KDOT Construction Materials Testing & Quality Control 3 — Questions and Answers
Question 1: A highway inspector observes that HMA mat temperatures during paving are consistently below 250°F behind the screed. What is the primary quality concern?
- Excessive thermal expansion causing shoving
- Inadequate density due to insufficient compaction window (Correct answer)
- Over-compaction leading to aggregate fracture
- Binder drain-down at low viscosity
Correct answer: Inadequate density due to insufficient compaction window
Low mat temperatures reduce the compaction window, making it difficult to achieve specified density before the asphalt cools and stiffens.
Question 2: When testing Portland cement concrete for air content using the pressure method (AASHTO T 152), what is the purpose of the aggregate correction factor?
- To account for air trapped within porous aggregate particles (Correct answer)
- To adjust for temperature effects on air volume
- To correct for sample size variations
- To compensate for admixture interactions
Correct answer: To account for air trapped within porous aggregate particles
The aggregate correction factor accounts for air absorbed within porous aggregate particles that is not part of the paste air content.
Question 3: In soil classification using AASHTO M 145, a soil with LL=45 and PI=22 would be classified as:
- A-2-4
- A-4
- A-6
- A-7-6 (Correct answer)
Correct answer: A-7-6
With LL > 41 and PI > 11, the soil plots in the A-7-6 group (PI ≥ LL – 30), indicating a highly plastic clay with poor subgrade characteristics.
Question 4: During a nuclear density gauge calibration check, the gauge reads 2.1% higher than the standard reference block value. The operator should:
- Apply a +2.1% correction factor to all field readings
- Adjust field readings by –2.1% to compensate
- Remove the gauge from service and have it recalibrated (Correct answer)
- Continue use since 2.1% is within acceptable tolerance
Correct answer: Remove the gauge from service and have it recalibrated
A gauge reading that deviates from the reference block value beyond acceptable tolerance (typically ±1%) requires removal from service and recalibration by a qualified technician.
Question 5: What is the primary purpose of performing a Los Angeles abrasion test on coarse aggregate?
- Determine aggregate specific gravity
- Measure resistance to degradation from abrasion and impact (Correct answer)
- Evaluate freeze-thaw durability
- Assess particle shape and angularity
Correct answer: Measure resistance to degradation from abrasion and impact
The LA abrasion test (AASHTO T 96) measures aggregate resistance to degradation caused by abrasion and impact, expressed as percent loss after tumbling with steel charges.
Question 6: For KDOT acceptance of structural concrete, flexural strength specimens must be moist-cured for a minimum of how many days before testing?
- 3 days
- 7 days
- 14 days
- 28 days (Correct answer)
Correct answer: 28 days
Standard flexural strength acceptance testing is performed at 28 days of moist curing to allow full hydration and strength development per AASHTO T 97.
Question 7: A field density test on a granular subbase shows the in-place moisture content is 3.2% above the optimum moisture content determined in the lab. How does this affect compaction?
- Compaction efficiency improves due to better lubrication
- Density readings will likely be inflated by the nuclear gauge
- The material is on the wet side and may not achieve maximum density (Correct answer)
- The material will achieve higher density than the Proctor maximum
Correct answer: The material is on the wet side and may not achieve maximum density
Compacting granular material significantly above optimum moisture content places it on the wet side of the curve, where additional compaction effort cannot increase density beyond the lab-established maximum.
KDOT Construction Materials Testing & Quality Control 3
A highway inspector observes that HMA mat temperatures during paving are consistently below 250°F behind the screed.
What is the primary quality concern?