NETTCP Soils and Aggregates 2 — Questions and Answers
Question 1: According to AASHTO classification, a soil with a group index of 0 indicates:
- Very poor subgrade material
- Good subgrade material (Correct answer)
- Highly plastic clay
- Expansive soil requiring stabilization
Correct answer: Good subgrade material
A group index of 0 indicates a good subgrade material with minimal potential for poor performance.
Question 2: Which sieve size is used to separate fine aggregate from coarse aggregate in AASHTO testing?
- No. 4 (4.75 mm) (Correct answer)
- No. 10 (2.00 mm)
- No. 40 (0.425 mm)
- No. 200 (0.075 mm)
Correct answer: No. 4 (4.75 mm)
The No. 4 sieve (4.75 mm) is the standard dividing line between fine and coarse aggregate.
Question 3: What does a high Los Angeles abrasion loss percentage indicate about aggregate quality?
- High resistance to wear
- Low resistance to wear and degradation (Correct answer)
- High specific gravity
- Excellent freeze-thaw resistance
Correct answer: Low resistance to wear and degradation
A high LA abrasion loss percentage means the aggregate breaks down easily under impact and abrasion, indicating poor durability.
Question 4: The shrinkage limit of a soil is defined as the water content at which:
- Soil transitions from plastic to liquid state
- Further drying causes no additional volume change (Correct answer)
- Soil loses all shear strength
- Compaction becomes ineffective
Correct answer: Further drying causes no additional volume change
The shrinkage limit is the water content below which no further volume change occurs as the soil dries.
Question 5: In a sieve analysis, if 15% of aggregate passes the No. 200 sieve, this material is classified as:
- Clean coarse aggregate
- Aggregate with acceptable fines content
- Aggregate likely exceeding fines limits for base course (Correct answer)
- Fine aggregate meeting NETTCP standards
Correct answer: Aggregate likely exceeding fines limits for base course
Most NETTCP base course specifications limit minus No. 200 material to around 8–12%, so 15% likely exceeds allowable fines.
Question 6: Which laboratory test determines the maximum dry density and optimum moisture content of a soil?
- Atterberg limits test
- Proctor compaction test (Correct answer)
- Hydrometer analysis
- Sand equivalent test
Correct answer: Proctor compaction test
The Proctor compaction test (standard or modified) establishes the compaction curve to find maximum dry density and optimum moisture content.
Question 7: Frost susceptibility in soils is most strongly associated with which soil type?
- Clean gravels
- Well-graded sands
- Silty soils with high capillary action (Correct answer)
- Coarse crushed stone
Correct answer: Silty soils with high capillary action
Silty soils are highly frost-susceptible because their fine pores promote strong capillary rise that feeds ice lens formation.
NETTCP Soils and Aggregates 2
According to AASHTO classification, a soil with a group index of 0 indicates: