labratory reports.pdf

Bahir Dar University

Institute of Technology

School of Water Resource

and

Civil Engineering

Construction Management

& Technology Department

Construction Materials CENG 6105

Laboratory Report

Submitted to: Dr. Yoseph Birru

By: Getaneh Emiru

Yoseph Zelalem

Meserte Ejigu

Asratu Setargew

September, 2012

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Table of Contents

I-Test Method for Standard consistency ......................................................................................................................... 5

1. Scope: .............................................................................................................................................................................. 5

2. Definition: ..................................................................................................................................................................... 5

3. Apparatus used: .......................................................................................................................................................... 5

4. Test Procedure: ........................................................................................................................................................... 5

4.1. Test 1 ..................................................................................................................................................................... 5

4.2. Test 2 ..................................................................................................................................................................... 6

4.3. Test 3 ..................................................................................................................................................................... 6

5. Observation: ................................................................................................................................................................. 7

6. Result: ............................................................................................................................................................................. 7

7. Analysis: ......................................................................................................................................................................... 7

8. Recommendation ....................................................................................................................................................... 7

II-Time of setting of Hydraulic cement by Vicat Needle ........................................................................................... 8

1. Scope: .............................................................................................................................................................................. 8

2. Definition: ..................................................................................................................................................................... 8

3. Apparatus used: .......................................................................................................................................................... 8

4. Procedure: ..................................................................................................................................................................... 8

5. Observation: ................................................................................................................................................................. 9

6. Result: ............................................................................................................................................................................. 9

7. Recommendation: ...................................................................................................................................................... 9

8. Frequently asked questions: ................................................................................................................................. 9

III-Test Method for the determination of Organic Impurities for Fine Aggregate ..................................... 11

1. Object: .......................................................................................................................................................................... 11

2. Theory: ........................................................................................................................................................................ 11

3. Procedure: .................................................................................................................................................................. 11

4. Observation: .............................................................................................................................................................. 11

5. Precautions: ............................................................................................................................................................... 11

6. Conclusion and recommendation: ................................................................................................................... 11

7. Frequently Asked Questions: ............................................................................................................................. 12

IV-Particle Size Distribution ............................................................................................................................................. 13

& Fineness Modules of Aggregates Tests..................................................................................................................... 13

1. Scope: ........................................................................................................................................................................... 13

2. Definition: .................................................................................................................................................................. 13

3. Apparatus: .................................................................................................................................................................. 13

4. Sampling: .................................................................................................................................................................... 13

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5. Procedure: .................................................................................................................................................................. 13

6. Observation and Calculation: ............................................................................................................................. 14

6.1 Sieve Analysis of Coarse Aggregate............................................................................................................... 14

6.2 Sieve Analysis of Fine Aggregate .................................................................................................................... 15

7. Results in Log Chart: .............................................................................................................................................. 15


9. Frequently Asked Questions (FAQ): ................................................................................................................ 18

V-Specific Gravity and Absorption of Coarse Aggregate Tests ........................................................................... 21

1. Scope: ........................................................................................................................................................................... 21

2. Definition: .................................................................................................................................................................. 21

3. Apparatus: .................................................................................................................................................................. 21

4. Sampling: .................................................................................................................................................................... 22

5. Procedure: .................................................................................................................................................................. 22

6. Measurement Data: ................................................................................................................................................ 23

7. Calculations and computations: ........................................................................................................................ 23

7.1 Specific Gravity: ....................................................................................................................................................... 23

7.2 Percentage of absorption: ................................................................................................................................... 23

8. Results of Computation: ....................................................................................................................................... 23


10. Frequently Asked Questions (FAQ): ................................................................................................................ 24

VI-Determination of Bulk Density of Coarse Aggregate ........................................................................................ 26

1. Scope: ........................................................................................................................................................................... 26

2. Theory: ........................................................................................................................................................................ 26

3. Apparatus: .................................................................................................................................................................. 26

4. Condition of sample: .............................................................................................................................................. 26

5. Procedure: .................................................................................................................................................................. 26


7. Conclusion: ................................................................................................................................................................ 27

8. Question: ..................................................................................................................................................................... 27

VII-Determination of Bulk Density of Fine Aggregate ............................................................................................ 28

1. Scope: ........................................................................................................................................................................... 28

2. Theory: ........................................................................................................................................................................ 28

3. Apparatus: .................................................................................................................................................................. 28

4. Condition of sample: .............................................................................................................................................. 28

5. Procedure: .................................................................................................................................................................. 28


VIII-Test Method for the determination of compressive strength of concrete ............................................ 29

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1. Scope: ........................................................................................................................................................................... 29

2. Theory: ........................................................................................................................................................................ 29

3. Apparatus: .................................................................................................................................................................. 29

4. Procedure: .................................................................................................................................................................. 29

5. Observations and Calculations: ......................................................................................................................... 30

6. Conclusion: ................................................................................................................................................................ 30

IX-Test Method for the determination of Moisture Content of Coarse Aggregate ..................................... 31

1. Scope: ........................................................................................................................................................................... 31

2. Definition: .................................................................................................................................................................. 31

3. Apparatus: .................................................................................................................................................................. 31

4. Procedure: .................................................................................................................................................................. 31

5. Observation and Calculation .............................................................................................................................. 31

6. Conclusions and recommendation: ................................................................................................................. 32

X-Silt content of fine aggregate ........................................................................................................................................ 33

1. Object: .......................................................................................................................................................................... 33

2. Theory: ........................................................................................................................................................................ 33

3. Apparatus: .................................................................................................................................................................. 33

4. Procedure: .................................................................................................................................................................. 33

5. Measurement from the test: ............................................................................................................................... 33

6. Calculations: .............................................................................................................................................................. 34


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I-Test Method for Standard consistency

1. Scope: This test method covers the determination of standard consistency and setting times of

cement sample.

