🏗️ Resistance of aggregate to fragmentation — the Los Angeles coefficient

Construction PN-EN 1097-2

Overview

The standard PN-EN 1097-2 describes the reference method — the Los Angeles test — used in type testing and in cases of dispute, and an alternative method (the impact test, the SZ value) for determining the resistance to fragmentation of coarse aggregates and of aggregates for railway ballast (Annex A). It applies to natural, manufactured and recycled aggregates for building and civil engineering; for other purposes, especially factory production control, other methods may be used once their relationship with the reference method has been established. The 2020 edition replaced PN-EN 1097-2:2010 — among other things a definition of the LA coefficient for ballast (LARB) and guard sieves were added, the test procedure was made more precise and a drying procedure at (40 ± 5) °C was introduced for recycled aggregates sensitive to temperature.

The Los Angeles coefficient LA is the percentage by mass of the test portion passing a 1.6 mm sieve at the end of the test (the 10/14 mm fraction in the main text, 31.5/50 mm for railway ballast). The lower the LA, the greater the resistance of the aggregate to fragmentation. The categories of PN-EN 12620 run from LA15 to LA50 (for example LA25 ≤ 25, LA35 ≤ 35, LA40 ≤ 40); for concrete of classes from C20/25 to C45/55 a category of ≤ LA35 is recommended, and for pavements of cement concrete the WWiORB technical specifications of GDDKiA require a category no higher than LA25 for 10/14 aggregate.

In Polish practice the LA test is the basic criterion for accepting a coarse aggregate for structural concrete in engineering structures (the general technical specifications, OST): the main criterion is LA25, relaxed to LA40 for aggregates with a loss of mass in the freeze-thaw test in salt of ≤ 2 % — which makes it possible to use granites, whose LA is about 40.

Method principle

A sample of aggregate is tumbled with steel balls in a rotating drum. At the end of the tumbling, the amount of material retained on a 1.6 mm sieve is determined. The Los Angeles drum: a steel cylinder of an internal diameter of (711 ± 5) mm and an internal length of (508 ± 5) mm, closed at both ends, rotating about a horizontal axis, with an opening (150 ± 3) mm wide closed by a cover and with an internal shelf of a section of (90 ± 2) × (25 ± 1) mm placed 380–820 mm from the edge of the opening; the drive 31–33 rpm with a counter stopping the motor after the set number of revolutions. The ball charge: 11 balls of 400–445 g each, 4690–4860 g in all (a diameter of about 47 mm). The coefficient LA = (5000 − m)/50, where m is the mass retained on the 1.6 mm sieve in grams; the result is rounded to a whole number.

Applications

• Type testing and factory production control of aggregates for concrete (PN-EN 12620) and for bituminous mixtures
• Acceptance of coarse aggregate for structural concrete in road engineering structures (the general technical specifications OST: LA25, conditionally LA40)
• Aggregate for pavements of cement concrete (the WWiORB technical specifications of GDDKiA: a category no higher than LA25)
• Assessment of the resistance to fragmentation of aggregates for railway ballast (Annex A, the 31.5/50 mm fraction)
• Selection of aggregate for high-strength concretes (classes ≥ C50/60: ≤ LA30)

Key parameters

Standard

Standard number

PN-EN 1097-2:2020-09

Title (PL)

Badania mechanicznych i fizycznych właściwości kruszyw — Część 2: Metody oznaczania odporności na rozdrabnianie

Title (EN)

Tests for mechanical and physical properties of aggregates — Part 2: Methods for the determination of resistance to fragmentation

Step-by-step procedure

1. Laboratory sample

   Take a laboratory sample in accordance with PN-EN 932-2 containing at least 15 kg of particles in the range 10–14 mm.

2. Separation of the fractions

   Sieve on 10, 11.2 (or 12.5) and 14 mm sieves into the fractions 10/11.2 (or 10/12.5) and 11.2/14 (or 12.5/14) mm. Wash each fraction on the lower sieve and dry it to constant mass at (110 ± 5) °C (recycled aggregates sensitive to temperature: (40 ± 5) °C).

   🌡 Temperature: 110 ± 5 °C

3. Making up the test portion

   After cooling, mix the fractions so as to meet one of the conditions: 60–70 % passing 12.5 mm or 30–40 % passing 11.2 mm. Reduce in accordance with PN-EN 932-2 to a test portion of (5000 ± 5) g (each fraction may be reduced separately to the mass required).

4. Test in the drum

   Check that the drum is clean; put the balls in carefully and then the test portion; close the cover and run 500 revolutions at a constant speed of 31–33 rpm.

5. Emptying of the drum

   Tip the contents onto a tray placed under the machine (the opening just above the tray, so that no material is lost), clean the drum and collect all the particles, especially at the shelf; take the balls out carefully without losing any particles.

6. Sieving and washing

   Sieve the material from the tray on the 1.6 mm sieve protected by guard sieves in accordance with PN-EN 933-1; wash the material retained on the sieves with a jet of clean water and transfer it into a bowl.

7. Drying and weighing

   Dry at (110 ± 5) °C (or (40 ± 5) °C) to constant mass, cool and record the mass m to the nearest 1 g.

8. Calculation and test report

   LA = (5000 − m)/50, rounded to a whole number. In the test report: a reference to the standard with its year, the identification and origin of the sample, the laboratory, the date, the LA, any departures from the reference method and any unusual observations.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The drum with its ball charge is noisy — hearing protection; do not open the cover while it is rotating
• Put the steel balls and the test portion in and take them out with the drive switched off; take care not to trap the fingers
• Dust from the drying and sieving of aggregates — goggles and a dust mask when sieving dry

Frequently asked questions