🏗️ Shape index of coarse aggregate (SI) — classification of particles with a calliper according to the ratio of length to thickness
In short
The particles of a coarse aggregate are classified individually according to the ratio of their length L to their thickness E, measured where necessary with a particle calliper. The test is performed according to PN-EN 933-4:2008; Range of application: Size fractions di/Di in which Di ≤ 63 mm and di ≥ 4 mm. The procedure comprises 8 steps; it is used for: Type testing of coarse aggregate and the settling of disputes about particle shape, Qualification of aggregate for cement concrete pavements (categories SI40, SI20, SI15), Assessment of aggregate for bituminous mixtures.
At a glance
- Standard: PN-EN 933-4:2008
- Category: Construction
- Procedure steps: 8
- Range of application: Size fractions di/Di in which Di ≤ 63 mm and di ≥ 4 mm
- Condition for the fraction tested: The test is carried out on every fraction di/Di meeting Di ≤ 2di
- Limit for a non-cubical particle: A ratio of length to thickness L/E greater than 3
Overview
The standard describes the reference method used for type testing and in cases of dispute when determining the shape index of coarse aggregates. For other purposes, in particular for factory production control, other methods may be used, provided that their proper relationship with the reference method has been established.
The method is applied to size fractions di/Di in which the upper size Di does not exceed 63 mm and the lower size di is at least 4 mm. The shape index is tested on fractions meeting the condition Di ≤ 2di — samples with a wider grading range are separated into such fractions in the course of the test.
The shape index is one of the two permitted measures of the shape of a coarse aggregate; the other is the flakiness index determined according to Part 3 of the same series. The technical documents of GDDKiA treat them as interchangeable and set the requirements in the form of categories — for aggregate for cement concrete pavements it is a category not higher than SI40 or FI35 for the lower layer, SI20 or FI20 for the upper layer, and for exposed-aggregate pavements SI15 or FI15. The figure in the designation of the category is the upper permissible value of the index as a percentage.
Non-cubical particles — elongated and flat — worsen the workability of the mix, increase the water demand and break more easily during compaction, which is why their proportion is limited in aggregate for concrete and for bituminous mixtures.
Method principle
Individual particles from a sample of coarse aggregate are classified on the basis of the ratio of their length L to their thickness E, using where necessary a particle calliper. The length L is the greatest dimension of the particle, defined as the greatest distance between two parallel planes tangential to its surface; the thickness E is the smallest dimension of the particle, defined as the smallest distance between two such planes. Particles with a ratio of dimensions L/E greater than 3 are classified as non-cubical and set aside separately. The shape index is calculated as the mass of the particles with a ratio L/E greater than 3, expressed as a percentage of the total dry mass of the particles tested.
Applications
- Type testing of coarse aggregate and the settling of disputes about particle shape
- Qualification of aggregate for cement concrete pavements (categories SI40, SI20, SI15)
- Assessment of aggregate for bituminous mixtures
- Control of a delivery of aggregate whose quality raises doubts
- Factory production control at the aggregate producer’s works — as the reference method for working methods
Key parameters
| Parameter | Value |
|---|---|
| Range of application | Size fractions di/Di in which Di ≤ 63 mm and di ≥ 4 mm |
| Condition for the fraction tested | The test is carried out on every fraction di/Di meeting Di ≤ 2di |
| Limit for a non-cubical particle | A ratio of length to thickness L/E greater than 3 |
| Smallest mass of the test portion | D = 63 mm — 45 kg; D = 32 mm — 6 kg; D = 16 mm — 1 kg; D = 8 mm — 0.1 kg (Table 1); for other D the values are interpolated |
| Drying | At a temperature of 110 °C ± 5 °C to constant mass |
| Constant mass | Successive weighings after drying, made at an interval of at least 1 h, differing by not more than 0.1 % |
| Accuracy of weighing | A balance with a scale interval of 0.1 % of the mass weighed |
| Particles rejected | Those retained on the 63 mm sieve and those passing the 4 mm sieve |
| Correction for density | For aggregates with a particle density below 2.00 Mg/m³ or above 3.00 Mg/m³ the masses of Table 1 are corrected in proportion to the density |
| Requirement categories (concrete pavements, GDDKiA) | SI40 or FI35 for the lower layer, SI20 or FI20 for the upper layer and for NGCS pavements (Next Generation Concrete Surface — a concrete pavement with a texture produced by diamond grinding), SI15 or FI15 for exposed-aggregate pavements |
Standard
- Standard number
- PN-EN 933-4:2008
- Title (PL)
- Badania geometrycznych właściwości kruszyw — Część 4: Oznaczanie kształtu ziarn — Wskaźnik kształtu
- Title (EN)
- Tests for geometrical properties of aggregates — Part 4: Determination of particle shape — Shape index
Step-by-step procedure
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Reducing the sample
Reduce the laboratory sample in accordance with the requirements of PN-EN 932-2.
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Drying
Dry the sample at a temperature of 110 °C ± 5 °C to constant mass, that is until successive weighings made at an interval of at least an hour differ by not more than 0.1 %.