2. Definition: Standard Consistency – This test method is intended to be used to determine the amount

of water required to prepare hydraulic cement pastes for testing. The consistency, which

will permit the vicat plunger to penetrate to a depth 9 –11 mm from the original surface is

the standard limit.

3. Apparatus used: 3.1 Vicat apparatus with vicat plunger

3.2 Vicat needle and vicat mould with 40mm depth

3.3 Gauging trowel, measuring jar, mixer, weighing balance, stop watch and glass plate.

4. Test Procedure:

4.1. Test 1 First we put the container on the weighing balance and tare to neglect the weight of

the container. We measured 500gm sample of PPC Derba cement on the container Using the same procedure we measured 130gm clean water which is 26% of the

500gm cement measured.

i.e. % Water = (A/500gm) *100

= (130/500) *100

= 26%

(The usual range of water / cement ratio for normal consistence is between 26 and 33

percent.)

The cement sample was thoroughly mixed with the measured quantity of clean water for 3 minutes by means of a trowel mortar mixer.

We filled the cement paste in to the mould and we centrally placed it on a plate under the rod. (The temperature of the cement and water and that of the test room during gauging and filling the mould should be 17.7-23.3 oc.)

Immediately after filling the mould and placing it on the plate we gently lower the plunger and brought in contact with the surface of the paste and quickly released.

Thirty seconds after releasing the plunger, we recorded a penetration of 5mm from the original surface or 35mm un penetrated depth from the bottom, which is not acceptable since it is out of the required standard range, 9-11mm.

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The test is repeated with varying percentage of water until standard consistence is

obtained.

4.2. Test 2 Following the same procedure we put the container on the weighing balance and

tare to neglect the weight of the container. We measured 500gm sample of PPC Derba cement on the container We measured 150gm clean water which is 30% of the 500gm cement measured.

i.e. % Water = (A/500gm) *100

= (150/500) *100

= 30%


We filled the cement paste in to the mould and we centrally placed it on a plate under the rod.


Thirty seconds after releasing the plunger, we recorded a penetration of 20mm from the original surface or 20mm unpenetrated depth from the bottom, which is not acceptable since it is out of the required standard range, 9-11mm.

The test is repeated again with varying percentage of water until standard consistence

is obtained.

4.3. Test 3 Following the same procedure we put the container on the weighing balance and

tare to neglect the weight of the container. We measured 500gm sample of PPC Derba cement on the container Using the same procedure we measured 137.5gm clean water which is 27.5% of the

500gm cement measured.

i.e. % Water = (A/500gm) *100

= (137.5/500) *100

= 27.5%

(The usual range of water / cement ratio for normal consistence is between 6

and 33 percent.)


We filled the cement paste in to the mould and we centrally placed it on a plate under the rod. (The temperature of the cement and water and that of the test room during gauging and filling the mould should be 17.7-23.3 oc.)

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Thirty seconds after releasing the plunger, we recorded a penetration of 10.8mm from the original surface or 29.2mm un penetrated depth from the bottom, which is acceptable since the penetration is within the required standard range, 9-11mm.

5. Observation:

STANDARD CONSISTENCY OF CEMENT

Trial

No

Percentage of

water taken

Un penetrated Depth From the

bottom(mm)

1 26% 35mm

2 30% 20mm

3 27.5% 29.2mm

6. Result:

Standard consistence of cement= 27.5%

The amount of water required for consistency of 500g PPC Derba cement, which will permit the vicat plunger to penetrate to a depth 9 –11 mm from the original surface is 27.5%.

7. Analysis:

The consistency of cement is affected by different factors such as the type of cement used, type and cleanness of sand, quality of water, temperature and water content. There are three cases which will occur due to water content:

If the amount of water added is much more than the required amount the mix will fluidish so that it will not be consistent.

If the amount of water added is within the required range the mix will be consistent.

If the amount of water added is less than the required amount the mix will not for a consistent paste.

8. Recommendation

For the type of cement specified, 500g Derba PPC cement, from the standard consistency test conducted, the amount of water required to prepare hydraulic cement pastes for testing become 27.5%. Here we can conclude that if the water added is exceeded or less than the required range, we will not get a consistent cement paste.

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II-Time of setting of Hydraulic cement by Vicat Needle

1. Scope: These methods determines the time of hydraulic cement by means of vicat needle. Two test

methods are given; method A is the reference of Test Method using the manual operated

standard Vicat apparatus, while Method B permits the use of an automatic vicat machine

that has, in accordance with the qualification requirements of this method, demonstrated

acceptable performance.

