PIC Quality Acceptance Sampling 3 — Questions and Answers
Question 1: A nuclear density gauge reading shows 93.5% of the maximum theoretical density (MTD). The specification requires a minimum of 92%. What is the inspector's correct action?
- Accept the area; it meets the density specification (Correct answer)
- Reject the area; it is below the minimum density
- Require additional compaction passes immediately
- Request a core sample to verify the nuclear gauge
Correct answer: Accept the area; it meets the density specification
93.5% MTD exceeds the 92% minimum, so the area passes the density requirement and should be accepted.
Question 2: Which factor most directly affects the reliability of a field-extracted asphalt core for density testing?
- Core location relative to longitudinal joints and wheelpath (Correct answer)
- The time of day the core is extracted
- The brand of coring equipment used
- The color of the pavement surface
Correct answer: Core location relative to longitudinal joints and wheelpath
Cores taken near joints or wheel paths can yield anomalous density readings that do not represent the broader lot quality.
Question 3: What is the purpose of a random number table or random number generator in acceptance sampling?
- To remove inspector bias in selecting sample locations (Correct answer)
- To calculate the lot average density
- To determine the number of sublots needed
- To schedule the paving contractor's deliveries
Correct answer: To remove inspector bias in selecting sample locations
Random number tools ensure sample locations are selected without intentional or unintentional bias, supporting statistical validity.
Question 4: When using the 'percent within limits' (PWL) method, a higher PWL value indicates:
- A greater proportion of the lot meets specification limits (Correct answer)
- Higher variability in the test results
- Lower air void content in the mix
- A reduced number of tests were performed
Correct answer: A greater proportion of the lot meets specification limits
PWL represents the estimated percentage of the lot that falls within upper and lower specification limits; higher PWL means more conforming material.
Question 5: An inspector notices that all density cores from a lot were taken in the center of the lane, away from edges. This sampling approach is best described as:
- Biased sampling that may overestimate lot quality (Correct answer)
- Stratified random sampling as required by AASHTO
- Systematic sampling based on stationing
- Composite sampling for mix design verification
Correct answer: Biased sampling that may overestimate lot quality
Sampling only the center of lanes avoids areas that typically have lower compaction (edges), introducing bias that inflates average density results.
Question 6: Which test method is commonly used to determine the maximum theoretical density (Rice value) of an HMA mix?
- AASHTO T 209 (Correct answer)
- AASHTO T 166
- AASHTO T 30
- AASHTO T 283
Correct answer: AASHTO T 209
AASHTO T 209 (the Rice test) determines the theoretical maximum specific gravity of loose HMA, which is used to calculate percent density from cores.
Question 7: During lot acceptance, if the standard deviation of air voids is very high relative to the mean, the inspector should:
- Investigate production variability and consider reduced pay or rejection (Correct answer)
- Accept the lot if the mean air void value meets the target
- Increase roller passes to reduce air voids
- Reduce the lot size to lower the standard deviation
Correct answer: Investigate production variability and consider reduced pay or rejection
High variability signals inconsistent production; even if the mean is acceptable, large swings indicate portions of the lot likely fall outside specification limits.
PIC Quality Acceptance Sampling 3
A nuclear density gauge reading shows 93.5% of the maximum theoretical density (MTD).
The specification requires a minimum of 92%.
What is the inspector's correct action?