CTQP Materials Sampling and Testing 5 — Questions and Answers
Question 1: When computing the average of two companion concrete cylinder breaks, if one result deviates more than what percentage from the average, additional cylinders must be tested?
- 5%
- 8%
- 10%
- 15% (Correct answer)
Correct answer: 15%
Per ASTM C39, if individual cylinder strength deviates more than 8% of the average, ASTM C39 recommends investigating; many agency specs use a 10% threshold for triggering additional testing.
Question 2: The Atterberg limits test is used to characterize which property of fine-grained soils?
- Relative density
- Shear strength under load
- Plasticity and moisture sensitivity (Correct answer)
- Gradation and particle size
Correct answer: Plasticity and moisture sensitivity
Atterberg limits (liquid limit, plastic limit, plasticity index) classify fine-grained soil plasticity and its sensitivity to moisture changes.
Question 3: The purpose of the Los Angeles Abrasion test (AASHTO T 96) is to measure:
- Aggregate soundness under freeze-thaw cycles
- Resistance of aggregate to degradation by impact and abrasion (Correct answer)
- Specific gravity of coarse aggregate particles
- Flat and elongated particle content
Correct answer: Resistance of aggregate to degradation by impact and abrasion
The LA Abrasion test measures the percentage of material lost when aggregate is subjected to impact and grinding inside a rotating steel drum with steel balls.
Question 4: A volumetric flask used in specific gravity testing of fine aggregate must be calibrated at what temperature?
- 68°F (20°C)
- 73.4°F (23°C) (Correct answer)
- 77°F (25°C)
- 98.6°F (37°C)
Correct answer: 73.4°F (23°C)
AASHTO T 84 requires calibration of the pycnometer or volumetric flask at 73.4°F (23°C) to ensure accurate volume measurements.
Question 5: When obtaining a core sample from an asphalt pavement for thickness verification, the minimum core diameter recommended by FDOT specifications is:
- 2 inches
- 3 inches
- 4 inches (Correct answer)
- 6 inches
Correct answer: 4 inches
A minimum 4-inch diameter core is typically required for asphalt thickness and density testing to ensure a representative sample with adequate material for testing.
Question 6: The sand equivalent test (AASHTO T 176) measures the relative proportion of which two components in fine aggregate?
- Organic material and inorganic mineral particles
- Clay-like fines and sand-size particles (Correct answer)
- Silt and gravel particles
- Moisture content and dry aggregate weight
Correct answer: Clay-like fines and sand-size particles
The sand equivalent test separates clay-like or plastic fines from sand-size particles to assess the cleanliness and quality of fine aggregate used in pavements.
Question 7: During a proctor compaction test, if the soil is too wet and the moisture-density curve shows density decreasing, the technician should:
- Add more water and continue compacting
- Air-dry the soil and retest at lower moisture contents (Correct answer)
- Increase compactive effort by adding more blows
- Discard the sample and start fresh with new material
Correct answer: Air-dry the soil and retest at lower moisture contents
When the curve descends on the wet side of optimum, the soil must be air-dried to lower moisture content points to properly define the full compaction curve and identify the true maximum dry density.
CTQP Materials Sampling and Testing 5
When computing the average of two companion concrete cylinder breaks, if one result deviates more than what percentage from the average, additional cylinders must be tested?