2. Definition: Setting times – The setting time measures the time taken for the cement paste to offer

certain degree of resistance to the penetration of a special attachment pressed in to it. The

time of setting is calculated as the difference between the time that a measurement of 25

mm penetration is measured and the time of the initial contact between the cement and

water.

3. Apparatus used: 3.1 Vicat apparatus with vicat plunger

3.2 Vicat needle and vicat mould

3.3 Gauging trowel, measuring jar, mixer, weighing balance, stop watch and glass plate.

4. Procedure: A fresh cement paste of normal consistence was prepared and filled into the vicat

mould. At 30 minutes after mixing, the mould resting on a plate was placed under the

rod and the needle was gently lowered and brought in contact with the surface of the paste and quickly released. The penetration was recorded thirty seconds after releasing the needle. This was repeated every 15 minutes until a penetration of 25mm or less is obtained in thirty seconds.

The results of all penetration tests were recorded, and the time when a penetration of 25mm is obtained was determined by interpolation. The period elapsing between the time when the water is added to the cement and the time at which the needle penetrates 25mm is taken as the initial setting time.

We found 28mm penetration in 75min and 21mm penetration in 90min so by interpolation; we found 25mm penetration in 81minutes and 40seconds.

Final setting time was determined after replacing the needle of the Vicat apparatus by the needle with an annular attachment. The cement shall be considered as finally set when, upon applying the needle gently to the surface of the test block, only the needle makes an impression, while the attachment fails do so.

We found the final setting time of the cement at 90min.

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5. Observation:

INITIAL SETTING TIMES OF CEMENT

Trial

No

Time in min. Un penetrated Depth From

the bottom(mm)

1 75min. 28mm

2 90min. 21mm

3 X 25mm

6. Result:

Let Initial setting time of cement= X

By interpolating the observed values we get the initial setting time

(75-90)/ (75-X) = (28-21)/ (28-25)

X= 81.4min

Initial setting time of cement= 81.4min

Final setting time of cement= 90min.

7. Recommendation:

ASTM C 150, Standard Specification for Portland cement, requires the initial setting time to

be not less than 45 min, and the final setting time to be not more than 375 min, as

determined by the Vicat Needle (ASTM C 191).

8. Frequently asked questions:

a. What do you understand by the term standard consistency, initial setting time and final setting time of a cement sample?

[Answer]

Almost universally, the initial and the final setting times are determined by the Vicat

apparatus, which measures the resistance of a cement paste of a standard consistency to

the penetration of a needle.

Standard Specification for Portland cement requires the initial setting time to be not less

than 45 min, and the final setting time to be not more than 375 min, as determined by the

Vicat Needle (ASTM C 191).

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The initial set is the beginning of solidification, marks the point in time when the paste has become unworkable. The initial setting time is an arbitrary time in the setting process which is said to have been reached when the needle is no longer able to penetrate a 40mm deep cement paste touch to approximately 5 to 7mm from the bottom.

The final set is the time taken to solidify completely. The final setting time is said to be reached when the needle makes an impression on the surface of the paste but does not penetrate.

b. What is the importance of the above three tests?

[Answer]

These tests are used primarily to determine and reproduce the consistency required for the

optimum consistency.

c. What is the difference between setting and hardening?

[Answer]

In concrete technology, the phenomenon of strength gain with time is called hardening. But

setting is the rate at which hardening of concrete occurs.

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III-Test Method for the determination of Organic Impurities for Fine Aggregate

1. Object: The objective is to test the organic impurity content of fine aggregate.

2. Theory: The aggregate must be checked for organic impurities such as decayed vegetation, humus,

coal dust, etc. Color test is a reliable indicator of the presence of harmful organic matter in

aggregates except in areas where there are deposits of lignite.

3. Procedure: We filled a 350 ml clear glass medicine bottle up to 75ml mark with a 3% solution of

caustic soda or sodium hydroxide. A 3% solution of caustic soda was made by dissolving 3gm of sodium hydroxide in 100ml of water. The solution was kept in glass bottle tightly closed with a rubber stopper. Care was taken during handling sodium hydroxide and not to spill the solution for it is highly injurious.

The sand was next added gradually until the volume measured by the sandy layer became 125ml. The volume was then made up to 200 ml by the addition of more of the solution. The bottle was then crocked and shaken vigorously and allowed to stand for 24 hours.

At the end of this period, the color of the liquid will indicate whether the sand contains a dangerous amount of matter. A colorless liquid indicates clean sand free from organic matter. A straw-colored solution indicates some organic matter but not enough to be seriously objectionable. Darker color means that the sand contains injurious amounts and should not be used unless it is washed, and a re-test then shows that is satisfactory.

Note: the acids in the sample are neutralized by a 3% solution of NaOH, prescribed

quantities of aggregate and of solution being placed in a bottle. The mixture is vigorously

taken to allow the intimate contact necessary for chemical reaction, and then left to sand

for 24 hours and then the organic contact can be judged by color.

4. Observation: Color of the solution observed was straw color which indicates some organic matter but

not enough to be seriously objectionable.

5. Precautions: a) Use every possible care while handling sodium hydroxide solution. b) The sand and the sodium hydroxide should be shaken vigorously to get good results.

