What is Fineness Modulus of Coarse Aggregates?
The fineness modulus is an index number that represents the average particle size of coarse aggregates. It is determined by conducting sieve analysis using standard sieves. The cumulative percentage of material retained on each sieve is added and subtracted from 100, which gives the value of the fine aggregate. Generally, larger aggregate size results in a higher fineness modulus compared to smaller aggregates. Coarse aggregate refers to the material retained on a 4.75mm sieve when sieved through it. To calculate the fineness modulus of coarse aggregate, a set of standard sieve sizes is required, which includes 80mm, 40mm, 20mm, 10mm, 4.75mm, 2.36mm, 1.18mm, 0.6mm, 0.3mm, and 0.15mm.
In the calculation of the fineness modulus of coarse aggregate, all the sizes of sieves are necessary. The fineness modulus provides an estimation of the average particle size of the aggregate, counting from the lower-order sieve size to the higher-order sieve. Therefore, sieve analysis is crucial in determining the fineness modulus of coarse aggregate.
Determination of Fineness Modulus of Coarse Aggregates
To determine the fineness modulus, it is necessary to conduct a sieve analysis. This involves the use of specific sieve sizes, a mechanical shaker, and a digital weigh scale. The sieve sizes that are required for the analysis have been previously mentioned. The mechanical shaker is used to separate the different sizes of particles in a given sample, while the digital weigh scale is used to weigh the individual fractions obtained from the sieves.
By conducting the sieve analysis, the fineness modulus of a given material can be determined. The fineness modulus is a measure of the average size of the particles in the material, and is calculated by adding together the cumulative percentages of material that is retained on each sieve, and dividing this by 100. The result gives an indication of the particle size distribution of the material, and is useful for a variety of engineering applications, such as determining the suitability of aggregates for use in concrete mixes.
Sample preparation
A sample of coarse aggregate is taken and placed in a pan. The pan is then put into a dry oven and subjected to a temperature of 100 – 110oC. The purpose of this process is to dry the sample. Once the sample is dry, its weight is taken to the nearest gram.
Test Procedure for Fineness Modulus of Coarse Aggregates
To determine the fineness modulus of coarse aggregate accurately, it is recommended to arrange the sieves in descending order and set them up on a mechanical shaker. This is because a mechanical shaker can handle a larger number of sieves and heavier particles, resulting in more accurate results than hand shaking.
After arranging the sieves, sieve the sample thoroughly and record the weight of the retained particles on each sieve. Then, calculate the cumulative weight of retained particles as well as the cumulative percentage retained on each sieve. The cumulative percentage retained is obtained by adding up the weight of the retained particles on a particular sieve and dividing it by the total weight of the sample.
To obtain the fineness modulus, sum up all the cumulative percentage retained values and divide the result by 100. This value represents the average particle size of the coarse aggregate and can be used to compare the fineness of different aggregates. By following these steps, an accurate fineness modulus value can be obtained for the coarse aggregate sample.
Example for Fineness Modulus Calculation
The given context mentions the dry weight of coarse aggregate as 5000g and states that values after sieve analysis are available. However, the specific details regarding the results of the sieve analysis are not provided.
Sieve analysis is a common method used in the field of civil engineering and construction to determine the particle size distribution of aggregates. This analysis involves passing a sample of the aggregate through a series of sieves with progressively smaller openings, and weighing the material retained on each sieve. The results of the analysis provide important information about the quality and characteristics of the aggregate, which are critical factors in determining its suitability for use in construction projects.
Without more information about the specific results of the sieve analysis in this context, it is difficult to provide any further insights or conclusions about the coarse aggregate being tested. However, it is important to note that sieve analysis is just one of many tests that may be conducted to assess the properties of aggregate materials, and that additional tests may be required depending on the specific application or use case.
| Sieve size | Weight retained(g) | Cumulative weight retained (g) | Cumulative % retained (g) |
| 80mm | 0 | 0 | 0 |
| 40mm | 250 | 250 | 5 |
| 20mm | 1750 | 2000 | 40 |
| 10mm | 1600 | 3600 | 72 |
| 4.75mm | 1400 | 5000 | 100 |
| 2.36mm | 0 | 5000 | 100 |
| 1.18mm | 0 | 5000 | 100 |
| 0.6mm | 0 | 5000 | 100 |
| 0.3mm | 0 | 5000 | 100 |
| 0.15mm | 0 | 5000 | 100 |
| Sum | = | 717 |
The given context pertains to the calculation of the fineness modulus of coarse aggregates. According to the context, the fineness modulus is determined by adding up the cumulative percentage of retained particles and dividing the sum by 100. In this case, the resulting value is 7.17. This value indicates that the average size of particles in the sample falls between the 7th and 8th sieves, which corresponds to particle sizes ranging from 10mm to 20mm.
In summary, the context explains the process of calculating the fineness modulus of coarse aggregates and the resulting value that is obtained. The value of 7.17 is indicative of the average particle size in the sample falling within a particular range of sieve sizes.
Limits of Fineness Modulus
The given context discusses the range of fineness modulus for different types of aggregates. Coarse aggregates have a fineness modulus range of 5.5 to 8.0, while all-in or combined aggregates have a range of 3.5 to 6.5. Additionally, there are different ranges of fineness modulus for aggregates with varying maximum sizes.
In summary, the context provides information about the fineness modulus of different types of aggregates and their corresponding ranges.
| Maximum size of coarse aggregate | Fineness modulus range |
| 20mm | 6.0 – 6.9 |
| 40mm | 6.9 – 7.5 |
| 75mm | 7.5 – 8.0 |
| 150mm | 8.0 – 8.5 |