KDOT Asphalt & Concrete Paving Inspection 5 — Questions and Answers
Question 1: What is the purpose of the 'nuclear density gauge' in asphalt paving inspection?
- To measure the asphalt binder content of a core sample
- To rapidly measure in-place density and moisture content of compacted pavement non-destructively (Correct answer)
- To determine the gradation of aggregate in the hot mix
- To test the tensile strength of the compacted mat
Correct answer: To rapidly measure in-place density and moisture content of compacted pavement non-destructively
The nuclear density gauge uses gamma radiation to measure the density of compacted asphalt in place quickly and non-destructively, allowing the inspector to assess compaction in real time.
Question 2: What does 'segregation' in an asphalt mat visually appear as, and what equipment issue typically causes it?
- Smooth, uniform texture indicating excellent aggregate coating
- Coarse, open-textured streaks or areas where fines are absent, often caused by paver hopper or auger problems (Correct answer)
- Dark, shiny areas on the mat indicating excess binder
- Transverse cracks spaced at regular intervals behind the screed
Correct answer: Coarse, open-textured streaks or areas where fines are absent, often caused by paver hopper or auger problems
Segregation appears as coarse-textured, open areas where fine aggregate is missing, often caused by cold hopper wings being folded in, auger starvation, or improper truck loading practices.
Question 3: When concrete pavement is placed in cold weather (air temperature below 40°F and falling), what primary precaution must the inspector verify?
- Concrete must be placed at a slower rate to prevent thermal shock
- Concrete and subgrade must be protected from freezing; insulated blankets or enclosures required until adequate strength is gained (Correct answer)
- Only high-early-strength cement (Type III) may be used in all cold-weather pours
- Finishing must be delayed until after the initial set to retain heat
Correct answer: Concrete and subgrade must be protected from freezing; insulated blankets or enclosures required until adequate strength is gained
Concrete must not freeze before it reaches sufficient strength (typically 500 psi), so the inspector must verify that insulated curing blankets, enclosures, or heated water are used to maintain the concrete above 50°F.
Question 4: A KDOT inspector is checking the asphalt mix for 'fat spots.' What are fat spots and what do they indicate?
- Areas of high density caused by over-compaction with the breakdown roller
- Shiny, excess-binder areas in the mat indicating localized over-asphalting or mix design issues (Correct answer)
- Dark spots caused by contamination from the truck bed
- Areas of low temperature visible on an infrared camera scan
Correct answer: Shiny, excess-binder areas in the mat indicating localized over-asphalting or mix design issues
Fat spots are localized areas on the mat surface that appear shiny and rich in binder, indicating either excess asphalt in those areas or migration of binder due to mix instability.
Question 5: What is the maximum allowable water-to-cementitious material (w/cm) ratio for KDOT Class P (pavement) concrete?
- 0.38
- 0.45 (Correct answer)
- 0.53
- 0.60
Correct answer: 0.45
KDOT Class P concrete for paving typically has a maximum w/cm ratio of 0.45 to ensure adequate durability and strength for pavement applications.
Question 6: During asphalt paving, the inspector notices that the breakdown roller is leaving a wavy pattern (washboarding) in the mat. The most likely cause is:
- The roller is traveling too slowly and vibration frequency is too low
- The roller is traveling too fast or vibration amplitude/frequency is mismatched for the mix temperature (Correct answer)
- The mat is too thick for a single pass with the steel roller
- The paver screed is not heated properly
Correct answer: The roller is traveling too fast or vibration amplitude/frequency is mismatched for the mix temperature
Washboarding (a corrugated surface pattern) during breakdown rolling is typically caused by the roller traveling too fast, causing the drum to bounce rather than continuously compact the mat.
Question 7: For a KDOT paving project, what must be documented in the inspector's daily diary for concrete pavement placement?
- Only the total volume placed and mix design number
- Weather conditions, air/concrete temperatures, mix design, volume placed, slump tests, cylinder samples, curing method, and any non-conformances (Correct answer)
- Truck arrival and departure times only
- Finish method and joint sawing schedule only
Correct answer: Weather conditions, air/concrete temperatures, mix design, volume placed, slump tests, cylinder samples, curing method, and any non-conformances
The inspector's daily diary is a legal project record and must capture all placement conditions, test results, quantities, curing details, and any deviations from specifications.
KDOT Asphalt & Concrete Paving Inspection 5
What is the purpose of the 'nuclear density gauge' in asphalt paving inspection?