Code of practice for the use of immersion vibrators for consolidating concrete
1983 Edition

Overview of Scope for Concrete Vibration Practices

• Standard Compliance: Immersion vibrators should meet IS 2505-1980 specifications.
• Selection Factors: Based on concrete consistency, placing conditions, and member geometry.
• Role of Engineer: Determines vibrator size tailored to project demands.

Needle Diameter Selection Table

Additional Notes:

• Multiple vibrators may be necessary for large mass concrete pours.
• Proper vibrator sizing is critical for effective consolidation.
• Reference IS 2505-1980 for vibrator details.

flowchart TD
    A[Concrete Characteristics] --> B{Choose Vibrator Needle Diameter}
    B -->|Thin Sections| C[25-35 mm]
    B -->|Thin Walls & Beams| D[40-50 mm]
    B -->|Standard Construction| E[60 mm]
    B -->|Mass Concrete ≤ 2 m³| F[75 mm]
    B -->|Mass Concrete ≤ 8 m³| G[90 mm + Multiple Units]

This serves as guidance for vibrator selection as per Clause 5.1 and Table 1 of the code.

Details on Types and Suitability of Immersion Vibrators

Specifications (Clause 3.1 & Table 1)

Usage Instructions (Clause 3.1.1)

• Always fully immerse the vibrating needle.
• Effective thickness of concrete layer should be between two-thirds to full length of needle, preferably not exceeding 600 mm.
• Minimum concrete layer thickness for vibration is 100 mm.
• Needle should be inserted vertically for optimal consolidation.
• Flexible shaft vibrators need careful maintenance; motor-in-head types are more robust.

Types of Immersion Vibrators (Clause 3.1.2)

• Flexible shaft models: Powered by compressed air, electric motors, petrol, or diesel engines.
• Motor-in-head models: Electrically or pneumatically driven, with greater durability and simpler upkeep.

graph LR
    A[Plastic Concrete Thin Members] --> B(25 & 35 mm)
    C[Thin Walls, Columns, Beams] --> D(40 & 50 mm)
    E[General Construction] --> F(60 mm)
    G[Mass Concrete ≤ 2 m³] --> H(75 mm)
    I[Mass Concrete ≤ 8 m³] --> J(90 mm)

Refer to IS 3558 Clauses 3.1 and 5.1 (Table 1), as well as IS 2505-1980 for detailed vibrator specifications.

Power Units and Specifications for Concrete Vibrators

Types of Power Units (Clause 3.2.1):

• Electric motors (direct or flexible shaft driven)
• Petrol or diesel internal combustion engines
• Compressed air motors

Recommended Power Ratings (Clause 3.2.6):

Notes:

• Electric motors are preferable where electrical supply is reliable due to constant speed and easier management.
• Power rating selection depends on vibrator design and manufacturer’s guidelines.
• Power units should conform to these ratings for optimal vibrator operation.

graph LR
    A[Vibrator Power Units] --> B[Electric Motor]
    A --> C[Petrol Engine]
    A --> D[Diesel Engine]
    A --> E[Compressed Air Motor]

    B --> F[Power: 0.75 - 2.5 kW]
    C --> G[Power: 1.5 - 3.5 kW]
    D --> H[Power: Up to 3.3 kW]
    E --> I[Power: 7.5 kW]

Refer to Appendix A for maintenance schedules to ensure reliable operation.

Key Guidance on Handling Immersion Vibrators

Selection and Suitability (Clause 5.1 and Table 1)

• Vibrators must comply with IS 2505-1980.
• Choice depends on concrete mix characteristics, workability, member dimensions, and placing environment.

• For pours exceeding 4 m³, use multiple vibrators.

Concrete Layer Thickness (Clause 3.1.1)

• Denote needle length as l.
• Effective vibration depth should be between (2/3)l and l.
• Maximum concrete layer thickness: 600 mm.
• Minimum layer thickness for vibration: 100 mm.
• Vertical insertion is preferred to avoid poor consolidation.

Operational Tips

• Fully immerse the vibrating needle.
• Keep flexible shaft clear to prevent damage.
• Ensure concrete depth allows complete needle immersion.

