Compaction Factor Test For workability Of Concrete

The Compaction Factor Test is a laboratory method used to determine the workability of concrete. This test is especially suitable for concrete mixes with low workability, which may not be evaluated effectively using the slump test.

Purpose of the Test

  • To measure the workability of concrete indirectly by determining the ratio of the weight of partially compacted concrete to the weight of fully compacted concrete.
  • Helps assess the ease with which concrete can flow into forms and around reinforcements.

Apparatus

  1. Compaction Factor Apparatus:
    • Two conical hoppers (upper and lower) connected vertically.
    • A cylindrical mold at the bottom.
  2. Tamping Rod: For leveling concrete.
  3. Weighing Balance: To measure the weights.
  4. Trowel: For placing concrete.
  5. Measuring Cylinder: For measuring concrete.

Procedure

  1. Preparation:

    • Mix the concrete with the required proportions of cement, fine aggregate, coarse aggregate, and water.
    • Ensure uniform mixing.

  2. Filling the Upper Hopper:

    • Fill the upper hopper with concrete using a trowel, ensuring no segregation occurs.
    • Level the surface.

  3. Allowing Free Fall:

    • Open the trap door of the upper hopper, allowing the concrete to fall into the lower hopper.
    • Ensure smooth flow without manual intervention.

  4. Filling the Bottom Cylinder:

    • Open the trap door of the lower hopper, allowing the concrete to fall into the cylindrical mold.

  5. Weighing the Partially Compacted Concrete:

    • Level the surface of the cylindrical mold and weigh the concrete. This gives the partially compacted weight.

  6. Weighing the Fully Compacted Concrete:

    • Remove the concrete from the mold, compact it fully by hand or vibration, and weigh it again. This gives the fully compacted weight.

Formula

The compaction factor is calculated as:

Compaction Factor=Weight of Partially Compacted ConcreteWeight of Fully Compacted Concrete\text{Compaction Factor} = \frac{\text{Weight of Partially Compacted Concrete}}{\text{Weight of Fully Compacted Concrete}}

Interpretation of Results

  • High Compaction Factor (Close to 1): Indicates high workability.
  • Low Compaction Factor: Indicates low workability, meaning the mix is stiff.

Typical Values

  • Low Workability (0.78 - 0.85): Used for RCC with heavy reinforcement.
  • Medium Workability (0.85 - 0.92): Used for manually compacted concrete.
  • High Workability (0.92 - 0.95): Used for concrete with low vibration requirements.

Advantages

  1. Accurate for low-workability mixes.
  2. Simple and quick to perform.
  3. Suitable for site and laboratory use.

Limitations

  1. Not suitable for very high-workability concrete.
  2. Requires precise equipment and handling.

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