6. Conclusion and recommendation: Give your comments on the color of the liquid. Do you recommend this sand for civil

Engineering Construction?

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Color of the solution observed was straw color which indicates some organic matter but not enough to be seriously objectionable.

We recommend that it can be used for Civil Engineering Construction if some correction measures are made on it like sieving and washing the sand to remove and dissolve the organic contents.

7. Frequently Asked Questions:

a) What do you understand by organic impurities in aggregates?

[Answer]

Organic impurities are impurities found in aggregates resulted from decayed vegetation,

humus, coal dust, etc which causes concrete setting and hardening problems.

b) Does this impurity occur in fine or coarse aggregate or in both?

[Answer]

Organic impurities mostly occur in fine aggregates but it may also be seen in course

aggregates if it is not cleaned before or after crushing.

c) Under what color of liquid the organic impurity is ascertained in aggregate?

[Answer]

In Darker color which means that the sand contains injurious amounts and should not be used unless it is washed, and a re-test then shows that is satisfactory.

d) What effect will dirty aggregates have on the strength of the concrete?

[Answer]

Dirty aggregates will reduce bonding capacity with rebar or other embedded structures

and strength of concrete will also reduce significantly, soundness of concrete also will be

affected.

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IV-Particle Size Distribution & Fineness Modules of Aggregates Tests

1. Scope: This test method covers the determination of particle size distribution of fine, coarse and

all- in aggregates by sieving.

2. Definition: According to ASTM, the term coarse aggregate is used to describe particles larger than 4.75

mm (retained on No. 4 sieve), and the term fine aggregate is used for particles smaller than

4.75 mm.

3. Apparatus: 3.1 Balance – The balance or scale shall be such that it is readable and accurate to 0.1%

of the weight of the sample.

3.2 Sieves – Sieves of the size shown in table 1.1 and 1.2 conforming to BS.

4. Sampling: Fine aggregate: the size of the test sample, after drying shall be 300gm minimum.

Coarse Aggregate: the size of the test sample of coarse aggregate shall conform with the

following data:

Nominal maximum size

square opening (mm)

Test sample size

minimum (Kg)

9.5 1 12 2 19 5 25 10

37.5 15 50 20 63 35 75 60 90 100

100 150 125 300

5. Procedure: 5.1 The sample shall be brought to an air-dry condition before weighing and sieving. The

air-dry sample shall be weighed and sieved and sieved successively on the

appropriate sieves starting with the largest size sieve. Care shall be taken to ensure

that the sieves are clean before use.

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5.2 If sieving is carried out with a nest of sieves on a sieve shaker the nest of sieves shall

be shaken for a period, not less than 10min. But if not each sieve shall be shaken

separately over a clean tray for a period of not less than 2min.

6. Observation and Calculation:

6.1 Sieve Analysis of Coarse Aggregate

Weight of sample taken 5.1888Kg

Fineness Modulus (FM)=547.43%/100%=5.47

Sieve

size

(mm)

Weight % retained % Pass ASTM

Limit

Sample(kg) Pan Sample+Sieve Sample(kg) Individual Cumulative

37.5 0.7080 0.8756 0.1676 3.23% 3.23% 96.77%

25 0.7254 3.717 2.9916 57.65% 60.88% 39.12%

19 0.7200 2.2167 1.4967 28.84% 89.72% 10.28%

12.5 0.6785 1.0626 0.3841 7.40% 97.12% 2.88%

9.5 0.6998 0.7249 0.0251 0.48% 97.61% 2.39%

4.75 0.7354 0.8178 0.0824 1.59% 99.19% 0.81%

2.36 1.2384 1.2636 0.0252 0.49% 99.68% 0.32%

pan 0.4102 0.4268 0.0166 0.32% - - -

Total sample weight 5.1893 100.00% 547.43% - -

Total Original Sample 5.1888

Difference -0.0005

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6.2 Sieve Analysis of Fine Aggregate

Weight of sample taken=2.657-1.263=1.3940(kg)

Sieve

Size

(mm)

Weight % retained

% Pass ASTM

Limit Pan Sample+Sieve Sample(kg) Individual Cumulative

9.5 0.6998 0.7532 0.0534 3.8% 3.8% 96.2% 100

4.75 0.7354 0.7784 0.0430 3.1% 6.9% 93.1% 95-100

2.36 1.2384 1.3004 0.0620 4.4% 11.4% 88.6% 80-100

1.18 0.3529 0.5310 0.1781 12.8% 24.1% 75.9% 50-85

0.6 0.3181 0.8530 0.5349 38.4% 62.5% 37.5% 25-60

0.3 0.2939 0.7306 0.4367 31.3% 93.9% 6.1% 10-30

0.15 0.2674 0.3443 0.0769 5.5% 99.4% 0.6% 2-10

0.075 0.2626 0.2694 0.0068 0.5% 99.9% 0.1%

pan 0.2473 0.2492 0.0019 0.1% - - -

Total 1.3937 100.0% 401.9% - -

Total original sample 1.3940

Difference 0.0003

Fineness Modulus (FM)=401.9%/100%=4.02

7. Results in Log Chart: The percent pass against sieve opening as plotted as shown below sing log scale.

8. Conclusion and recommendation:

As it can be seen from chart the coarse aggregate is not well graded one; nearly 50% of the mass lies between size 20mm and 30mm and more than 85% of the aggregate are found between aggregate size of 20mm and 38mm. The aggregate is therefore uniformly graded. This is also evident in the log chart-vey steep chart.

