NETTCP Quality Control 3 — Questions and Answers
Question 1: According to AASHTO standards, what is the minimum number of compressive strength cylinders that should be cast per concrete sample?
- Two cylinders per sample (Correct answer)
- One cylinder per sample
- Four cylinders per sample
- Three cylinders per sample
Correct answer: Two cylinders per sample
AASHTO T 23 / ASTM C 31 typically requires at least two cylinders per test age so results can be averaged and outliers identified.
Question 2: What does a Proctor compaction test establish for a given soil?
- Optimum moisture content and maximum dry density (Correct answer)
- In-place relative compaction percentage
- Gradation and plasticity index
- California Bearing Ratio (CBR) value
Correct answer: Optimum moisture content and maximum dry density
The Proctor test (AASHTO T 99 or T 180) determines the optimum moisture content at which a soil achieves its maximum dry density under a specific compactive effort.
Question 3: Which property of an asphalt binder is measured by the Dynamic Shear Rheometer (DSR)?
- Viscoelastic properties including complex shear modulus and phase angle (Correct answer)
- Penetration depth at 77°F
- Flash point temperature
- Rolling Thin Film Oven mass loss
Correct answer: Viscoelastic properties including complex shear modulus and phase angle
The DSR measures G* (complex shear modulus) and δ (phase angle), which describe an asphalt binder's stiffness and elastic behavior at service temperatures.
Question 4: When sampling freshly mixed concrete from a truck mixer, ASTM C 172 requires that the sample be obtained within what time period after sampling begins?
- Within 5 minutes (Correct answer)
- Within 15 minutes
- Within 30 minutes
- Within 10 minutes
Correct answer: Within 5 minutes
ASTM C 172 requires that the composite sample be obtained within 5 minutes to ensure it represents a single batch without significant hydration changes.
Question 5: A QC technician receives failing density results from a nuclear gauge on a freshly compacted aggregate base course. What should be done before requesting a retest?
- Verify gauge calibration with a standard count and check moisture assumption (Correct answer)
- Immediately rip up and recompact the material
- Notify the contractor and halt all operations
- Increase the number of roller passes and retest without further checks
Correct answer: Verify gauge calibration with a standard count and check moisture assumption
Before acting on failing results, the technician should confirm the gauge is properly calibrated and that the moisture correction is accurate to rule out equipment error.
Question 6: What is the purpose of the Los Angeles (LA) Abrasion test for aggregate?
- To measure resistance to degradation by abrasion and impact (Correct answer)
- To determine the specific gravity of coarse aggregate
- To assess the flat and elongated particle content
- To evaluate aggregate soundness under freeze-thaw cycles
Correct answer: To measure resistance to degradation by abrasion and impact
The LA Abrasion test (AASHTO T 96 / ASTM C 131) measures the percentage of material lost when aggregate is subjected to impact and abrasion in a rotating drum with steel balls.
Question 7: In a pay factor system, what happens to the contractor's payment when the quality level (QL) of a lot falls below the target specification?
- The pay factor is reduced, resulting in a lower payment for that lot (Correct answer)
- The lot is automatically rejected and removed
- No financial penalty is applied unless the lot fails outright
- The engineer can choose to waive the penalty
Correct answer: The pay factor is reduced, resulting in a lower payment for that lot
Pay factor systems apply a deduction factor to the contract price for lots that fall below the target quality level, incentivizing better quality control.
NETTCP Quality Control 3
According to AASHTO standards, what is the minimum number of compressive strength cylinders that should be cast per concrete sample?