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.
- 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.
Ravg = (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.