The Fineness modulus of cement is an empirical figure obtained by adding the total percentage of the sample of an aggregate retained on each of a specified series of sieves, and dividing the sum by 100. The proportion of cement of which the grain sizes are larger than the specified mesh size is thus determined.
Fineness Modulus of Cement by Dry Sieving
- 90µm Sieve.
- Balance capable of weighing 10g to the nearest 10mg.
- Glass rod
- Stoppered jar
- Pan and Lid
Procedure to Determine Fineness of Cement
- Stir the sample of cement to be tested by shaking for 2 minutes in a stoppered jar to disperse lumps. Stir the resulting powder gently using a clean dry rod in order to distribute the fines throughout the cement.
- Attach a pan under the sieve to collect the cement passing the sieve.
- Weigh approximately 10 g of cement to the nearest 0.01 g and place it on the sieve. Fit the lid over the sieve.
- Shake the sieve by swirling, planetary and linear movement until no more fine material passes through it.
- Remove and weigh the residue. Express its mass as a percentage (R1) of the quantity first placed in the sieve.
- Repeat the steps 3 to 5 with a fresh sample to obtain R2.
- If the results differ by more than 1 percent absolute, carry out a third sieving and calculate the mean of the three values.
CalculationRavg = (R1+R2+R3) / 3 Fineness modulus of cement = Ravg/ 100 Importance of Cement Fineness
- The fineness of cement affects hydration rate, and in turn, the strength. Increasing fineness causes an increased rate of hydration, high strength, and high heat generation.
- Bleeding can be reduced by increasing fineness. However, increased fineness can also lead to the requirement of more water for workability, resulting in a higher possibility of dry shrinkage.
- The increased surface area-to-volume ratio will ensure a more available area for water-cement interaction per unit volume.