Concrete Workability TEST ( Complete) PDF

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TABLE OF CONTENT

NO.

TITLE

PAGE

1

Introduction

2

2

Objective

3

3

Apparatus

4

4

Procedure

4

5

Result

11

6

Discussion / Analysis

12

7

Conclusion

16

8

References/Appendix

17

1

CONCRETE WORKABILITY TEST a) SLUMP TEST b) VEBE TEST c) COMPACTING FACTOR TEST

INTRODUCTION Workability of concrete describes the ease or difficulty with which the concrete is handled, transported and placed between the forms with minimum loss of homogeneity. Depending to the water cement ratio in the concrete mix, the workability may be determined by the following three methods: 1) Slump Test 2) Vebe Test 3) Compacting Factor Test These methods have found universal acceptance and their merit is due to the simplicity of operation with and ability to detect variations in the uniformity of a mix of given nominal proportions as shown on Table 1.0: Workability category

Slump (mm)

Vebe time (s)

Compacting factor

Applications

Extremely low

0

Over 20

0.65-0.7

Lean mix concrete for roads (compacted by vibrating roller). Precast paving slabs

Very low

0-10

12-20

0.7-0.75

Roads compacted by power operated machines

Low

10-30

6-12

0.75-0.85

High quality structural concrete. Mass concrete compacted by vibration

Medium

30-60

3-6

0.85-0.95

Normal purposes reinforced concrete compacted by vibrating poker or manually

High

60-180

0-3

0.95-1.0

Areas with congested reinforcement, concrete for placing underwater

Table 1.0 : Workability categories and applications

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OBJECTIVES 1) To determine the workability or consistency of concrete mix prepared. 2) To measure of consistency or the wetness of the mix.

WORKABILITY TEST SLUMP TEST This method is suitable only for the concrete of high workability and being used extensively on site. There are three type of slumps which is true slump, shear slump and collapse slump. Figure 1.0 shows the method to measure the slump.

Figure 1.0 Method of measuring slump in slump test together with types of slump

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APPARATUS 1) Slump Cone 2) Base plate 3) Temping Rod

PROCEDURE

The mould was placed on a smooth, horizontal, rigid and non-absorbent surface free from vibration and shock.

The mould was hold firmly against the surface below. The three layer was filled in, each approximately one-third of the height of the mould when tamped.

Each layer was temped with 25 strokes of the tamping rod.

The internal surface of the mould was ensured to be clean and damp but free from superfluous moisture before commencing the test.

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After the top layer has been tamped, the concrete level was stroked off with the top of the mould with using a tamping rod.

Remove the mould immediately, ensuring its movement in vertical direction.

The slump was measured to the nearest 5 mm using a measuring scale to determine the difference between height of the mould and highest point of the specimen.

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VEBE TEST The Vebe test use to measure concrete’s workability by determining the characteristics of mobility and compatibility. The principle of the test is to change the shape of the concrete and measure the remoulding in seconds. This is in contrast to the compacting factor test where error may be introduced by the additional advantages that the treatment of concrete during the test is comparatively closely related to the method of placing in practice.

FIGURE 2

The apparatus is paced on top of a vibrating table. The fresh concrete is compacted into a conical slump mould. The mould is removed and a clear plastic disc is placed on the top of the concrete. The vibrating table is started and the time taken for the transparent disc to be fully in contact with the concrete (the Vebe time), is measured.

APPARATUS 1) Vebe-consistometer 2) Vibrating table 3) Stop watch

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PROCEDURE

A sample was prepared with mix ratio given by the instructor

The concrete was filled inside the slump cone and then the cone was removed.

A disc – shaped rider was placed on top of the concrete cone.

A watch is used to count the time which is from the moment where the vibrating table is switched on until it is switched off.

The vibrating was switched on and let the concrete vibrate until the concrete cone change to the shape of cylinder, which take the shape of its container.

Vibrating time (in second) which is taken from the moment vibrating table is switched on until it is switched off are called Vebe degree or Vebe time for the mix

COMPACTING FACTOR TEST The compaction factor test is carried out to measure the workability of fresh concrete with regard to the internal energy required for compacting the concrete thoroughly. For example, the ratio of density actually achieved in the test to density of the same concrete fully compacted. The test is suitable for concrete with a maximum size of aggregate up to 40 mm.

APPARATUS 1) Compacting factor apparatus 2) Balance 3) Tamping rod

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PROCEDURE

The sample was prepared with the mix ratio given by the instructor.

