Determination of Flakiness Index and Elongation Index of Coarse Aggregates

Objective : To determination of Flakiness Index and Elongation Index of Course Aggregates.

Reference : IS : 2386 ( Part I) – 1963, IS: 383-1970, IS : 460-1962

Theory : Particle shape and surface texture influence the properties of freshly mixed concrete more than the properties of hardened concrete. Rough-textured, angular, and elongated particles require more water to produce workable concrete than smooth, rounded compact aggregate. Consequently, the cement content must also be increased to maintain the water-cement ratio. Generally, flat and elongated particles are avoided or are limited to about 15 % by weight of the total aggregate.

Apparatus :
The metal gauge shall be of the pattern shown in Fig. 10.1 & 10.2, Balance.

Procedure :
1. Sample - A quantity of aggregate shall be taken sufficient to provide the minimum number of 200 pieces of any fraction to be tested.

2. Sieving - The sample shall be sieved in accordance with the method described in with the sieves specified in Table 3.18.

3. Separation of Flaky material- Each fraction shall be gauged in turn for thickness on a metal gauge of the pattern shown in Fig. 10.1, or in bulk on sieves having elongated slots. The width of the slot used in the gauge or sieve shall be of the dimensions specified in co1umn 3 of Table 3.18 for the appropriate size of material.

4. Weighing of Flaky Material - The total amount passing the gauge shall be weighed to an accuracy of at least 0.1 percent of the weight of the test sample.

5. The flakiness index is the total weight of the material passing the various thickness gauges or sieves, expressed as a percentage of the total weight of the sample gauged.

6. Sieving - The sample shall be sieved in accordance with the method described in with the sieves specified in Table 3.18.

7. Separation of Elongated Material- Each fraction shall be gauged individually for length on a metal length gauge of the pattern shown in Fig. 10.2. The gauge length used shall be that specified in co1 4 of Table 3.18 for the appropriate size of material.

8. Weighing of Elongated Material - The total amount retained by the length gauge shall be weighed to an accuracy of at least 0.1 percent of the weight of the test sample.

9. The elongation index is the total weight of the material retained on the various length gauges, expressed as a percentage of the total weight of the sample gauged.

Figure :

                                                               figure 10.1

                                                               figure 10.2

Observation :
1. Total weight of course aggregate. . . . . . . g (Flakiness Index)

2. Total weight of course aggregate. . . . . . . g (Elongation Index)

Calculation :

Conclusion / Result :
i) The flakiness index of a given sample of fine aggregate is ………. %
ii) The elongation index of a given sample of fine aggregate is ……..%

Limits :
The combined FI+EI permissible as per IS 383 for construction work is 40%.

Gradation of Coarse Aggregates

Objective : To determination of particle size distribution of coarse aggregates by sieving or
screening.

Reference : IS : 2386 ( Part I) – 1963, IS: 383-1970, IS : 460-1962

Theory :
Grading refers to the determination of the particle-size distribution for aggregate. Grading limits and
maximum aggregate size are specified because grading and size affect the amount of aggregate used as well as cement and water requirements, workability, pumpability, and durability of concrete. In general, if the water-cement ratio is chosen correctly, a wide range in grading can be used without a major effect on strength. When gap-graded aggregate are specified, certain particle sizes of aggregate are omitted from the size continuum. Gap-graded aggregate are used to obtain uniform textures in exposed aggregate concrete. Close control of mix proportions is necessary to avoid segregation.

Apparatus :
Test Sieves conforming to IS : 460-1962 Specification of 80 mm, 40 mm, 20 mm, 10 mm, 4.75 mm, Balance, Gauging Trowel, Stop Watch, etc.

Procedure :
1. The sample shall be brought to an air-dry condition before weighing and sieving. This may be achieved either by drying at room temperature or by heating at a temperature of 100‖ to 110°C. The air-dry sample shall be weighed and sieved successively on the appropriate sieves starting with the largest. Care shall be taken to ensure that the sieves are clean before use.

