5.4
Consider a sample of fine aggregates being sieved through a standard set of sieves. Note the weight of aggregates retained on each sieve.
Calculate the cumulative weight of aggregates retained on each sieve and express it as a percentage of the total sample weight.
If, for instance, all the particles are retained on or above a particular sieve, and nothing passes through it, the cumulative percentage retained for that sieve and those stacked underneath it is entered as 100.
The fineness modulus is calculated by summing the cumulative percentage retained on each sieve and dividing the total by 100.
The fineness modulus is a numerical index that represents the grading of aggregates.
When aggregates from the same source are used, slight variations in the gradation of fine aggregates are less visually obvious than with coarse aggregates.
These differences will be reflected in the fineness modulus value, which will be more insightful for fine aggregates than coarse aggregates.
Typically, the value of the fineness modulus for fine aggregates ranges from 2.3 to 3.1; the higher the value, the coarser the aggregates.
The fineness modulus (FM) of aggregate is a numerical index that measures the coarseness or fineness of the particles. It is calculated by adding the cumulative percentages of aggregate retained on each of a specified series of sieves and dividing the sum by 100.
Consider performing sieve analysis on sand through a set of ASTM sieves. The weight of aggregate retained in each sieve and pan placed at the bottom is recorded, as given in Column B of Table 1.
To determine the fineness modulus of sand, calculate the cumulative weight of aggregate retained on each sieve (Column C of Table 1) and express it as a percentage of the total weight (Column D of Table 1). Finally, the sum of the cumulative percentages of aggregate retained on each sieve is determined and multiplied by 100 to obtain the fineness modulus of the sand.
Table 1: Sieve analysis on sand
| Column A | Column B | Column C | Column D |
| ASTM Sieve | Weight retained on each sieve (g) | Cumulative weight retained on each sieve (g) | Cumulative percentage retained on each sieve (%) |
|
⅜ inch | 0 | 0 | 0 |
| No. 4 | 5 | 0+5 = 5 | 5/500 = 1 |
| No. 8 | 55 | 5+55 = 60 | 60/500 = 12 |
| No. 16 | 65 | 60+65 = 125 | 125/500 = 25 |
| No. 30 | 90 | 125+90 = 215 | 215/500 = 43 |
| No. 50 | 160 | 215+160 = 375 | 375/500 = 75 |
| No. 100 | 90 | 375+90 = 465 | 465/500 = 93 |
| Bottom pan | 35 | Total weight = 465+35 = 500 |
In general, sand has a fineness modulus of around 2.3 to 3.1. Lower values indicate finer sand, while higher values mean the sand is more coarse.
Consider a sample of fine aggregates being sieved through a standard set of sieves. Note the weight of aggregates retained on each sieve.
Calculate the cumulative weight of aggregates retained on each sieve and express it as a percentage of the total sample weight.
If, for instance, all the particles are retained on or above a particular sieve, and nothing passes through it, the cumulative percentage retained for that sieve and those stacked underneath it is entered as 100.
The fineness modulus is calculated by summing the cumulative percentage retained on each sieve and dividing the total by 100.
The fineness modulus is a numerical index that represents the grading of aggregates.
When aggregates from the same source are used, slight variations in the gradation of fine aggregates are less visually obvious than with coarse aggregates.
These differences will be reflected in the fineness modulus value, which will be more insightful for fine aggregates than coarse aggregates.
Typically, the value of the fineness modulus for fine aggregates ranges from 2.3 to 3.1; the higher the value, the coarser the aggregates.
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