The Fineness Modulus (FM) of aggregates can be an intimidating term, but it’s just an empirical value that describes the average size of particles in a sample of aggregate. It is not a precise value, as it provides a way to estimate the amount of aggregate needed to proportion mix designs.
The origins of the Fineness Modulus Concept were developed in 1918 by an American materials researcher named Duff Abrams.
It is a way of characterizing concrete aggregates, simplifying the gradation curve, and estimating the correct proportions to use in mix designs.
This term is a key component used in the concrete mix design to describe the gradation curve as well as the texture and uniformity of the material. The FM of fine aggregate (Sand) fraction is also an important indicator of other characteristics of both plastic and hardened concrete such as workability, finish ability, shrinkage, porosity, permeability, and strength.
ASTM C-33 requires the FM of fine aggregate to be between 2.3 and 3.1 with a variance of 0.2.
A typical mix design, fine aggregate may have a target FM of 2.7, the variance is then 2.5 to 2.9.
As a sand producer, this becomes a key production target.
If you are interested, you can choose this link to the article written by Ben Backus.
www.globalgilson.com/blog/fineness-modulus-of-concrete-aggregates
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