Question

What is the representative geometric mean size of an aggregate sample if its fineness modulus is 3.0?

• A. $150\mu m$
• B. $300\mu m$
• C. $600\mu m$
• D. $12\mu m$

Answer 1

The correct option is C $600\mu m$

The fineness modulus is a numerical index of fineness, giving some idea of the mean size of the particles present in the entire body of the aggregate. The sieves used in calculating fineness modulus are arranged in the following order as per IS : 2386 (Part-I)-1963 are 80 mm, 40 mm, 20 mm, 10 mm, 4.75 mm, 2.36 mm, 1.18 mm, $600\mu m,300\mu mand150\mu m$. The fineness modulus can be regarded as a weighted average size of a sieve on which material is retained, and the sieves being counted from the finest.
Here the fineness modulus of the sample is 3.0. It means that the third sieve i.e $600\mu m$ is the average size.