The empty cylinder was weighted and records its mass to the nearest 10 gram.

The internal surface of the hoppers and cylinder was make sure to be smooth, clean and damp but free from moisture.

The trap door was closed and the two floats was placed on the cylinder so as cover its top.

The sample of the concrete was placed gently in the upper hopper using the scoop until hopper is filed to the level of the rim.

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The upper trap door was opened so that the concrete can falls into the lower hopper. After the concrete has come to rest, immediately the float was removed from the top of the cylinder.

The trapdoor of the lower hopper was opened and the concrete was allowed to fall into the cylinder below.

The excess of concrete above the top level of cylinder was cut by using trowels and level it.

The cylinder with concrete was weight to the nearest 10 g. This weight is known as the weight of partially compacted concrete (W1).

The partially compacted concrete was emptied from the cylinder and refilled with concrete from the sample, being heavily rammed to obtain full compaction.

The cylinder was weighted. This weight is known as the weight of fully compacted concrete (W2).

Find the weight of empty cylinder (W).

RESULTS SLUMP TEST Height of Slump = 5mm Type of Slump = True Slump

VEBE TEST Vebe time = 15 seconds COMPACTING FACTOR TEST Mass of cylinder = 4.172kg 𝑀𝑝 = 14.734 − 4.172 = 10.562 kg 𝑀𝑓 = 16.041 − 4.172 = 11.869 kg Compacting factor

= =

𝑀𝑝 𝑀𝑓 10.562 11.869

= 0.890 kg Where 𝑀𝑝 = 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑝𝑎𝑟𝑡𝑖𝑎𝑙𝑙𝑦 𝑐𝑜𝑚𝑝𝑎𝑐𝑡𝑒𝑑 𝑐𝑜𝑛𝑐𝑟𝑒𝑡𝑒 (𝑔) 𝑀𝑓 = 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑓𝑢𝑙𝑙𝑦 𝑐𝑜𝑚𝑝𝑎𝑐𝑡𝑒𝑑 𝑐𝑜𝑛𝑐𝑟𝑒𝑡𝑒 (𝑔)

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DISCUSSION 1) Discuss the result above. The test is based on the procedure given and the slump shows a result of true slump. The slump turned up with height of 5mm. The result shows the slump test falls under very low degree of workability which range between 0-10. The Slump Test is not a success since it falls under the very low workability category as requested for the test. The height of slump test was affected by the uncorrect amount of compaction which was 25 times every layer. The result taken in Vebe test for the vebe time is 15 second. According to the result of the test it shows that the Vebe test result actually falls under the workability of extremely low which ranges over 20 second. The test is a failure since the required workability category for this test is supposed to be low which ranges between 6-12 seconds. The test maybe caused by the addition of water in while mixing the mixture. Besides that, the result might come from the error of the time keeper when taking the time. For the Compacting Factor Test, the final result obtained 0.89. This final result is obtained by dividing the mass of the partially compacted concrete with mass of fully compacted concrete. Thus, the mass of the partially compacted concrete was 10.56 kg and the mass of fully compacted concrete was 11.87 kg. This test falls under the required workability category which falls under low, which ranges between 0.75-0.85. The result may be influenced by the tamping process. With the results from the three tests, it can be said that the mix is very difficult to handle.

2) Compare the following test for the workability of concrete in term of application a) Slump Test b) Compacting factor test c) Vebe test

It can be said that the Slump test, Compacting factor test and Vebe test have the same function which is to test the workability of a mixture but these three tests did not provide the same best results of workability. First is Slump test. Slump test is most common method for measuring the workability of freshly mixed concrete. Uniformity of the concrete regarding workability and quality aspects can be assessed from batch to batch by observing the nature in which the concrete slumps. It is not very suitable for very wet or very dry concrete. Slump test does not give an indication of plastic viscosity and are less relevant to modern more newer advanced concrete mix. Secondly, compacting factor test focuses more on compatibility of the mixture. Although this test takes a long 12

procedure and time to do, we can achieve the maximum possible density by a standard amount of work done by allowing the concrete to fall through a standard height, which will also increase the compressive strength. Comparing with test with the other two tests, we can conclude that this is the perfect test to test the concrete mixture dynamically. The large and heavy compacting factor device reduces its usefulness in the field. A balance is required to measure the mass of the concrete in the cylinder. Lastly, Vebe test is a good laboratory test suitable for stiff concrete mixes having low and very low workability. This test ensures that the flow ability of the mixture is improved through vibration. Even though, this test seems convincing but it’s not a popular test in the site due to its complex and heavy instruments. This test focuses on low slump concretes only. Nowadays, this test also used mostly in lab works only.

