Overview

Fineness of cement is measured by sieving it on standard sieve. The proportion of cement of which the grain sizes are larger than the specified mesh size is thus determined.

Apparatus

Measuring Instruments

 NAME CAPACITY / RANGE / SIZE ACCURACY / LEAST COUNT Sieve 90 micron mesh — Balance 10g (max.) 10 mg

Supplementary accessories

 Glass rod, stoppered jar, pan, lid

Procedure

1. Agitate the sample of cement to be tested by shaking for 2 minutes in a stoppered jar to disperse agglomerates. Stir the resulting powder gently using a clean dry rod in order to distribute the fines throughout the cement.
2. Attach a pan under the sieve to collect the cement passing the sieve.
3. Weigh approximately 10 g of cement to the nearest 0.01 g and place it on the sieve. Fit the lid over the sieve.
4. Agitate the sieve by swirling, planetary and linear movement until no more fine material passes through it.
5. Remove and weigh the residue. Express its mass as a percentage (R1) of the quantity first placed in the sieve.
6. Repeat the steps 3 to 5 with a fresh sample to obtain R2.
• Note :: If R1 & R2 differ by more than 1%, then carryout a third sieving and calculate R3.

Calculation

Calculate the residue of cement R as the mean of R1 & R2 (or R1, R2 & R3) in %, expressed to the nearest 0.1%.

Procedure To Check Sieve

1. Follow the steps (1 to 6) as mentioned earlier with a reference cement sample or certified reference material (i.e. CRM).
2. Calculate two values ‘P1’ & ‘P2’ and calculate mean ‘P’ of ‘P1’ & ‘P2’.
3. From the certificate of reference cement sample find out the known value of residue on 90 micron mesh sieve.
4. Calculate a correction factor as per the below mentioned formula.

Where

R0=Known value of residue as per reference material certificate.

P=Mean value of P1 & P2.

(The value of F may be 1.00±0.20)

5.  Multiply this correction factor ‘F’ with mean value of ‘R’

Precaution

• Before sieving, air set lumps of cement should be broken
• Sieving should be done by rotating the sieve and not by translation.

Technical Discussions

• Fineness of cement has a great effect on the rate of hydration and hence the rate of gain of strength.
• Fineness of cement increases the rate of evolution of heat.
• Finer cement offers a great surface area for hydration and hence faster the development of strength.
• Increase in fineness of cement also increases the drying shrinkage of concrete and hence creates cracks in structures.
• Excessive fineness requirement increases cost of grinding.
• Excessive fine cement requires more water for hydration, resulting reduced strength and durability.
• Fineness of cement affects properties like gypsum requirement, workability of fresh concrete & long term behavior of structure.
• Coarse cement particles settle down in concrete which causes bleeding.

Test Standard Reference

• IS:4031(Part 1):1996-Method of physical test for cement(Determination of fineness by dry sieving)