Guidelines of Selection, Operation and Maintenance of Bituminous Hot Mix Plant (First Revision)
2010 Edition

Summary of Scope & Main Features of IRC 90

• Coverage: IRC 90 specifies criteria for design, operation, upkeep, and safety of Hot Mix Plants (HMP) for road construction.

• Plant Types Included:

  • Continuous Hot Mix Plants
  • Batch Hot Mix Plants

• Production Capacity: Ranges between 60 to 90 tonnes per hour typically.

• Major Plant Elements:

  • Cold aggregate feeders and conveyors
  • Drying drum (counterflow or parallel flow types)
  • Primary and secondary pollution control systems (e.g., bag filters)
  • Hot aggregate elevators and screening units
  • Weighing hoppers, bitumen heating units, pugmill mixers
  • Mineral filler handling systems and control consoles

• Calculation of Running Costs (per hour):

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

where:

• (H) = wages of operating staff/hour

• (I) = wages of servicing staff/hour

• (J) = cost of fuel and lubricants/hour

• (K) = expenses for oil and fuel consumption/hour

• Hire Charges Formula:

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

Overhead is typically 5% of total hourly costs.

• Maintenance & Safety Instructions: Provided in Annex-G to ensure safe, efficient plant function.

• Sample Output Data (Annex-H):

This scope promotes uniform quality, safety, and operational efficiency for hot mix plants in pavement projects.

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

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

Key Points:

• Capacity is measured in tonnes per hour (TPH).
• Output specified for two aggregate moisture levels:
  • 6% moisture content (lower throughput)
  • 2% moisture content (higher throughput)

Example:

• A plant rated 40/60 TPH means:
  • 40 tonnes per hour at 6% moisture
  • 60 tonnes per hour at 2% moisture

Batch Type Hot Mix Plants (Clause 3.2.2)

• Mixes are produced in discrete batches, each taking approximately 45 to 60 seconds.
• Capacity calculated as number of batches per hour multiplied by batch size.
• Internationally, batch plants can reach up to 400 TPH.

Sample Output Calculation (Annex-H)

Note: Bulk density assumed as 2.2 tonnes/cum.

Summary of Running & Hire Charges (Clause 1.4)

Maintenance Guidelines Highlights (Annex-G)

• Ensure belt alignment and lubrication.
• Preheat dryer drum before aggregate feed.
• Calibrate load cells regularly.
• Avoid operating beyond rated capacity.
• Safety: Proper earthing, no welding while powered, no smoking near flammable materials.

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

Primary Components of Hot Mix Plants (IRC 90 - Clauses 5.6.3 onwards):

• Cold Aggregate Feeders and Bucket Elevators: For feeding and lifting aggregates to drying units.
• Dryer Drum: Heats and dries aggregates.
• Burner Unit: Supplies heat energy for drying.
• Hot Elevator: Transports heated aggregates.
• Screening Units: Segregate aggregates by size.
• Mixer (Pugmill): Combines aggregates, bitumen, and filler.
• Bitumen Heating & Storage Unit: Provides heated bitumen supply.
• Mineral Filler System: Adds mineral fillers to the mix.
• Pollution Control (Bag House Filter): Captures dust emissions.
• Hot Mix Surge Silo: Temporary storage before dispatch.
• Control Room: Centralized operational control.

Operational Sequence (Clauses 5.6.3 & 6.3)

• Cold feed → drying → hot aggregate lifting → screening and weighing → mixing with bitumen → storage or dispatch.
• Monitor moisture levels, temperature, and dust emissions.
• Maintain burner efficiency and conduct daily lubrication and filter cleaning.

Bitumen Content Calculation (% by weight):

[ \text{Bitumen , Content} = \left( \frac{\text{Bitumen Weight}}{\text{Total Mix Weight}} \right) \times 100 ]

Hot Mix Plant Process Flow (Mermaid Diagram):

flowchart TD
    A[Cold Aggregate Feeders] --> B[Bucket Elevator]
    B --> C[Dryer Drum]
    C --> D[Hot Elevator]
    D --> E[Screening Unit]
    E --> F[Weigh Hopper]
    F --> G[Bitumen Unit]
    G --> H[Mixer (Pugmill)]
    H --> I[Hot Mix Surge Silo]
    I --> J[Dispatch]

Benefits of Double Barrel Drum Mix Plants (Clause 5.6.3)

• Continuous operation capability.
• Higher output rates.
• Reduced fuel consumption.

