Sand (fine aggregate) has a fineness modulus, which is an index number that gauges the sand’s average particle size.
Sieve analysis with conventional sieves is used to compute it.
The fineness modulus is calculated by adding and subtracting the cumulative percentage retained on each filter by 100.
Material that goes through a 4.75mm screen is considered fine aggregate.
To determine the fineness modulus of fine aggregate, sieve diameters of 4.75mm, 2.36mm, 1.18mm, 0.6mm, 0.3mm, and 0.15mm are required.
The fineness modulus of finer aggregate is smaller than that of coarse aggregate.
In this article you’ll learn:
- Determination of the Fineness modulus of fine aggregates.
- Calculations of Fineness modulus of fine aggregates.
- Merits and Demerits of Fineness modulus of fine aggregates.
So, if you’re ready to go with the Fineness modulus of fine aggregates, this article is for you.
Let’s dive right in.
Determination Fineness Modulus (Sand) of Fine Aggregate Test:
Standard sieves, a mechanical sieve mixer (optional), a dry oven, and a digital weight scale are required to estimate the fineness modulus.
Preparation of the sample:
Place a sample of fine aggregates in a pan and place it in a dry oven set to 100 – 110oC.
Take the sample when it has dried and weighed it.
Procedure test Fineness modulus (Sand) of Fine Aggregate:
- Arrange the sieves in descending order with the biggest sieve on top.
- If a mechanical mixer is used, arrange the ordered sieves and pour the sample onto the top sieve before closing it with a sieve plate.
- After that, switch on the machine and shake the sieves for at least five minutes.
- Place the sample into the top sieve, close it, and shake the top two sieves inwards and outwards, vertically and horizontally.
- After some time, shake the third and fourth sieves, followed by the last sieves.
- During sifting, keep track of the sample weights on each sieve.
- Next, calculate the overall weight maintained.
- Finally, sum the percentage retained on each sieve.
- Add all cumulative percentage values and divide by 100 to get the fineness modulus value.
Calculation of Fineness Modulus of Fine Aggregate:
Assume the dry weight of the sample is 1000gm, the values obtained through sieve analysis are listed below:
|Sieve size||Weight retained (g)||Cumulative weight retained(g)||Cumulative percentage weight Retained (%)|
As a result, fineness modulus = (cumulative percent maintained) / 100 = (275/100) = 2.75.
The fine aggregate has a fineness modulus of 2.75.
It denotes that the aggregate’s average value is between the second and third sieves.
It signifies that the average aggregate size ranges from 0.3mm to 0.6mm.
Values Fineness Modulus of Fine Aggregate:
The fineness modulus ranges from 2.0 to 3.5mm, Its fineness moduli more than 3.2 should not be called fine aggregates.
The fineness modulus values for several grains of aggregates are shown below.
|Type of sand||Fineness modulus range|
|Fine aggregates||2.2 – 2.6|
|Medium aggregates||2.6 – 2.9|
|Coarse aggregates||2.9 – 3.2|
Fineness modulus limits for various zones of sand according to IS 383-1970 are tabulated below:
Advantages of Fineness Modulus of Fine Aggregate:
- The fineness modulus (FM) is used to calculate the ratios of fine and coarse particles in concrete mixtures.
- The course the aggregate, the greater the value of FM.
- A lower FM yields more paste, making the concrete easier to complete.
Disadvantages of Fineness Modulus of Fine Aggregate:
- The impact of sand fineness on concrete density.
- The effect of sand fineness on the compressive strength of concrete.
- Its effect of sand fineness on concrete flexural strength.
- The influence of sand fineness on concrete permeability
- Failures are typical at the contact between aggregate and mortar.
Also read: Types of Aggregates | Soil Classification
The fineness modulus of fine aggregate effects the compressive and flexural strength of concrete.
The cost-benefit ratio clearly shows that using sand with a higher FM makes the whole concrete mix more cost-effective.
The findings reveal that when FM increases, workability suffers significantly.