🪨 Los Angeles Abrasion Test: Procedure, Calculation & Result
Not all aggregates are created equal. Some wear down quickly under traffic and impact, while others stay tough for decades. 🛣️ The Los Angeles Abrasion Test is the standard method for measuring this toughness. It tells engineers whether an aggregate is suitable for concrete, road surfaces, or railway ballast. In this civil engineering explainer, you'll learn the full procedure as per IS 2386 Part 4, the calculation formula, and how to interpret the results.
🎬 Watch the full explainer video above 👆
🧱 What Is the Los Angeles Abrasion Test?
The Los Angeles Abrasion Test—also called the L.A. Rattler Test—is a laboratory test used to assess the hardness and wear resistance of coarse aggregates. It simulates the abrasive forces that aggregates experience during handling, mixing, and in-service traffic loading.
The test is performed according to IS 2386 (Part IV): 1963, which covers the mechanical properties of aggregates. The principle is to measure the percentage wear caused by the relative rubbing action between the aggregate and steel balls inside a rotating drum.
🧰 Apparatus Required
| Apparatus | Specification |
|---|---|
| 🔄 Los Angeles Testing Machine | Hollow steel cylinder, inside diameter 70 cm, inside length 50 cm, with a removable shelf and revolution counter. |
| ⚙️ Abrasive Charge | Cast iron or steel balls, approximately 48 mm diameter, each weighing 390–445 g. |
| ⚖️ Balance | Capacity 5–10 kg, accurate to 1 g. |
| 🔲 Sieves | IS sieves of sizes 80, 63, 50, 40, 25, 20, 12.5, 10, 6.3, 4.75, 2.36, and 1.70 mm. |
| 🌡️ Drying Oven | Capable of maintaining 105–110°C. |
⚙️ Step-by-Step Procedure (IS 2386 Part 4)
1️⃣ Prepare the Sample
Clean the aggregate and oven-dry it at 105–110°C to constant weight. Select the appropriate grading (A to G) based on the aggregate size.
2️⃣ Weigh the Sample
Take 5 kg for gradings A–D, or 10 kg for gradings E–G. Record the original weight as W₁.
3️⃣ Add the Abrasive Charge
Place the sample and the specified number of steel balls (6 to 12, depending on grading) into the machine.
4️⃣ Rotate the Machine
Rotate at 30–33 rpm. Use 500 revolutions for gradings A–D, or 1000 revolutions for gradings E–G.
5️⃣ Sieve and Weigh
After rotation, discharge the material and sieve it on the 1.70 mm IS sieve. Wash, oven-dry, and weigh the retained material as W₂.
🧮 Calculation Formula
Los Angeles Abrasion Value (LAAV) =
(W₁ – W₂) / W₁ × 100 %
Where:
W₁ = original weight of oven-dried sample (g)
W₂ = weight of material retained on the 1.70 mm IS sieve after the test (g)
The result is reported to the nearest 1% by mass. For accuracy, two tests should be performed, and the average value is reported.
📊 Gradation and Abrasive Charge (IS 2386 Part 4)
| Grading | Passing / Retained (mm) | Sample Weight (g) | No. of Spheres | Charge Weight (g) | Revolutions |
|---|---|---|---|---|---|
| A | 80–63, 63–50, 50–40, 40–25, 25–20, 20–12.5, 12.5–10 | 5000 | 12 | 5000 ± 25 | 500 |
| B | 20–12.5, 12.5–10 | 5000 | 11 | 4584 ± 25 | 500 |
| C | 10–6.3, 6.3–4.75 | 5000 | 8 | 3330 ± 20 | 500 |
| D | 6.3–4.75, 4.75–2.36 | 5000 | 6 | 2500 ± 15 | 500 |
| E | 80–63, 63–50, 50–40 | 10000 | 12 | 5000 ± 25 | 1000 |
| F | 50–40, 40–25 | 10000 | 12 | 5000 ± 25 | 1000 |
| G | 40–25, 25–20 | 10000 | 12 | 5000 ± 25 | 1000 |
📈 How to Interpret LAAV Results
| LAAV (%) | Quality | Typical Use |
|---|---|---|
| Below 30% | 🟢 Excellent | High-quality concrete, heavy-duty pavements, wearing courses. |
| 30% – 40% | 🟡 Good / Satisfactory | General concrete, road bases, most structural works. |
| 40% – 50% | 🟠 Fair | Lighter-duty concrete, subbase, lower-traffic roads. |
| Above 50% | 🔴 Poor | Generally unsuitable for high-quality concrete or wearing surfaces. |
According to IS 2386 Part 4, lower LAA values indicate tougher, more abrasion-resistant aggregates. For most concrete and road works, a value of 40% or less is considered satisfactory. For wearing surfaces and heavy-traffic roads, a value of 30% or less is often specified.
🎯 Why Is the LAA Test Important?
- 🛡️ Predicts durability: aggregates with low LAAV resist wear and last longer in service.
- 🛣️ Ensures road quality: abrasion-resistant aggregates are essential for wearing courses and heavy-traffic pavements.
- 🏗️ Controls concrete quality: softer aggregates can lead to surface defects, dust, and reduced strength.
- 📋 Specification compliance: most standards set maximum allowable LAAV for different applications.
- 💰 Cost-effective selection: helps engineers choose the right aggregate for the right job, avoiding premature failures.
⚠️ Limitations to Consider
- 🔬 Laboratory test: does not fully replicate real-world field conditions.
- 📏 Gradation dependent: results can vary with the grading used, so the correct grading must be selected.
- ⏱️ Time-consuming: requires careful sample preparation and multiple steps.
- 🧪 Single property: measures abrasion resistance only, not other important properties like soundness or reactivity.
❓ Frequently Asked Questions
🤔 What is the Los Angeles Abrasion Test in simple words?
The Los Angeles Abrasion Test measures how resistant an aggregate is to wear and impact. Aggregate and steel balls are tumbled inside a rotating drum, and the percentage of material that breaks off is the LAA value.
🧮 What is the formula for Los Angeles Abrasion Value?
LAAV = ((W₁ - W₂) / W₁) × 100, where W₁ is the original oven-dried weight of the sample and W₂ is the weight retained on the 1.70 mm IS sieve after the test.
📉 What does a lower LAA value mean?
A lower LAA value indicates a tougher, more abrasion-resistant aggregate. Higher values mean the aggregate wears away more easily and may not be suitable for high-quality concrete or road surfaces.
📊 What are the acceptable limits for LAAV?
As a general guide, LAA values below 30% are considered excellent, 30–40% satisfactory for most concrete and road works, 40–50% acceptable for lighter duty, and above 50% generally unsuitable for high-quality work.
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