From the grading it can be concluded that the maximum size of aggregate is 25mm since more than 15% of the aggregate is retained on sieve size of 25mm.

The aggregate is the not suitable for concreting as it will not produce a good quality dense concrete. The aggregate can be improved by blending or another better source must be looked for.

The sand has higher fineness modulus (4.02) even above the most recommended range (2 to 4). Higher fineness modulus means the sand is coarser and deficient in finer particles. This also can be attested by comparing with ASTM gradation limit and the log chart. The former shows that the sand is deficient in 0.3mm and 0.15mm particles and the latter shows that the curve is flatter at small sieve openings.

The sand will be unsuitable for aggregate as it is deficient of finer particles and it will produce harsh mix for given water-cement ratio and will be less dense. The sand can be improved by introducing a finer crushed aggregate or other sources must be looked for.

9. Frequently Asked Questions (FAQ):

a) What is a fineness module of an aggregate and what is its importance?

[Answer]

In practice, fineness modulus is often used as an index of the fineness of aggregate. The fineness modulus is cumulative percentages of aggregate retained on each of a specified series of sieves, and dividing the sum by 100.

FM tells us how much finer or coarser an aggregate is; the higher the fineness modulus, the coarser the aggregate is. It is also used for mix design to choose the dry-rodded unit weight in conjunction of maximum size of aggregate.

Very fine sand will increase the water demand of the mix, while very coarse sand could compromise its workability.

b) What is the significance of grading of aggregate and what is meant by good grading?

[Answer]

The most important is their influence on workability and cost. For example, very coarse sands produce harsh and unworkable concrete mixtures, and very fine sands

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increase the water requirement (therefore, the cement requirement for a given water-cement ratio) and are uneconomical. Aggregate grading has also considerable effect on the cement paste requirement of a concrete mixture and aggregates that do not have a large deficiency or excess of any particular size produce the most workable and economical concrete mixtures.

ASTM C33 requires that the sand be less than 45 percent retained on any one sieve. Too much material on one sieve means gap-grading which will increase the water demand of the mix.

The amount of material passing the #50 and #100 sieves will affect workability, slab surface texture, and bleeding. Increased bleeding will occur as the portion passing the #50 sieve increases. The flatwork finishability of a mix also increases as the portion passing the #50 sieve increases.

ASTM C33 limits the amount of material passing the #200 sieve to 3 percent for natural sand that contains clay. Clay is a very fine particle that greatly increases the water demand of a mix, reduces strength significantly, and promotes bleeding

Good grading is an aggregate which don’t have deficiency or excess of any particular size and contains all ranges of particle sizes.

c) How should aggregate be stockpiled on a construction site?

[Answer]

Aggregates should be stockpiled on places, which is level, well-drained and have adequate bearing capacity to support the weight of the material which is to be placed thereon.

Stockpiles shall be constructed at locations and by methods that will neither interfere with nor damage utility lines, pipe lines or underground utilities. Access to stockpiles shall be readily available at all times.

d) What is the difference between fine, coarse and mixed aggregate?

[Answer]

The term coarse aggregate is used to describe particles larger than 4.75 mm (retained on No. 4 sieve), and the term fine aggregate is used for particles smaller than 4.75 mm. Mixed aggregate is an aggregate which contain both fine and coarse aggregate.

e) The fineness modules of sand should lie in what range of limits?

[Answer]

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Fine aggregates range from a FM of 2.00 to 4.00, and coarse aggregates smaller than 38.1 mm range from 6.50 to 8.00. Combinations of fine and coarse aggregates have intermediate values. ASTM C33 suggests that the fineness modulus be kept between 2.3 and 3.1.

f) How does the size of an aggregate affect its fineness modules?

[Answer]

If the aggregate is coarser, fineness modulus will be higher or vice versa.

g) What is a grading curve and where it is used?

[Answer]

Grading curve (say ASTM grading curve) is shaded area that depicts the range of well graded aggregate and can be used by plotting the aggregate gradation and checking whether it lies within the shaded area.

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V-Specific Gravity and Absorption of Coarse Aggregate Tests

1. Scope:

This test method covers the determination of specific gravity and absorption of coarse

aggregate. The specific gravity may be expressed as bulk specific gravity (SSD), or apparent

specific gravity. The bulk specific gravity and absorption are based on aggregate after 24hr.

soaking in water.

2. Definition:

2.1 Absorption- the increase in the weight of aggregate due to water in the pore of the

material, but not including water adhering to the outside surface of the particles,

expressed as percentage of the dry weight. The aggregate is considered “dry” when

it has been maintained at a temperature of 105-115 oc for sufficient time to remove

all uncombined water.

2.2 Specific gravity- the ratio of the mass (or weight in air) of a unit volume of material

the mass of the same volume of water at stated temperature. Values are

dimensionless.

2.3 Apparent specific gravity- the ratio of the weight in air of unit volume of the

impermeable portion of the aggregate at a stated temperature to the weight in air of

an equal volume of gas free distilled water at a stated temperature.