Formula for Layer Thickness

[ \frac{2}{3} l \leq \text{Layer thickness} \leq l, \quad \text{and} \quad \text{Layer thickness} \leq 600 \text{ mm} ]

flowchart TD
    A[Select Vibrator Needle Size] --> B{Based on Concrete Type & Member Size}
    B -->|Thin members| C[25-35 mm]
    B -->|Thin walls or beams| D[40-50 mm]
    B -->|Standard construction| E[60 mm]
    B -->|Mass concrete ≤ 2 m³| F[75 mm]
    B -->|Mass concrete ≤ 8 m³| G[90 mm]

This procedure ensures effective consolidation according to IS 3558.

Performance and Dimension Guidelines for Concrete Vibrators

• Compliance with IS 2505-1980 is mandatory.
• Selection depends on concrete mix properties, workability, member size and shape, and placing conditions.
• The engineer responsible must determine the appropriate vibrator size.

Power Unit Recommendations

graph TD
    A[Vibrator Needle Size] --> B[Applications]
    B --> C[25-35 mm: Thin & confined concrete]
    B --> D[40-50 mm: Thin walls and beams]
    B --> E[60 mm: General construction]
    B --> F[75 mm: Mass concrete ≤ 2 m³]
    B --> G[90 mm: Mass concrete ≤ 8 m³, requires multiple vibrators]

This ensures suitable vibrator size and power for specific concrete jobs.

Compatibility of Concrete Mix for Effective Vibration

• Mix Consistency: Must be stiff enough to prevent cavity formation upon slow withdrawal of the vibrator (Clause 6.1.1).

• Compacting Factor: Optimal range is 0.75 to 0.85 (Clause 6.1).

  • The fine mortar should appear greasy wet when vibrator is removed.
  • Excessive workability leads to segregation; over-vibrating may produce laitance.

• Frequency versus Aggregate Size:

• Vibrator Needle Size Selection:

Summary

• Select vibrator needle size according to member thickness and concrete consistency.
• Maintain compacting factor between 0.75 and 0.85.
• Match vibration frequency to aggregate size for optimal compaction.
• Avoid over-vibration and very fluid concrete to prevent segregation.

flowchart LR
    A[Concrete Stiffness] --> B[No Cavities on Needle Withdrawal]
    A --> C[Compacting Factor 0.75-0.85]
    B --> D[Select Appropriate Needle Size]
    C --> D
    D --> E[Vibration Frequency Matched to Aggregate Size]
    E --> F[Effective Compaction Without Segregation]

This approach guarantees optimal concrete quality and vibration compatibility.

Key Considerations for Concrete Placement and Formwork

Formwork Strength (Clause 7.1)

• Must resist increased pressure caused by vibrating concrete.
• Design should accommodate local pressure variations near the vibrator head.
• Joints must be sealed tightly to prevent grout leakage or air suction, which could cause honeycombing or voids.

Vibration Frequency Recommendations (Clause 6.1.2)

Layer Thickness (Clause 8.2)

• Place concrete in layers not exceeding 600 mm thickness.
• Initial layers should be no thicker than 150 mm.
• Thicker layers can trap air and limit compaction effectiveness.

Vibrator Selection (Clause 5.1 & Table 1)

flowchart TD
    A[Concrete Mix] --> B[Place in Layers ≤ 600 mm]
    B --> C[Vibrate at Frequency Matching Aggregate Size]
    C --> D[Formwork Designed to Withstand Vibration Pressure]
    D --> E[Ensure Tight Joints to Prevent Leakage and Voids]

Use vibrators compliant with IS 2505-1980 and select them based on member and mix characteristics.

Recommended Practices for Concrete Vibration

Vibrator Needle Sizes and Their Applications (Clause 5.1, Table 1)

• For concrete volumes of 4 m³ or more, simultaneous use of multiple vibrators is advised.
• Vibrators must adhere to IS 2505-1980.

Concrete Mix Requirements (Clause 6.1)

• Use stiff concrete with compacting factor between 0.75 and 0.85.
• Concrete should exhibit a greasy wet appearance upon slow withdrawal of the vibrator.
• Avoid high workability mixes to prevent segregation.
• Excess vibration can cause segregation and laitance formation.
• Proper mix design and controlled placement are essential for effective vibration.

graph LR
A[Needle Diameter] --> B[Applications]
B --> C1[25,35 mm: Thin members, lab specimens, auxiliary]
B --> C2[40,50 mm: Thin walls, columns, light floors]
B --> C3[60 mm: General construction, heavy floors]
B --> C4[75 mm: Mass concrete ≤ 2 m³, heavy structures]
B --> C5[90 mm: Mass concrete ≤ 8 m³, large dams]

Refer to IS 2505 for vibrator specifications and IS 3558 for operational guidelines.

