🏗️ Particle shape of aggregate — the flakiness index FI
In short
Sieving in two stages: separation into di/Di fractions on square-hole sieves, then sieving of each fraction on a bar sieve with a slot of Di/2; FI = the mass passing the bar sieves as a percentage of the mass of the test portion. The test is performed according to PN-EN 933-3:2012; Range of particle sizes: 4–100 mm. The procedure comprises 6 steps; it is used for: Type testing and production control of aggregates for concrete and for asphalt mixtures, Coarse aggregate for pavements of cement concrete (the WWiORB technical specifications of GDDKiA: FI15 for exposed aggregate, FI20 or FI35 in other applications), Assessment of the particle shape of crushed and recycled aggregates in the range 4–100 mm.
At a glance
- Standard: PN-EN 933-3:2012
- Category: Construction
- Procedure steps: 6
- Range of particle sizes: 4–100 mm
- Square-hole sieves: 100; 80; 63; 50; 40; 31.5; 25; 20; 16; 12.5; 10; 8; 6.3; 5; 4 mm according to PN-EN 933-2
- Bar sieves: A slot of Di/2: from 50 ± 0.5 mm (80/100) to 2.5 ± 0.15 mm (4/5)
Overview
The standard PN-EN 933-3 describes the reference method, used in type testing and in cases of dispute, for determining the flakiness index of natural, manufactured and recycled aggregates. The method does not apply to particles smaller than 4 mm or larger than 100 mm. For other purposes, especially production control, other methods may be used once their relationship with the reference method has been established.
The flakiness index describes the shape of the particles of a coarse aggregate: flaky particles pass through the slots of a bar sieve whose width equals half the upper size of the fraction. The bar sieves have slots from 50 mm (the 80/100 fraction) to 2.5 mm (the 4/5 fraction) with tolerances from ± 0.5 mm to ± 0.15 mm; the bars are cylindrical, of a diameter of 5–15 mm, in a metal frame of a length of 250–300 mm.
The shape of a coarse aggregate is a requirement in road specifications: for pavements of cement concrete the WWiORB technical specifications of GDDKiA allow the test according to PN-EN 933-3 (the flakiness index FI) or PN-EN 933-4 (the shape index SI) and require a category no higher than FI15 or SI15 for aggregate for an exposed-aggregate top layer, and FI20/SI20 or FI35/SI40 for other applications.
Method principle
The test consists of two sievings. First the sample is separated on square-hole sieves into the di/Di fractions of table 1 of the standard (80/100, 63/80, 50/63, 40/50, 31.5/40, 25/31.5, 20/25, 16/20, 12.5/16, 10/12.5, 8/10, 6.3/8, 5/6.3, 4/5 mm). Then each fraction is sieved on a bar sieve with parallel slots of a width of Di/2. The overall flakiness index is calculated as the total mass of the particles passing the bar sieves as a percentage of the total dry mass of the particles tested; if need be, the flakiness index of each fraction is also calculated as the mass passing the corresponding bar sieve as a percentage of the mass of that fraction.
Applications
- Type testing and production control of aggregates for concrete and for asphalt mixtures
- Coarse aggregate for pavements of cement concrete (the WWiORB technical specifications of GDDKiA: FI15 for exposed aggregate, FI20 or FI35 in other applications)
- Assessment of the particle shape of crushed and recycled aggregates in the range 4–100 mm
- An alternative to the shape index SI of PN-EN 933-4 in road specifications
Key parameters
| Parameter | Value |
|---|---|
| Range of particle sizes | 4–100 mm |
| Square-hole sieves | 100; 80; 63; 50; 40; 31.5; 25; 20; 16; 12.5; 10; 8; 6.3; 5; 4 mm according to PN-EN 933-2 |
| Bar sieves | A slot of Di/2: from 50 ± 0.5 mm (80/100) to 2.5 ± 0.15 mm (4/5) |
| Dimensions of the bar sieve | L = 250–300 mm, H = 75 mm, h = 55–65 mm, bars of Ø 5–15 mm |
| Drying | (110 ± 5) °C to constant mass (weighings at intervals of ≥ 1 h differing by ≤ 0.1 %) |
| Result | The overall FI in % by mass; optionally the FI of each fraction; the categories FI15, FI20, FI35 in the specifications |
Standard
- Standard number
- PN-EN 933-3:2012
- Title (PL)
- Badania geometrycznych właściwości kruszyw — Część 3: Oznaczanie kształtu ziarn za pomocą wskaźnika płaskości
- Title (EN)
- Tests for geometrical properties of aggregates — Part 3: Determination of particle shape — Flakiness index
Step-by-step procedure
-
Test portion
Reduce the laboratory sample in accordance with PN-EN 932-2 to a test portion and dry it at (110 ± 5) °C to constant mass.
