The Fineness modulus of cement is a value that is determined empirically. It involves adding up the total percentage of an aggregate sample that is retained on each sieve in a specified series, and then dividing the sum by 100. This calculation provides information about the proportion of cement particles that have a grain size larger than the designated mesh size.
To determine the Fineness modulus of cement, various sieves are used to sort the aggregate sample into different size fractions. The proportion of the sample that remains on each sieve is measured and recorded. By adding up the percentages retained on each sieve, the total amount of aggregate in the sample is determined. Dividing this sum by 100 yields the Fineness modulus of the cement, which provides insight into the particle size distribution of the cement.
Fineness Modulus of Cement by Dry Sieving
Apparatus
To perform a particle size analysis, a 90µm sieve, a balance with a 10g capacity and a precision of 10mg are required. Additionally, a glass rod can be used to assist with the sieving process. A stoppered jar can be used to contain the sample before and after sieving, and a pan and lid can be used to weigh the sample before and after sieving to determine the amount of material that passed through the sieve.
Fig 1: Fineness of cement test apparatus
Procedure to Determine Fineness of Cement
To test a sample of cement, it is necessary to first disperse any lumps by shaking it in a stoppered jar for 2 minutes. Once the lumps have been dispersed, a clean and dry rod should be used to gently stir the powder and distribute the fines evenly throughout the cement.
To collect the cement passing through the sieve, a pan should be attached underneath it. Approximately 10 grams of cement, accurate to within 0.01 grams, should be weighed and placed on the sieve. The lid should be fitted over the sieve, and then the sieve should be shaken using swirling, planetary, and linear movements until no more fine material passes through it.
After the sieve has been shaken, the residue should be removed and weighed. Its mass should be expressed as a percentage, R1, of the quantity that was originally placed on the sieve. This process should be repeated with a fresh sample to obtain R2. If the results differ by more than 1 percent absolute, it is necessary to carry out a third sieving and calculate the mean of the three values.
Calculation
The fineness of cement is a crucial factor that affects its performance in construction. One way to measure fineness is by calculating the average particle size of the cement particles using the Ravg formula, which is obtained by adding the values of R1, R2, and R3 and dividing them by three.
The fineness of cement plays a critical role in the hydration rate and the resulting strength of the concrete. When the cement particles are finer, they tend to hydrate more quickly, resulting in higher strength and increased heat generation during the hydration process.
Another advantage of having finer cement particles is that it can reduce the bleeding of water from the concrete mixture. However, it is important to note that increasing the fineness of cement can also require the use of more water for workability, which can result in a higher risk of dry shrinkage.
Furthermore, when the cement particles are finer, they provide a larger surface area-to-volume ratio, which increases the available area for water-cement interaction per unit volume. This increased interaction between water and cement particles leads to better bonding, resulting in stronger and more durable concrete structures.
In conclusion, the fineness of cement is an essential factor that affects the performance of concrete. The use of finer cement particles can lead to higher strength, reduced bleeding, and increased surface area for water-cement interaction. However, it is crucial to balance the fineness with the water-cement ratio to ensure proper workability and minimize the risk of dry shrinkage.