2.4 Bulk specific gravity – the ratio of the weight in air of a unit volume of aggregate

(including the permeable and impermeable voids in the particles, but not including

the voids between particles) at a stated temperature to the weight in air of equal

volume of gas free distilled water at a stated temperature.

2.5 Bulk specific gravity (SSD) –the ratio of the weight in air of a unit volume of

aggregate, including the weight of water with in the voids filled to the extent

achieved by submerging in water for approximately 24 hr.(but not including the

voids between particles) at a stated temperature ,compared to the weight in air of

an equal volume of gas free distilled water at a stated temperature.

3. Apparatus:

3.1 Balance: A weighing device that is sensitive, readable, and accurate 0.1% of the

sample weight.

3.2 Sample container: A wire basket of 3.35mm or finer mesh, or a bucket of

approximately equal breadth and height.

3.3 Water tank: A watertight tank in to which the sample container may be placed

while suspended below the balance.

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4. Sampling:

The minimum mass of test sample to be used is given as follows. Testing the coarse

aggregate in several sizes fraction is permitted. If the sample contains more than 155

retained on the 37.5mm sieve, test the material larger than 37.5mm in one or more size

fractions separately from the smaller size fractions, the minimum mass of the test sample

for each fraction shall be the difference between the masses prescribed for the maximum

and minimum sizes of the fraction.

Nominal Maximum size Minimum mass of test of

sample (Kg)

12.5 2

19 3

25 4

37.5 5

50 8

63 12

75 18

90 25

100 40

125 75

5. Procedure:

5.1 Dry the test sample to constant weight at a temperature of 105 – 150, cool in air at room temperature for 1-3hours for test samples of 37.5mm nominal maximum size, or longer for larger sizes until the aggregate in water at room temperature for a period of 20 - 28hrs.

5.2 Where the absorption and specific gravity values are to be used in proportioning concrete mixtures in which the aggregates will be in their naturally moist condition, the requirement for initial drying may be eliminated.

5.3 Remove the test sample from the water and roll it in a large absorbent cloth until all visible films of water removed. Wipe the larger particles individually. Take care to avoid evaporation of water from aggregate pores during the surface dry operation. Weigh the test sample in the saturated surface dry (SSD) condition. Record this and all subsequent weights to the nearest 0.5gm.

5.4 After weighing, immediately place the SSD test sample in the container and determine its weight in water at 21.3- 24.7 oc, having a density of 995-999 kg/m3. Take care to remove all entrapped air before weighing by shaking the container while immersed.

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5.5 Dry the test sample to constant weight at a temperature of 105-115 oc, cool in air at room temperature 1-3 hrs, or until the aggregate has cooled to a temperature that is comfortable to handle, and weigh.

6. Measurement Data:

Description Var. Weight in gm

Weight of oven dry sample in air A 980.1

Weight of saturated -surface dry sample in air B 1012.5

Weight of saturated -surface dry sample in water C 647.5

7. Calculations and computations:

7.1 Specific Gravity:

7.1.1 Bulk Specific Gravity:

Bulk sp. gr. =

7.1.2 Bulk Specific Gravity (SSD):

Bulk sp. gr. (SSD) =

= 2.77

7.1.3 Apparent Specific Gravity:

Apparent sp. gr. =

= 2.95

7.2 Percentage of absorption:

Absorption, %=

= 3.31%

8. Results of Computation:

No. Description Value

8.1 Bulk sp. Gr 2.69

8.2 Bulk sp. gr. (SSD) 2.77

8.3 Apparent sp. gr. 2.95

8.4 Absorption, % 3.31%

24


The apparent specific gravity, which is 2.95, is a bit higher than the range for common rocks. This amount shall be used for mix design since density of aggregate including impermeable pores is sufficient for mix design. Though the absorption is a bit higher (<3% which limits in BS standard), the aggregate can be used for normal concrete as there is no freezing thawing problem in Ethiopia. However, the moisture content should be adjusted while mix designing.

10. Frequently Asked Questions (FAQ):

a) Does hardness affect specific gravity of an aggregate?

[Answer]

Hardness depends on mainly on porosity and chemical and mineralogical composition of the parent rock. Density of aggregate also depends on porosity of aggregate. Thence, it can be said that hardness can affect specific gravity of aggregate.

b) Why should we test coarse aggregate sample for absorption?

[Answer]

Moisture absorption of coarse aggregate is very important to adjust aggregate weight in mix design of concrete i.e. it tells us how much extra water is needed to bring the aggregate to saturated surface dry (SSD), which is the basis for mix design. It is also indirect measure of permeability of the aggregate which, in turn, can relate to physical characteristic such as mechanical strength, shrinkage, soundness and durability potential.

c) Why should we test the value of specific gravity of a coarse aggregate?

[Answer]

Determination of specific gravity of a coarse aggregate has number advantages: it used for mix design when absolute volume method, which is more exact than mass method; it tells indirectly the strength, porosity and hardness of aggregate.

d) What are the limits for the values of specific gravity and absorption of good aggregate?

