KDOT Asphalt & Concrete Paving Inspection 3 — Questions and Answers
Question 1: What is the primary purpose of tack coat applied between asphalt pavement layers?
- To improve skid resistance at the surface
- To bond successive asphalt layers and prevent slippage (Correct answer)
- To act as a moisture barrier below the base course
- To increase the overall thickness of the pavement structure
Correct answer: To bond successive asphalt layers and prevent slippage
Tack coat (typically emulsified asphalt) creates a bonding interface between existing and new asphalt layers to resist shear forces and prevent inter-layer slippage.
Question 2: An HMA inspector observes that the vibratory rollers are operating with vibration turned on during the breakdown rolling pass near the end of the paving run. What problem could this cause?
- Insufficient density in the mat
- Checking or cracking of the cool mat at the end of the run (Correct answer)
- Excess aggregate crushing during compaction
- Improper joint formation at the longitudinal edge
Correct answer: Checking or cracking of the cool mat at the end of the run
Using vibration on cooler asphalt (at the end of a run) can cause checking — a surface cracking pattern — because the stiff mix cannot absorb the impact energy.
Question 3: What information must the contractor provide on a concrete mix delivery ticket for KDOT projects?
- Only the total cubic yards delivered
- Mix design number, water added, time batched, and truck number (Correct answer)
- Driver's license number and delivery route
- Aggregate source and haul distance only
Correct answer: Mix design number, water added, time batched, and truck number
KDOT requires batch tickets to include the mix design ID, water additions, batch time, cumulative water, and truck/load identification for traceability and acceptance.
Question 4: What does a 'tender' asphalt mix feel like under the roller, and what typically causes it?
- Mix that resists compaction due to high aggregate angularity
- Mix that shoves or waves ahead of the roller due to excess asphalt or fine aggregate (Correct answer)
- Mix that cracks under roller pressure due to low temperature
- Mix that sticks to the roller drum due to insufficient tack coat
Correct answer: Mix that shoves or waves ahead of the roller due to excess asphalt or fine aggregate
A tender mix has insufficient internal friction and shoves or pumps under roller loads, typically caused by excess binder, excess fines, or mix temperature in a critical zone.
Question 5: For KDOT concrete pavement, which type of joint is designed to control where transverse cracking occurs?
- Expansion joint
- Construction joint
- Contraction (control) joint (Correct answer)
- Isolation joint
Correct answer: Contraction (control) joint
Contraction joints (also called control joints) are sawed to a depth of about one-quarter to one-third of slab thickness to create a weakened plane where controlled cracking occurs.
Question 6: The inspector observes concrete being placed during hot weather with an air temperature of 95°F. What is the primary concern?
- Concrete will gain strength too slowly
- Accelerated hydration may reduce workability, increase water demand, and cause early stiffening (Correct answer)
- Aggregate will expand and cause popouts
- Reinforcing steel may corrode before hardening
Correct answer: Accelerated hydration may reduce workability, increase water demand, and cause early stiffening
High ambient temperatures accelerate cement hydration, reduce slump life, increase water demand, and can lead to plastic shrinkage cracking and reduced long-term strength.
Question 7: What is the function of dowel bars at transverse joints in KDOT concrete pavement?
- To allow thermal expansion and contraction of slabs
- To transfer load across the joint while allowing longitudinal movement (Correct answer)
- To tie adjacent slabs together and prevent any movement
- To reinforce the slab against reflective cracking
Correct answer: To transfer load across the joint while allowing longitudinal movement
Dowel bars transfer wheel loads between adjacent slabs across a transverse joint while being greased or sleeved on one end to allow the slab to expand and contract freely.
KDOT Asphalt & Concrete Paving Inspection 3
What is the primary purpose of tack coat applied between asphalt pavement layers?