Los Angeles Abrasion Testing Flashcards

The shelf (lifter) inside the LA abrasion machine drum is positioned:

Answer: Projecting inward along the full length of the drum

The shelf projects inward along the full interior length of the drum to lift and tumble the charge during rotation.

If a technician finds that the LA machine drum rotational speed is 40 rpm instead of the specified range, the test result will likely:

Answer: Be invalid and must be discarded per ASTM C131

ASTM C131 specifies a speed of 30–33 rpm; results obtained outside this range are not valid per the standard.

Which characteristic of the steel balls (charge) must be verified before each LA abrasion test?

Answer: Total mass of the charge within the specified tolerance

The total charge mass must meet the specification for the grading used (e.g., 5,000 ± 25 g for Grading A), verified by weighing.

A technician performing the LA abrasion test washes and dries the test sample before testing. The drying temperature should be:

Answer: 110 ± 5°C (230 ± 9°F)

The sample must be dried to constant mass at 110 ± 5°C (230 ± 9°F) before testing per ASTM C131.

After running the LA abrasion test, the retained material on the No. 12 sieve should be:

Answer: Washed, dried to constant mass, then weighed

The material retained on the No. 12 sieve is washed and dried to constant mass at 110 ± 5°C before final weighing.

An aggregate sample has an original dry mass of 5,000 g. After the LA abrasion test, 4,150 g is retained on the No. 12 sieve. What is the percent loss?

Answer: 17%

Loss = (5,000 − 4,150) ÷ 5,000 × 100 = 850 ÷ 5,000 × 100 = 17%.

Which aggregate type generally produces the HIGHEST LA abrasion loss values?

Answer: Soft limestone

Soft limestone is less resistant to abrasion and impact than granite, quartzite, or basalt, yielding higher percent loss.