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Preliminary sieving
Sieve the material on the appropriate test sieves, vigorously enough to separate completely the particles larger than 4 mm. Reject the particles retained on the 63 mm sieve and those passing the 4 mm sieve.
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Establishing the test portion
If necessary reduce the material again in accordance with PN-EN 932-2 to obtain a test portion. The mass of the test portion is to be greater than the smallest given in Table 1; it must not, however, be adjusted to a fixed round value in advance — one takes as much material as the reduction produced. Record the mass of the test portion as M0.
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Separating the fraction to be tested
The test is carried out on every size fraction di/Di meeting the condition Di ≤ 2di. Separate such a fraction from the test portion by sieving in accordance with PN-EN 933-1, reject the particles smaller than di and larger than Di. Record the fraction tested di/Di and its mass as M1. Samples with a range D > 2d are separated into such fractions in the course of the test.
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Classifying the particles
Assess the length L and the thickness E of each particle, using where necessary a particle calliper, and set aside separately the particles with a ratio of dimensions L/E greater than 3 — these are the non-cubical particles. The number of particles requiring measurement with the calliper can be reduced by first separating out those whose ratio L/E clearly differs from 3.
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Weighing the non-cubical particles
Weigh the non-cubical particles and record their mass as M2.
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Calculating the index
Calculate the shape index SI as the mass of the particles with a ratio L/E greater than 3 expressed as a percentage of the total dry mass of the particles tested — that is how the principle of the method in clause 4 of the standard reads. A RECONSTRUCTION, not the content of the standard: writing this operation as the quotient of the mass of non-cubical particles M2 to the mass of the fraction tested M1, multiplied by 100, follows directly from the principle and from the notation of the masses introduced in 7.2, but the formula itself from clause 8 is not covered by the preview and we do not reproduce it. The requirements concerning the test report in clause 9 are likewise not covered by the preview.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Particle calliper | A jaw instrument for measuring the length and the thickness of a single particle, an example of which is shown in Figure 1 of the standard | — |
| Test sieves | With nominal aperture sizes according to PN-EN 933-2, together with a tightly fitting pan and lid | — |
| Ventilated drying oven | With thermostatic control maintaining 110 °C ± 5 °C; other drying equipment is admissible provided it does not cause breakdown of the particles | — |
| Balance | Of sufficient capacity, with a scale interval of 0.1 % of the mass weighed | — |
| Trays | For laying out and sorting the particles during the classification | — |
| Mechanical sieve shaker | Optional equipment, assisting the separation of the fractions | — |
| General equipment according to PN-EN 932-5 | All the apparatus, unless otherwise stated, meets the general requirements of that standard | — |
Health and safety (OHS)
- A drying oven heated to 110 °C — thermal gloves and tongs for taking out the trays
- Mineral dust when sieving — protection of the respiratory tract and of the eyes, the sieve shaker under extraction or with a cover
- Test portions of 63 mm aggregate weigh up to 45 kg — carrying by two persons or on a trolley, a risk of back injury
- The noise of the mechanical sieve shaker — hearing protectors
- Sharp edges of crushed aggregate particles — gloves during manual classification and measurement with the calliper
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN 933-4:2008 — “Tests for geometrical properties of aggregates — Part 4: Determination of particle shape — Shape index”.
How does this method work?
Individual particles from a sample of coarse aggregate are classified on the basis of the ratio of their length L to their thickness E, using where necessary a particle calliper. The length L is the greatest dimension of the particle, defined as the greatest distance between two parallel planes tangential to its surface; the thickness E is the smallest dimension of the particle, defined as the smallest distance between two such planes.
What is the measuring range and accuracy?
Range of application: Size fractions di/Di in which Di ≤ 63 mm and di ≥ 4 mm; Condition for the fraction tested: The test is carried out on every fraction di/Di meeting Di ≤ 2di; Limit for a non-cubical particle: A ratio of length to thickness L/E greater than 3; Smallest mass of the test portion: D = 63 mm — 45 kg; D = 32 mm — 6 kg; D = 16 mm — 1 kg; D = 8 mm — 0.1 kg (Table 1); for other D the values are interpolated.
How long does the test take?
The procedure comprises 8 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Particle calliper, Test sieves, Ventilated drying oven, Balance, Trays, Mechanical sieve shaker, General equipment according to PN-EN 932-5.
Where is this test used?
Type testing of coarse aggregate and the settling of disputes about particle shape; Qualification of aggregate for cement concrete pavements (categories SI40, SI20, SI15); Assessment of aggregate for bituminous mixtures; Control of a delivery of aggregate whose quality raises doubts; Factory production control at the aggregate producer’s works — as the reference method for working methods.
What safety precautions apply?
A drying oven heated to 110 °C — thermal gloves and tongs for taking out the trays; Mineral dust when sieving — protection of the respiratory tract and of the eyes, the sieve shaker under extraction or with a cover; Test portions of 63 mm aggregate weigh up to 45 kg — carrying by two persons or on a trolley, a risk of back injury; The noise of the mechanical sieve shaker — hearing protectors; Sharp edges of crushed aggregate particles — gloves during manual classification and measurement with the calliper.
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 933-4.