CCIL Hot Mix Asphalt Field Density Testing 4 — Questions and Answers
Question 1: When performing a nuclear gauge density test on HMA, the gauge must be placed at least how far from any vertical obstruction or edge of pavement?
- 150 mm (6 in)
- 300 mm (12 in) (Correct answer)
- 600 mm (24 in)
- 900 mm (36 in)
Correct answer: 300 mm (12 in)
Nuclear gauges must be placed at least 300 mm (12 in) from vertical obstructions to avoid backscatter interference that would give false readings.
Question 2: In the context of HMA density acceptance, what does the term 'lot' typically refer to?
- A single truckload of asphalt mix
- A defined quantity of pavement used as a statistical unit for acceptance (Correct answer)
- One lane-mile of compacted pavement
- The total volume of a paving project
Correct answer: A defined quantity of pavement used as a statistical unit for acceptance
A lot is a defined quantity of pavement material (often by area, tonnage, or linear distance) used as the statistical basis for acceptance decisions.
Question 3: Which of the following conditions would most likely cause a nuclear density gauge to read LOWER than the actual density of HMA?
- High chloride content in the mix aggregate
- Air gap between the gauge and the pavement surface (Correct answer)
- Elevated pavement surface temperature
- Presence of reclaimed asphalt pavement (RAP) in the mix
Correct answer: Air gap between the gauge and the pavement surface
An air gap between the gauge and the pavement surface allows gamma rays to scatter in air rather than the material, resulting in a falsely low density reading.
Question 4: When using the core-and-weigh method to determine field density of HMA, which measurement is taken to calculate air void content?
- The core diameter and lift thickness only
- The bulk specific gravity of the core and the theoretical maximum specific gravity of the mix (Correct answer)
- The weight of the core in air and the weight of the core in water only
- The core's dry weight and compacted thickness
Correct answer: The bulk specific gravity of the core and the theoretical maximum specific gravity of the mix
Air void content is calculated as the percentage difference between theoretical maximum specific gravity (Gmm) and the bulk specific gravity (Gmb) of the compacted core.
Question 5: A technician notices the roller pattern used during HMA compaction did not achieve the required density. What is the FIRST corrective action that should be taken?
- Immediately mill and replace the deficient area
- Stop paving and notify the contractor and engineer of record
- Apply additional heat to the mat surface
- Increase the number of roller passes on the still-workable mat (Correct answer)
Correct answer: Increase the number of roller passes on the still-workable mat
If the mat is still within the workable temperature range, additional roller passes should be applied immediately to achieve the required density before the mix cools.
Question 6: According to typical CCIL protocols, what is the standard procedure when a density test result falls below the project specification minimum?
- The failing area is automatically removed and replaced
- Additional tests are taken to define the extent of the deficient area before disposition (Correct answer)
- A pay factor reduction is automatically applied without further testing
- The result is discarded and the test is repeated at the same location
Correct answer: Additional tests are taken to define the extent of the deficient area before disposition
When a result is below specification, additional tests are conducted to delineate the extent of the deficiency before determining corrective action or penalty.
Question 7: Which type of roller is MOST effective for achieving the final surface texture and smoothness of an HMA mat while maintaining density?
- Pneumatic tire roller
- Vibratory steel drum roller
- Static steel drum roller (finish roller) (Correct answer)
- Padfoot compactor
Correct answer: Static steel drum roller (finish roller)
A static steel drum roller is used as the finish roller to eliminate roller marks and achieve a smooth surface texture without disturbing the final density.
CCIL Hot Mix Asphalt Field Density Testing 4
When performing a nuclear gauge density test on HMA, the gauge must be placed at least how far from any vertical obstruction or edge of pavement?