4 Types of Concrete Slump Tests – Values, Procedures & Results

The slump test of concrete or slump cone test value is a measure of the workability of concrete mix prepared at the laboratory or the construction site during the progress of the construction work. A slump is an indication of the consistency, workability, or flow of a concrete mix. The drier the concrete mix, the lower will be the slump, and the wetter or lose the concrete mix is, the slump will be higher.

Concrete slump test is done for each batch to check the uniformity of concrete workability and quality during construction.

Importance of Slump Test

The importance of the slump test is to find the workability of concrete for various water-cement ratios, or quantity of admixtures used. The slump test values are the indication of the amount of water added during the mixing process, and help to identify the ease with which concrete can be transported, placed, and compacted at the site. The slump test values required depends on the types of concrete, methods of placement, and strength and durability requirements for the concrete construction.

The slump test of concrete is a low-cost and simplest method of workability test that provides immediate results a the construction site, without any wastage of material. Due to this fact, it has been widely used for workability tests since 1922. The factors such as properties of aggregate materials, types of cement, concrete mixing methods, the dosage of admixtures, etc. affect the concrete slump test values.

Standard Code for Slump Test

• In the United States, the slump test is carried out as per ASTM C143 – Standard Test Method for Slump Of Portland Cement Concrete and as per AASHTO T 119M/T 119 – Standard Method of Test for Slump of Hydraulic Cement Concrete.
• In the United Kingdom and Europe, the older standard BS 1881–102 was used for the British Code, now European standard EN 12350-2 is used.
• Indian Standard of the slump test of concrete used is IS1199-1959

Equipment for Slump Test

The items required for a slump test:

1. Slump Cone Mold – Abrams cone,
2. Nonporous, none absorbent base plate,
3. Tape measure or a ruler to record the test result
4. Tamping rod
5. Sponge or Brush & Water to dampen the cone and base before the test.

The mold for the slump test is in the form of the frustum of a cone having a height of 12-inches (30cm), bottom diameter of 8-inches (20cm), and top diameter of 4-inches (10cm). The tamping rod is made of steel 5/8-inch (16mm) in diameter with a smooth surface and 24-inch (60cm) in length which is rounded at one end.

Materials and Preparation for Slump Test

Obtain a concrete sample using ASTM C172 – Standard Practice for Sampling Freshly Mixed Concrete methods. The concrete mix can be M15 or higher, as per the requirement, with a suitable water-cement ratio.
Begin slump test carried out within five minutes of collecting and remixing the concrete sample over a smooth, non-absorbent test base placed on a level surface. The slump test must be completed at a place free from Vibrations or shock within 2 minutes and 30 seconds after it was started.

For a bagged concrete, rules defined by ASTM C387 – Standard Specification for Packaged, Dry, Combined Materials for Concrete and High Strength Mortar should be used.

Procedure for Concrete Slump Test

1. First, the internal surface of the mold is cleaned, and oil is applied to make the surface smooth.
2. Mold is placed on a smooth horizontal non-porous base plate.
3. Mold is filled with the prepared concrete mix in 3 approximately equal layers. First 1/3rd of the mold with filled with concrete sample.
4. Then the first layer is tamped 25 strokes of the rounded end of the tamping rod in a uniform manner taking care to distribute rodding evenly over the entire cross-section of the sample.
5. Then 2/3rd of the mold is filled with the sample and tamping is done 25 times as above. The tamping should penetrate into the underlying layer.
6. Now the mold is filled completely to the top and again tamping is done 25 times penetrating into the underlying layer.
7. The excess concrete is removed and the surface is leveled with a trowel.
8. The mortar or water leaked out between the mold and the base plate is cleaned.
9. Mold is now raised from the concrete immediately and slowly in the vertical direction.
10. Slump value is measured which is the difference between the height of the mold and that of the height point of the specimen being tested.

Slump Test Values

The slump (Vertical settlement) measured shall be recorded in terms of inches or millimeters of subsidence of the specimen during the test.

Results of Slump Test on Concrete

Slump for the given sample= _____ in.

4 Types of Slump Test Results

When the slump test is carried out, the following shapes of the concrete slump can be observed:

1. True Slump – True slump is the only slump that can be measured during the test. The true slump is measured between the top of the cone and the top of the concrete after the cone has been removed.
2. Zero Slump – Zero-slump is an indication of a very low water-cement ratio concrete sample, that has resulted in a mixed. This can also be a type of bagged concrete. Zero slump concrete is generally used for road construction.
3. Collapsed Slump – Collapsing of concrete is an indication that the water-cement ratio is too high, i.e. concrete mix is too wet or it is a high workability mix, for which a slump test is not appropriate. This type of slump is used for self-compacted concrete.
4. Shear Slump – The shear slump indicates that the result is incomplete, and concrete to be retested.

Ready-mixed concrete delivered to the construction site generally has a slump value of 4 ±1 inches, unless specified. Ready-mixed concrete can be batched to meet the exact specifications of the slump for the concreting job.

Concrete Slump Test Values for Different Construction Jobs

Factors Affecting Concrete Slump Test

Following are the various factors that affect the slump test results:

1. Concrete material properties like chemistry, fineness, particle size distribution, moisture content, and temperature of cementitious materials. Size, texture, combined grading, cleanliness, and moisture content of the aggregates.
2. Chemical admixtures usage quantity, type of admixture, combination, interaction, sequence of addition, and its effectiveness.
3. Air content of concrete
4. Concrete batching, mixing, and transporting methods and equipment,
5. The temperature of the concrete.
6. A sampling of concrete, slump-testing technique, and the condition of test equipment.
7. The amount of free water in the concrete, and
8. Time since mixing of concrete at the time of testing.

K-Slump Tester – New Method

For a quick slump test of concrete, a new apparatus called ‘K-Slump Tester’ is developed. This device can measure slump value within a minute after it is inserted into fresh concrete. And it can also measure the relative workability of concrete.

FAQs About Slump Test of Concrete

Also Read: Initial and Final Setting Time of Cement Concrete

References

1. ASTM C143 – https://www.astm.org/standards/c143