NETTCP Sampling Methods 4 — Questions and Answers
Question 1: What is the purpose of a 'split sample' in transportation materials testing?
- To create two identical samples for independent testing or referee analysis (Correct answer)
- To separate coarse from fine aggregate before testing
- To reduce sample size by half using quartering
- To eliminate moisture from the sample
Correct answer: To create two identical samples for independent testing or referee analysis
Split samples allow independent verification by the agency and contractor, or serve as a referee sample if results are disputed.
Question 2: When sampling liquid asphalt binder from a delivery tanker, from which location should the sample be drawn?
- Top access hatch only
- Bottom drain valve only
- Through the sample valve at a mid-level or from multiple points (Correct answer)
- From the pump inlet exclusively
Correct answer: Through the sample valve at a mid-level or from multiple points
Sampling through a dedicated sample valve or at multiple tank levels ensures a representative sample of the homogeneous binder.
Question 3: According to AASHTO practice, pavement cores taken for density determination should be extracted at what minimum distance from the edge of the pavement?
- 3 inches
- 6 inches
- 12 inches (Correct answer)
- 18 inches
Correct answer: 12 inches
Cores must be taken at least 12 inches from the pavement edge to avoid edge effects that could produce unrepresentative density results.
Question 4: A technician is sampling embankment fill for moisture-density control. The fill lifts are 8 inches thick. Where should in-place density tests be located vertically within the lift?
- At the very top surface
- At mid-depth of the compacted lift (Correct answer)
- At the bottom interface with the underlying lift
- Alternating between top and bottom on each lift
Correct answer: At mid-depth of the compacted lift
Density tests should be performed at mid-depth of the compacted lift to measure the representative density of that layer.
Question 5: What does the term 'lot' refer to in pavement quality acceptance sampling plans?
- A single truckload of material
- A defined quantity of material for which one acceptance decision is made (Correct answer)
- The entire project material supply
- A sample taken at a specific station
Correct answer: A defined quantity of material for which one acceptance decision is made
A lot is a defined quantity (e.g., by tonnage or area) that is evaluated together to make a single accept/reject or pay-factor decision.
Question 6: When using a nuclear density gauge on a compacted aggregate base, the gauge must be kept at what minimum distance from vertical obstructions like curbs or pavement edges?
- 3 inches
- 6 inches
- 12 inches (Correct answer)
- 18 inches
Correct answer: 12 inches
Nuclear density gauges require at least 12 inches of clearance from vertical edges to prevent scatter readings from distorting results.
Question 7: For Portland cement concrete pavement testing, cylinder specimens are fabricated from field samples. Which curing condition is required immediately after fabrication?
- Oven drying at 105°C for 24 hours
- Initial moist curing at 60–80°F for the first 24–48 hours at the field site (Correct answer)
- Immediate freezing to arrest hydration
- Air curing in direct sunlight for 7 days
Correct answer: Initial moist curing at 60–80°F for the first 24–48 hours at the field site
Freshly cast concrete cylinders must be moist-cured at the field site within the specified temperature range to prevent early drying or freezing before transport to the lab.
NETTCP Sampling Methods 4
What is the purpose of a 'split sample' in transportation materials testing?