NETTCP Lab Testing Procedures 5 — Questions and Answers
Question 1: Which AASHTO test method covers the determination of specific gravity and absorption of coarse aggregate?
- AASHTO T 84
- AASHTO T 85 (Correct answer)
- AASHTO T 176
- AASHTO T 209
Correct answer: AASHTO T 85
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:
- Inserted into the ground at different depths
- Located at the gauge base on the surface (Correct answer)
- Suspended above the pavement surface
- Inserted at a 45-degree angle
Correct answer: Located at the gauge base on the surface
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?
- 3.0%
- 5.0% (Correct answer)
- 7.5%
- 10.1%
Correct answer: 5.0%
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:
- 1:1 to 2:1
- 2:1 to 2.5:1 (Correct answer)
- 3:1 to 4:1
- 4:1 to 5:1
Correct answer: 2:1 to 2.5:1
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:
- Chemical reactivity with cement
- Resistance to weathering and freeze-thaw deterioration (Correct answer)
- Abrasion resistance under traffic loading
- Affinity for asphalt binders
Correct answer: Resistance to weathering and freeze-thaw deterioration
The soundness test simulates freeze-thaw action; salt crystallization in aggregate pores mimics ice expansion and reveals susceptibility to weathering.
Question 6: For HMA mixture design, the maximum theoretical specific gravity (Gmm) is determined per AASHTO T 209 by:
- Compacting specimens in a gyratory compactor and weighing them
- Weighing a loose uncompacted asphalt mixture in air and submerged in water (Correct answer)
- Burning off binder in an ignition oven and sieving remaining aggregate
- Measuring void content with a vacuum chamber only
Correct answer: Weighing a loose uncompacted asphalt mixture in air and submerged in water
T 209 (Rice method) determines Gmm by measuring the mass of loose mix in air and the volume of mix plus water in a vacuum flask after removing air voids.
Question 7: According to AASHTO M 231, balances used in transportation materials testing must be verified and calibrated at a minimum of:
- Every use
- Annually, or whenever moved or repaired (Correct answer)
- Every 5 years
- Only when purchased new
Correct answer: Annually, or whenever moved or repaired
AASHTO M 231 requires balance verification at least annually and after any event that could affect accuracy, such as relocation, repair, or overloading.
NETTCP Lab Testing Procedures 5
Which AASHTO test method covers the determination of specific gravity and absorption of coarse aggregate?