Particle Size Distribution
of Fine Aggregates is 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 : F.M. : 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.
AIM:
To determine fineness modulus of fine
aggregate.
Apparatus:
·
Test Sieves conforming to IS: 460-1962
o 4.75 mm,
o 2.36 mm,
o 1.18 mm,
o 600 micron,
o 300 micron,
o 150 micron
·
Balance,
·
Stop Watch.
FIGURE:
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:
I S Sieve
|
Weight Retained
on Sieve (gms)
|
Percentage of
Weight Retained
(%)
|
Percentage of
Weight Passing
(%)
|
Cumulative
Percentage of
Passing (%)
|
Remark
|
4.75
mm
|
|||||
2.36
mm
|
|||||
1.18
mm
|
|||||
600
micron
|
|||||
300
micron
|
|||||
150
micron
|
|||||
Total
|
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 anarbitrary number 100.
Finess
Modulus, FM = (Total of Cumulative Percentage of Passing (%) / 100)
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.
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