PIC Roller Pattern & Compaction Equipment 2 — Questions and Answers
Question 1: When using a vibratory steel drum roller, at what speed should the roller typically operate to achieve effective compaction without causing mix displacement?
- 1–3 mph (Correct answer)
- 4–6 mph
- 7–9 mph
- 10–12 mph
Correct answer: 1–3 mph
Vibratory rollers should operate at 1–3 mph to allow sufficient dwell time for the vibration to densify the mix without shoving or tearing.
Question 2: Which roller configuration is BEST suited for breakdown rolling immediately behind the paver?
- Pneumatic tire roller
- Steel tandem vibratory roller (Correct answer)
- Three-wheel static roller
- Pad-foot compactor
Correct answer: Steel tandem vibratory roller
A steel tandem vibratory roller is typically used for breakdown rolling because it provides high compactive effort closest to the paver while the mix is hottest.
Question 3: What is the primary purpose of the finish (third) pass in a three-stage compaction operation?
- To achieve target density
- To remove roller marks and surface blemishes (Correct answer)
- To increase the number of roller passes
- To cool the mat rapidly
Correct answer: To remove roller marks and surface blemishes
The finish pass uses a static roller or smooth-drum pass to remove any marks, tears, or surface irregularities left by previous rolling stages.
Question 4: A roller operator notices the asphalt mat is cracking transversely ahead of the drum. What is the MOST likely cause?
- Mix temperature is too high
- Mix temperature is too low (Correct answer)
- Roller speed is too slow
- Vibration frequency is too low
Correct answer: Mix temperature is too low
Transverse cracking ahead of the drum indicates the mix has cooled below the minimum compaction temperature and has become too stiff to compact without fracturing.
Question 5: For a 4-inch compacted lift of dense-graded HMA, how many passes with a vibratory roller are typically required to achieve 92–96% density?
- 1–2 passes
- 3–5 passes (Correct answer)
- 8–12 passes
- 15–20 passes
Correct answer: 3–5 passes
Typically 3–5 passes of a vibratory roller are needed for standard HMA lifts; exact count depends on mix type, roller weight, and amplitude settings.
Question 6: What effect does increasing the amplitude on a vibratory roller have on compaction of a thin HMA lift?
- Improves density uniformly throughout the lift
- May cause mix displacement and segregation (Correct answer)
- Reduces compaction effort
- Has no effect on thin lifts
Correct answer: May cause mix displacement and segregation
High amplitude generates large force that can over-compact or displace a thin lift, causing shoving and segregation rather than uniform densification.
Question 7: During compaction, an inspector observes that the pneumatic tire roller is leaving depressions in the mat. What corrective action should be taken FIRST?
- Increase tire inflation pressure (Correct answer)
- Slow down roller speed
- Reduce tire inflation pressure
- Switch to a steel drum roller immediately
Correct answer: Increase tire inflation pressure
Increasing tire inflation pressure distributes the roller's load over a smaller contact area, reducing the indentation caused by under-inflated tires on a soft mat.
PIC Roller Pattern & Compaction Equipment 2
When using a vibratory steel drum roller, at what speed should the roller typically operate to achieve effective compaction without causing mix displacement?