CCIL Hot Mix Asphalt Field Density Testing 5

Question 1

What is the primary reason for performing a thin-lift correction when using a nuclear density gauge on HMA lifts less than 75 mm (3 in) thick?

Accepted Answer

Gamma radiation penetrates beyond the lift into the underlying layer, affecting the reading

Answer

In thin lifts, gamma rays penetrate into the underlying layer(s), causing the gauge to measure a composite density rather than the density of only the lift being tested.

Question 2

A field density test on HMA yields a percent compaction of 91.5% where the specification requires a minimum of 92%. The theoretical maximum specific gravity (Gmm) used was from a mix design produced six months ago. What should the technician consider?

Accepted Answer

The Gmm should be verified with a current mix sample, as mix properties can change over time

Answer

Gmm can vary if mix materials or proportions have changed; using an outdated Gmm can introduce error in percent compaction calculations, so a current Gmm should be confirmed.

Question 3

During HMA paving in warm weather, a technician observes the mat temperature is still 155°C (311°F) when the first breakdown roller pass begins. What is the concern?

Accepted Answer

The mix is too hot and may shoving or rutting under the roller

Answer

Rolling HMA that is too hot can cause shoving, displacement, and surface distortion because the binder viscosity is too low to resist roller-induced shear forces.

Question 4

What does the 'percent of theoretical maximum density' (%Gmm) express in HMA compaction testing?

Accepted Answer

The ratio of the bulk specific gravity of the compacted mix to its theoretical maximum specific gravity, expressed as a percentage

Answer

%Gmm = (Gmb / Gmm) × 100, representing how close the compacted field density is to a theoretically void-free density.

Question 5

Which ASTM standard governs the use of the nuclear method for determining in-place density of bituminous paving mixtures?

Accepted Answer

ASTM D6938

Answer

ASTM D6938 covers the use of nuclear methods (both transmission and backscatter) for determining in-place density and moisture content of soil and paving mixtures.

CCIL - Canadian Council of Independent Laboratories Practice Test

CCIL - Canadian Council of Independent Laboratories Practice Test

CCIL Hot Mix Asphalt Field Density Testing 5