Procedures for Vibrating Concrete Adjacent to Hardened Concrete

• Challenges: Insufficient vibration near hardened concrete or rock can generate defects.
• Guidelines: Follow Clause 8.7.1 to ensure thorough vibration at the interface, preventing voids.

Formwork Requirements (Clauses 7.1 and 7.1.1)

• Must withstand elevated vibration pressures.
• Joints should have gaps no larger than 1.5 mm to prevent grout leakage or air suction.
• Properly assembled formwork avoids honeycombing and rock pockets.

Vibrator Needle Sizes (Clause 5.1 & Table 1)

Practical Advice

• Use multiple vibrators for volumes greater than 4 m³.
• Ensure comprehensive vibration near hardened concrete interfaces to avoid honeycombing.
• Adjust vibration duration and frequency according to mix and member size.

flowchart LR
    A[Interface: Hardened Concrete] --> B[Apply Thorough Vibration]
    B --> C[Achieve Compacted, Defect-Free Junction]
    B -.-> D[Insufficient Vibration]
    D --> E[Honeycombing and Voids]

Proper vibrator size, tight formwork, and appropriate vibration ensure durable concrete joints.

Key Guidelines for Vibrating Reinforced Concrete

1. Reinforcement Spacing (Clause 8.8):

• Minimum clear spacing between bars or groups: 75 mm to allow vibrator head passage.
• Within groups, spacing must be at least two-thirds the nominal maximum aggregate size.
• Maximum width for a group of reinforcement: 250 mm.

2. Vibrator Needle Selection (Clause 5.1, Table 1):

• Vibrator size depends on concrete mix, placing conditions, and member geometry.
• For volumes above 4 m³, multiple vibrators should be employed.

3. Formwork Considerations (Clause 7.1):

• Must withstand increased pressure and pressure variations around vibrator head.
• Joints must be tight to avoid grout loss and air suction, preventing honeycombing.

flowchart TD
    A[Concrete Placement] --> B[Maintain Reinforcement Spacing ≥ 75 mm]
    B --> C[Select Appropriate Vibrator Needle Size]
    C --> D{Needle Diameter}
    D -->|25-35 mm| E[Thin Members]
    D -->|40-50 mm| F[Thin Walls & Columns]
    D -->|60 mm| G[General Construction]
    D -->|75 mm| H[Mass Concrete ≤ 2 m³]
    D -->|90 mm| I[Mass Concrete > 2 m³]
    A --> J[Formwork with Strong, Tight Joints]

This ensures proper vibration and compaction around reinforcement.

Maintenance and Service Documentation for Flexible Shaft Vibrators

Key Points (Clause 4.1 and Appendix A)

• Regular maintenance is critical to sustain vibrator efficiency under tough working conditions.
• After every use, clean the vibrator thoroughly and store it in a dry, clean environment.
• Repairs must follow manufacturer’s guidelines and be supervised carefully.
• Maintain spare vibrators to avoid interruptions during maintenance.
• It is recommended to keep a service log book for tracking maintenance activities, especially when multiple vibrators are in use.

Sample Service Log Book Format

Tips

• Use only manufacturer-approved lubricants for flexible shafts.
• Document all maintenance actions, repairs, and parts replacements.
• Timely cleaning and inspection help prevent equipment breakdown.

flowchart TD
    A[Vibrator Operation] --> B[Cleaning & Inspection]
    B --> C[Lubrication]
    C --> D[Repair if Necessary]
    D --> E[Record in Service Log]
    E --> F[Proper Storage]
    F --> A

For technical support, contact the Central Laboratory and Regional Offices listed in IS 3558 Appendix.

Electrical Safety Features and Protective Devices for Vibrators

• Electrical Protection (Clause 4.3.1):

  • Immersion vibrators powered by electric motors must include shock protection as per IS 1356 (Part I)-1972 and Indian Electricity Rules.
  • Adequate earthing is mandatory to prevent electrical hazards to operators.
  • Use four-core rubber-sheathed cables or equivalent to maintain continuous safety lead.

