NETTCP Lab Testing Procedures 4 — Questions and Answers
Question 1: A nuclear density gauge used for field compaction testing must be licensed under which U.S. federal agency because it contains radioactive material?
- OSHA
- EPA
- NRC (Nuclear Regulatory Commission) (Correct answer)
- DOT
Correct answer: NRC (Nuclear Regulatory Commission)
Nuclear density gauges contain radioactive sources (Cesium-137 and Americium-241/Beryllium) and are regulated by the NRC or agreement states.
Question 2: In the Superpave gyratory compactor (SGC), what parameter is adjusted to simulate field compaction effort at different design levels?
- Rotation speed
- Number of gyrations (Ndesign) (Correct answer)
- Mold temperature
- Aggregate gradation
Correct answer: Number of gyrations (Ndesign)
Ndesign is the number of gyrations used to compact asphalt specimens and is selected based on design traffic level (ESALs).
Question 3: Per AASHTO T 166, the bulk specific gravity of a compacted asphalt mixture specimen is determined using:
- Air weighing only
- Saturated surface dry (SSD) weighing in air and submerged in water (Correct answer)
- Vacuum saturation followed by pressure testing
- Ignition oven mass loss
Correct answer: Saturated surface dry (SSD) weighing in air and submerged in water
Gmb is calculated from the dry mass, the SSD mass, and the submerged mass in water using Archimedes' principle.
Question 4: The California Bearing Ratio (CBR) test measures the strength of a subgrade soil relative to:
- Standard Ottawa sand
- A standard crushed limestone base material (Correct answer)
- A freshly cured concrete reference
- Compacted Class A gravel
Correct answer: A standard crushed limestone base material
CBR expresses the penetration resistance of the test material as a percentage of the resistance of a standard well-graded crushed limestone.
Question 5: When splitting a bulk aggregate sample using a riffle splitter (sample splitter), the correct technique is to:
- Pour material into one side only to retain the coarser fraction
- Feed material uniformly across all chutes at a controlled rate (Correct answer)
- Wet the aggregate before splitting to prevent segregation
- Split only after oven-drying for 24 hours
Correct answer: Feed material uniformly across all chutes at a controlled rate
Material must be fed uniformly across the full width of the splitter to ensure each half is a representative portion of the original sample.
Question 6: In a concrete compressive strength test per AASHTO T 22, cylinders are capped or ground to ensure the end surfaces are perpendicular to within:
- 0.5 degrees (Correct answer)
- 1 degree
- 2 degrees
- 5 degrees
Correct answer: 0.5 degrees
End surfaces must be perpendicular to the axis within 0.5° and plane within 0.002 inches to ensure uniform load distribution during testing.
Question 7: The sand equivalent test (AASHTO T 176) is used to measure the proportion of:
- Fine dust and clay-like material in fine aggregate (Correct answer)
- Organic content in coarse aggregate
- Air voids in compacted sand
- Moisture absorbed by aggregate
Correct answer: Fine dust and clay-like material in fine aggregate
The sand equivalent value indicates the relative proportion of fine dust or clay-like material in fine aggregate — a higher value means cleaner aggregate.
NETTCP Lab Testing Procedures 4
A nuclear density gauge used for field compaction testing must be licensed under which U.S. federal agency because it contains radioactive material?