Fineness Modulus of Coarse aggregate

Objective:

To find mean size of particle in coarse aggregate.

What is Fineness modulus of Coarse aggregate?

Fineness modulus of coarse aggregate is a index number, which represent the mean size of particle in coarse aggregates.

Fineness modulus is found by performing the sieve analysis.

The formula to find out the fineness modulus is, all the sum of percentage cumulative retention of each sieve divided by 100, provides values of Fineness modulus.

Fineness modulus

Determination of Fineness modulus of coarse aggregates:

Test to find out Fineness modulus of Coarse Aggregates:

Generally, sieve analysis is done to find out fineness modulus of Coarse Aggregates as well as coarse aggregate. (As per IS 2083 Part 4)

IS Code for Fineness Modulus of Coarse AggregatesIS : 383 -1970

Sample Preparation:

Take the aggregates sample of exact 1kg by weighing it. (Make sure that all aggregates should be oven dried at 110℃ before measurement) and note down the measurement as W1 (1kg or 1000gm)

Sieve Analysis: Test procedure (IS : 2386 (Part 1) and IS : 2386 (Part 4))

Apparatus:

  • Different type of sieves (As per IS standards)
  • Weighing Balance (Accuracy upto 0.01gm)
  • Mechanical Sieve shaker
  • Oven

Procedure:

Following steps are need to follow for sieve analysis:

  1. Take the aggregates sample of exact 1kg by weighing it. (Make sure that all aggregates should be oven dried before measurement) and note down the measurement as W1 (1kg or 5000gm)
  2. If the particles are lumped then crush the lumps with hand or pestle.
  3. Weigh all the empty sieves and record their weight in gms.
  4. Prepare the all sieves for testing by dusting all. And stack them all together with respect to their size. Note that the largest sieve size should be at top and smallest at bottom by arranging them in descending order, it shall collect the sieved samples from above sieve.
  5. Place the sample(W1), in top most sieve close the lid, pack the sieve stacker by fixing the clamps.
  6. And start mechanical sieve shaker for 10 to 15 minutes. And switch it off after the rotating period.
  7. Unpack the all sieves and measure the mass of each sieve to find out the weight of retain aggregates on each sieve.
  8. Calculate the wright of retained material on each sieve by subtracting the empty weight of that particular sieve.
  9. Analysis the all readings. Make sure that sum of all retained material should be equal to weight of sample taken.
  10. Calculate the cumulative percentage of retention on each sieve.

Data Recording and Calculations:

Sample Details:______________

Sample weight taken(W):  __________gms

Day & date:_______

Time:______________

Table for Reading Reference: (Coarse Aggregates only)

Sr. No.Sieve Size  Sieve numberWeight Retained (gm)Cumulative weight retained (gm)Percentage weight retainedPercentage weight passing
     (C/W) x100 
180mm10000100
240mm9200200595
320mm81270147036.7663.24
410mm72100350087.512.5
54.75mm6143050001000
62.36mm5050001000
71.18mm4050001000
80.6mm3050001000
90.3mm2050001000
100.15mm1050001000
    Total729.36 

Fineness modulus of Coarse Aggregate = Sum of cumulative percentage retained/ 100 = 729.36/100= 7.29

Therefore, the Fineness modulus of Coarse Aggregate is 2.76.

Result:

The Fineness modulus of coarse aggregates is 2.76.

  • It means the mean size of particle in Coarse Aggregate is between the 7th and 8th sieve.
  • It simply means the average or mean particle size of Coarse Aggregate lies is in between 10mm to 20mm.

General range of Fineness modulus of Coarse aggregate:

Maximum size of coarse aggregateFineness modulus range
20mm6.0 – 6.9
40mm6.9 – 7.5
75mm7.5 – 8.0
150mm8.0 – 8.5

 Grading Limit for Coarse Aggregates: (Based on Clause 4.1 and 4.2 of IS: 383- 1970)

IS SievePercentage passing for single sized aggregates of nominal size(mm)
63 mm40 mm20 mm16 mm12.5 mm10 mm
80 mm100
63 mm85 – 100100
40 mm0 – 3085 – 100100
20 mm0 – 50 – 2085 – 100100
16 mm85 – 100100
12.5 mm85 – 100100
10 mm0 – 50 – 50 – 200 – 300 – 4585 – 100
4.75 mm0 – 50 – 50 – 100 – 20
2.36 mm0 – 5

 

Read more on: Grading of aggregates>>>

 

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