ATT Aggregate Sampling & Reduction 2 — Questions and Answers
Question 1: According to ASTM D75, what is the minimum number of increments required to constitute a field sample of aggregate from a conveyor belt?
- 3 increments taken at random intervals (Correct answer)
- 5 increments taken at random intervals
- 10 increments taken at regular intervals
- 2 increments taken from the head and tail of the belt
Correct answer: 3 increments taken at random intervals
ASTM D75 requires a minimum of 3 increments taken at random intervals to form a representative field sample from a conveyor belt.
Question 2: When sampling aggregates from a stockpile, where should samples generally NOT be taken from?
- The center of the stockpile at mid-height
- The outer surface or slope of the stockpile (Correct answer)
- The base of the stockpile using a trenching method
- Freshly placed material near the delivery point
Correct answer: The outer surface or slope of the stockpile
Segregation occurs along the outer slopes of stockpiles, making surface samples unrepresentative of the bulk material.
Question 3: The purpose of a sample splitter (riffle splitter) is to:
- Increase the moisture content of the sample before testing
- Reduce a large sample to a smaller representative portion (Correct answer)
- Separate fine aggregate from coarse aggregate by size
- Measure the bulk specific gravity of the sample
Correct answer: Reduce a large sample to a smaller representative portion
A riffle splitter divides a sample into two equal halves, allowing repeated halving to reach a target sample mass while maintaining representativeness.
Question 4: Under ASTM C702, which method of sample reduction is acceptable for both fine and coarse aggregate?
- Miniature stockpile method only
- Quartering method only
- Both the mechanical splitter and quartering method (Correct answer)
- Incremental sampling from a belt only
Correct answer: Both the mechanical splitter and quartering method
ASTM C702 permits both mechanical splitting and the quartering method for reducing aggregate samples of fine or coarse aggregate.
Question 5: When using the quartering method per ASTM C702, after forming the flat circular pile and dividing into four quarters, which portions are kept?
- All four quarters are combined into one container
- Two diagonally opposite quarters are discarded and the other two are combined (Correct answer)
- Two adjacent quarters are kept and two are discarded
- One random quarter is selected and the rest are discarded
Correct answer: Two diagonally opposite quarters are discarded and the other two are combined
In quartering, two diagonally opposite quarters are kept and recombined; the other two opposite quarters are discarded, ensuring a representative half-sample.
Question 6: What is the primary reason aggregate samples should be transported to the laboratory in sealed, airtight containers or bags?
- To prevent loss of fines and moisture change (Correct answer)
- To allow gases to escape from the aggregate pores
- To maintain the aggregate's specific gravity
- To prevent oxidation of the aggregate surface
Correct answer: To prevent loss of fines and moisture change
Sealing samples prevents loss of fine material and limits evaporation or absorption of moisture, both of which affect test results.
Question 7: In ASTM D75, what does the term 'lot' refer to when sampling aggregates from a production unit?
- A single truck delivery to a job site
- A defined quantity of material from which a sample is obtained for quality acceptance (Correct answer)
- The total annual output of a quarry
- A stockpile formed from one day's crushing operation
Correct answer: A defined quantity of material from which a sample is obtained for quality acceptance
A 'lot' is a defined quantity of material selected for sampling and evaluation to determine whether it meets specification requirements.
ATT Aggregate Sampling & Reduction 2
According to ASTM D75, what is the minimum number of increments required to constitute a field sample of aggregate from a conveyor belt?