University Tenaga NasionalCollege of Engineering

Department of Civil Engineering

CEMB111 Civil Engineering Materials LaboratoryLaboratory Experiment (4)

(COMPACTING FACTOR OF CONCRETE MIX)

Name: Jubair Ahmad MusazayID: CE081471 Section: 01Group Number: 2Group Members:

1. Looi Kam Hoe CE0814762. Fadhil Afandi Mohammad Azahar CE0814683. Kevin Tan Wei Jin CE0814734. Khairunnisa Affifah Iddris CE0814695. Harizah Bt. Haris CE0814706. Muhd Ridhwan B. Abd. Aziz CE079050

Date of Laboratory session: 06/ 08/ 2008Date of Report submission: 12/ 08/ 2008

Laboratory Instructor Name: Ms. Najwa Juaini Azmi

No. Reports Allocated (%) Achieved (%) Totals1 Performance 10%

Jubair Ahmad Musazay

2 Cover 1%3 Summary 8%4 Table of content 1%5 Introduction

10%6 Objectives7 Apparatus8 Materials9 Procedure10 Results 20%11 Discussion 40%12 Conclusion 10%131415

Table of content

No. Title/ Subject Page

1. Cover Page ……………………………………………………… 1

2. Table of content ………………………………………………… 2

3. Summary ……………………………………………………….. 3

4. Introduction, objectives, apparatus, materials ……………… 3, 4

5. Procedure ……………………………………………………… 4, 5

6. Results …………………………………………………………. 6, 7

7. Discussion ………………………………………………………. 8, 9, 10

8. Conclusion ……………………………………………………… 10, 11, 12

9. Reference ……………………………………………………….. 12

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Summary:

Determining the compacting factor of a sample of the concrete is a more precise

and accurate way of testing workability of the concrete. Although, the slump test is good

enough to test the workability of the concrete, but when we talk about accuracy or being

more precise, the slump test may not gives us the exact value or time that we want.

However, there are many other types of experiment which determine the workability of

the concrete, but compacting factor test is one the experiments that we can get a better

level of accuracy in it.

Basically, getting the compacting factor is by measuring the mass of the partially

compacted concrete divided by the mass of the fully compacted concrete and that yields

the compacting factor of that specific concrete. The compacting factor test is sometimes

known as ‘drop test’ as well. Because, the upper hopper in the apparatus is filled with the

made concrete, and then allowed to be dropped to the second hopper, and from the

second hopper its then allowed to be dropped in the bottom cylinder to test the

workability and consistency of the concrete.

Beside the slump test and compacting factor test, if we are looking for an extra or

very high accuracy of the workability of some concrete, there is another way of doing so

by using VEB Test Apparatus.

Introduction:

Compacting factor is the degree of the compaction i.e. the ration of the density

actually achieved in the compacting factor test to the density of the same concrete fully

compacted. The compacting factor of a concrete mix would also indicate the workability

of the mix. The test is useful for drier mixes for slump test would be unreliable.

Objective:

The objective of this experiment is to determine the compacting factor of the

concrete mix. The experiment is prescribed in BS 1881: Part 103: 1993 and ACI 211.3-75

(Revised 1987) (Re-approved 1992).

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Apparatus:

1. Compacting factor apparatus (figure attached)

2. Trowel or float

3. Scoop

4. Balance

5. Stopwatch

6. Sample trays

Materials:

Basic Materials:

1. Ordinary Portland Cement (OPC)

2. Clean water

3. Air-dried fine aggregate (sand) that is free from any lumps

4. Air-dried coarse aggregate of 20mm nominal size that is free from any lumps

Concrete Mix:

1. Proportion of cement: fine aggregate: coarse aggregate = 1: 2: 4

2. Water / Cement ratio of 0.45, 0.55, 0.65 and 0.75

Procedure:

Introduction: The compacting factor of the concrete mix is the density of the concrete

mix inside the cylinder (that has fallen from the hopper and uncompacted)

divided by the density of the same concrete mix that has been compacted

inside the cylinder.

1. A concrete mix sample of water/cement ratio of 0.75 (based on the water/cement

ration of experiment NO. 5) was prepared.

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Precaution: It was made sure that the internal surface of the hopper and cylinder of the

compacting factor apparatus is clean and damp before usage.

2. The concrete mix was placed carefully into the upper hopper using the scoop until

it was filling up to the level of the hopper’s rim.

3. The bottom door of the upper hopper was opened and released to let the concrete

mix falls down into the second hopper.

4. Then the second hopper bottom was opened and released at the time which no

more concrete mix sample was falling from the upper hopper.

5. Excess concrete mix was cut off by using two floats to slide across the top of the

cylinder from the side to the center of the cylinder. The exterior part of the

cylinder was cleaned.

