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

The LA test uses a dry rotating drum with large steel balls, while the Micro-Deval test uses water and small steel balls to simulate wet abrasion conditions.

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

Different gradings use different steel ball charges and particle sizes, so LA loss values between gradings are not directly comparable.

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

Pre-existing dust and fines would pass the No. 12 sieve regardless of abrasion, inflating the measured loss; washing removes them before testing.

Question 4

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

Accepted Answer

2%

Answer

ASTM C131 precision data show a single-operator coefficient of variation of approximately 2%, meaning repeat tests by the same operator should be within about 6% of each other.

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 C covers material passing 3/8 in. and retained on No. 4, while Grading B covers 3/4–3/8 in.; for material all passing 3/4 in. and retained on No. 4, the composite falls under Grading C.

(ATT) ACI Aggregate Testing Technician Practice Test

(ATT) ACI Aggregate Testing Technician Practice Test

ATT Los Angeles Abrasion Testing 5