The Los Angeles (LA) abrasion test is the most widely used method for assessing the toughness and abrasion resistance of coarse aggregates in construction. It evaluates how well aggregates withstand the mechanical stresses they encounter during handling, production, and service life. A coarse aggregate sample—retained on a No. 12 (1.70 mm) sieve—is placed in a rotating steel drum with steel spheres and subjected to impact and grinding forces. After a specified number of revolutions, the percentage of material that has broken down and passed through the 1.70 mm sieve is calculated. This percentage is the LA abrasion loss value: a result of 40 means 40% of the original sample degraded during testing. Lower values indicate greater toughness and abrasion resistance.

Why Aggregate Durability Matters on Site

Aggregates endure substantial wear throughout their lifecycle—from manufacturing and stockpiling to mixing, placing, and compaction. They must be hard and tough enough to resist crushing and disintegration at every stage, and they need to transmit loads effectively from the pavement surface down through underlying layers to the subgrade. This requirement is especially critical in open- or gap-graded hot-mix asphalt (HMA), where coarse particles experience high contact stresses without the cushioning effect of fine aggregate. Aggregates with poor abrasion resistance can cause premature structural failure, loss of skid resistance, and excessive dust formation during production—creating both environmental and mixture-control problems.

How the LA Abrasion Test Works

The test apparatus consists of a steel drum with an inside diameter of 710 mm ± 2 mm and an inside length of 510 mm ± 2 mm. A radial shelf projects 90 mm into the drum. The machine rotates at a uniform peripheral speed between 30 and 33 revolutions per minute for the full test duration. Steel spheres—each approximately 48 mm in diameter and weighing 417 g ± 27.5 g—serve as the "charge" that abrades and impacts the aggregate sample as the drum rotates.

You begin by recording the initial mass of your sample to the nearest gram, then load the sample and steel charge into the drum. After sealing the cover, you set the number of revolutions according to the aggregate grading. Once the test completes, you extract the sample and steel balls, remove any residue with a soft brush, and separate the steel spheres. The test portion is sieved by hand or mechanical shaker, and all material passing the 1.70 mm sieve is weighed. The material retained on the sieve is washed over a 1.70 mm sieve until the water runs clear, dried to constant mass, cooled to room temperature, and re-sieved. The final mass of material coarser than 1.70 mm is recorded, and the LA abrasion loss is calculated as the percentage of the original sample that passed through the sieve.

Standards and Regional Variations

The standard Los Angeles abrasion test is governed by AASHTO T 96 and ASTM C 131, titled "Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine." In Australia, testing follows AS 1141.23, with regional variations documented in standards such as Queensland's MR Method Q229A and Western Australia's MRWA 220.1 and 220.2. The test is used by 47 U.S. states, making it the predominant toughness indicator for aggregates in North America.

Test Limitations: Lab Results vs. Field Performance

Despite its widespread use, the LA abrasion test is an empirical method and does not directly predict field performance. Field observations generally show poor correlation between LA abrasion values and actual pavement durability. Some aggregates—particularly slag and certain limestones—exhibit high LA abrasion loss in the laboratory yet perform adequately in service. The test does correlate reasonably well with dust formation during handling and HMA production: aggregates with higher LA abrasion loss values typically generate more dust, which can complicate mixture control and raise environmental concerns.

Alternative Methods: The Micro-Deval Test

Research has identified the Micro-Deval apparatus as the only common alternative with improved predictive capability for field performance. Unlike the LA abrasion test, the Micro-Deval method incorporates water during abrasion, simulating wet conditions more representative of real-world exposure. For aggregates that show high LA abrasion loss but good field performance, the Micro-Deval test may provide a more reliable durability assessment.

Practical Takeaways for Specifiers

When you specify aggregates based on LA abrasion values, keep these points in mind:

  • Lower LA values indicate tougher material, but do not assume they guarantee superior field performance in all applications.
  • Some aggregate types—particularly slag and limestone—can perform well despite high LA loss values. Review local experience and field data before rejecting materials solely on test results.
  • High LA abrasion loss correlates with dust generation during handling and production. If dust control is critical, favor aggregates with lower loss values.
  • For high-stress applications—such as open-graded HMA or heavy-duty pavements—LA abrasion resistance becomes more important, as coarse particles carry higher contact stresses without fine-aggregate cushioning.
  • Consider supplementing LA abrasion data with Micro-Deval results if field performance concerns arise or if wet conditions dominate the service environment.

The LA abrasion test remains a standard tool for aggregate qualification, but it works best as part of a broader materials evaluation that includes field history, mineralogy, and site-specific loading conditions. For further guidance on aggregate durability and construction material performance, consult regional specifications and performance records from comparable projects.