6. The concrete in the cylinder was weighted. (The concrete which is regarded as

partially compacted.)

7. The concrete mix was filled out of the cylinder.

8. The cylinder was filled up with concrete used for the test in six layers. Each layer

was compacted by applying 25 strokes using the compacting bar and was well

distributed across each layer.

9. The concrete in the cylinder was weighted. (Which this concrete inside the

cylinder is regarded as fully compacted.)

10. The results were recorded in Table 4.2.

11. The steps 2 – 10 were repeated for the second trial.

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Results:

Figure 4.1 Compacting Factor Apparatus

Table 4.1

Description of workability and compacting factor

Description of workability Compacting Factor Correspond Slump (mm)

Very Low 0.78 0 – 25

Low 0.85 25 – 50

Medium 0.92 50 – 100

High 0.95 100 – 175

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Table 4.2

Test data results for compacting factor of concrete mix

SampleMass of

Cylinder (kg)

Mass of partially

compacted concrete, = A

(kg)

Mass of fully compacted

concrete, = B (kg)

Compacting factor, = A/B

0 Minutes3.85 16.345 - 3.85

= 12.495

15.685 - 3.85= 11.535 1.083

15 Minutes3.85 7.850 - 3.85

= 4

15.735 - 3.85= 11.885 0.336

30 Minutes3.85 4.475 - 3.85

= 0.625

15.700 - 3.85= 11.850 0.053

Sample of calculations:

For 0 minutes:

For 15 minutes:

Mass of partially compacted concrete, A = A – Mass of Cylinder A = (7.850 – 3.85) = 4kg

Mass of fully compacted concrete, B = B – Mass of Cylinder B = (15.735 – 3.85) kg = 11.885kg

Compacting factor,

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Discussion:

1. Comment on the possibility of committing errors and mistakes in performing of

the test based on the given procedures.

Answer:

Based on the given procedure, in the step 8, it says that, “Fill up the cylinder with

the concrete mix used for the test in six layers. Compact each layer by apply 30 strokes

using the compacting bar and is well distributed across each layer” commenting on this

step is that we can’t really get the exact six layers in a cylinder which is not very high

also, therefore we used, 3 layers and 25 strokes for each layer as per was instructed by the

lab technicians and instructors.

And also based on the procedures, weighting of the concrete inside the cylinder is

sometimes not very accurate since the digital scale in the lab is sometimes reading

different numbers for the same weight, plus that scale can not weight a mass of more than

30kg. All thought we didn’t have it in our cylinder, but if we need to weight a higher

mass we need to do it 2 or more than 2 times, which if it’s a mix concrete we won’t be

able to get an exact value, due to the left concretes attached with the cylinder and some

wastages.

The next is that, equipment failure can also cause errors. As in this experiment, at

the fist time we had to hold the second hopper door when we opened the upper hopper

door for the concrete to be dropped into the second hopper, because if we wouldn’t take

the concrete would have dropped directly to the cylinder because the second hopper’s

door was not tied well. And that was due to some extra dried cement and concrete

materials which were attached in the equipment from the past experiments. Then after we

cleaned the apparatus from any other unwanted and extra materials we could close the

second hopper’s door tidily. This point also proves that, the improper handling of the

equipment can cause errors and mistakes.

Beside all these above mentioned factors, another factor which always can be

mentions is human mistake that can also cause errors. Using old or unusable equipment is

also considered as one of the reasons for committing errors and mistakes.

2. Comment on possible ways to improve the accuracy of the test result.

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Answer:

There are a lot of possible ways that can actually improve the accuracy which are

as follows:

Using the right or new equipment

Proper handling of the equipment

Carefully and step by step implementing of the procedures of the experiment

Being accurate and consistent in regard with size, weight, length, height, or any

other measurement of the materials.

Referring to the lab instructor or lab technician upon facing any difficulties or

doubt.

Cleaning the equipment before usage. Or making sure that the equipment is ready

to use for the experiment.

Etc …

3. Comment on the usefulness and application of the result of this experiment.

Answer:

Usefulness: The usefulness of the result of this experiment is to gives us an

idea about the workability of the concrete mix. Not only the idea or the knowledge that

we get from this experiment about the workability of the concrete, we also get to know

that this experiment is an alternative way of determining the workability and consistency

of concrete, beside the Slump Test experiment. Plus this experiment is more accurate

than the slump test experiment.

