ATT Aggregate Sampling & Reduction 3 — Questions and Answers
Question 1: Per ASTM C702, which reduction method is NOT recommended for fine aggregate because it can introduce segregation errors?
- Mechanical splitter method
- Miniature stockpile method (Correct answer)
- Quartering method
- Incremental belt sampling
Correct answer: Miniature stockpile method
The miniature stockpile method is not recommended for fine aggregate because fine particles can segregate when formed into a small conical pile.
Question 2: What minimum sample mass of coarse aggregate (3/4-in. maximum size) is typically required for a field sample per ASTM D75?
- 5 kg (11 lb)
- 25 kg (55 lb) (Correct answer)
- 50 kg (110 lb)
- 100 kg (220 lb)
Correct answer: 25 kg (55 lb)
ASTM D75 specifies approximately 25 kg (55 lb) as the minimum field sample mass for coarse aggregate with a 3/4-in. nominal maximum size.
Question 3: When sampling freshly mixed concrete at a job site for aggregate content verification, which standard governs obtaining the composite sample of fresh concrete?
- ASTM D75
- ASTM C702
- ASTM C172 (Correct answer)
- ASTM C136
Correct answer: ASTM C172
ASTM C172 covers sampling freshly mixed concrete, from which aggregate-related tests such as unit weight and air content are then performed.
Question 4: What effect does over-drying an aggregate sample before splitting have on test results?
- It has no effect because splitting is a purely mechanical process
- It can cause soft particles to break down, altering gradation results
- It permanently increases the bulk specific gravity reading
- It prevents accurate moisture content determination of the field sample (Correct answer)
Correct answer: It prevents accurate moisture content determination of the field sample
If a field sample is oven-dried before splitting, its original field moisture is destroyed, making it impossible to determine the as-received moisture content.
Question 5: Which of the following best describes a 'composite sample' as defined in ASTM D75?
- A sample taken from the highest point of a stockpile only
- A single grab taken rapidly from a flowing stream
- A sample made up of several increments combined together (Correct answer)
- A sample taken from finished laboratory-prepared material
Correct answer: A sample made up of several increments combined together
A composite sample is formed by combining multiple individual increments collected from different points or times to represent a lot of material.
Question 6: When sampling from a truck or rail car, at how many approximately equal depth-interval locations across the load should increments be taken?
- One increment from the geometric center only
- Two increments from opposite corners
- At least three locations across the load (Correct answer)
- Five locations only at the edges
Correct answer: At least three locations across the load
ASTM D75 recommends collecting increments from at least three locations across the load at approximately equal depth intervals to account for variation within the unit.
Question 7: Why is it important to sample aggregate from a moving conveyor belt rather than from a stationary pile whenever possible?
- Belt samples have higher moisture content, making them easier to handle
- Moving belt samples capture the full cross-section of material flow, reducing segregation bias (Correct answer)
- Belt sampling is faster and requires less equipment
- Stationary piles are restricted areas under OSHA regulations
Correct answer: Moving belt samples capture the full cross-section of material flow, reducing segregation bias
Sampling from a moving belt captures the complete cross-section of aggregate being conveyed, avoiding the segregation bias inherent in stockpile sampling.
ATT Aggregate Sampling & Reduction 3
Per ASTM C702, which reduction method is NOT recommended for fine aggregate because it can introduce segregation errors?