CCIL Superpave Mix Design 4

Question 1

What traffic parameter determines the N_design level in Superpave mix design?

Accepted Answer

Design Equivalent Single Axle Loads (ESALs) over the pavement design life

Answer

N_design is selected based on the 20-year design ESALs, with higher traffic volumes requiring more gyrations to simulate greater compaction under loading.

Question 2

In Superpave, the 'coarse aggregate angularity' (CAA) test measures:

Accepted Answer

The percentage of coarse aggregate particles with one or more fractured faces

Answer

CAA is expressed as the percentage of aggregate particles by count (or weight) with at least one or two mechanically fractured faces, which improve shear strength and resistance to rutting.

Question 3

Which test method is used to determine the bulk specific gravity (Gmb) of a compacted Superpave specimen?

Accepted Answer

AASHTO T166 (saturated surface-dry method) or T331 (CoreLok)

Answer

Gmb is typically measured by AASHTO T166 (SSD weighing in water) or T331 (CoreLok vacuum-sealed bag) for permeable specimens, providing the compacted specimen density.

Question 4

What is the purpose of the AASHTO T283 (modified Lottman) test in Superpave mix design evaluation?

Accepted Answer

To evaluate the susceptibility of the mix to moisture-induced damage (stripping)

Answer

AASHTO T283 compares the tensile strength of conditioned (freeze-thaw cycled, vacuum-saturated) specimens to unconditioned specimens; a TSR ≥ 0.80 is typically required.

Question 5

In Superpave, what is 'binder absorption' and how does it affect mix design?

Accepted Answer

Absorption is binder drawn into permeable aggregate pores; it reduces the effective binder and must be accounted for in volumetric calculations

Answer

Absorbed binder fills permeable pores in the aggregate and is not available for film formation; failing to account for it leads to underestimating the needed total binder content.

CCIL - Canadian Council of Independent Laboratories Practice Test

CCIL - Canadian Council of Independent Laboratories Practice Test

CCIL Superpave Mix Design 4