3) A sample of concrete was divided into three portions and result for the slump, compacting factor test and Vebe test obtained as follows: Slump = 5mm, Compacting Factor = 0.93, Vebe Time = 18 s Assume that only one result was in error, which result is incorrect? Explain it.

When a sample of concrete is divided into three portions and the result obtained were slump = 5mm, compacting factor = 0.93 and Vebe time = 18s, we can see that one of the result was incorrect, that is compacting factor. There are five workability categories: a) Extremely low b) Very low c) Low d) Medium e) High From the result given above, it shows that slump test and vebe time belongs to very low workability category except for compacting factor test which under the medium workability category. Hence, the incorrect result is for the compacting factor test. Firstly, the error might have occurred due to the addition of water which increased the weight of the partially compacted to the fully compacted concrete. Besides that, the tamping might have done properly which can cause some air holes to be trapped inside so the results will be affected. The compacting factor test should belong in the 0.7-0.75 range.

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4) Indicate two alternative reasons for using: a) Plasticisers b) Retarders Two alternative reasons for using: a. Plasticizer Plasticizer, which sometimes known as water-reducing admixtures functions to reduce the water requirement of a concrete mixture by about 5 to 10 percent. For treated concrete, less water is needed to produce a desired slump than untreated concrete. This is because low water content means the concrete can have a lower water-cement ratio which translates to higher concrete strength. Other than that, it is also a method to help improve the workability of the concrete. The plasticizer will be absorbed on the surface of binder particles in the concrete when added, causing them to repel each other and thus resulting in a lower workability.

b. Retarders Retarders can be used to delay the setting of concrete and keep the concrete workable for a longer period of time. Retarders slow down the chemical reaction of cement of water and thus leading to longer setting time and slower initial strength gain. Slow setting rate of concrete are used to counteract the accelerating effect of hot weather on concrete setting. Retarders may extend the concrete placing time by reducing the rate of heat evolution so that workability of concrete can be maintained at high temperature. High temperature may causes the rate of hardening to increase which make placing and finishing difficult. Hence, retarder is used to reduce the temperature of concrete by cooling the mixing of water and aggregate. However, retarder does not decrease the initial temperature of concrete.

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ANALYSIS Comparison between theoretical and experimental: 1. The experiment is considered a failure. The results obtained from the test shows the concrete falls under different workability category most of them are either medium or very low workability. This might be due to human error in handling the procedures that causes inaccurate results.

Causes and error during experiment: 1. The method of tamping is incorrect. 2. Some fresh concrete fell out of the cylinder when conducting compacting factor test. This is due to improper placement of the cylinder. Precaution and safety measure during experiment: 1. Make sure each layer of the concrete approximately one-third of the height of the mould when tamped. 2. Make sure the height of tamping is correct and each layer only tamp for 25 times. 3. Remove the slump cone vertically, slowly and carefully to avoid the collapsing of the concrete. 4. Make sure the apparatus for Vebe test is set up correctly. 5. Stop the stop watch immediately after the side of glass plate rider is full with fresh concrete.

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CONCLUSION Slump result was between 5 mm and the type of slump is true slump. Hence the concrete is acceptable. This happened because the water content is less, the concrete look a bit dry during the test. Water content in the concrete, means lower the workability, the higher the strength. We concluded that our experiment was a success since it achieved our expectation which is true slump. Vebe test result is 15s which did not achieve to our expectation which supposed to be 612 s. This means the flow properties of the concrete is low. So the ability of concrete to remould from one shape to another under applied vibration are failed. The compacting factor is mass of partially compacted concrete and mass of fully compacted concrete. From our result, the mass of partially compacted concrete is 10.562 kg whereas the mass of fully compacted concrete is 11.869 kg. While we are doing test for compacting factor test, it can be seen that the test suffered from the disadvantage that cohesive concrete tends to stick in the hopper and must be encouraged to fall by pushing a rod through it. This is particularly for air-entrained concrete.

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REFERENCES

Chemical Admixtures for Concrete, ACI Committee 212.3R-91 Report. ACI 238.1R-08 – Report on Measurements of Workability and Rheology of Fresh Concrete https://theconstructor.org/concrete/factors-affecting-workability-concrete/11190/ https://www.engr.psu.edu/ce/courses/ce584/concrete/library/materials/Admixture/Admixtures Main.htm

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