The Los Angeles Abrasion Test: How Well Does Rock Resist Impact and Wear?
The Los Angeles test measures aggregate resistance to abrasion and impact. Learn ASTM C131 and C535, how percent loss is calculated and what it means.
Quality and technical information
Flat and Elongated Particles: Why Particle Shape Matters
Flat and elongated particles reduce compaction and workability and break under load. Learn how they are measured, what they do and how production reduces them.
Two aggregate samples with the same grading curve can behave very differently. A main reason is particle shape. A flat particle is thin, an elongated one is long, and both are far from a cubical particle.
Why these particles are undesirable
- In concrete: they have more specific surface, raise water demand and reduce workability.
- In asphalt: they break during compaction and change the grading of the mix.
- In road layers: they interlock poorly and make compaction harder.
How they are measured
ASTM D4791 measures the dimensional ratios of each particle with a proportional caliper. Ratios such as 3:1 or 5:1 are chosen according to the project specification. In European standards, the flakiness index is determined by EN 933-3 using slotted sieves. These methods do not give the same result, so the test method must be stated when comparing numbers.
What affects them in production
Particle shape is largely made at the crushing stage:
- The rock type and its layered structure
- The crusher type and its setting
- The reduction ratio at each stage
- Continuity of feed, especially in cone crushers, which work best with a full chamber
Impact crushers usually produce more cubical particles. See Types of crusher.
Place in specifications
The limit depends on the use and is usually stricter in road and asphalt specifications. To find it, see the project specification and the reference publications on the quality and standards page.
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