Fineness Modulus of Coarse Aggregates

The fineness modulus of coarse aggregates is an index value that indicates the average particle size in such aggregates.

The sieve analysis is used to determine the fineness modulus.

The fineness modulus can be calculated by dividing the total percentage cumulative retention of each filter by 100 to get its values.

In this article you’ll learn:

So, if you’re ready to go with a fineness modulus of coarse aggregates, this article is for you.

Let’s dive right in.

What is Fineness Modulus of Coarse Aggregates?

The fineness modulus of coarse aggregates uses an index number to reflect the average particle size in the coarse aggregate.

Using common sieves, sieve analysis is used to calculate it.

The value of a fine aggregate is calculated by adding and subtracting the cumulative percentage of material retained on each filter by 100.

The fineness modulus increases with aggregate size, hence coarse aggregate has a greater fineness modulus than the fine aggregate.

When an aggregate is sieved via a 4.75mm sieve, it is said to be coarse aggregate.

We require sieve sizes of 80mm, 40mm, 20mm, 10mm, 4.75mm, 2.36mm, 1.18mm, 0.6mm, 0.3mm, and 0.15mm to determine the fineness modulus of coarse aggregate.

When counting from lower-order sieve size to higher-order sieve, the fineness modulus is the value at which the average particle size is identified.

Therefore, all sizes of sieves are required in the calculation of coarse aggregate.

Determination of the Coarse Aggregates Fineness Modulus:

We need to do a sieve analysis in order to determine the fineness modulus, the mechanical shaker, digital weigh scale, and sieve sizes described are needed.

Preparing a sample:

Put a sample of coarse aggregate in a pan and heat the oven to between 100 and 110 degrees Celsius.

Once the sample has dried, weigh it to the closest gram.

Equipment:

• Various kinds of sieves (As per IS standards).
• A Weighing Scale (Accuracy up to 0.01gm).
• shaker for mechanical sieve.
• Oven.

Procedure:

For sieve analysis, the following procedures must be followed:

Weigh the aggregate sample to get an exact 1kg sample (Be sure to oven dry all aggregates prior to measurement). Record the measurement as W1 (1kg or 5000gm)

If the particles are aggregated, break them up with your hands or a mortar and pestle.

Weigh each empty sieve, then note its gram weight.

Dust each sieve in preparation for testing and arrange them all in a pyramid according to size.

Keep in mind that when placing them in descending order to find the fineness modulus, the greatest sieve size should be at the top and the smallest at the bottom.

This is done to gather the sieved samples from the top sieve.

Place the sample (W1) in the upper-most sieve, then secure the lid and load the sieve stacker.

For 10 to 15 minutes, start the mechanical sieve shaker and after the rotation period, turn it off.

To determine the weight of the retained aggregates on each sieve, unpack all of the sieves and weigh each one.

Subtract the empty weight of each sieve to determine the weight of material that has been kept on that particular sieve.

Analyse all of the readings.

Make the total amount of material retained is equal to the weight of the sample that was taken.

Determine the overall retention percentage for each sieve.

Calculations and Recording:

Sample Information:

Taken sample weight (W): __________gms.

Date:

Time: ______________

Reference Table for Reading: (Coarse Aggregates only)

Sieve size	Weight retained(g)	Cumulative weight retained (g)	Cumulative % retained (g)
80mm	0	0	0
40mm	250	250	5
20mm	1750	2000	40
10mm	1600	3600	72
4.75mm	1400	5000	100
2.36mm	0	5000	100
1.18mm	0	5000	100
0.6mm	0	5000	100
0.3mm	0	5000	100
0.15mm	0	5000	100
	Sum	=	717

As a result, the fineness modulus of coarse aggregates is equal to the sum (cumulative% retained) / 100 or (717/100), which equals 7.17.

A coarse aggregate sample with a fineness modulus of 7.17 indicates that the average particle size falls between the 7th and 8th sieves or between 10mm and 20mm.

Fineness Modulus Limits:

The coarse aggregate’s fineness modulus ranges from 5.5 to 8.0.

 Additionally, the fineness modulus for all aggregates or combination aggregates ranges from 3.5 to 6.5.

Below is a list of the fineness modulus ranges for various maximum-sized aggregates.

Maximum size of coarse aggregate	Fineness modulus range
20mm	6.0 – 6.9
40mm	6.9 – 7.5
75mm	7.5 – 8.0
150mm	8.0 – 8.5

Also read: Fineness Modulus of Fine Aggregate | Fineness Modulus of Cement

Conclusion:

The fineness modulus of coarse aggregates uses an index number to reflect the average particle size in the coarse aggregate.

Using common sieves, sieve analysis is used to calculate it.

The value of a fine aggregate is calculated by adding and subtracting the cumulative percentage of material retained on each filter by 100.