NETTCP Lab Testing Procedures 5

Question 1

Which AASHTO test method covers the determination of specific gravity and absorption of coarse aggregate?

Accepted Answer

AASHTO T 85

Answer

AASHTO T 85 covers specific gravity (bulk, SSD, apparent) and absorption of coarse aggregate, while T 84 covers fine aggregate.

Question 2

During a field density test with a nuclear gauge in backscatter mode, the gamma source and detectors are both:

Accepted Answer

Located at the gauge base on the surface

Answer

In backscatter mode, both the source and detectors remain at the surface; the gauge measures density of only the top few inches of material.

Question 3

A bituminous concrete specimen has a theoretical maximum specific gravity (Gmm) of 2.520 and a bulk specific gravity (Gmb) of 2.394. What is the air void content?

Accepted Answer

5.0%

Answer

Va = (1 − Gmb/Gmm) × 100 = (1 − 2.394/2.520) × 100 = 5.0%; typical Superpave design targets 4% air voids.

Question 4

When performing the unconfined compressive strength test on a soil specimen, the height-to-diameter ratio of the specimen should be:

Accepted Answer

2:1 to 2.5:1

Answer

ASTM D 2166 requires a height-to-diameter ratio between 2:1 and 2.5:1 to ensure proper failure plane development without end-restraint effects.

Question 5

The purpose of performing a soundness test on aggregates (AASHTO T 104) using sodium sulfate or magnesium sulfate is to evaluate:

Accepted Answer

Resistance to weathering and freeze-thaw deterioration

Answer

The soundness test simulates freeze-thaw action; salt crystallization in aggregate pores mimics ice expansion and reveals susceptibility to weathering.

(NETTCP) New England Transportation Technician Certification Program Practice Test

(NETTCP) New England Transportation Technician Certification Program Practice Test

NETTCP Lab Testing Procedures 5