3 METHODS OF DETERMINING WORKABILITY OF CONCRETE

Based on the water-cement ratio in the concrete mix, workability can be determined by the following three methods.

  1. slump test
  2. compaction factor test
  3. V-B Consistometer Test

suitability

This method is only suitable for high workability concrete.

This test is done with a mold called a slump cone whose top diameter is 10 cm, the bottom diameter is 20 cm and the height is 30 cm.

deceleration tool
deceleration tool

Process

The test is done in the following steps:

  1. Place the slump mold on a smooth flat and non-absorbent surface.
  2. Mix the dry ingredients of the concrete well until a uniform color is obtained and then add the required amount of water.
  3. Place the mixed concrete into the mold about one-fourth of its height.
  4. Compact the concrete 25 times with the help of tamping rod evenly over the entire area.
  5. Place the mixed concrete in the mold at about half its height and compact it again.
  6. Similarly, keep the concrete up to three-fourths of its height and then on top of it. Compact each layer evenly 25 times with the help of tamping rod. For the second and subsequent layers, the tamping rod must penetrate the underlying layer.
  7. Hit the top surface of the mold with a trowel or tamping rod so that the mold is filled to the top of it.
  8. Immediately remove the mold, ensuring its movement in the vertical direction.
  9. When concrete settling has stopped, measure the bottom of the concrete in millimeters that is needed recession Of concrete.

Recommended deceleration value for various concrete works

construction type mm. recommend fall in
the minimum maximum
sidewalk 25 50
Mass Concrete Structure 25 50
unrestricted footings 25 75
Caissons and Bridge Deck 25 75
Reinforced foundations, bases and walls 50 100
Reinforced slabs and beams 30 125
column 75 125

Limitations of recession test

Following are the limits:

  • Not suitable for concrete that contains aggregates larger than 40 mm.
  • Not suitable for dry mix concrete.
  • Not suitable for very wet concrete.
  • Not reliable as recession can be of any size.

According to this test, workability can be defined as the amount of applied work required to compact the concrete to its maximum density.

suitability

This method is adopted in laboratories to determine the workability of concrete mix. It gives very good results for low workability concrete.

Process

The equipment required to perform compaction factor test is shown below.


compaction-factor-testing-equipment
compaction-factor-testing-equipment
  1. The test is done in the following steps:
  2. Clean and dry the inner surface of the mold.
  3. With the help of a hand scoop, place the concrete in the upper hopper A.
  4. Open the trap door of the hopper to facilitate the concrete to fall into the lower hopper B. The concrete sticking to the sides of Hopper A should be pushed down with the help of a steel rod.
  5. Open the trap door of Hopper B and let the concrete fall into Cylinder C.
  6. Remove the excess concrete from the top of the cylinder with the help of a trowel. Wipe clean the outer surface of the cylinder.
  7. With the partially solidified concrete weigh the cylinder closer to 10 grams.
  8. Fill the cylinder with fresh concrete in layers no more than 5 cm thick and compact each layer until 100% compaction is achieved.
  9. Wipe clean the outer surface of the cylinder and weigh the cylinder to close to 10 grams of fully compacted concrete.
  10. Calculate the value of compaction factor using the following formula.

Compaction factor = Weight of partially compacted concrete / Weight of fully compacted concrete

Recommended values ​​of practicality for different placement situations

Conditions degree value of practicality
Concreting of shallow sections with vibration Very little 20 – 10 sec V-B Time

or 0.75 to 0.80 compaction factor

Concreting of lightly reinforced sections with vibration Less 10 – 5 sec V-B time or

0.80 to 0.85 compaction factor

Concreting of lightly reinforced sections without vibration or heavily reinforced sections with vibration medium 5-2 seconds V-B time or

0.85 to 0.92 compaction factor or

Deceleration for 25 – 75 mm 20 mm aggregates

Concreting of heavily reinforced sections without vibration High Compaction factor above 0.92 or 75-125 mm deceleration for 20 mm aggregates.

Advantages of Compaction Factor Testing

Following are the advantages:


  • Suitable for testing practicality in laboratories
  • Suitable for concrete of low workability
  • Suitable for detecting variation in functionality over a wide range
  • Its results are more accurate and sensitive.

The equipment used in this method of testing is shown below.

v-b-consistometer
v-b-consistometer

suitability

This method is suitable for dry concrete with very low workability

Process

The test is done as described below

  1. Mix the dry ingredients of the concrete well until a uniform color is obtained and then add the required amount of water.
  2. Pour the concrete into the slump cone with the help of a funnel attached to the stand.
  3. Remove the slump mold and rotate the stand so that the transparent disc touches the top of the concrete.
  4. Turn on the vibrator on which the cylindrical container is placed.
  5. Due to the vibrating action, the concrete begins to mold again and occupies the cylindrical container. Keep moving the cylinder until the concrete surface is horizontal.
  6. The time required for complete remolding in seconds is the required measure of workability and is expressed as the number of V–B seconds.
feasibility statement mm. decline in V-B time in seconds compaction factor
extremely dry , 32 – 18
Very strict , 18 – 10 0.70
Harsh 0 – 25 10 – 5 0.75
Rigid Plastic 25 – 50 5 – 3 0.85
plastic 75 – 100 3 – 0 0.90
Flowing 150 – 175 , 0.95

Er. Mukesh Kumar

Photo of author
Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.