NETTCP Sampling Methods 5 — Questions and Answers
Question 1: Which AASHTO standard practice specifically addresses sampling of freshly mixed Portland cement concrete?
- AASHTO R 60
- AASHTO T 141 (Correct answer)
- AASHTO T 23
- AASHTO M 231
Correct answer: AASHTO T 141
AASHTO T 141 is the standard method for sampling freshly mixed concrete.
Question 2: When sampling HMA from windrows (material deposited ahead of the paver), what precaution is most critical?
- Sample only from the center of the windrow, avoiding the edges where heat loss is greatest (Correct answer)
- Avoid sampling windrows — only sample from trucks
- Collect only the top layer to avoid pavement contamination
- Sample immediately before the paver picks up the material to minimize heat loss
Correct answer: Sample only from the center of the windrow, avoiding the edges where heat loss is greatest
Windrow edges lose heat faster and may include pavement contact contamination, so sampling the center provides a more representative and thermally consistent specimen.
Question 3: A technician is directed to obtain a 'random location' for a density test using the random-number method. The test section is 500 feet long and 12 feet wide. If the random numbers generated are 187 and 7, what do these represent?
- Test number 187 at a depth of 7 inches
- Station 187 feet and 7 feet from the reference edge (Correct answer)
- 187th sample in the lot at 7-hour intervals
- Lot 187, sublot 7
Correct answer: Station 187 feet and 7 feet from the reference edge
In the random-number method, the first number typically gives the longitudinal station and the second gives the transverse offset from a reference edge.
Question 4: When a field sample of aggregates is collected, it must be transported to the laboratory in a container that:
- Is always plastic to prevent contamination from metal
- Is clean, rigid, and prevents moisture loss or gain (Correct answer)
- Is open-topped to allow air circulation
- Is pre-heated to prevent thermal shock
Correct answer: Is clean, rigid, and prevents moisture loss or gain
Sample containers must be clean and rigid to prevent contamination, and sealed to preserve the in-situ moisture content if required.
Question 5: In acceptance testing, what statistical parameter is most commonly used alongside the mean of test results to quantify variability within a lot?
- Median
- Mode
- Standard deviation (Correct answer)
- Coefficient of variation only
Correct answer: Standard deviation
Standard deviation quantifies the spread of individual test results around the mean, which is used in PWL (percent within limits) calculations for lot acceptance.
Question 6: For sampling soils from a borrow area, which sampling device is best suited to obtain minimally disturbed samples from cohesive soils at depth?
- Bulk auger sampler
- Thin-walled Shelby tube sampler (Correct answer)
- Split-spoon sampler
- Grab sampler
Correct answer: Thin-walled Shelby tube sampler
The thin-walled Shelby tube is designed to obtain minimally disturbed cohesive soil samples by pushing (not driving) the tube into the formation.
Question 7: A project specification requires that sampling locations be documented with GPS coordinates and station references. This documentation requirement primarily serves to:
- Reduce the number of samples needed per lot
- Enable accurate retesting at the exact same location if results are disputed (Correct answer)
- Satisfy environmental permitting requirements only
- Speed up laboratory processing time
Correct answer: Enable accurate retesting at the exact same location if results are disputed
Accurate location documentation allows the same spot to be retested for verification, ensuring the dispute resolution sample reflects the original test conditions.
NETTCP Sampling Methods 5
Which AASHTO standard practice specifically addresses sampling of freshly mixed Portland cement concrete?