KDOT Construction Materials Testing & Quality Control 4 — Questions and Answers
Question 1: What does the term 'ride quality' refer to in pavement acceptance testing, and which instrument measures it?
- Skid resistance measured by a locked-wheel skid tester
- Pavement smoothness measured by a profilograph or inertial profiler (Correct answer)
- Structural capacity measured by a falling weight deflectometer
- Surface texture measured by the sand patch method
Correct answer: Pavement smoothness measured by a profilograph or inertial profiler
Ride quality refers to pavement smoothness and is quantified using a profilograph or high-speed inertial profiler to produce an International Roughness Index (IRI) value.
Question 2: When conducting a sieve analysis on combined aggregate for HMA, a gap in the gradation curve most likely causes:
- Improved workability and compaction
- Potential for tenderness, rutting, or instability in the mix (Correct answer)
- Higher air void content at all compaction levels
- Increased resistance to fatigue cracking
Correct answer: Potential for tenderness, rutting, or instability in the mix
A gap gradation can create a tender mix prone to rutting and shoving because certain particle sizes are missing, reducing interlock and internal friction.
Question 3: According to KDOT quality control requirements, who is responsible for maintaining a QC plan on a hot mix asphalt paving project?
- The KDOT district materials engineer
- The prime contractor (Correct answer)
- The independent testing laboratory
- The Kansas Turnpike Authority
Correct answer: The prime contractor
The prime contractor is responsible for developing and implementing the Quality Control plan, which defines sampling, testing, and corrective action procedures.
Question 4: What is the significance of the 'P200' value in aggregate gradation analysis?
- The percentage of aggregate passing the 200 mm sieve
- The percentage of material passing the No. 200 (0.075 mm) sieve, indicating fines content (Correct answer)
- The aggregate's permeability rating at 200 kPa
- The plastic fines content measured at 200°F
Correct answer: The percentage of material passing the No. 200 (0.075 mm) sieve, indicating fines content
P200 is the percent passing the No. 200 sieve (75 microns), representing fines content that significantly affects HMA mixture performance and concrete workability.
Question 5: A reinforced concrete bridge deck core extracted for evaluation has a carbonation depth of 18 mm. What does this indicate?
- The concrete has excellent air void distribution
- The pH of the concrete near the surface has dropped, potentially depassivating rebar (Correct answer)
- The concrete mix had excess water-cement ratio throughout
- The deck has achieved full design strength
Correct answer: The pH of the concrete near the surface has dropped, potentially depassivating rebar
Carbonation reduces concrete pH from ~12.5 to below 9, destroying the passive oxide layer on reinforcing steel and initiating corrosion if rebar is within the carbonation front.
Question 6: Under KDOT specifications, what action is required when HMA mat air voids from extracted cores fall below the minimum specification limit?
- The lot is automatically accepted at full pay
- A pay adjustment or corrective action is required per the specification table (Correct answer)
- Additional aggregate is spread over the mat surface
- The rollers are required to make additional passes only
Correct answer: A pay adjustment or corrective action is required per the specification table
When core air voids fall outside specification limits, KDOT specifications require a pay adjustment reduction or corrective action such as removal and replacement of the deficient area.
Question 7: Which condition requires a concrete test cylinder to be discarded and the test result invalidated?
- The cylinder was cured at 68°F instead of 73°F
- The end surface was not perpendicular within 0.5° (Correct answer)
- The cylinder exhibits a shear cone failure pattern
- The cylinder was transported in a padded cooler
Correct answer: The end surface was not perpendicular within 0.5°
Cylinders with end surfaces that are not perpendicular to the axis by more than 0.5° produce eccentric loading during compression testing and must be capped or the result invalidated.
KDOT Construction Materials Testing & Quality Control 4
What does the term 'ride quality' refer to in pavement acceptance testing, and which instrument measures it?