PIC Lift Thickness & Surface Tolerance 2 — Questions and Answers
Question 1: A contractor places a base course lift measuring 4.2 inches compacted when the specification requires 4.0 inches maximum. What is the inspector's appropriate action?
- Accept the lift since it exceeds minimum thickness
- Reject the lift for exceeding the maximum thickness tolerance (Correct answer)
- Allow it if surface smoothness meets spec
- Document it and move on without rejection
Correct answer: Reject the lift for exceeding the maximum thickness tolerance
Maximum lift thickness specifications exist to ensure proper compaction throughout the depth, and exceeding them is a contractual non-conformance requiring rejection or corrective action.
Question 2: What tool is most commonly used to verify compacted lift thickness in the field?
- Nuclear density gauge
- Profilograph
- Pin probe or depth gauge inserted through the mat (Correct answer)
- Straight edge and feeler gauge
Correct answer: Pin probe or depth gauge inserted through the mat
A pin probe or depth gauge inserted through the freshly compacted mat directly measures lift thickness at the point of placement.
Question 3: Surface tolerance for a finished wearing course on an interstate highway is typically measured with a how-long straightedge?
- 4-foot
- 8-foot
- 10-foot (Correct answer)
- 16-foot
Correct answer: 10-foot
A 10-foot straightedge is the standard reference length used to check surface smoothness and tolerance on most state DOT specifications for wearing courses.
Question 4: When compacting multiple thin lifts instead of one thicker lift, the primary disadvantage is:
- Lower pavement density
- Increased risk of tender zone behavior in each lift (Correct answer)
- Higher material cost per ton
- Reduced aggregate interlock
Correct answer: Increased risk of tender zone behavior in each lift
Multiple thin lifts cool faster, increasing tender zone risk where the mix is susceptible to shoving under roller load before it stiffens.
Question 5: A specification allows a surface tolerance of ±0.01 foot from design grade. A measured elevation is 0.013 foot below design grade. The inspector should:
- Accept the reading as within normal variation
- Flag the area as out of tolerance and document it (Correct answer)
- Require immediate milling of the entire lane
- Average it with adjacent readings before deciding
Correct answer: Flag the area as out of tolerance and document it
A reading of 0.013 foot exceeds the ±0.01 foot (±0.12 inch) allowable deviation and must be flagged as out of tolerance per specification.
Question 6: Which factor most significantly affects the required loose lift thickness before compaction?
- Ambient air temperature
- Expected compaction ratio of the mix (Correct answer)
- Asphalt binder grade
- Truck haul distance
Correct answer: Expected compaction ratio of the mix
The compaction ratio (ratio of loose to compacted thickness, typically 1.15–1.35) determines how thick the loose mat must be placed to achieve the specified compacted thickness.
Question 7: On a resurfacing project, the existing pavement surface has a measured rut depth of 1.5 inches. If specification requires final surface tolerance of ±0.25 inch, the leveling course strategy must:
- Place a single 1.5-inch lift and compact to grade
- Use variable-depth leveling passes to fill ruts before wearing course (Correct answer)
- Mill 1.5 inches and place standard lift thickness
- Apply surface treatment rather than hot mix
Correct answer: Use variable-depth leveling passes to fill ruts before wearing course
Rutted surfaces require variable-depth leveling lifts that fill low spots first so the wearing course can be placed at uniform thickness and meet surface tolerance.
PIC Lift Thickness & Surface Tolerance 2
A contractor places a base course lift measuring 4.2 inches compacted when the specification requires 4.0 inches maximum.
What is the inspector's appropriate action?