Superpave Mix Design Flashcards

In Superpave mix design, what does the term 'N_design' refer to?

Answer: The number of gyrations used to compact specimens to the design air void level

N_design is the number of gyrator compaction cycles at which the mix must achieve 4% air voids, representing the expected traffic loading.

Which Superpave aggregate property measures resistance to polishing under traffic?

Answer: Flat and Elongated particle content

The Los Angeles Abrasion (LAA) test measures aggregate resistance to degradation, but polishing resistance is assessed via the British Pendulum or other polish tests; however, in Superpave, CAA and uncompacted void content address angularity, not polishing — polishing resistance is evaluated through aggregate source approval.

What is the primary purpose of the Superpave gyratory compactor (SGC)?

Answer: To simulate field compaction by applying a kneading action with a fixed angle and pressure

The SGC simulates field compaction by rotating specimens at a 1.25° angle under 600 kPa pressure, replicating the kneading action of rubber-tired rollers.

In Superpave volumetric design, VMA stands for:

Answer: Voids in the Mineral Aggregate

VMA (Voids in the Mineral Aggregate) is the intergranular void space in the compacted aggregate skeleton, including air voids and effective binder content.

A Superpave mix design shows VFA = 58% at the design air void content. What does this indicate?

Answer: The binder fills only 58% of the VMA, which may be too low for adequate durability

VFA below 65% is generally below the minimum threshold, indicating insufficient binder to coat aggregates adequately, which can reduce durability and fatigue life.

Which parameter is used to select the Superpave performance grade (PG) binder for a given project?

Answer: Design pavement temperature range at the project location and traffic level

PG binder selection is based on the high pavement design temperature (rutting) and low pavement design temperature (cracking) at the project site, adjusted for traffic speed and volume.

In Superpave, what is the significance of the 'restricted zone' on the 0.45-power gradation chart?

Answer: Gradations passing through this zone were found to produce tender mixes prone to rutting, though its use is now optional

The restricted zone was originally established to avoid tender, rut-prone mixes from excess fine sand, but NCHRP research showed it was not always necessary and AASHTO made it optional.