KDOT Construction Materials Testing & Quality Control 5 — Questions and Answers
Question 1: What is the purpose of the 'ignition oven' method (AASHTO T 308) in HMA quality control?
- Determine the moisture content of aggregate stockpiles
- Measure the asphalt binder content of a mix by burning off the binder (Correct answer)
- Evaluate the thermal susceptibility of the asphalt binder
- Determine the flash point of recovered asphalt binder
Correct answer: Measure the asphalt binder content of a mix by burning off the binder
The ignition oven method burns the organic asphalt binder from the aggregate at high temperature, allowing calculation of binder content by weight difference.
Question 2: During concrete paving operations, a KDOT inspector notices bleed water sheen on the surface during finishing operations. The correct action is to:
- Add dry cement to the surface to absorb moisture
- Delay finishing operations until the bleed water evaporates (Correct answer)
- Apply a curing compound immediately to seal in moisture
- Increase the vibrator penetration depth to force water upward
Correct answer: Delay finishing operations until the bleed water evaporates
Finishing concrete before bleed water evaporates traps water in the surface layer, creating a weak, porous layer prone to scaling and dusting.
Question 3: A geosynthetic fabric is being placed as a separator layer between subgrade and aggregate base. What test property is most critical for this application?
- Grab tensile strength and elongation
- Apparent opening size (AOS) and permittivity (Correct answer)
- UV resistance after 500 hours of exposure
- Creep reduction factor under sustained load
Correct answer: Apparent opening size (AOS) and permittivity
For a separator application, the fabric must allow water drainage (permittivity) while retaining fine soil particles, making apparent opening size and permittivity the critical design properties.
Question 4: When sampling freshly mixed concrete from a transit mixer per AASHTO T 141, composite samples must be collected over what minimum time span?
- Within 15 seconds
- Between 10% and 90% of the load discharge (Correct answer)
- After the first and last cubic yard only
- Within 5 minutes of discharge start
Correct answer: Between 10% and 90% of the load discharge
AASHTO T 141 requires composite samples to be collected from the middle portion of the load, between 10% and 90% of the total discharge, to avoid non-representative material.
Question 5: A field moisture test on a soil sample using the speedy moisture tester (calcium carbide method) reads 8.2%. The true oven-dry moisture content is 7.9%. What does this indicate about the speedy tester result?
- The speedy tester underestimated moisture content by 0.3%
- The speedy tester overestimated moisture content by 0.3%
- Both methods agree within acceptable tolerance for field use (Correct answer)
- The oven-dry test was performed incorrectly
Correct answer: Both methods agree within acceptable tolerance for field use
A 0.3% difference between the speedy moisture tester and oven-dry method is within the acceptable tolerance for field quality control decisions.
Question 6: What is the definition of 'lot' in KDOT's statistical acceptance plan for HMA pavement?
- One day's production regardless of tonnage
- A defined quantity of material, typically 1,000–3,000 tons, used as the acceptance unit (Correct answer)
- A single truck load of mix delivered to the project
- The total tonnage placed on a single roadway segment
Correct answer: A defined quantity of material, typically 1,000–3,000 tons, used as the acceptance unit
A lot is a defined quantity of material (typically 1,000–3,000 tons) that serves as the unit for statistical acceptance testing and pay adjustment calculations.
Question 7: During subgrade proof rolling with a loaded tandem-axle dump truck, which observation requires immediate corrective action?
- Slight deflection of less than 1/2 inch that rebounds quickly
- Pumping or rutting greater than 1 inch with no rebound (Correct answer)
- Surface dust generated by tire contact
- Cracks parallel to the direction of travel less than 1/4 inch wide
Correct answer: Pumping or rutting greater than 1 inch with no rebound
Pumping, rutting greater than 1 inch, or lack of rebound indicates inadequate support or saturated conditions requiring subgrade stabilization or replacement before paving.
KDOT Construction Materials Testing & Quality Control 5
What is the purpose of the 'ignition oven' method (AASHTO T 308) in HMA quality control?