The key difference between flakiness index and elongation index is that flakiness index determines the concentration of flaky particles in a sample, whereas elongation index determines the concentration of elongated particles in a sample.
Flakiness index and elongation index are two important types of indices useful in determining the concentration of a given sample by means of the particles that are present in the sample.
CONTENTS
1. Overview and Key Difference
2. What is Flakiness Index
3. What is Elongation Index
4. Flakiness Index vs Elongation Index in Tabular Form
5. Summary – Flakiness Index vs Elongation Index
What is Flakiness Index?
The flakiness index can be described as the percentage of stones in an aggregate consisting of an ALD (Average Least Dimension) less than 0.6 times the average dimension of stones. In other words, this index value of aggregates gives the percentage by weight of aggregate particles having the least dimension that is less than 0.6 times their mean dimension.
Moreover, flaky aggregates tend to produce seals having less amount of voids due to their tendency to pack tightly compared to cubical aggregates. As a consequence, flaky particles require less amount of binders.
In the calculation of the flakiness index of a sample of aggregates, we need to note the weight of each fraction of the aggregates that are passing through and retaining on the specific sieve we are using for the experiment. In this method, we need to make pieces of aggregates pass through the slot of the specific thickness of a gauge. Thereafter, we can measure the weight of these slots. The calculation of the flakiness index after this experiment is given below:
In this equation, W1 is the total weight of aggregates, and W2 is the weight of aggregates passed through the 0.6 x dmean size sieve.
For example, the flakiness index of the aggregates we can use in the construction of roads is typically less than 15%, and it should not exceed 25%.
What is Elongation Index?
The elongation index can be described as the total weight of the material retained on the various length gauges that are expressed as a percentage of the total weight of the sample. In other words, it is the percentage by weight of the particles whose greatest dimension tends to be greater than 1.8 times the mean dimension of particles. We can measure the elongation index of particles that are passing through a mesh size 63 mm and the particles retained on a mesh size 6.3 mm.
The presence of elongated aggregate particles in a mixture can disturb the packing of particles and also creates more space. These aggregate particles consist of a high ratio of surface area to volume, which is useful in reducing the workability of concrete. Moreover, if we use elongated particles for the pavement base course construction, it can cause an easy breakdown of the pavement when a heavy load or stress is applied. Therefore, it is very important to understand the elongation index of a given aggregate mix.
We can calculate the elongation index as follows:
Here, W1 refers to the weight of particles that are retained in the length gauge, and W2 refers to the weight of the total sample used for the test.
What is the Difference Between Flakiness Index and Elongation Index?
The flakiness index and elongation index are two important types of indices useful in determining the concentration of a given sample by means of the particles that are present in the sample. The key difference between flakiness index and elongation index is that flakiness index determines the concentration of flaky particles in a sample, whereas the elongation index determines the concentration of elongated particles in a sample.
The below infographic presents the differences between flakiness index and elongation index in tabular form for side by side comparison.
Summary – Flakiness Index vs Elongation Index
Flakiness index is the percentage of stones in an aggregate consisting of an average least dimension less than 0.6 times the average dimension of stones. Elongation index is the total weight of the material retained on the various length gauges that are expressed as a percentage of the total weight of the sample is gauged. The key difference between flakiness index and elongation index is that flakiness index determines the concentration of flaky particles in a sample, whereas the elongation index determines the concentration of elongated particles in a sample.
Reference:
1. “Flakiness Index Test for Aggregates.” Civil Engineering Portal – Biggest Civil Engineering Information Sharing Website, 20 June 2020.