The Kelly Ball Test is a quick and practical method used to measure the workability of fresh concrete on-site. It offers an easy alternative to the traditional slump test, helping engineers understand how easily concrete can be placed and compacted. In this blog, we break down what the Kelly Ball Test is, the procedure for conducting the test, and the standard codes governing it.
What is the Kelly Ball Test?
The Kelly Ball Test, or the Ball Penetration Test, is a field test used to measure the workability of fresh concrete by determining how far a standard hemispherical metal ball sinks into the concrete under its own weight. The test was developed by J.W. Kelly in the United States in the early 1950s and remains a reliable method for assessing concrete workability. This test is mainly useful for medium-consistency concrete mixes and provides results that closely correlate with the slump test.
What are the Kelly Ball Test Apparatus?
The following is the main Kelly ball test apparatus setup used in the laboratory:
- Metal hemisphere (Ball): This hemispherical metal ball weighs around 13.6 kilograms (30 pounds) with a 15 cm (6 inches) diameter. The ball’s flat end will be connected to a graduated stem featuring a handle.
- Frame: The frame will be installed between the ball and stem, enabling the stem to slide vertically through it during movement. This frame often rests on the concrete surface during the testing procedure.
- Graduated Scale: Every penetration reading of the hemisphere (ball) will be shown in the graduated scale.
- Handle
- Spacious container: Minimum depth of approximately 203 mm (20 cm) and a minimum diameter (width) of about 460 to 500 mm (46 to 50 cm) to accommodate the Kelly ball apparatus.
Stepwise Kelly Ball Test Procedure
To carry out the Kelly ball test, the engineer or lab performer needs to follow these steps:
Prepare the Equipment: Make sure the complete apparatus setup is clean, dry and in good working condition.
Pour Concrete: Prepare the fresh concrete mix and pour it into the container until it fills a depth of at least 20 cm. Level the concrete surface with appropriate tools.
Place the Kelley Ball Penetration Apparatus: Position the Kelly ball apparatus on the surface of concrete through the handle. Ensure the frame sits flat on the surface and that the centre of the metal ball is at least 23 cm (230 mm) from any container edge.
Release the handle: Slowly release the handle and allow the ball to penetrate through the concrete by its own weight. Observe the reading on the graduated stem and note it down to the nearest 0.6 cm (1/4 inch).
Repeat 3 times: Follow the same test procedure at different portions of the container at least 3 times. Take the average values of these readings.
Calculation for the Kelly Ball Test
The standard Kelly ball test’s results can be correlated with the slump test, i.e.,
Average Value of the reading = Slump value
The following table indicates the correlation of the Kelly Ball Penetration test and the Slump test for the consistency of concrete:
| Kelly Ball Penetration Values | Slump (Inches) | |
| (Individual, Inches) | (Average, Inches) | |
| 2.5–2.4 | 2.4 | 4.7 |
| 2.8 | 2.8 | 4.0 |
| 3.7 | 3.7 | 4.4 |
| 2.7 | 2.7 | 4.3 |
| 2.3–2.5 | 2.4 | 3.7 |
| 1.7–1.9–1.5 | 1.7 | 2.3 |
| 3.7–3.1 | 3.4 | 4.1 |
| 1.4–1.4–1.1 | 1.3 | 0.7 |
| 2.5–2.6–1.9 | 2.3 | 3.9 |
| 1.8–1.0 | 1.4 | 1.7 |
| 2.6–2.8 | 2.7 | 3.7 |
| 2.0 | 2.0 | 3.3 |
| 1.4–1.6 | 1.5 | 2.6 |
| 3.2–3.4 | 3.3 | 4.5 |
| 1.1–1.2–1.2 | 1.2 | 2.3 |
| 2.7–3.5–2.6 | 2.9 | 4.7 |
| 4.2–4.7–3.7 | 4.2 | 5.3 |
| 2.2–2.2–2.4 | 2.3 | 3.7 |
| Average value | 2.4 | 3.6 |
Result of Kelly Ball Test
The Kelly Ball test result is expressed as the average penetration depth of the ball into fresh concrete, rounded to the nearest 0.25 inch. This depth indicates the concrete’s workability. The slump value is approximately 1.1 to 2.0 times the Kelly Ball penetration, or about 1.3 to 1.4 times on average. The test allows conversion of penetration results into equivalent slump values for easier comparison. However, accuracy depends on the concrete mix and aggregate size, and the test is less reliable for mixes with large aggregates.
Relationship Between Slump and Kelly Ball (KB) Penetration
Graph: KB Penetration vs. Slump for Concrete
Standard Code for the Kelly Ball Test
The Kelly Ball test, standardised earlier as ASTM C360-92, was a method for assessing the workability of fresh hydraulic cement concrete by measuring ball penetration depth. The ASTM standard was suspended in 1999 due to a lack of widespread use. In India, the Kelly Ball test has not been incorporated into the Indian Standards and remains largely unutilised. It is known to be less suitable for concretes with large aggregate sizes and requires a levelled surface.
Advantages of the Kelly Ball Test
The following are the major benefits of the Kelly ball test:
- This test is simple and can be performed quickly on-site by any experienced person.
- Compared to the slump test, this test gives instant and more accurate results.
- Users don’t have to make lengthy calculations to find the workability of concrete.
- Presents a quantitative measure of the consistency of concrete.
Limitations of the Kelly Ball Test
The following are the major limitations of the Kelly ball test:
- This test is limited to checking only certain aspects of concrete behaviour.
- Test results depend greatly on various factors, including aggregate size and shape.
- This test is not practical for larger-sized aggregates.
- The test performer must have experience and familiarity with test conditions.
- This test is not recognised in India and doesn’t have an Indian standard.
The Kelly ball test is a simple yet effective method for evaluating the workability of concrete. This test is mainly designed for fresh mixes of ‘medium’ workability. This test is also applicable to many special mixes, including both lightweight and heavyweight. Although this test has its own limitations, it is considered essential for ensuring the quality of concrete. Leading construction firms such as Brick & Bolt utilize the Kelly ball test alongside other evaluation methods to verify material quality, guaranteeing that every concrete batch meets the required workability standards before application.
Frequently Asked Questions
1. What is the Kelly Ball Test?
The Kelly Ball Test is a field method to measure the workability of fresh concrete by dropping a weighted metal ball on it and measuring penetration depth.
2. What is a Kelly ball?
A Kelly ball is a hemispherical metal weight, approximately 15 cm in diameter and 13.6 kg in weight, used to measure the workability of fresh concrete by recording its penetration depth when dropped onto the concrete surface. It provides a quick, simple field test for concrete consistency and plasticity without requiring complex equipment.
3. How does the Kelly Ball Test compare to the slump test?
It is generally faster and provides reliable results similar to the slump test, but requires more concrete volume and is less common outside the US.
4. Is the Kelly Ball Test accepted by Indian Standards?
No, Indian Standards have not adopted the Kelly Ball Test, and it is not commonly used in India.
5. What are the advantages of the Kelly Ball Test?
It is simple, quick, and can be done on-site, providing immediate workability feedback without elaborate equipment.