2. Each sieve shall be shaken separately over a clean tray until not more than a trace passes, but in any case for a period of not less than two minutes. The shaking shall be done with a varied motion, backward sand forwards, left to right, circular clockwise and anti-clockwise, and with frequent jarring, so that the material is kept moving over the sieve surface in frequently changing directions.

3. Material shall not be forced through the sieve by hand pressure. Lumps of fine material, if present, may be broken by gentle pressure with fingers against the side of the sieve.

4. On completion of sieving, the material retained on each sieve, together with any material cleaned from the mesh, shall be weighed.

Observation :

Conclusion / Result :
The results may be observed with the below table

Determination of Specific Gravity of Coarse Aggregate

Objective : To determine specific gravity of a given sample of course aggregate.

Reference : IS : 2386 ( Part III ) - 1963

Apparatus :
A wire basket of not more than 6-3 mm mesh, A stout watertight container in which the basket may be freely suspended, well-ventilated oven, Taping rod, An airtight container of capacity similar to that of the basket, etc.

Figure : 

Procedure :
1. A sample of not less than 2000 g of the aggregate shall be thoroughly washed to remove finer particles and dust, drained and then placed in the wire basket and immersed in distilled water at a temperature between 22°C to 32°C with a cover of at least 5 cm of water above the top of the basket.

2. Immediately. after immersion the entrapped air shall be removed from the sample by lifting the basket containing it 25 mm above the base of the tank and allowing it to drop 25 times at the rate of about one drop per second. The basket and aggregate shall remain completely immersed during the operation and for a period of 24 ± l/2 hours afterwards.

3. The basket and the sample shall then be jolted and weighed in water at a temperature of 22°C to 32°C (weight A1).

4. The basket and the aggregate shall then be removed from the water and allowed to drain for a few minutes, after which the, aggregate shall be gently emptied from the basket on to one of the dry clothes, and the empty basket shall be returned to the water and weighed in water ( weight A2 ).

5. The aggregate placed on the dry cloth shall be gently surface dried with the cloth, transferring it to the second dry cloth when the first will remove no further moisture. The aggregate shall then be weighed (weight B).

6. The aggregate shall then be placed in the oven in the shallow tray, at a temperature of 100 to 110°C and maintained at this temperature for 24 ± l/2 hours. It shall then be removed from the oven, cooled in the airtight container and weighed (weight C).

7. Calculations— Specific gravity, apparent specific gravity and water &sorption shall be calculated as follows:

A = Weight of saturated aggregate in water = (A1-A2)
B = Weight of the saturated surface - dry aggregate in air
C = Weight of oven dried aggregate in air
A1 = Weight of aggregate and basket in water
A2 = Weight of empty basket in water

Conclusion / Result :
i) The Specific Gravity of a given sample of course aggregate is found to be …….

ii) The Water Absorption of a given sample of course aggregate is found to be ……. %

Determination of Specific Gravity of Fine Aggregate

Objective : To determine specific gravity of a given sample of fine aggregate.


Reference :  IS : 2386 ( Part III ) - 1963

Apparatus : Pycnometer, A 1 000-ml measuring cylinder, well-ventilated oven, Taping rod, Filter papers and funnel, etc.

Figure :

Procedure :

1. A sample of about 500 g shall be placed in the tray and covered with distilled water at a temperature of 22 to 32°C. Soon after immersion, air entrapped in or bubbles on the surface of the aggregate shall be removed by gentle agitation with a rod. The sample shall remain immersed for 24 ± l/2 hours.

2. The water shall then be carefully drained from the sample, by decantation through a filter paper, any material retained being return& to the sample. The fine aggregate including any solid matter retained on the filter paper shall be exposed to a gentle current of warm air to evaporate surface moisture and the material just attains a ‗free-running‘ condition. The saturated and surface-dry sample shall be weighed (weight A).

3. The aggregate shall then be placed in the pycnometer which shall be filled with distilled water. Any trapped air shall be eliminated by rotating the pycnometer on its side, the hole in the apex of the cone being covered with a finger. The pycnometer shall be dried on the outside and weighed (weight B).

