Code of practice for the use of screed board concrete vibrators
1987 Edition

Scope Overview - IS 11993

• Pertains to the use of screed board vibrators in concrete consolidation.
• Terminology is adopted from IS 2505-1980 and IS 2506-1985.
• Performance testing procedures follow IS 6923-1973.

Key Technical Requirements:

• Concrete consistency should be the stiffest workable mix for vibration efficiency.
• Compacting factor range: 0.75 to 0.85 as per IS 456-1978.
• Avoid mixes with excessive workability to prevent segregation and watery grout.
• Vibrator performance must be verified according to IS 6923-1973, targeting resonant frequency for optimum compaction.

Reference Table:

Practical Guidance:

• Use low workability concrete for vibration.
• Monitor grout appearance; watery surface indicates excessive workability.
• Match vibrator frequency to resonant conditions for best results.

Terminology Reference - IS 11993

• Clause 2.0 incorporates definitions directly from IS 2505:1980 and IS 2506:1985.
• Terms like screed board vibrator, internal vibrator, external vibrator, frequency, amplitude, and power rating are defined therein.
• Manufacturer must specify power unit ratings in kilowatts (kW) as per Clause 3.2.3.

Summary Table of Key Terms:

Additional Information:

• Testing of screed board vibrators must comply with IS 6923-1973.
• Power and type details should be clearly provided by manufacturers.

Overview of Operational and Safety Practices

• All terms and definitions refer to IS 2505-1980 and IS 2506-1985.
• Performance testing of screed board vibrators must be conducted as per IS 6923-1973.
• Only certified and tested vibrators should be employed for concrete compaction.

Typical Performance Specifications:

Important Notes:

• Refer to IS 6923-1973 for detailed test methods.
• Ensure compliance with safety and operational requirements to prevent accidents.

Power Source Selection and Operational Criteria

• Clause 1.3 highlights safety and reliability requirements for power units.
• Clause 3.2.3 requires manufacturers to specify power unit types and ratings in kilowatts.
• Electric motors are preferred where power supply is stable due to advantages like steady speed and lighter cabling.

Typical Power Ratings Based on Vibrator Size:

Operational Requirements:

• Maintain consistent speed for uniform vibrations.
• Ensure proper insulation and overload protection.
• Design units to be lightweight and easily portable.

Decision Flow:

• Use electric motor if electricity is accessible.
• Otherwise, opt for portable internal combustion engines.
• Manufacturer must confirm power and safety compliance.

Concrete Mix Parameters for Effective Vibration

• Use the stiffest workable concrete mix compatible with vibrator efficiency (compacting factor 0.75 to 0.85).
• Maintain low workability according to IS 456:1978; avoid high workability to prevent segregation and watery grout.
• Proper formwork design to withstand vibration pressure is essential.

Workability Classification (IS 456:1978):

Formwork Guidelines:

• Steel channels with stakes for straight sections.
• Wooden formwork with 50 mm angle iron caps for curved sections.
• Tight joints to prevent grout leakage and air suction.

Process Flow:

• Select appropriate materials.
• Proportion and mix concrete.
• Ensure stiff consistency within specified ranges.
• Apply vibration at resonant frequency for compaction.

Design Requirements for Formwork Under Vibrated Concrete

• Use steel channels supported by stakes for straight runs.
• For curves, employ wooden formwork capped with 50 mm angle iron.
• Formwork must resist increased lateral pressures caused by vibration.
• Joints must be sealed tightly to prevent grout leakage and air suction, avoiding defects.

Pressure Calculation:

• Lateral pressure (p = \gamma \times h \times K), where:
  • (\gamma) = unit weight of concrete (~24 kN/m³)
  • (h) = height of concrete pour
  • (K) = pressure coefficient (1.0 to 1.2 for vibrated concrete)

Summary of Materials and Joint Details:

Design Flow:

• Concrete placement → Vibration → Increased pressure → Formwork design → Material selection and joint sealing

Essential Practices for Concrete Vibration

• Employ the stiffest concrete mix possible with a compacting factor between 0.75 and 0.85.
• Avoid overly workable mixes to prevent surface segregation and watery grout.
• Design formwork to endure increased lateral pressures from vibration with tight, leak-proof joints.
• Place concrete in horizontal layers to avoid segregation.
• Position the screed vibrator on side forms and lower vertically for uniform compaction.

Ideal Parameters:

Procedure Flow:

• Choose stiff concrete → Place in layers → Position vibrator → Lower vertically → Compact → Monitor grout → Adjust mix if segregation occurs

Maintenance and Safety Requirements for Screed Board Vibrators

• All vibrators must meet IS 6923-1973 performance testing.
• Routine inspection and servicing are vital to prevent operational failures.
• Operators should receive training and wear appropriate PPE.
• Safety guards and emergency stops must be operational.

Performance Testing Includes:

• Vibration frequency
• Amplitude
• Power consumption

Maintenance Schedule:

• Daily visual inspections of electrical connections and vibration output.
• Periodic lubrication, motor check-ups, and replacement of worn parts.
• Safety device checks including emergency stops and insulation resistance.

Support:

• Regional centers and laboratories are available for technical assistance and testing.

Maintenance Flow:

• Start operation → Conduct safety check → Perform performance tests → If pass, continue operation; if fail, perform maintenance → Repeat safety check

Safety Precautions to Mitigate Risks During Operation

• All moving components must be fully enclosed to prevent accidental contact and injury.
• Proper earthing of electric motors is mandatory to avoid electric shock hazards.
• Protective devices such as fuses and circuit breakers should be installed and inspected daily.
• Electrical components must adhere to relevant Indian Standards (e.g., IS 325, IS 555, IS 4691).
• Motors must be equipped with automatic overload protection to prevent overheating.

Safety Checklist:

Safety Operation Flow:

• Check protective devices → Verify motor earthing → Ensure guards are in place → Confirm safe to start operation