Limitations:

• Higher initial investment.
• More complex upkeep requirements.

Refer to IRC 90:2010 Clauses 5.6.3 to 6.3.8 and maintenance protocols in Clauses 8.1.1 onward for detailed specifications.

Pollution and Emission Management in Hot Mix Plants (IRC 90)

Main Control Devices (Clause 5.2.14)

1. Primary Dust Control: Dust collection systems such as cyclones or baghouse filters (Clause 5.6.2.5).
2. Secondary Pollution Control Devices:
   • Wet Scrubbers:
     • Open Spray Tower Type: Dust-laden gases sprayed with water; slurry collects at the base.
     • Venturi Scrubber Type: Gas flows through a venturi wetted by high-pressure water spray; higher dust capture efficiency.
   • Bag House Filter: Fabric filters capturing fine dust particles down to 5 microns.

Wet Scrubber Operation & Efficiency

• Removes particulate matter ≥5 microns.
• Requires significant water volumes and slurry collection ponds.
• Slurry must be removed every 2-3 days to maintain effectiveness.

Venturi Scrubber Diagram:

flowchart LR
    DG[Dirty Gas Inlet] --> VT[Venturi Section]
    VT --> CA[Clean Air Outlet]
    VT --> DS[Slurry Discharge]

Notes

• Venturi scrubbers outperform open spray towers in dust removal.
• Baghouse filters are preferred for finer particulate control.
• See Annex-C for emission limits and control details.

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

Specifications and Calculations for Aggregate Handling Systems (IRC 90)

1. Cold Aggregate Feeders (Clauses 6.3.1 & 4.1.1)

• Minimum of four segregated bins to avoid mixing.
• Bin capacity sufficient for at least 30 minutes of operation.
• Gate openings regulated using graduated scales calibrated to control tonnage per hour.
• Vibrators installed on fine aggregate bins to prevent material arching.
• Variable speed motors govern conveyor speeds enabling proper aggregate proportioning.
• Discharge gate openings sized ≥1.5 times maximum aggregate size to prevent belt damage.
• Optional grizzly screens above bins to prevent oversized stones.
• Periodic roller cleaning to prevent material build-up.

2. Flow Rate Estimation & Calibration

• Approximate flow (Q) through gate calculated by:

[ Q = k , A , \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 Recommendations

• Maintain minimal material in bins during rainy conditions.
• Regularly inspect and clean rollers to prevent clogging.

Aggregate Handling System Summary Table

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

Operational and Safety Procedures for Hot Mix Plants (IRC 90 Summary)

1. Pre-Operational Checklist (Clause 7.1)

Before initiating operations, operators should confirm:

• Completion of scheduled daily maintenance.
• Adequate oil levels in tanks, gearboxes, and air filters.
• Proper tensioning of belts and chains.
• Lubrication of all grease points.
• Presence of safety guards and covers.
• Bitumen pipelines adequately heated.
• Clearance of bucket elevator from stones.
• Inspection of conveyor belts and rollers.
• Controlled fuel spray into combustion chamber.
• Absence of water in bitumen storage.

2. Safety Measures (Clauses 9.1 & 9.2)

• Site Safety:

  • Employ medically fit, trained personnel.
  • Use appropriate PPE: helmets, gloves, goggles, safety harnesses.
  • Maintain clean, well-lit access areas.
  • Keep firefighting equipment and first aid kits ready.
  • Install emergency sirens and stop mechanisms.
  • Prohibit smoking near fuel or bitumen areas.

