Fineness Modulus

Definition

Fineness Modulus is a factor obtained by adding the total percentages by weight of an aggregate sample retained on each of a specified series of sieves and dividing the sum by 100. In the United States, the standard sieve sizes are No. 100 (150 µm), No. 30 (600 µm), No. 16 (1.18 mm), No. 8 (2.36 mm), No. 4 (4.75 mm), and ⅜ in. (9.5 mm), ¾ in. (19 mm), 1½ in. (38.1 mm), 3 in. (75 mm), and 6 in. (150 mm).

Purpose

The purpose of Fineness Modulus is to provide an index number that represents the mean size of the particles in a given aggregate sample. It helps in assessing the aggregate’s suitability for different types of construction work and mix designs.

Examples of Use

• Concrete Mix Design: Determining the appropriate proportions of fine and coarse aggregates.
• Quality Control: Ensuring the consistency and quality of aggregates used in construction projects.
• Asphalt Production: Adjusting the aggregate blend to achieve desired properties in asphalt mixtures.

Related Terms

• Aggregate: Materials such as sand, gravel, or crushed stone used in construction.
• Sieve Analysis: A test used to determine the particle size distribution of granular material.
• Grading: The process of categorizing aggregates based on their particle size distribution.

Notes

• The fineness modulus is not an absolute measure but a useful index for comparing the coarseness or fineness of aggregates.
• Aggregates with a high fineness modulus are coarser, while those with a low fineness modulus are finer.