-
First sieving
Sieve the test portion on square-hole sieves, separating it into the di/Di fractions of table 1 (discard particles < 4 mm and > 100 mm, which the method does not cover).
-
Weighing of the fractions
Weigh each fraction to ± 0.1 % of the mass of the test portion.
-
Sieving on the bar sieves
Sieve each di/Di fraction on a bar sieve with a slot of Di/2 (for example the 10/12.5 fraction on the 6.3 mm sieve, the 16/20 fraction on the 10 mm sieve).
-
Weighing of the passing material
Weigh the particles passing each bar sieve.
-
Calculation
The overall FI = the total mass of the particles passing the bar sieves / the total dry mass of the particles tested × 100 %. If need be, the FI of a fraction = the mass passing the bar sieve / the mass of the fraction × 100 %.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Square-hole test sieves | A set of 4–100 mm according to PN-EN 933-2 | — |
| Bar sieves | Parallel cylindrical bars in a metal frame, the slots according to table 1 of the standard (the tolerance over the whole length of the slot) | — |
| Balance | Accuracy ± 0.1 % of the mass of the test portion | — |
| Ventilated oven | Thermostatically controlled at (110 ± 5) °C or other equipment for drying without breaking the particles | — |
| Equipment for reducing samples | According to PN-EN 932-2; the general apparatus according to PN-EN 932-5 | — |
Health and safety (OHS)
- The bar sieves have sharp edges on the bars — gloves when sieving by hand
- Dust from the dry sieving of aggregate — goggles and a dust mask or extraction
- The oven at 110 °C — heat-resistant gloves
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN 933-3:2012 — “Tests for geometrical properties of aggregates — Part 3: Determination of particle shape — Flakiness index”.
How does this method work?
The test consists of two sievings. First the sample is separated on square-hole sieves into the di/Di fractions of table 1 of the standard (80/100, 63/80, 50/63, 40/50, 31.
What is the measuring range and accuracy?
Range of particle sizes: 4–100 mm; Square-hole sieves: 100; 80; 63; 50; 40; 31.5; 25; 20; 16; 12.5; 10; 8; 6.3; 5; 4 mm according to PN-EN 933-2; Bar sieves: A slot of Di/2: from 50 ± 0.5 mm (80/100) to 2.5 ± 0.15 mm (4/5); Dimensions of the bar sieve: L = 250–300 mm, H = 75 mm, h = 55–65 mm, bars of Ø 5–15 mm.
How long does the test take?
The procedure comprises 6 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Square-hole test sieves, Bar sieves, Balance, Ventilated oven, Equipment for reducing samples.
Where is this test used?
Type testing and production control of aggregates for concrete and for asphalt mixtures; Coarse aggregate for pavements of cement concrete (the WWiORB technical specifications of GDDKiA: FI15 for exposed aggregate, FI20 or FI35 in other applications); Assessment of the particle shape of crushed and recycled aggregates in the range 4–100 mm; An alternative to the shape index SI of PN-EN 933-4 in road specifications.
What safety precautions apply?
The bar sieves have sharp edges on the bars — gloves when sieving by hand; Dust from the dry sieving of aggregate — goggles and a dust mask or extraction; The oven at 110 °C — heat-resistant gloves.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN 933-3.