4. The contents of the pycnometer shall be emptied into the tray, care being taken to ensure that all the aggregate is transferred. The pycnometer shall be refilled with distilled water to the same level as

before, dried on the outside and weighed (weight C).

5. The water shall then be carefully drained from the sample by decantation through a filter paper and

any material retained returned to the sample. The sample shall be placed in the oven in the tray at a

temperature of 100 to 110°C for 24 f l/2 hours, during which period it shall be stirred occasionally to

facilitate drying. It shall be cooled in the air-tight container and weighed (weight D).

6. Calculations— Specific gravity, apparent specific gravity and water &sorption shall be calculated as follows:

A = weight in g of saturated surface - dry sample,

B = weight in g of pycnometer or gas jar containing sample and filled with distilled water,

C = weight in g of pycnometer or gas jar filled with distilled water only, and

D = weight in g of oven - dried sample.

Conclusion / Result : 

i) The Specific Gravity of a given sample of fine aggregate is found to be …….

ii) The Water Absorption of a given sample of fine aggregate is found to be ……. %

Determination of Silt Content in Fine Aggregate

Objective : To determine silt content in a given sample of fine aggregate by sedimentation
method.

Reference : IS : 2386 ( Part II ) - 1963

Theory :
This is a gravimetric method for determining the clay, fine silt and fine dust, which includes particles up to 20 micron. Differences in the nature and density of materials or in the temperature at the time of testing may vary the separation point.

Apparatus :
A watertight screw-topped glass jar of dimensions similar to a 1-kg fruit preserving jar, A device for rotating the jar about its long axis, with this axis horizontal, at a speed of 80 ± 20 rev/min, A sedimentation pipette, A 1000-ml measuring cylinder, scale, well-ventilated oven, Taping rod etc.

Chemical :
A solution containing 8 g of sodium oxalate per liter of distilled water shall be taken. For use, this stock solution is diluted with distilled water to one tenth (that is 100 ml diluted with distilled water to one liter).

Figure: 

Procedure :

1. Approximately 300 g of the sample in the air-dry condition, passing the 4.75-mm IS Sieve, shall be weighed and placed in the screw-topped glass jar, together with 300 ml of the diluted sodium oxalate solution. The rubber washer and cap shall be fixed, care being taken to ensure water tightness.

2. The jar shall then be rotated about its long axis, with this axis horizontal, at a speed of 80 ± 20

rev/min for a period of 15 minutes.

3. At the end of 15 minutes, the suspension shall be poured into the 1 000-ml measuring cylinder and

the residue washed by gentle swirling and decantation of successive 150-ml portions of sodium

oxalate solution, the washings being added to the cylinder until the volume is made up to 1000 ml.

4. The suspension in the measuring cylinder shall be thoroughly mixed by inversion and the tube and

contents immediately placed in position under the pipette.

5. The pipette A shall then be gently lowered until the tip touches the surface of the liquid, and then

lowered a further 10 cm into the liquid.

6. Three minutes after placing the tube in position, the pipette A and the bore of tap B shall be filled by opening B and applying gentle suction at C.

7. A small surplus may be drawn up into the bulb between tap B and tube C, but this shall be allowed to run away and any solid matter shall be washed out with distilled water from E.

8. The pipette shall then be removed from the measuring cylinder and its contents run into a weighed

container, any adherent solids being washed into the container by distilled water from E through the

tap B.

9. The contents of the container shall be dried at 100 to 110°C to constant weight, cooled and weighed.

10. Calculations— The proportion of fine silt and clay or fine dust shall then be calculated from the

following formula:

W = weight in g of the original sample,

W = weight in g of the dried residue,

V = volume in ml of the pipette, and

0.8 = weight in g of sodium oxalate in one litre of the diluted solution

Conclusion / Result :

The clay, fine silt and fine dust content of given sample of fine aggregate is found to be ……. %

Limits :

As per IS 383 and CPWD permissible amount of silt in sand is 3% by mass and 8% by volume respectively.

Bulking of Sand

Determination of Bulking of Fine Aggregate

Objective : To determine bulking of a given sample of fine aggregate.