• Equipment Safety:

  • Only operate well-maintained, safe machinery.
  • Operators must be familiar with controls.
  • Never service running equipment.
  • Avoid loose electrical wiring.
  • Switch off and immobilize equipment when unattended.
  • Follow proper shutdown procedures: neutral controls, idle engine, then stop.
  • Prevent fuel leaks, overheating, and backfire risks.
  • Store flammable materials safely.

3. Safety Procedure Flowchart

flowchart TD
    A[Start Pre-Operational Checks] --> B{Are All Checks Satisfactory?}
    B -- Yes --> C[Start Plant Operation]
    B -- No --> D[Address Issues]
    D --> A
    C --> E[Operate with Safety Precautions]
    E --> F{Emergency Situation?}
    F -- Yes --> G[Activate Emergency Stop]
    F -- No --> H[Continue Operations]
    H --> I[Shutdown Procedure]
    I --> J[End]

4. Safety Essentials Reference Table

Plant and Equipment Specifications as per IRC 90

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

• Capacity ranges from 3 TPH to 650 TPH.
• Types include batch and continuous plants; static, portable, or mobile configurations; conventional or tower layouts; and parallel, counter, or double barrel flow systems.
• Selection criteria include production volume, project timeline, site space, emission regulations, fuel efficiency, and use of reclaimed bituminous pavement (RBP).

2. Emission Factors & Controls (Annex-C)

• Control device efficiencies:
  • Baghouse filters remove 99-99.7% PM10
  • Cyclones remove 50-75%
  • Venturi scrubbers remove 90-99.5%

3. Output Influencing Factors (Annex-D)

• Aggregate moisture drastically affects output (e.g., at 2% moisture output is 100%, at 10% moisture output drops to ~34%).
• Dust content also impacts output (40% dust = 100% output; 70% dust = 82% output).
• Altitude reduces output due to lower oxygen levels (sea level = 100%, 10,000 ft = 69%).

4. Maintenance Guidelines (Annex-G)

• Regular lubrication, oil level checks, belt alignment.
• Avoid exceeding rated production capacity.
• Safety compliance including earthing and avoiding welding under live power.
• Monthly load cell calibration.

5. Cost Calculations (Annex-F)

• Salvage value equals 15% of equipment cost.
• Storage costs at 1% annual investment.
• Repair and maintenance costs estimated at 150% annual investment.
• Overhead set at 5% of wages and servicing costs.
• Hire charges computed accordingly.

Burner System Specifications (IRC 90, Clause 4.1.3.1)

• Fuel Used: Light diesel oil or furnace oil typical in India.
• Burner Components and Their Functions:

• Fuel Tank and Piping: Tank positioned near burner at equal elevation; piping designed with minimal bends and appropriate diameter.

Drum Insulation (Clauses 10.4 & 2.5)

• Maintain approx. 60°C temperature difference between inner and outer drum surfaces.
• Use glass wool insulation or aluminium paint on drum exterior.
• Benefits include a 2.5% increase in output and 4% reduction in fuel consumption.

Altitude Adjustment (Clause 3.5)

• Output reduced by approximately 3.5% for every 300 meters elevation above sea level.

Simplified Burner Air-Fuel Control Flow

flowchart TD
    FuelSupply --> ControlValve --> Nozzle
    Blower --> AirDamper --> CombustionChamber
    FlameDetector -->|Flame Confirmed| ControlPanel
    ControlPanel -->|Adjust Air| AirDamper
    ControlPanel -->|Adjust Fuel| ControlValve
    AutoTempController --> ControlPanel

Summary: Effective burner operation depends on proper fuel atomization through pre-heating and pressure regulation along with precise air flow control.

Calibration and Performance Assessment of Hot Mix Plants (IRC 90, Annex-J and related clauses)

1. Load Cell Calibration for Drum Mix Plants

• Slinger Conveyor Speed (m/s):

[ v = \frac{L \times N}{60} ]

where:

• (L) = slinger conveyor length in meters

• (N) = conveyor RPM

• Theoretical Production Rate (TPH):

[ TPH_{theoretical} = Weight (kg) \times v \times \frac{3600}{1000} ]

• Load Cell Calibration Constant:

[ Constant = \frac{Actual TPH}{Theoretical TPH} ]

• Calibration performed at multiple control settings spanning expected output range.

