ATT Los Angeles Abrasion Testing 5

Question 1

How does the LA abrasion test differ from the Micro-Deval abrasion test (ASTM D6928)?

Accepted Answer

LA uses a dry drum with large steel balls; Micro-Deval uses water and small steel balls

Answer

LA uses water and small steel balls; Micro-Deval uses a dry drum only

Answer

LA tests fine aggregate only; Micro-Deval tests coarse aggregate only

Answer

Both tests are identical but use different revolution counts

Question 2

An aggregate source produces two gradations: one tested per Grading C and one per Grading D of ASTM C131. Which statement about comparing the results is correct?

Accepted Answer

Results may not be directly comparable because gradation and charge differ between gradings

Answer

Results are directly comparable because the test machine is the same

Answer

Grading D always gives a lower loss value than Grading C for the same source

Answer

Results must be averaged to obtain the representative value for the source

Question 3

What is the purpose of washing the aggregate sample before the LA abrasion test?

Accepted Answer

To remove dust and fines that would falsely inflate the abrasion loss

Answer

To increase particle density before weighing

Answer

To activate the aggregate surface for better steel-ball contact

Answer

To check for water absorption before the dry test

Question 4

The single-operator precision (1s%) for the LA abrasion test per ASTM C131 is approximately:

Accepted Answer

2%

Answer

0.5%

Answer

10%

Answer

20%

Question 5

A recycled concrete aggregate (RCA) source is suspected to have high abrasion loss. Which grading would most likely be selected for an LA abrasion test if the RCA is all passing 3/4 in. (19 mm) and retained on No. 4 (4.75 mm)?

Accepted Answer

Grading C

Answer

Grading A

Answer

Grading B

Answer

Grading D

Question 6

During an LA abrasion test, the drum is accidentally stopped at 450 revolutions due to a power outage. The technician should:

Accepted Answer

Discard the sample and start the test over with a fresh specimen

Answer

Extrapolate the result to 500 revolutions mathematically

Answer

Complete the remaining 50 revolutions after power is restored

Answer

Report the result as-is, noting the deviation in the test report

Question 7

Which scenario would cause the LA abrasion loss to be artificially LOWER than the true value?

Accepted Answer

Failing to wash fines off the sample before testing

Answer

Using more steel balls than specified for the grading

Answer

Drying the sample to a higher temperature than specified

Answer

Running the drum at a slightly higher speed than specified