Application: This experiment is applied when we want to know the workability

of the concrete. Either this experiment or slump test experiment both can indicate the

workability. This experiment is usually done in the lab because of the lack of apparatus in

the site, but slump test can be done anywhere and is usually used in the site, because we

will only need to have a cone or a conic shape can. Since by performing of this

experiment we get the workability of the concrete, therefore we need to know the

workability in cases such as transferring or carrying the fresh concrete from one place to

another one. Because, when we carry it, it takes some time which we don’t want our

concrete to be changed or to get harder during that specific time. So that’s why we need

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to know the workability to have the knowledge of how long we can keep the concrete

before using it. Although, there are other factors that this experiment can be applied as

well, but its main application is when we need to keep our fresh concrete fresh and

without any changes for sometime before using it.

4. What is the significance of the conducting this experiment?

Answer: Although this question is the same as question 3, because the usefulness

and significance is exactly the same thing, but I am going to contribute for the answer of

this question too, but it is going to be the same, or only with slightest difference.

Achieving the objective of this experiment is the significance of the experiment, and

objective of this experiment is talking about the compacting factor of concrete. Why do

we need to know about the compacting factor is because, compacting factor of the

concrete is showing the workability and consistency of the concrete. Again if we ask

ourselves that why do we need to know about the workability is because of keeping the

fresh concrete fresh for a while before using it in a beam or slab or wall or whatever. For

example in our experiment, we got a compacting factor of 1.083 for our first trial in

0minutes, it means that this concrete is more workable, or in the other words, we can

actually keep this concrete mix for a while before using it. And this characteristic of the

concrete is due to the excessive amount of water inside the concrete. More water can

keep the concrete mix fresh, because extra more water molecules can reduce the rate of

hydration in the hydration process and that can cause the concrete mix to stay fresh

longer since the hydration process does not take place vigorously, but of course

increasing the workability of concrete will decrease its strength, which is not really

recommended, so that’s why we need to have a workability of the concrete inside the

range of the limitations of the workability, which based on some sources, it should not be

more than one.

Conclusion:

Based on the objectives of this experiment, that is determining the compacting

factor of the concrete mix, we made the sample of the concrete as per experiment 5 and

we used in 3 different time intervals of 0 minutes, 15 minutes and 45 minutes. Weight of

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the cylinder that we used was 3.85kg, which in our first trial for the partially compacted

concrete, we had all of our concrete dropped to the second hopper and then to the

cylinder which had a total weight of 16.345kg. The pure weight of the concrete was =

(total weight – weight of the cylinder) which is equal to 16.345 – 3.85 = 12.495kg, at the

same trial we had a pure mass of 11.535kg for fully compacting concrete. Which the

compacting factor between them is 1.083, achieved by dividing mass of partially

compacted by mass of fully compacted concrete.

In our second trial after 15minutes which not all of our concrete dropped down to

the cylinder, therefore we had a pure concrete mass of 4kg only in the partially

compacted and a mass of 11.885kg for the fully compacted concrete, the compacting

factor between them is 0.336, this time when we let 15minutes to pass, it means the

hydration process was started inside the concrete mix due the reaction of the cement

molecule with water, so it was getting harder and the workability was reducing, since the

compacting factor is a test for determining the workability, then when workability

reduces the compacting factor also reduce, which simply means less workable. The

higher the compacting factor the more workable the concrete is, but a compacting

factor of more than one is not recommended.

In our last trial after 45 minutes, definitely the concrete was much harder and less

workable. So, by inspection we could expect a lesser compacting factor, which this

expectation was satisfied. Because we had only 0.626kg of the concrete dropped down

inside the cylinder in our partially compacted test, but we still had a mass of 11.850kg for

our fully compacted concrete. The compacting factor between these tow masses is 0.053,

which our expectation of getting a smaller number was accurate.

Therefore, based on the standard calculation and data from the Table 4.1, our first

trial with a compacting factor of 1.083 is considered very high workable, since the value

0.95 from the table is considered high workable. But based on the standards (internet source

is cited at the end) a compacting value of more than one is not recommended, or this

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“difference should not be more than 1”. If we use the slump test, a slump value of 100 –

175mm will correspond to this compacting factor value, 1.083.

Our second trial with a compacting factor value of 0.336 is considered very low

workable since based on the standards from Table 4.1 a compacting factor value of 0.78

is already considered very low. In a slump test, a slump value of 0 – 20mm will respond

to the value of 0.78 from a compacting factor test, so therefore, there is no slump value

for our second trial which has a compacting factor of 0.336, or we can also say that, it has

a totally True Slump.

And also in our last trial which had a compacting factor of 0.053, so basically,

there is no corresponding slump value since a slump value of 0 – 20mm corresponds to a

compacting factor value of 0.78. Or this one also can be considered as a totally True

Slump and very less workable concrete.

Sample of calculation is shown in the page 7 of this experiment.

Reference:

< http://www.streetworks.fsnet.co.uk/concrete_testing.htm >

~~~THE END~~~

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