• Connection Integrity (Clause 4.3.3):

  • Special care must be taken with vibrator and plug connections to avoid wire breakage, which could interrupt safety circuits or expose dangerous voltages.
  • Anti-tension devices are required on all cable entry points to prevent wire damage.

Summary Table

graph LR
A[Power Source] --> B[Vibrator Motor]
B --> C[Grounding (Safety Lead)]
C --> D[Four-core Rubber Cable]
D --> E[Anti-tension Device]
E --> F[Operator Protection]

Installation must be performed by authorized personnel following applicable IS codes and regulations to ensure operator safety.

Effects and Mitigation of Excessive Vibration

• Over-vibration is unlikely with well-designed mixes using standard aggregates.

• Excessive vibration in high workability or mortar-rich mixes can cause:

  • Segregation and bleeding.
  • Lighter material rising to form a laitance or mortar layer on the surface.
  • Leakage through formwork joints.
  • Weak planes between successive concrete layers.

• Indicators of over-vibration:

  • Frothy surface with numerous small bubbles.
  • Settling of coarse aggregates beneath the surface.

• Corrective Measures:

  • Reduce concrete workability rather than vibration duration.
  • Apply vibration only sufficient to consolidate and expel entrapped air.

Needle Diameter and Application

Power Unit Ratings

Concrete Workability

• Compacting factor: 0.75 to 0.85 (stiffest workable mix).
• Fine mortar should appear greasy wet upon vibrator withdrawal.
• Avoid very high workability to prevent segregation.
• Over-vibration wastes effort and may impair concrete quality.

flowchart TD
    A[Proper Mix Design] --> B[Stiff Concrete (CF 0.75-0.85)]
    B --> C[Minimal Vibration Duration]
    C --> D[Insert Vibrator Without Spreading]
    D --> E[Avoid Over-vibration Symptoms]
    E --> F[Reduce Workability if Required]

Following these guidelines ensures durable, segregate-free concrete.

Re-vibration of Concrete: Principles and Practices

Concept and Benefits (Clauses 8.12, 8.12.1 & 8.12.2)

• Re-vibration refers to applying vibration again to concrete that has been placed and partially set.
• It enhances compressive strength and bonding, reduces honeycombing, and expels trapped water and air around reinforcement and aggregates.
• Concrete must regain plasticity to allow vibrator insertion by its own weight; earliest re-vibration is after one hour from initial vibration.
• Effectiveness improves with increased time after initial vibration but while concrete remains workable.

Vibrator Needle Sizes (Clause 5.1 & Table 1)

Practical Recommendations

• Only re-vibrate if concrete is sufficiently plastic for vibrator penetration.
• Avoid re-vibrating exposed concrete surfaces.
• Follow vibrator size recommendations based on member size and application.
• Controlled re-vibration improves concrete microstructure and strength.

flowchart LR
    A[Initial Placement] --> B[Vibration]
    B --> C{Wait ≥ 1 Hour}
    C -->|Yes| D[Check Plasticity]
    D -->|Plastic| E[Re-vibrate]
    D -->|Not Plastic| F[No Re-vibration]
    E --> G[Improved Strength and Durability]
    F --> H[Proceed Without Re-vibration]

Refer to IS 2505-1980 for detailed vibrator specifications.

Summary of Appendices and Manufacturer Instructions

Appendix A (Clause 4.1) — Service Log Book for Flexible Shaft Vibrators

• Record manufacturer details and purchase date.
• Maintenance schedule includes:
  • Cleaning and inspection
  • Lubrication
  • Part replacement
• Logs track frequency and type of preventive maintenance for vibrator components.

Vibrator Performance and Size (Clause 5.1, Table 1)

Important Notes

• Vibrators must comply with IS 2505-1980.
• Selection depends on concrete mix, workability, member size and shape, and placing conditions.
• Use multiple vibrators for increments exceeding 4 m³.

Example Maintenance Schedule

flowchart TD
    A[Vibrator Selection] --> B{Needle Diameter}
    B -->|25,35 mm| C[Thin members, lab specimens]
    B -->|40,50 mm| D[Thin walls, light floors]
    B -->|60 mm| E[General construction]
    B -->|75 mm| F[Mass concrete up to 2 m³]
    B -->|90 mm| G[Mass concrete up to 8 m³]
    G --> H[Use multiple vibrators for >4 m³]

Adhering to these instructions ensures effective vibrator operation and maintenance.