Determination of fineness modulus of fine aggregate

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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