What Is Fineness Modulus of Sand?
The fineness modulus of sand, which is a type of fine aggregate, is a numerical index used to represent the average particle size of the sand. It is calculated by conducting a sieve analysis using standard sieves. In this process, the cumulative percentage of sand retained on each sieve is added together and subtracted from 100, resulting in the value of the fineness modulus.
Fine aggregate, as defined in this context, refers to sand that is able to pass through a sieve with a size of 4.75mm. To determine the fineness modulus of this fine aggregate, it is necessary to use sieves with sizes of 4.75mm, 2.36mm, 1.18mm, 0.6mm, 0.3mm, and 0.15mm.
It is worth noting that the fineness modulus of finer aggregates is lower than that of coarser aggregates. In other words, if the fineness modulus of a sand sample is low, it means that the sand particles are relatively small and fine, while a high fineness modulus indicates that the sand particles are larger and coarser.
Determination of Fineness Modulus of Sand
The fineness modulus can be calculated using several equipment and tools. Firstly, standard sieves are required to separate the different sizes of particles present in the sample. A mechanical sieve shaker can also be used to make the process more efficient, although it is not mandatory. The sample must then be dried in a dry oven before being weighed using a digital weight scale. Once the weight of each particle size has been recorded, the fineness modulus can be calculated.
Sample preparation
To determine the dry weight of a sample of fine aggregate, first, a pan is filled with the sample and placed in a dry oven. The temperature of the oven is set to 100-110°C and the sample is left to dry. Once the drying process is complete, the sample is removed from the oven and weighed. This weight is noted down for further analysis. The purpose of this process is to determine the moisture content of the fine aggregate, which is an important factor in construction materials. By knowing the moisture content, engineers and builders can better predict the behavior of the aggregate in concrete or other applications.
Test Procedure – Fineness Modulus of Sand
To begin the process of sieving, the sieves should be arranged in descending order with the largest sieve on top. If a mechanical shaker is being used, the ordered sieves should be positioned and the sample should be poured into the top sieve. The sieve plate should then be closed, and the machine should be switched on, shaking the sieves for at least 5 minutes. If shaking is being done by hand, the sample should be poured into the top sieve and closed, and then the top two sieves should be held and shaken inwards and outwards, both vertically and horizontally. After some time, the 3rd and 4th sieves should be shaken, followed by the last sieve.
After sieving, the weights of the sample retained on each sieve should be recorded. Then, the cumulative weight retained should be calculated. To determine the cumulative percentage retained on each sieve, the weight retained on each sieve should be divided by the total weight of the sample and multiplied by 100. Finally, the cumulative percentage values should be added together and divided by 100 to obtain the value of the fineness modulus.
Calculation of Fineness Modulus of Sand
Based on the given information, a sample with a dry weight of 1000 grams underwent sieve analysis. The results of this analysis were tabulated and are available for further study.
| Sieve size | Weight retained (g) | Cumulative weight retained(g) | Cumulative percentage weight Retained (%) |
| 4.75mm | 0 | 0 | 0 |
| 2.36mm | 100 | 100 | 10 |
| 1.18mm | 250 | 350 | 35 |
| 0.6mm | 350 | 700 | 70 |
| 0.3mm | 200 | 900 | 90 |
| 0.15mm | 100 | 1000 | 100 |
| Total | 275 |
The given context describes the calculation of the fineness modulus of a fine aggregate. The fineness modulus is a measure of the average particle size of the aggregate and is calculated by dividing the cumulative percentage retained on sieves by 100. In this case, the cumulative percentage retained on sieves is 275, so the fineness modulus is calculated as 2.75.
A fineness modulus of 2.75 indicates that the average value of the aggregate is between the 2nd and 3rd sieve, with an average aggregate size between 0.3mm and 0.6mm. This information is shown in a figure, which helps to visualize the range of aggregate sizes. Overall, the given context provides important information about the particle size distribution of the fine aggregate, which is essential for determining its suitability for use in concrete or other construction applications.
Values of Fineness Modulus of Sand
The fineness modulus of fine aggregate is typically within the range of 2.0 to 3.5mm. However, it is important to note that any fine aggregate with a fineness modulus above 3.2 should not be considered suitable for use. Different types of sands have varying values of fineness modulus, which are listed in detail below.
| Type of sand | Fineness modulus range |
| Fine sand | 2.2 – 2.6 |
| Medium sand | 2.6 – 2.9 |
| Coarse sand | 2.9 – 3.2 |
The Indian Standard IS 383-1970 provides guidelines for the grading of fine aggregates, specifically sand, based on its fineness modulus. The standard specifies different limits for the fineness modulus for various zones of sand. These limits are presented in a table format in the standard document. The table lists the upper and lower limits of the fineness modulus for each zone of sand. By following these guidelines, the quality of the sand used in construction can be ensured to meet the desired specifications.
| Sieve size | Zone-1 | Zone-2 | Zone-3 | Zone-4 |
| 10mm | 100 | 100 | 100 | 100 |
| 4.75mm | 90-100 | 90-100 | 90-100 | 95-100 |
| 2.36mm | 60-95 | 75-100 | 85-100 | 95-100 |
| 1.18mm | 30-70 | 55-90 | 75-100 | 90-100 |
| 0.6mm | 15-34 | 35-59 | 60-79 | 80-100 |
| 0.3mm | 5-20 | 8-30 | 12-40 | 15-50 |
| 0.15mm | 0-10 | 0-10 | 0-10 | 0-15 |
| Fineness modulus | 4.0-2.71 | 3.37-2.1 | 2.78-1.71 | 2.25-1.35 |