CCIL Superpave Mix Design 5

Question 1

What does 'Percent Gmm at N_design' represent, and what is the target value?

Accepted Answer

The ratio of bulk density to maximum density expressed as a percentage; target is 96% (4% air voids)

Answer

Percent Gmm at N_design equals (Gmb/Gmm)×100; reaching 96% means 4% air voids remain, which is the Superpave design target.

Question 2

How does the Superpave system account for very slow-moving or stationary traffic loads when selecting a PG binder grade?

Accepted Answer

By bumping up the high-temperature PG grade one or two grades to account for increased rutting risk

Answer

AASHTO M320 specifies that slow-moving traffic (< 70 km/h) requires the high-temperature PG grade to be increased by one grade, and stationary loads require an increase of two grades.

Question 3

In Superpave mix design, what is the function of the N_maximum gyration criterion?

Accepted Answer

To ensure the mix does not over-compact under extended traffic to below 2% air voids

Answer

At N_maximum, the mix must not compact to less than 2% air voids (≥98% Gmm), ensuring it will not become unstable or exhibit bleeding under the maximum anticipated traffic loading.

Question 4

What aggregate property is evaluated by the 'flat and elongated' particle test in Superpave?

Accepted Answer

The percentage of particles with a length-to-thickness ratio exceeding a specified limit (typically 5:1)

Answer

Flat and elongated particles with a ratio > 5:1 are prone to breakage during compaction and traffic, reducing the mix's long-term structural integrity.

Question 5

A Superpave mix design trial at the estimated optimum binder content shows VFA = 82%. For a high-traffic roadway, this result indicates:

Accepted Answer

The VFA is likely too high, indicating insufficient air voids and potential rutting risk

Answer

For high-traffic levels, Superpave specifies a maximum VFA of 75–80%; a value of 82% suggests excess binder, which can lead to flushing and rutting under heavy loads.

CCIL - Canadian Council of Independent Laboratories Practice Test

CCIL - Canadian Council of Independent Laboratories Practice Test

CCIL Superpave Mix Design 5