ATT Sampling Aggregates 3 — Questions and Answers
Question 1: When sampling coarse aggregate from a stationary truck, what depth below the surface should increments be obtained?
- At least 300 mm (12 in.) below the surface (Correct answer)
- From the top 50 mm only
- From the exact center of the load by depth
- Any depth is acceptable if spread evenly
Correct answer: At least 300 mm (12 in.) below the surface
ASTM D75 requires digging at least 300 mm below the surface to avoid the biased, segregated layer at the top of the load.
Question 2: Which of the following is the most reliable method for obtaining a representative sample of fine aggregate from a stockpile?
- Sampling from the flowing stream as material is loaded from the pile (Correct answer)
- Scooping from multiple surface locations on the pile
- Taking a single large sample from the pile base
- Sampling only from the pile center
Correct answer: Sampling from the flowing stream as material is loaded from the pile
Sampling from the moving stream during loading captures material from throughout the stockpile and avoids surface segregation bias.
Question 3: The term 'field sample' in ASTM D75 refers to:
- The sample collected at the source before any reduction (Correct answer)
- A sample taken directly from the field pavement
- A reduced sample prepared in the laboratory
- Any sample collected outside a controlled environment
Correct answer: The sample collected at the source before any reduction
The field sample is the total quantity of aggregate collected on-site from the source before it is reduced to individual test specimens.
Question 4: Which condition makes it necessary to increase the number of increments when sampling from a conveyor belt?
- When the material shows high variability or segregation (Correct answer)
- When the belt is moving slowly
- When the aggregate is fine-grained only
- When ambient temperature is above 90°F
Correct answer: When the material shows high variability or segregation
Higher material variability requires more increments to achieve a composite sample that adequately represents the aggregate being sampled.
Question 5: Aggregate sampling plans should be developed with input from which parties?
- All parties involved in the project including purchaser, producer, and testing laboratory (Correct answer)
- Only the project owner and contractor
- Only the testing laboratory
- Only the aggregate producer
Correct answer: All parties involved in the project including purchaser, producer, and testing laboratory
ASTM D75 recommends that sampling plans be developed cooperatively among all stakeholders to ensure the plan meets project acceptance requirements.
Question 6: What is the minimum sample mass recommended for a field sample of 37.5 mm (1.5 in.) nominal maximum size coarse aggregate per ASTM D75?
- Approximately 100 kg (220 lb) (Correct answer)
- Approximately 10 kg (22 lb)
- Approximately 50 kg (110 lb)
- Approximately 5 kg (11 lb)
Correct answer: Approximately 100 kg (220 lb)
ASTM D75 Table 1 specifies approximately 100 kg for 37.5 mm NMAS to ensure enough material is available for all required tests after reduction.
Question 7: When a sample of aggregate is transported to the laboratory, it should be stored in:
- A clean, sealed container that prevents contamination and moisture change (Correct answer)
- An open bucket for air drying
- A permeable burlap bag
- Any available container as long as it is labeled
Correct answer: A clean, sealed container that prevents contamination and moisture change
A sealed, clean container prevents contamination from foreign materials and preserves the in-situ moisture content until testing.
ATT Sampling Aggregates 3
When sampling coarse aggregate from a stationary truck, what depth below the surface should increments be obtained?