ATT Los Angeles Abrasion Testing 3 — Questions and Answers
Question 1: The shelf (lifter) inside the LA abrasion machine drum is positioned:
- On the outside of the drum parallel to the axis
- Projecting inward along the full length of the drum (Correct answer)
- At a 45-degree angle to redirect aggregate flow
- Bolted to the drum door as a removable insert
Correct 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.
Question 2: If a technician finds that the LA machine drum rotational speed is 40 rpm instead of the specified range, the test result will likely:
- Be unaffected because total revolutions still equals 500
- Overestimate abrasion loss due to increased impact energy
- Underestimate abrasion loss due to reduced tumbling action
- Be invalid and must be discarded per ASTM C131 (Correct answer)
Correct 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.
Question 3: Which characteristic of the steel balls (charge) must be verified before each LA abrasion test?
- Surface hardness using a Rockwell hardness tester
- Total mass of the charge within the specified tolerance (Correct answer)
- Individual ball diameter measured with calipers
- Ball roundness verified with a sphericity gauge
Correct 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.
Question 4: A technician performing the LA abrasion test washes and dries the test sample before testing. The drying temperature should be:
- 60 ± 3°C (140 ± 5°F)
- 110 ± 5°C (230 ± 9°F) (Correct answer)
- 150 ± 5°C (302 ± 9°F)
- 175 ± 5°C (347 ± 9°F)
Correct 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.
Question 5: After running the LA abrasion test, the retained material on the No. 12 sieve should be:
- Weighed as-is immediately after sieving
- Washed, dried to constant mass, then weighed (Correct answer)
- Air-dried for 24 hours then weighed
- Weighed wet and corrected using absorption factor
Correct 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.
Question 6: 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?
- 15%
- 17% (Correct answer)
- 19%
- 21%
Correct answer: 17%
Loss = (5,000 − 4,150) ÷ 5,000 × 100 = 850 ÷ 5,000 × 100 = 17%.
Question 7: Which aggregate type generally produces the HIGHEST LA abrasion loss values?
- Granite
- Quartzite
- Soft limestone (Correct answer)
- Basalt
Correct answer: Soft limestone
Soft limestone is less resistant to abrasion and impact than granite, quartzite, or basalt, yielding higher percent loss.
ATT Los Angeles Abrasion Testing 3
The shelf (lifter) inside the LA abrasion machine drum is positioned: