Workability of Concrete by Slump Cone Test – Procedure and Result

Workability of Concrete by Slump Cone Test – Procedure and Result 

Objective:-

The word ―workability or workable concrete signifies much wider and deeper meaning than the other terminology ―consistency often used loosely for workability. Consistency is a general term to indicate the degree of fluidity or the degree of mobility. The factors helping concrete to have more lubricating effect to reduce internal friction for helping easy compaction are : (a) Water Content (b) Mix Proportions (c) Size of Aggregates (d) Shape of Aggregates (e) Surface Texture of Aggregate (f) Grading of Aggregate (g) Use of Admixtures.


The concrete slump test is an on-the-spot test to determine the consistency as well as workability of fresh concrete. This test plays a vital role in ensuring immediate concrete quality in a construction project. It is used almost in every construction sites.
 
The slump test is very simple and easy to handle. It also demands comparatively less equipment and can be done in a short period of time. These advantages of slump test have made it very popular all over the world. 

In the slump test, workability of concrete is not measured directly. Instead, consistency of concrete is measured which gives a general idea about the workability condition of concrete mix. It is not a suitable method for very wet or very dry concrete. It does not measure all factors contributing to workability, nor it is always representative of the placeability of the concrete.

Concrete Slump Test International Standard:-

Various international codes have specific testing standards for concrete slump test. These standards specify methods, equipment for determining the consistency of fresh concrete by the slump test. For acceptance and reliability, It is essential to maintain strict compliance with these standards during the slump test for concrete. The standards for the concrete slump test are followings:

1.  American Society for Testing and Materials (ASTM): ASTM slump test standards are ASTM C 143, ASTM C143M.

2. The American Association of State Highway and Transportation Officials (AASHTO): AASHTO slump test standards are AASHTO T119, AASHTO BS1881.

3. British & European standard: British & European slump test standard is BS EN 12350-2.

4. Indian standard: IS 1199 – 1959

Concrete Slump Test Equipment:-

 

Slump test requires some equipment to perform the test. One can easily find these test kit set in the market. The test equipment must comply with the standards mentioned above. The equipment mainly used for slump test are followings:

Mould:  Shape of the mould is a frustum of a cone. The cone is known as slump cone or Abrams cone. Slump cone is made of steel, plastic, etc. Its height is 12 inches (30 cm). The diameter of the base opening is 8 inches (20 cm) and the top opening is 4 inches (10 cm).

Base plate: Base plate may be made of Aluminum, polymer, steel, etc. It may be equipped with a holding attachment.

Tamping rod: Temping rod used in the slump test is made of steel. Tamping Rod is usually 24" long and has a diameter of 5/8" diameter. Temping rod used in the slump test is made of steel. Tamping Rod is usually 24" long and has a diameter of 5/8" diameter.

Tape measure: Standard tap should be used for measurement.

Reference :-

IS 1199:1959 Methods of Sampling and Analysis of Concrete. Reaffirmed- Dec 2013. 

Factors which influence the concrete slump test:-

1. 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 dosage, type, combination, interaction, sequence of addition and its effectiveness, 

3. Air content of concrete,

4. Concrete batching, mixing and transporting methods and equipment,

5. Temperature of the concrete,

6. 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.

Pre-Cautions Required During Test:-

To get the proper result, some cautions must be taken during the test. Following are the list of major caution that can be maintained. 
Inside of the mould and base should be moistened before every test. It is necessary to reduce surface friction.

Prior to lifting mould, the area around the base of the cone should be cleaned from concrete which may be dropped accidentally.
The mould and base-plate should be non-porous.

This test should be performed in a place free of vibration or shocks.
The concrete sample should be very fresh, the delay must be avoided and the test should be done just after mixing.

Procedure :-

1. If this test is being carried out in the field, the sample mixed concrete shall be obtained. In the case of concrete containing aggregate of maximum size more than 38 mm, the concrete shall be wet-sieved through one and half inch screen to exclude aggregate particles bigger than 38 mm.

2. The internal surface of the mould shall be thoroughly cleaned and freed from superfluous moisture and any set concrete before commencing the test. The mould shall be placed on a smooth, horizontal, rigid and non-absorbent surface, such as a carefully levelled metal plate, the mould being firmly held in place while it is being filled. 

3. The mould shall be filled in four layers, each approximately one-quarter of the height of the mould. Each layer shall be tamped with twenty-five strokes of the rounded end of the tamping rod. The strokes shall be distributed in a uniform manner over the cross-section of the mould and for the second and subsequent layers shall penetrate into the underlying layer. 

4. The bottom layer shall be tamped throughout its depth. After the top layer has been rodded, the concrete shall be struck off level with a trowel or the tamping rod, so that the mould is exactly filled.

5. After the top layer has been rodded, strike off the surface of the concrete by means of screeding and rolling motion of the tamping rod. 

6. Any mortar which may have leaked out between the mould and the base plate shall be cleaned away. The mould shall be removed from the concrete immediately by raising it slowly and carefully in a vertical direction. This allows the concrete to subside and the slump shall be measured immediately by determining the difference between the height of the mould and that of the highest point of the specimen being tested. 

The above operations shall be carried out at a place free from vibration or shock, and within a period of two minutes after sampling. 

Observation :-

The vertical difference between top of the mould and the displaced original center of the top surface of the specimen ………… mm 

Results and Conclusions:-

 

 

When the slump test is carried out, following are the shape of the concrete slump that can be observed:

True Slump – True slump is the only slump that can be measured in the test. The measurement is taken between the top of the cone and the top of the concrete after the cone has been removed.

Zero Slump – Zero slump is the indication of very low water-cement ratio, which results in dry mixes. These type of concrete is generally used for road construction.

Collapsed Slump – This 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.

Shear Slump – The shear slump indicates that the result is incomplete, and concrete to be retested.

Workability	Compaction Factor	Slump (mm)
Very Low	0.78	0 - 25
Low	0.85	25 - 50
Medium	0.92	50 - 100
High	0.95	100 - 175

If shear slump or collapse slump occurs, the test should be repeated. We can get the result from the only true slump. We can classify the result within some ranges according to the slump value.

According to 'Fresh Concrete' by P. Bartos, slump results can be classified as given below:

Workability	Slump (mm)
Very Low	5 - 10
Low	15 - 30
Medium	35 - 75
High	80 - 155
Very High	180 & Above

According to European Standard ENV 206: 1992, workability is classified in 4 categories of S1, S2, S3, and S4. Slump ranges are:

Workability	Slump (mm)
S1	10 - 40
S2	50 - 90
S3	100 – 150
S4	160 & Above

Though there are different types of workability classification, the main rule is that low slump value indicates less workability and high sump value indicates high workability.