NETTCP Lab Testing Procedures 3 — Questions and Answers
Question 1: The Modified Proctor compaction test (AASHTO T 180) differs from the Standard Proctor primarily in its:
- Mold diameter
- Number of soil layers and hammer energy (Correct answer)
- Soil sample preparation method
- Moisture measurement technique
Correct answer: Number of soil layers and hammer energy
AASHTO T 180 uses 5 layers and a 10-lb hammer dropped 18 inches, resulting in about 4.5 times the compaction energy of the Standard Proctor.
Question 2: When testing aggregate for flat and elongated particles per ASTM D 4791, a particle is considered elongated if its longest dimension exceeds its shortest dimension by a ratio of:
- 2:1
- 3:1 (Correct answer)
- 4:1
- 5:1
Correct answer: 3:1
ASTM D 4791 defines elongated particles as those with a length-to-thickness ratio exceeding 3:1 at the specified ratio being tested.
Question 3: Which equipment is used to measure the air content of freshly mixed concrete by the pressure method per AASHTO T 152?
- Air entrainment meter (Type B pressure meter) (Correct answer)
- Volumetric roll-a-meter
- Slump cone and tamping rod
- Unit weight bucket
Correct answer: Air entrainment meter (Type B pressure meter)
The Type B pressure meter (air meter) applies a known pressure to the concrete sample and measures the volume change to calculate air content.
Question 4: A soil sample has a wet mass of 450 g and a dry mass of 380 g. What is the moisture content?
- 15.6%
- 18.4% (Correct answer)
- 84.4%
- 70 g
Correct answer: 18.4%
Moisture content = (wet mass − dry mass) / dry mass × 100 = (450 − 380) / 380 × 100 = 18.4%.
Question 5: During a Marshall stability test on compacted asphalt specimens, the loading rate specified by AASHTO T 245 is:
- 0.5 in/min
- 1 in/min
- 2 in/min (Correct answer)
- 4 in/min
Correct answer: 2 in/min
AASHTO T 245 requires a constant deformation rate of 2 inches per minute (50 mm/min) when determining Marshall stability and flow.
Question 6: The plasticity index (PI) of a soil is calculated as:
- Liquid limit minus shrinkage limit
- Plastic limit minus liquid limit
- Liquid limit minus plastic limit (Correct answer)
- Plastic limit divided by liquid limit
Correct answer: Liquid limit minus plastic limit
PI = LL − PL; it represents the range of moisture content over which a soil behaves plastically.
Question 7: When performing the Los Angeles Abrasion test (AASHTO T 96) on coarse aggregate, the abrasive charge used is:
- Glass beads
- Steel balls (Correct answer)
- Silica sand
- Rubber pellets
Correct answer: Steel balls
The Los Angeles machine uses a specified number of steel balls as the abrasive charge that impact and grind the aggregate during rotation.
NETTCP Lab Testing Procedures 3
The Modified Proctor compaction test (AASHTO T 180) differs from the Standard Proctor primarily in its: