Combined Flakiness & Elongation Index
(IS: 2386 Part I)
| IS Sieve Size (mm) | FLAKINESS INDEX | ELONGATION INDEX | |||
|---|---|---|---|---|---|
| Passing | Retained | Wt. of Fraction (W1) | Wt. Passing Thickness Gauge (W2) | Wt. Retained Thickness Gauge (W3) (Non-Flaky) |
Wt. Retained Length Gauge (W4) |
| 63 | 50 | 0 | |||
| 50 | 40 | 0 | |||
| 40 | 31.5 | 0 | |||
| 31.5 | 25 | 0 | |||
| 25 | 20 | 0 | |||
| 20 | 16 | 0 | |||
| 16 | 12.5 | 0 | |||
| 12.5 | 10 | 0 | |||
| 10 | 6.3 | 0 | |||
| TOTAL | 0 | 0 | 0 | 0 | |
Technical Guide: Combined Flakiness & Elongation Index
The **Combined Flakiness and Elongation Index** is a crucial quality control test for coarse aggregates used in road construction (DBM, BC, WBM) and concrete mixes. It determines the shape of the aggregate particles.
1. Why is this test important?
Aggregates that are "flaky" (thin like a coin) or "elongated" (long like a needle) are mechanically weak. Under heavy traffic loads (rollers or vehicles), these particles tend to break or crush easily compared to cubical (blocky) aggregates. This crushing reduces the strength of the road pavement or concrete structure.
2. Standard Definitions (IS 2386 Part 1)
- Flakiness Index: The percentage by weight of particles whose least dimension (thickness) is less than 0.6 times their mean dimension.
- Elongation Index: The percentage by weight of particles whose greatest dimension (length) is greater than 1.8 times their mean dimension.
3. Testing Procedure
- Step A: Sieve the aggregate and separate into fractions (e.g., 20-16mm, 16-12.5mm). Weigh each fraction (W1).
- Step B (Flakiness): Try to pass each particle through the slot of the Thickness Gauge. The weight passing is W2. The weight retained is W3 (Non-Flaky).
- Step C (Elongation): Take the Non-Flaky portion (W3) and test it on the Length Gauge. The weight retained (that doesn't fit) is W4.
4. Engineering Implications
Using poor quality aggregate with high flakiness results in:
- Poor Interlocking: Flaky particles do not lock together well, leading to road deformation.
- Higher Bitumen Consumption: Flaky particles have more surface area, requiring more bitumen to coat them, increasing costs.
- Reduced Strength: Concrete made with flaky aggregates has lower compressive strength.
Comprehensive Guide: Combined Flakiness & Elongation Index (IS: 2386 Part 1)
In the construction of high-speed highways, airport runways, and heavy-duty concrete structures, the shape of the coarse aggregate is just as critical as its crushing strength. Aggregates generally fall into categories like cubical, angular, flaky, or elongated. For structural integrity, cubical and angular particles are highly preferred because they interlock tightly and transfer loads efficiently.
This automated Combined Flakiness and Elongation Index Calculator is designed for Quality Control (QC) and Third-Party Inspection (TPI) engineers to rapidly verify aggregate shape compliance according to IS: 2386 (Part 1) and MORTH specifications.
1. Engineering Definitions & Mathematics
The test mathematically identifies particles that are disproportionately thin or excessively long compared to their overall mass:
- Flakiness Index: This is the percentage by weight of aggregate particles whose least dimension (thickness) is less than 0.6 times (or 3/5ths) of their mean dimension.
- Elongation Index: This is the percentage by weight of particles whose greatest dimension (length) is greater than 1.8 times (or 9/5ths) of their mean dimension.
2. The Physical Testing Apparatus
Before using this generator to simulate or record data, the physical test must be performed in the site laboratory using specific metal gauges:
The Thickness Gauge (Flakiness)
A metal panel featuring precisely cut slots of varying widths. The aggregate fraction (e.g., passing 20mm, retained 16mm) is passed through the corresponding slot. Any particle that passes through is classified as "Flaky" (W2). The particles that do not fit through the slot are "Non-Flaky" (W3).
The Length Gauge (Elongation)
A metal board with vertical metal pins spaced at specific intervals. Crucial Note: Only the "Non-Flaky" portion (W3) from the previous test is tested here. If a particle cannot pass lengthwise between the pins, it is classified as "Elongated" (W4).
3. Structural Implications of Failing Aggregates
Why do MORTH specifications strictly limit the Combined Index to a maximum of 30% for Dense Bituminous Macadam (DBM) and Bituminous Concrete (BC)?
- Poor Interlocking & Rutting: Flaky particles lay flat and slide against each other rather than locking together. Under heavy truck traffic, this causes the asphalt to deform, leading to dangerous wheel ruts in the road.
- Mechanical Crushing: Elongated, needle-like particles act like fragile bridges. When a heavy steel drum vibratory roller passes over them during compaction, they snap and crush, completely altering the mix design gradation and creating excessive dust.
- Increased Bitumen Consumption: Flat and elongated particles possess a significantly higher surface-area-to-volume ratio than cubical stones. This means the batching plant must use far more expensive bitumen to adequately coat the aggregates, drastically driving up project costs.
4. How to Use This Automation Tool
This combined index calculator streamlines your daily QA/QC reporting and material tracking workflows:
- Manual Data Entry: Enter your site metadata (Chainage, Date, Source). Then, manually input your physically weighed laboratory data into the W1, W2, and W4 columns. The tool will instantly calculate the W3 (Non-Flaky) weight and update the overall percentages dynamically.
- Simulation & Generator Mode: If you need to generate a mathematically compliant theoretical report for a specific aggregate size (e.g., 20mm or 40mm), select the aggregate type, input a total sample weight, and click Generate Data. The algorithm will populate the table with randomized, realistic weights that adhere to standard IS code gradations and ensure a combined index below the 30% MORTH limit.
- Print & Export: Click Print Report to launch a clean, styling-stripped PDF layout that removes the calculator controls and theory sections, leaving you with a perfectly formatted, professional laboratory printout ready for TPI signatures.
Disclaimer: The data generator function utilizes randomized distribution algorithms to create theoretically compliant aggregate profiles. It is intended strictly as an educational tool, mix-design simulator, and formatting aid. Always rely on actual physical laboratory weighments for official site execution and billing approvals.