NETTCP Asphalt Technology 5 — Questions and Answers
Question 1: Which type of asphalt mix is typically used for open-graded friction course (OGFC) applications?
- Dense-graded HMA with 4% air voids
- Gap-graded or open-graded mix with 15–20% air voids (Correct answer)
- Stone matrix asphalt (SMA) with polymer binder
- Cold-mix emulsion with fine aggregate
Correct answer: Gap-graded or open-graded mix with 15–20% air voids
OGFC mixes are intentionally open-graded with high air void content (15–20%) to allow water to drain through the surface, reducing hydroplaning.
Question 2: In reclaimed asphalt pavement (RAP) usage, what must be done to account for the aged binder already in RAP material?
- Add extra compaction effort to crush RAP particles
- Increase the virgin binder grade to compensate for stiffened RAP binder (Correct answer)
- Replace all RAP binder with emulsified asphalt
- Heat RAP to 500°F to rejuvenate the aged binder
Correct answer: Increase the virgin binder grade to compensate for stiffened RAP binder
Because RAP contains stiff, aged binder, the virgin binder grade is often softened (lower high-temp grade) to blend with RAP binder and achieve the target PG grade.
Question 3: What is 'shoving' in asphalt pavement, and what commonly causes it?
- Longitudinal cracking caused by frost heave
- Transverse displacement of the pavement surface caused by braking or turning forces on unstable mix (Correct answer)
- Edge cracking from lack of lateral support
- Surface delamination from poor tack coat application
Correct answer: Transverse displacement of the pavement surface caused by braking or turning forces on unstable mix
Shoving is a form of plastic deformation where traffic braking or turning forces push asphalt laterally, creating humps or waves, often from mix instability.
Question 4: What is the function of mineral filler (material passing the No. 200 sieve) in an asphalt mix?
- To increase the air void content of the compacted mix
- To fill the void space between larger aggregates and stiffen the asphalt mortar (Correct answer)
- To replace asphalt binder and reduce mix cost
- To improve aggregate angularity and interlock
Correct answer: To fill the void space between larger aggregates and stiffen the asphalt mortar
Mineral filler fills microscopic voids between aggregate particles and stiffens the asphalt mastic, improving mix stability and durability.
Question 5: Which test is used to evaluate moisture sensitivity (stripping susceptibility) of a compacted asphalt mix?
- Cantabro loss test
- Tensile strength ratio (TSR) test per AASHTO T 283 (Correct answer)
- Bending beam rheometer test
- Flat and elongated particle test
Correct answer: Tensile strength ratio (TSR) test per AASHTO T 283
The TSR test compares the tensile strength of conditioned (water-soaked) specimens to unconditioned specimens; a ratio below 0.80 indicates moisture susceptibility.
Question 6: What does 'raveling' describe as a pavement distress mode?
- Transverse cracking from thermal contraction
- Progressive loss of aggregate from the pavement surface due to loss of binder adhesion (Correct answer)
- Longitudinal cracking along the wheel paths
- Surface uplift from frost action
Correct answer: Progressive loss of aggregate from the pavement surface due to loss of binder adhesion
Raveling occurs when the asphalt binder fails to hold aggregate particles together, leading to surface deterioration and loss of aggregate.
Question 7: In New England climates, which pavement distress is most directly associated with freeze-thaw cycles and poor drainage?
- Rutting from high summer temperatures
- Thermal cracking and pothole formation (Correct answer)
- Bleeding from excess binder
- Shoving from heavy braking forces
Correct answer: Thermal cracking and pothole formation
Freeze-thaw cycles cause water in pavement cracks to expand as ice, widening cracks and dislodging chunks of pavement to form potholes.
NETTCP Asphalt Technology 5
Which type of asphalt mix is typically used for open-graded friction course (OGFC) applications?