The apparent specific gravity for many commonly used rocks ranges between 2.6 and 2.7; typical values for granite, sandstone and dense limestone are 2.69, 2.67, and 2.60, respectively.1

Generally there is no limit for absorption of aggregate. Limits generally will not be set unless absorption is related to some undesirable properties such as frosting. Water absorption greater than 1% is susceptible to frosting. BS standard recommends that absorption should not generally

1 Concrete Microstructure, Properties, and Materials, page 268

25

be greater than 3%. However, absorption less than 1% can reasonably be considered as low absorption.

26

VI-Determination of Bulk Density of Coarse Aggregate

1. Scope:

The aim of this test is to determine the bulk density in coarse aggregate.

2. Theory: The bulk density of an aggregate is the mass of the aggregate divided by the volume of

particles and the voids between particles. The unit weight effectively measures the volume

that the graded aggregate will occupy in concrete and includes both the solid aggregate

particles and the void between them. The bulk density is used in estimating quantities of

materials and in some mixture proportioning calculations.

3. Apparatus: 3.1. Cylindrical metal container

3.2. Balance, accurate to 0.2 % of the mass of the material to be weighed and adequate

capacity.

3.3. Straight metal tamping rod, of circular cross section, 16 mm in diameter 600mm

long.

4. Condition of sample: The test for bulk density was made on saturated surface dry material (coarse aggregate).

5. Procedure:

First we filled the container about one third full with the thoroughly mixed coarse aggregate by means of a shovel. Then we gave the required number of compact blows (40 times) to the aggregate, each blow being given by allowing the tamping rod to fall freely from a height 50 mm above the surface of the aggregate, the blows being evenly distributed over the surface. Then we added a further similar quantity of aggregate in the same manner and gave the same number of blows. Finally we filled the container to over flowing, tamped it again with the same number of blows, and removed the surplus aggregate by rolling the tamping rod across and in contact with the top of the container, any aggregate which impedes its progress being removed by hand, and added the aggregate to fill any obvious depressions. Then we determined the mass of the aggregate in the container.

27


BULK DENSITY OF COARSE AGGREGATE

No Calibrated

volume of

container

Weight of

container

Weight of

container plus

aggregate

Weight of

aggregate

Bulk density

(Kg/m3)

1 0.03m3 18Kg 65Kg 47Kg 1566.67

Bulk density (roded unit weight) is calculated as Follows

Bulk density (Roded Unit Weight) = ass of ggregate

olu e of ontainer =

= 1566.67kg/m3

7. Conclusion:

Most natural mineral aggregates, such as sand and gravel, have a bulk density of 1520 to

1680 kg/m3 and produce normal weight concrete with approximately 2400 kg/m3 unit

weight. For special needs, aggregates with lighter or heavier density can be used to make

correspondingly lightweight and heavyweight concretes. Generally, the aggregates with

bulk densities less than 1120 kg/m3 are called lightweight and those weighing more than

2080 kg/m3 are called heavy weight. Hence, our sample represents a medium weight

aggregate.

8. Question:

What are the factors that will affect bulk density of aggregate?

[Answer]

The bulk density depends on how densely the aggregate is packed and, consequently, on

the size distribution and shape of the particles; because the volume is occupied by

aggregates and voids.

28

VII-Determination of Bulk Density of Fine Aggregate

1. Scope: The aim of this test is to determine the bulk density in fine aggregate (sand).

2. Theory: Bulk density of fine aggregate is the weight of aggregate occupying a unit overall

volume of both the particles and the air voids between them. It is measured by

weighing a container of known volume filled with aggregate. The value will clearly

depend on the grading, which will govern how well the particles fit together, and also

on how well the aggregate is compacted.

3. Apparatus: 3.1. Cylinderical metal container

3.2. Balance, accurate to 0.2 % of the mass of the material to be weighed and adequate

capacity.

4. Condition of sample: The test for bulk density was made on saturated surface dry sample of sand.

5. Procedure: First we measure the weight of an empty container having a volume of 0.003m3. Then,

we fill the empty container with the sample of sand and weighted it with a balance.


BULK DENSITY OF FINE AGGREGATE

No Calibrated volume

of container

Weight of

container

Weight of

container plus

aggregate

Weight of

aggregate

Bulk density

(Kg/m3)

1 0.003m3 3kg 7.5Kg 4.5Kg 1500

Bulk density (roded unit weight) is calculated as Follows

Bulk density (Roded Unit Weight) = ass of and

olu e of ontainer =

= 1500 kg/m3

29

VIII-Test Method for the determination of compressive strength of concrete

1. Scope:

To determine the cube compressive strength of concrete that is casted 28 days ago for SATCON construction building project.

2. Theory:

The compressive strength of concrete is one of its most important and useful properties of

concrete. In most structural applications, concrete is employed primarily to resist

compressive stresses. The compressive strength is used as a measure of overall quality of

the concrete.

3. Apparatus:

Cube moulds 150 mm is size, weighing machine, mixer, tamping rods, compression testing machine.

Moulds for cube Test: These should be of steel or cast iron. The internal faces should be machined flat to a tolerance of 0.025 mm. All interior angles between internal faces should be 90 0.50. A base plate with machined plane surface, large enough to prevent leakage of cement slurry during filling of the mould should be provided. Spring clips or screws should be supplied to assist in holding the mould on the base plate.

