Compaction factor test – Workability of concrete-Test procedure

Compaction factor test is a practical and reliable method used to assess the workability of concrete, especially when the mix is stiff and does not show clear results in a slump test. The compaction factor test for workability of concrete evaluates how easily concrete flows and compacts under gravity by comparing partially compacted concrete with fully compacted concrete. In the workability of concrete compaction factor test, engineers gain a more accurate understanding of concrete consistency for low to medium workability mixes. Following the compaction factor test procedure helps achieve consistent results during laboratory testing. The compaction factor test of concrete is commonly applied in mix design and quality control and remains one of the dependable tests for workability of concrete used in practice. Compaction factor test is a lab test and is generally conducted on concrete samples having very low workability.

This article explains the compaction factor test, covering its principle, procedure, significance, advantages, limitations, and role in accurately evaluating the workability of concrete.

Significance of Quality tests on concrete

Quality tests on concrete are essential for ensuring strength, durability, and performance in construction. These tests help engineers assess the workability of fresh concrete and the quality of hardened concrete. Common quality tests on concrete include checks during the production stage (on fresh concrete before placing), tests on hardened concrete specimens, and evaluations performed directly on finished structures. Including tests like the flow table test for concrete ensures reliable results and consistent quality throughout a project.

Following are the stages of quality tests

• Production stage quality tests ( On fresh concrete before placing)
• Hardened stage quality tests ( hardened concrete specimens)
• On structures ( tests done on the structures )

Production stage quality tests on fresh concrete

Production stage quality tests on fresh concrete are crucial for ensuring the right workability and consistency before placement. These tests help engineers select the best mix for construction and maintain quality control. Key tests include the slump test, compaction factor test, Vee-Bee test, Kelly ball test, and the flow table test for concrete.

• Slump test
• Compaction Factor test
• Vee- Bee Test
• Kelly ball test
• Flow table test

This article focuses on the Compaction factor test, explaining its procedure, importance, and how it compares with other workability tests like the slump test and other tests

Significance of compaction factor test

The significance of the compaction factor test lies in its ability to accurately measure the workability of concrete, especially for stiff and low-slump mixes. This test provides more precise results than the slump test, supports effective mix design, and ensures consistent concrete quality through reliable laboratory-based workability assessment.

Compaction factor test for workability of concrete

The compaction factor test is used to determine the workability of concrete, which refers to the ease and uniformity with which freshly mixed concrete can be mixed, placed, compacted, and finished. Workability also represents the internal effort required to achieve full compaction. Developed by the Road Research Laboratory, UK, the compaction factor test of concrete provides more precise and accurate results than the slump test. This test is especially suitable for stiff concrete mixes that do not slump and require vibration for compaction. By measuring the degree of compaction under controlled conditions, the compaction factor test offers a reliable method for assessing concrete consistency in laboratory and quality control applications.

Also read : Bitumen – 9 lab tests on bitumen for flexible pavements.

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Compaction Factor Test – Relevant codes

• IS 1199 (Part 2): 2018 – Methods of Sampling and Analysis of Concrete – Workability
• BS 1881 (Part 103) – Testing Concrete – Method for Determination of Compaction Factor
• ASTM C1170 / C1170M – Workability of Fresh Concrete by Compaction Factor Method (Reference use)
• DIN 1048 – Testing Methods for Fresh Concrete

These codes provide standardized procedures for conducting the Compaction Factor Test and ensure reliable evaluation of concrete workability.

The Compaction Factor Test method followed in IS 1199 (Part 2) is fundamentally the same as those in British and other international standards. All codes measure workability by comparing partially compacted concrete with fully compacted concrete.

• Principle: Same across all standards
• Apparatus: Same (two hoppers + cylinder)
• Calculation: Same compaction factor ratio
• Differences: Minor variations in dimensions, tolerances, and wording

Apparatus used

• Compacting factor apparatus
• Cylindrical mould 
• Hand scoop 
• Trowel
• Weighing machine

The figure shows the dimension of the hopper and the mould. The inside area of the hopper should be smooth. The apparatus is made of bronze or cast brass. At the lower ends of the hopper, there is a trap door with a 3mm thickness. A rigid frame attaches the hoppers and cylinder. After the completion of mixing, the test is conducted at a constant time interval. 

Compaction factor test procedure

• Place the sample in the upper hopper of the apparatus using a hand scoop.
• Fill the hopper with its brim level and open the trap door.
• Then allow the concrete to fall into the lower hopper.
• Immediately after the concrete rests, uncover the cylinder and open the lower trap door.
• Cut off the excess amount of concrete above the cylinder using the trowel.
• Then weigh the concrete in the cylinder nearest to 10g. This is the weight of partially compacted concrete.
• Refill the cylinder with the same sample in the layers and the layer is heavily rammed or vibrated for full compaction.
• Then weigh the fully compacted concrete and the weight of the empty cylinder.
• Finally, Compute the compaction factor using the formula.

The compaction factor is the ratio of partially compacted concrete to fully compacted concrete.

Compaction factor = (W1 – W) / (W2 – W)

The compaction factor value varies from 0.7 to 0.95.

• Self Compacting Concrete (SCC)-Ingredients and Advantages
• Flow Table Test for Concrete: Ensuring Concrete Workability
• Compressive strength test of concrete | Cube test for Concrete
• Destructive tests (DT) on hardened concrete – Significance and Types
• Vee Bee Consistometer test – Workability of concrete

Key Takeaways

• The Compaction Factor Test is used to evaluate the workability of concrete, especially stiff mixes.
• It is more sensitive and accurate than the slump test for low-workability concrete.
• The compaction factor test for workability of concrete measures ease of compaction under gravity.
• It is best suited for laboratory-controlled conditions.
• The workability of concrete compaction factor test helps compare different mix designs.
• The test uses two hoppers and a cylindrical mould.
• Following the compaction factor test procedure ensures consistent results.
• The compaction factor test of concrete minimizes subjective judgment.
• It supports quality control and mix optimization.
• It is one of the reliable tests for workability of concrete.

Conclusion

The Compaction Factor Test remains an important method for assessing the workability of concrete, particularly for mixes that show little or no slump. By measuring the ratio of partially compacted to fully compacted concrete, the compaction factor test for workability of concrete provides a clear and quantitative indication of consistency. When engineers follow the standard compaction factor test procedure, the results help in evaluating mix performance and maintaining uniform quality. The workability of concrete compaction factor test is especially useful in laboratory testing and mix design studies. As one of the established tests for workability of concrete, the compaction factor test of concrete continues to support accurate quality control and better construction outcomes.