PIC Roller Pattern & Compaction Equipment 3 — Questions and Answers
Question 1: What is the term used to describe the overlap of successive roller passes to ensure full coverage of the mat width?
- Pass increment (Correct answer)
- Overlap strip
- Echelon offset
- Lane transition
Correct answer: Pass increment
A pass increment (or lane offset) defines how far the roller moves laterally between passes to ensure the entire mat width receives consistent compactive effort.
Question 2: When compacting a superpaved mix with a nominal maximum aggregate size of 19 mm, what is the recommended maximum loose lift thickness?
- 1.5 times NMAS (≈ 1.1 in)
- 3 times NMAS (≈ 2.25 in) (Correct answer)
- 5 times NMAS (≈ 3.75 in)
- 8 times NMAS (≈ 6 in)
Correct answer: 3 times NMAS (≈ 2.25 in)
A general rule of thumb is that loose lift thickness should not exceed 3 times the NMAS to ensure aggregate interlock and adequate compaction throughout the lift.
Question 3: A pneumatic tire roller is MOST effective for which compaction task?
- Breakdown rolling of open-graded friction course
- Kneading and sealing the surface after intermediate rolling (Correct answer)
- Achieving initial density on freshly placed HMA
- Compacting cold joints
Correct answer: Kneading and sealing the surface after intermediate rolling
Pneumatic tire rollers are best at intermediate and finish rolling where their kneading action seals the surface and fills voids without displacing the partially cooled mix.
Question 4: What minimum temperature (°F) is typically recommended for breakdown rolling of a PG 64-22 mix?
- 275°F (Correct answer)
- 290°F
- 220°F
- 175°F
Correct answer: 275°F
Breakdown rolling for a PG 64-22 mix should begin while the mat is still above approximately 275°F to allow adequate workability and density achievement.
Question 5: Which of the following BEST describes the 'echelon paving' technique and its effect on compaction?
- Pavers offset laterally to allow roller access to the hot longitudinal joint
- Multiple pavers paving adjacent lanes simultaneously to keep the joint hot (Correct answer)
- Pavers overlapping lanes by 6 inches to thicken the edge
- Single paver operating in reverse to achieve double density
Correct answer: Multiple pavers paving adjacent lanes simultaneously to keep the joint hot
Echelon paving uses multiple pavers operating side by side so the longitudinal joint between lanes is compacted while both sides are still hot, yielding higher joint density.
Question 6: What roller defect can occur when the vibratory frequency is set too high relative to roller travel speed?
- Insufficient compaction depth
- Chatter marks or washboard surface texture (Correct answer)
- Rapid cooling of the mat
- Horizontal cracking in the mat
Correct answer: Chatter marks or washboard surface texture
When frequency is too high relative to roller speed, the drum strikes the mat too frequently in a short distance, creating a repeating indentation pattern known as chatter or washboard marks.
Question 7: An inspector is checking compaction with a nuclear gauge near the centerline of a freshly compacted lane. The reading is lower than expected. Which roller pattern error is MOST likely?
- The roller made too many passes at the edge
- The roller made fewer passes at the centerline than at the edges (Correct answer)
- The roller operated at too high a frequency
- The finish roller was traveling too slowly
Correct answer: The roller made fewer passes at the centerline than at the edges
Insufficient pass count near the lane centerline is a common pattern error that results in a density trough in the middle of the mat.
PIC Roller Pattern & Compaction Equipment 3
What is the term used to describe the overlap of successive roller passes to ensure full coverage of the mat width?