2. Bitumen Flow Rate Calibration

• Operate plant at full load with specified bitumen percentage (e.g., 3%).
• Collect output sample over 30 seconds and weigh.
• Calculate theoretical bitumen weight:

[ W_{theoretical} = TPH \times \frac{1000}{3600} \times 30 \times \frac{Bitumen%}{100} ]

• Adjust pump speed if actual bitumen weight differs from theoretical.

3. Example of Output Data (Annex-H)

4. Key Checks and Specifications

• Minimum of four cold bins for aggregate feeders.
• Monthly calibration recommended.
• Ensure proper belt alignment, lubrication, and safety per Annex-G.

Calibration Process Diagram

flowchart TD
    A[Initiate Calibration] --> B[Verify Factory Settings]
    B --> C[Static Calibration with Standard Weights]
    C --> D[Calculate Theoretical TPH]
    D --> E[Conduct Dynamic Calibration]
    E --> F[Measure Output Weight]
    F -->

Purchaser Information Requirements for Hot Mix Plant (IRC 90 Annex-A Summary)

When requesting a hot mix plant, the purchaser must provide:

1. Site Details:

   • Available installation space
   • Altitude above sea level
   • Ambient temperature and climate conditions
   • Any special operating conditions

2. Plant Type:

   • Options such as drum mix with embedded burner, batch type, double barrel, etc.

3. Flow Type:

   • Counterflow or parallel flow configuration

4. Mix Preparation Mode:

   • Continuous or batch processing

5. Mobility:

   • Fixed or mobile plant

6. Required and Optional Units:

   • Cold aggregate feeders (minimum four bins)
   • Oversized aggregate rejection screens
   • Cold elevators or feed conveyors
   • Automatic weighing systems
   • Combined dryer and mixer drums
   • Pollution control devices like baghouse filters or wet scrubbers
   • Bitumen heating and mixing units
   • Mineral filler systems
   • Control panel and optional hot mix surge silo

Running Cost Computation (Clause 1.4)

Output Calculation Example (Annex-H)

flowchart TD
    A[Purchaser] --> B[Site Details]
    A --> C[Plant Type and Flow]
    A --> D[Mobility and Units]
    B --> E[Manufacturer Proposal]

Manufacturer’s Information Submission (IRC 90 Clause 11.3 & Annex-B Summary)

Manufacturers should supply comprehensive details to assist purchasers in plant selection and operation:

Details to Submit:

• Plant model and type.
• Description of plant components and their capacities.
• Special features or innovations.
• Type and number of dryer drum flights.
• Electric motor ratings for each unit.
• Required DG set capacity.
• Dimensions and weights for transport considerations.
• Location and contact for after-sales service.
• Spare parts catalog and operation/maintenance manuals.
• List of frequently replaced components.
• Records of previous plant deliveries with dates.
• Availability of operator training programs.

Summary Table:

Additional References:

• Purchaser info needs in Annex-A.
• Calibration details in Annex-J.
• Maintenance guidelines in Annex-G.
• Output examples in Annex-H.

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

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

Emission Management and Control in Hot Mix Plants — IRC 90 Key Points

1. Pollution Control Systems:

• Primary control: Dust collection via cyclones and scrubbers.
• Secondary control: Baghouse filters capturing fine particulate matter (Clause 4.1.13.3).
• Exhaust systems: To minimize particulate emissions from drying and mixing zones.

2. Related Components and References:

3. Typical Emission Control Practices:

• Employ baghouse filters for fine dust capture.
• Seal conveyors and transfer points to prevent fugitive dust.
• Conduct routine maintenance to ensure dust control efficacy.

4. Output Calculation (Annex-H): Output (tonnes/hour) = (Batch volume × Bulk density) / Cycle time

5. Operational Guidelines (Clauses 5.6 & 6.3):

• Maintain burner efficiency to reduce smoke generation.
• Control moisture in aggregates to minimize dust.
• Properly insulate dryer drums to reduce heat loss and emissions.

