NETTCP Sampling Methods 2 — Questions and Answers
Question 1: When sampling hot mix asphalt (HMA) from a truck, which location in the load is generally AVOIDED to reduce segregation bias?
- Middle of the load
- Top surface directly beneath the chute (Correct answer)
- Back of the truck
- Front of the truck
Correct answer: Top surface directly beneath the chute
Material directly beneath the truck's discharge chute tends to be coarser due to segregation and is avoided when sampling.
Question 2: What AASHTO standard governs the sampling of aggregates for road and bridge construction?
- AASHTO T 2 (Correct answer)
- AASHTO T 11
- AASHTO T 27
- AASHTO M 92
Correct answer: AASHTO T 2
AASHTO T 2 is the standard method of sampling aggregates.
Question 3: A technician needs a 5 kg sample but the field sample yielded 20 kg. What process reduces the sample to the required size?
- Scalping
- Quartering or splitting (Correct answer)
- Washing
- Sieving
Correct answer: Quartering or splitting
Mechanical splitting or the quartering method is used to reduce a large field sample to a representative test sample.
Question 4: For soils testing on a highway project, a random sampling plan is preferred over convenience sampling primarily because it:
- Reduces total number of samples needed
- Eliminates operator bias in sample location selection (Correct answer)
- Speeds up the testing process
- Allows sampling only stable areas
Correct answer: Eliminates operator bias in sample location selection
Random sampling removes operator bias, ensuring that every location has an equal probability of being selected.
Question 5: Which equipment is used for mechanical sample splitting of fine-grained soils and aggregates to ensure representative reduction?
- Vibratory screen
- Riffle splitter (sample splitter) (Correct answer)
- Gyrating compactor
- Centrifuge extractor
Correct answer: Riffle splitter (sample splitter)
A riffle splitter divides a sample into two equal halves by directing material alternately into opposite chutes.
Question 6: When collecting a concrete sample from a ready-mix truck, AASHTO R 60 requires discarding the first portion of discharge. How much is typically discarded?
- First 0.25 cubic yards (Correct answer)
- First 10% of the load
- First 1 cubic yard
- None — all discharge is sampled
Correct answer: First 0.25 cubic yards
The first approximately 0.25 cubic yards of discharge is discarded because it may not be representative of the full load.
Question 7: In stratified random sampling of a pavement project, the roadway is divided into equal sections and samples are taken randomly within each. What is the primary advantage of this approach?
- It requires fewer total samples than simple random sampling
- It ensures proportional coverage across the full project length (Correct answer)
- It eliminates the need for field technicians
- It focuses resources on highest-traffic areas
Correct answer: It ensures proportional coverage across the full project length
Stratified random sampling ensures every portion of the project is represented, avoiding gaps that pure random sampling might miss.