Reference : IS : 2386 ( Part III ) - 1963

Theory :

Free moisture forms a film around each particle. This film of moisture exerts what is known as surface tension which keeps the neighbouring particles away from it. Similarly, the force exerted by surface tension keeps every particle away from each other. Therefore, no point contact is possible between the particles. This causes bulking of the volume. It is interesting to note that the bulking increases with the increase in moisture content upto a certain limit and beyond that the further increase in the moisture content results in the decrease in the volume and at a moisture content representing saturation point, the fine aggregate shows no bulking.

Apparatus : Measuring jar, Taping rod etc.

Procedure :

1. Put sufficient quantity of the sand loosely into a container. Level off the top of the sand and pushing a steel rule vertically down through the sand at the middle to the bottom, measure the height. Suppose this is h1 cm.

2. Empty the sand out of the container into another container where none of it will be lost. Half fill the first container with water. Put back about half the sand and rod it with a steel rod, about 6 mm in diameter, so that its volume is reduced to a minimum. Then add the remainder of the sand and rod it in the same way.

3. The percentage of bulking of the sand due to moisture shall be calculated from the formula:

 

                                                                                                   

Conclusion / Result : Bulking of a given sample of fine aggregate is found to be ……. %                        

Gradation of fine aggregates

Sieve analysis of fine aggregates

Object - This method covers the procedure for the determination of particle size distribution of fine, coarse and all-in-aggregates by sieving or screening.

Reference - IS : 2386 ( Part I) – 1963, IS: 383-1970, IS : 460-1962.

Apparatus - Sieves of the sizes given in Table I, conforming to IS : 460-1962 Specification for Test Sieves ( Revised) shall be used.  

Theory : This is the name given to the operation of dividing a sample of aggregate into various fractions each consisting of particles of the same size. The sieve analysis is conducted to determine the particle size distribution in a sample of aggregate, which we call gradation. Many a time, fine aggregates are designated as coarse sand, medium sand and fine sand.

These classifications do not give any precise meaning. What the supplier terms as fine sand may be really medium or even coarse sand. To avoid this ambiguity fineness modulus could be used as a yard stick to indicate the fineness of sand. The following limits may be taken as guidance: Fine sand : Fineness Modulus : 2.2 - 2.6, Medium sand : F.M. : 2.6 - 2.9, Coarse sand : F.M. : 2.9 - 3.2. Sand having a fineness modulus more than 3.2 will be unsuitable for making satisfactory concrete.

Apparatus : Test Sieves conforming to IS : 460-1962 Specification of 4.75 mm, 2.36 mm, 1.18 mm, 600 micron, 300 micron, 150 micron, Balance.

Procedure :

1. The sample shall be brought to an air-dry condition before weighing and sieving. The air-dry sample shall be weighed and sieved successively on the appropriate sieves starting with the largest. Care shall be taken to ensure that the sieves are clean before use.

2. The shaking shall be done with a varied motion, backward sand forwards, left to right, circular clockwise and anti-clockwise, and with frequent jarring, so that the material is kept moving over the sieve surface in frequently changing directions.

3. Material shall not be forced through the sieve by hand pressure. Lumps of fine material, if present, may be broken by gentle pressure with fingers against the side of the sieve.

4. Light brushing with a fine camel hair brush may be used on the 150-micron and 75-micron IS Sieves to prevent aggregation of powder and blinding of apertures. 

5. On completion of sieving, the material retained on each sieve, together with any material cleaned from the mesh, shall be weighed. 

      Observation :

Calculation : Fineness modulus is an empirical factor obtained by adding the cumulative percentages of aggregate retained on each of the standard sieves ranging from 4.75 mm to 150 micron and dividing this sum by arbitrary number 100.

     Finess Modulus, FM = 

Conclusion / Result :

i) Fineness modulus of a given sample of fine aggregate is …….. that indicate Coarse sand/ Medium sand/ Fine sand.

ii) The given sample of fine aggregate is belong to Grading Zones I / II / III / IV 

Following Links are for your references: Sieve analysis and fineness modulus of fine aggregates