The fineness of cement is a measure of the mean size of grains of the cement. There are majorly three methods of measurement of fineness. The first is the sieve analysis method. The second is the Air-permeability method and the third is the Wagner turbiditimeter method.
In sieve analysis, the grain size of the cement particle is measured. Air-permeability and Wagner turbiditimeter methods measure the surface area.
Importance of fineness of cement
- Finer the cement more will be the strength. Because a larger surface area will be available for hydration of the cement.
- With the increase in fineness of cement, the initial strength of the cement increases but the final strength will remain the same.
- Finer cement is more cohesive thus requires less water. Due to less amount water requirement, bleeding reduces.
- However, if the cement is ground beyond a certain limit, pre-hydration due to atmospheric moisture occurs.
- Finer cement reacts more strongly in alkali reactive aggregate.
Conditions affecting fineness
Chemical composition and the temperature at which cement is burnt affects the hardness of the clinker which affect the fineness of the cement particle. Fineness of cement also depends on the grinding/pulverizing machines. Also cement becomes finer with age if not affected by the atmospheric moisture.
Procedure by Sieve analysis method
- Cement shall be free from the lumps. If any lump is present, rub the cement and make it lump-free.
- Take 10 g of cement sample and place it on the 90-micron sieve. Care should be taken to avoid the loss of cement.
- Disperse any agglomerates if present and fit the lid over the sieve.
- Shake the sieve for 15 minutes. You can swirl the sieve and can give planetary and linear movements until no fine material passes through it.
- Now, weigh the residue retained on the sieve and calculate the percentage of cement retained in the sieve.
- Repeat the procedure with fresh 10 g cement and calculate the percentage retained.
- If the percentage by the two tests differ more than 1% then, carry out third sieving.
- Take the mean of the three tests. The percentage retained is expressed to the two decimal values.
Demerits of Sieve analysis method
Since the sieve analysis is done with a 90-micron sieve. We cannot determine the true mean size of cement. In other words, the actual mean size of cement particles is not known. Also tiny cement particles conglomerates thus actual true size can’t be determined.
|Type of cement||Percentage of the residue by weight|
|Ordinary Portland Cement (OPC)||10|
|Rapid Hardening Cement (RHC)||5|
|Portland Pozzolona Cement (PPC)||5|