Emission Control Devices Summary

flowchart LR
    A[Cold Aggregate Feeder] --> B[Dryer Drum]
    B --> C[Primary Dust Collector]
    C --> D[Baghouse Filter]
    D --> E[Hot Mix Surge Silo]
    E --> F[Mixing Unit]
    F --> G[Hot Mix Dispatch]

Based on IRC:90-2010 Clauses 4.1.11, 4.1.13.3, 5.6.3, and Annex-H sample calculations.

IRC 90: Hot Mix Plant Output Variations with Key Parameters

1. Effect of Aggregate Moisture Content on Output (Annex-D, Clauses 10.1-10.3)

Higher moisture reduces plant output due to increased drying time.

2. Effect of Dust Content on Output

Increased dust content lowers output because of longer mixing times.

3. Altitude Effect on Output

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

Hire Charges Computation (Clause 1.4)

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

Where:

• H = Operator and labor wages per hour
• I = Servicing staff wages per hour
• J = Servicing materials cost per hour
• K = Lubricating oil and fuel cost per hour

Add overhead charges accordingly.

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

Primary Considerations:

• Plant Capacity: Align with project volume and timeline.
• Available Space: Ensure sufficient room for installation and operation.
• Manufacturer Reputation and Proven Designs: Reliable and maintainable equipment.
• Availability of Spare Parts: Stock fast-moving parts onsite to minimize downtime.
• Calibration Facility: Equipment such as pyrometers and thermocouples must be regularly calibrated.
• Qualified Operators: Skilled personnel for smooth operation and troubleshooting.
• Safety Compliance: Proper guarding, electrical insulation, and earthing.

Essential Components and Control Features

Operational and Maintenance Best Practices

• Strict adherence to manufacturer manuals.
• Maintain detailed logs for spare parts and maintenance.
• Inspect vibrating screens, control panels, and temperature sensors regularly.
• Use genuine spare parts to ensure compatibility and reduce failures.
• Implement daily maintenance routines including cleaning, lubrication, and calibration.
• Employ real-time data logging for process monitoring.

Safety and Quality Assurance

• Ensure all electrical wiring is properly insulated and earthed.
• Guard high-speed moving parts.
• Provide comprehensive operator training and enforce safety protocols.

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

Maintenance Guidelines for Hot Mix Plants (IRC 90:2010)

Recommended Practices

• Choose equipment from reputable manufacturers with proven designs.
• Adhere strictly to manufacturer maintenance schedules and instructions.
• Keep comprehensive history and log sheets for spare parts management.
• Maintain an adequate stock of frequently used spare parts onsite.
• Calibrate pyrometers and thermocouples regularly, at least once per operational period.
• Inspect vibrating screen covers for wear and tension and adjust as necessary.
• Regularly calibrate control panels to ensure mix accuracy.
• Use genuine manufacturer parts to maintain interchangeability.
• Employ trained and skilled operators and technicians.
• Ensure control panels record real-time operational data.
• Guard high-speed drives, insulate wiring properly, and maintain earthing.
• Comply fully with safety guidelines during installation, operation, and maintenance.

Practices to Avoid

• Do not disregard troubleshooting instructions provided in manuals.
• Avoid using counterfeit or non-genuine spare parts.
• Never neglect routine calibration and inspection of critical instruments.
• Avoid excessive spare parts stockpiling without usage tracking.

Maintenance Schedule Overview (Clause 8.1.1)

Safety and Performance Considerations

• Protect sensitive instruments from heat and vibration.
• Maintain insulation on dryer drums.
• Control moisture in aggregates to assure mix quality.
• Use pollution control devices such as baghouse filters effectively.

flowchart LR
    A[Begin Maintenance] --> B{Perform Daily Checks}
    B --> C[Lubricate Components]
    B --> D[Inspect Belts & Filters]
    B --> E[Check Electrical Systems]
    C --> F{Conduct Weekly Checks}
    D --> F
    E --> F
    F --> G[Inspect Burners & Mixers]
    G --> H{Monthly Calibration}
    H --> I[Calibrate Instruments]