

Summary Table: Emission Control Devices

flowchart LR
    A[Cold Aggregate Feeder] --> B[Dryer Drum]
    B --> C[Primary Dust Collector]
    C --> D[Bag House Filter (Secondary)]
    D --> E[Hot Mix Surge Silo]
    E --> F[Mixing Unit]
    F --> G[Hot Mix Output]

References: IRC:90-2010 Clauses 4.1.11, 4.1.13.3, 5.6.3, Annex-H (Sample calculation).

IRC 90: Hot Mix Plant Output vs Different Parameters

Key Charts & Tables (Annex-D, Clause 10.1 - 10.3)

1. Output vs Moisture Content in Aggregates

Output decreases significantly with increasing moisture due to drying time.

2. Output vs Dust Content in Mix

Higher dust content reduces output due to increased mixing time.

3. Effect of Altitude on Output

Output decreases with altitude due to reduced oxygen and combustion efficiency.

Formula for Hire Charges per Hour (Clause 1.4)

[ \text{Total Running Charges per hour} = H + I + J + K ]

Where:

• H = Operating staff & labour wages per hour
• I = Servicing staff wages per hour
• J = Servicing material cost per hour
• K = Cost of lubricating oil & fuel consumed per hour

Add overhead @

Checklist for Selection of Hot Mix Plant (IRC 90: Clause 11.4 & Annex-E Highlights)

Key Parameters for Selection:

• Plant Capacity: Match with project quantum & completion time.
• Space Availability: Ensure adequate space for installation & operation.
• Reputed Make & Proven Design: Reliability and ease of maintenance.
• Spare Parts Availability: Stock fast-moving spares onsite to avoid downtime.
• Calibration Facilities: Pyrometers, thermocouples, and control panel must be calibrated regularly.
• Skilled Operators: Trained personnel for smooth operation and troubleshooting.
• Safety Compliance: Proper guarding of moving parts, electrical insulation, and earthing.

Essential Specifications & Controls

Operational & Maintenance Guidelines

• Follow manufacturer's manual strictly.
• Maintain history sheets/log books for spare parts forecasting.
• Regularly inspect vibrating screen, control panel, and pyrometers.
• Use genuine spares to ensure interchangeability and reduce breakdowns.
• Implement daily maintenance schedules (cleaning, lubrication, calibration).
• Ensure real-time data logging in control panels for process monitoring.

Safety & Quality Assurance

• Electrical wiring must be well insulated and earthed.
• High-speed drives should be guarded.
• Operators must be trained and safety codes strictly followed.

flowchart LR
    A[Project Requirements] --> B[Select Plant Capacity]
    B --> C[Check Space Availability]
    C --> D[Choose Reputed Manufacturer]
    D --> E[Verify Spare Parts Availability]
    E --> F[Ensure Calibration Facilities]
    F --> G[Train Skilled Operators]
    G --> H

Do's and Don'ts for Maintenance of Hot Mix Plants (IRC 90:2010)

Do's

• Select reputed make and proven design for reliable operation.
• Follow manufacturer’s maintenance schedules and guidelines strictly.
• Maintain history sheets/log books for spare parts tracking and inventory control.
• Keep fast-moving spare parts stocked onsite to avoid plant idling.
• Calibrate pyrometers/thermocouples frequently (at least once per working period).
• Regularly inspect vibrating screen covers for sieve wear and tension; adjust as needed.
• Calibrate control panels regularly to ensure mix accuracy.
• Use genuine spare parts from the manufacturer to maintain interchangeability.
• Deploy trained/skilled operators and technicians for operation and maintenance.
• Ensure control panels store real-time process data for review.
• Guard high-speed drives, insulate wiring properly, and ensure proper earthing.
• Comply fully with relevant safety codes during design, erection, and operation.

Don'ts

• Don’t ignore breakdown troubleshooting instructions in the operational manual.
• Avoid using non-genuine spare parts that may cause breakdowns.
• Don’t neglect regular calibration and inspection of sensitive instruments.
• Avoid stockpiling excessive spare parts without proper usage data.

Maintenance Schedule Highlights (Clause 8.1.1)

Safety & Performance Factors

• Shield sensitive instruments from heat and vibration.
• Maintain insulation of dryer drum.
• Control moisture content in aggregates to avoid mix quality issues.
• Ensure dust control via pollution control devices (bag house filters).

flowchart LR
    A[Start Maintenance] --> B{Daily Checks}
    B --> C[Lubrication]
    B --> D[Belts & Filters]
    B --> E[Electrical Systems]
    C --> F{Weekly Checks}
    D --> F
    E --> F
    F --> G[Burner & Mixer Inspection]
    G --> H{Monthly Checks}
    H --> I[Instrument Calibration]