Fineness Modulus of Sand

F M = \frac{\sum cumulative % retained on specified sieves}{100}

FM uses sieves 4.75 mm down through 0.15 mm (No. 4–No. 100). Typical concrete sand FM is 2.3–3.1. Higher FM = coarser sand, needs less paste for the same slump but may finish poorly.

$F M$: Fineness modulus
: Cumulative percent retained

Step-by-step solved example

Cumulative % retained No.4 to No.100: 2, 15, 40, 70, 90, 97. FM?

Sieve stack: cumulative retained that defines FM.

1. Sum
2+15+40+70+90+97=314.
2. FM
314/100=3.14 (slightly coarse).

Answer: FM = 3.14

10 practice questions

0/10 correct

1.FM is dimensionless

2.Pan percent passing is not

3.Coarser sand has

4.If every cumulative is 0, FM=

5.Uniformity coefficient Cu is

6.ASTM C33 concrete sand FM typically

7.Six sieves summing to 270 give FM=

8.Replacing coarse sand with fine sand at the same w/c

9.Gap-graded agg can still have a numeric FM but

10.No. 200 sieve is about