4. Procedure:

Compression test of cube are made as soon as practicable after removing from curing tank. Test specimens during the period of their removal from the curing pit and testing are kept moist by a wet mat covering and tested in moist condition. The size of the specimens is determined to the nearest 0.2 mm by averaging the particular dimensions, at least at two places. The length of the cylinder including caps is measured to the nearest 0.2mm, The weight of each specimen is also recorded.

Place central the specimen in the compression-testing machine and load is applied continuously, uniformly and without shock. The load is increased until the specimen fails. Record the maximum load taken by each specimen during test. Also note the type of failure and appearance of cracks.

30

5. Observations and Calculations:

The following information is normally included in the report of each compression test.

Table 1

A Age of Specimen 28 days

B Curing Condition wet

C Dimensions of specimen 15x15x15

D Cross sectional area 0.0225

Table -2

Specimen No. 1 2 3 Average

Load on Cube (KN) 712.3 884.5 836.9 811.2

Weight of specimen (Kg) 8.6 8.4 8.6

specimencubeoftioncrossofArea

LoadAveragestrengthCube

sec

= 811.2/(0.0225)

=36Mpa

6. Conclusion:

The permissible variation in strength of a specimen while taking the average is 12%, 3%

and 8% respectively which shows that even though, the specimen satisfy the average

strength the deviation between specimens is large which is to mean not good quality of

concrete.

31

IX-Test Method for the determination of Moisture Content of Coarse Aggregate

1. Scope:

This is method covers the determination of moisture content of course aggregate by oven-dry method.

This method is sufficiently accurate for usual purpose such as adjusting batch weights of concrete. It will generally measure the moisture in the test sample more reliably than the sample can be made to represent the aggregate supply.

2. Definition:

Moisture content is the total amount of water present in the aggregate. I.e. both internally inside the pores and externally at the surface.

3. Apparatus:

Balance of suitable capacity, readable and accurate.

Containers, airtight, non-corrodible, of capacity suitable to the mass of the test portion.

Well ventilated oven, thermostatically controlled to maintain a temperature of 105 50c.

Means of reducing the laboratory sample, either metal tray for use in quartering or a riffle box.

4. Procedure:

We have Clean a container, dry it and then weigh it and tarred it (that is neglecting the weight of the container). Place the moisten sample prepared and weigh the whole (M1). And it becomes 1937.3gm.

We have Place the container with test portion in the oven and dry at a temperature 105 50c. And we have maintained this temperature until the test portion has reached a constant mass for 24hr.

We have removed the container and test portion from the oven and allow the whole to cool for 1hr, after which weigh again (M2). And it becomes 1837.7gm.

5. Observation and Calculation

Calculate the moisture content as a percentage of the dry mass from the following equation.

100)(

)21(

1

xM

MMcontentMoisture

32

Moisture Content =100

)3.1937(

)7.18373.1937(x

= 5.14%

6. Conclusions and recommendation:

The aggregate is in a wet or damp condition because it has free moisture, so when we use

the aggregate for any concrete making purpose we have to subtract the calculated volume

of water from the water to be mixed in the proportion.

33

X-Silt content of fine aggregate

1. Object:

To determine the silt content of a fine aggregate sample:

2. Theory:

It is important to use clean aggregate for concrete. If the aggregates are coated with dirt, silt or clay, it will result in a poor concrete because the dirt will prevent the cement from setting and also weaken the bond between the aggregates and the cement paste.

In the hand test, simply pick up a little sample of sand and rub it between your hands. If your palm stays clean the sand is alright from the cleanliness point of view. If it stained, something is wrong and you must proceed to perform the silt test.

3. Apparatus:

Measuring cylinder of 200 cc capacity, Salt (NaOH)

4. Procedure:

a) Fill a measuring cylinder with sand up to 100 cc mark and add water up to 150cc. To perform this test, more correctly better dissolve a little salt in the water (1 test spoonful to 250cc is the right proportion).

b) Shake the sample vigorously for one minute and the last few shakes being in a side wise direction to level off the sand.

c) Allow The cylinder to stand for three hours during which time any silt present will settle in a layer on the top of the sand and its thickness can be read off on the cylinder itself. There should not be more than 6cc of silt or about 6 to 10 percent of the amount of the sand.

5. Measurement from the test:

Layer Height (mm)

Sand+Silt 55

Silt 4

34

6. Calculations:

Silt content by volume = height of silt / (height of silt + sand)*100%

=4/55*100%

=7.27%

Or alternatively, converting the volumes to respective weights

Where hs, ha, γs, and γa are height of sand, height of aggregate, specific gravity of silt and

specific gravity of aggregate(fine) respectively.

Visually the silt is silty clay and the specific gravity may be taken as 1.26 and the sand

specific gravity may be taken as 2.6. Thence,


The silt content acceptable limit is usually between 5% and 10% by mass but the sand must be washed to be used for concrete. If the silt content is below 5%, the sand can be used without washing.

The approximate silt content by mass is 3.66% which is less than 5% and can be used for concrete without washing.

However, according to BS 882:1965, the clay and silt content should not be more than:-

15% of the total weight for crushed sand

3 % of the total weight for sand

1% of the total weight for aggregate

Consequently, if the sand is to be used for sensitive structures, it is highly recommended that the sand be washed before using for concreting.

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