Concrete slump test

File:Construction Worker Performing Slump Test.jpg

An engineer performing the Concrete Slump Test

In construction and civil engineering, the Concrete slump test (or simply the slump test) is an in situ test or a laboratory test used to determine and measure how hard and consistent a given sample of concrete is before curing.

The concrete slump test is, in essence, a method of quality control. For a particular mix, the slump should be consistent. A change in slump height would demonstrate an undesired change in the ratio of the concrete ingredients; the proportions of the ingredients are then adjusted to keep a concrete batch consistent. This homogeneity improves the quality and structural integrity of the cured concrete.

History

It is not exactly known when the slump test first was performed. One of the earliest documented usages and studies of concrete was during the Roman Empire: Vitruvius, a Roman architect and engineer mentioned in his book De Architectura, enhancing the strength of concrete by mixing it with other materials in certain ratios. Vitruvius also mentioned the process of tamping during the preparation of concrete.

Scientific advances were later used to "proportionalise" cement mixes, and in the 1820s the superior Portland Cement was discovered by a British cement manufacturer Joseph Aspdin. Altering the proportions of the different ingredients of concrete allowed manufacturers to adjust the strength of concrete to best serve its specific function. With the functions of concrete increasing, different component ratios were developed and a professional test to measure the consistency of concrete was needed. Thus the Concrete Slump Test method was developed and incorporated in the Concrete Standards worldwide.

Concept

"Slump" is simply a term coined to describe how consistent a concrete sample is, rather than using obscure descriptions such as "wet" or "runny". The height of the concrete mix after being placed in the slump cone differs from one sample to another. Samples with lower heights are predominantly used in construction, with samples having high slumps commonly used to construct roadway pavements.

Purpose

The goal of the test is to measure the consistency of concrete. Many factors are taken into account when satisfying requirements of concrete strength, and to make sure that a consistent mixture of cement is being used during the process of construction. The test also further determines the "workability" of concrete, which provides a scale on how easy is it to handle, compact, and cure concrete. Engineers use the results to then alter the concrete mix by adjusting the cement-water ratio or adding plasticizers to increase the slump of the concrete mix.

Procedure

The slump test has witnessed many technological advances, and some countries even perform the test using automated machinery. The simplified, generally accepted method to perform the test is as follows:

Apparatus

• Large pan
• Trowel to mix concrete mixture
• Steel tamping rod
• Slump cone
• Ruler
• Concrete (Cement, water, sand & aggregates).

Steps

1. Place the mixing pan on the floor and moisten it with some water. Make sure it is damp but no free water is left.
2. Firmly hold the slump cone in place using the 2 foot holds.
3. Fill one-third of the cone with the concrete mixture. Then tamp the layer 25 times using the steel rod in a circular motion, making sure not to stir.
4. Add more concrete mixture to the two-thirds mark. Repeat tamping for 25 times again. Tamp just barely into the previous layer(1")
5. Fill up the whole cone up to the top with some excess concrete coming out of top, then repeat tamping 25 times. (If there is not enough concrete from tamping compression, stop tamping, add more, then continue tamping at previous number)
6. Remove excess concrete from the opening of the slump cone by using tamping rod in a rolling motion until flat.
7. Slowly and carefully remove the cone by lifting it vertically (5 seconds +/- 2 seconds), making sure that the concrete sample does not move.
8. Wait for the concrete mixture as it slowly slumps.
9. After the concrete stabilizes, measure the slump-height by turning the slump cone upside down next to the sample, placing the tamping rod on the slump cone and measuring the distance from the rod to the original displaced center.

• 
  Slump Cone
• 
  Tamping Procedure
• 
  Removing Cone
• 
  Height Measurement

Differences in Standards

International building and testing standards are vital to ensure a regulated use of cement in construction. The slump test is referred to in several testing and building codes, with minor differences in the details of performing the test.

United States

In the United States, engineers use the ASTM standards and AASHTO specifications when referring to the concrete slump test. The American standards explicitly state that the slump cone should have a height of 12-in, a bottom diameter of 8-in and an upper diameter of 4-in. The ASTM standards also state in the procedure that when the cone is removed, it should be lifted up vertically, without any rotational movement at all.

The concrete slump test is known as "Standard Test Method for Slump of Hydraulic-Cement Concrete" and carries the code (ASTM C 143) or (AASHTO T 119).

United Kingdom & Europe

In the United Kingdom, the Standards specify a slump cone height of 300-mm, a bottom diameter of 200-mm and a top diameter of 100-mm. The British Standards do not explicitly specify that the cone should only be lifted vertically. The slump test in the British standards was first (BS 1881–102) and is now replaced by the European Standard (BS EN 12350-2).

Other Tests

Numerous tests exist to evaluate concrete: a similar test is the K-Slump Test (ASTM C 1362). Other tests evaluating consistency are the British compacting factor test (BS EN 12350-4), the Vebe consistometer for roller-compacted concrete (ASTM C 1170), and the German flow table test (DIN 1048-1).

See also

• Flow table test
• Plasticity