CTE Pavement Design & Materials 2 — Questions and Answers
Question 1: What is the primary structural advantage of jointed plain concrete pavement (JPCP) over flexible asphalt pavement?
- Lower initial construction cost
- High beam strength that distributes loads over a larger area, reducing subgrade stress (Correct answer)
- Better performance in cold climates
- No need for drainage layers
Correct answer: High beam strength that distributes loads over a larger area, reducing subgrade stress
Concrete pavement's high flexural strength distributes wheel loads over a larger area than flexible pavement, resulting in lower stress on the subgrade and potentially extending pavement life.
Question 2: What is 'load transfer efficiency' (LTE) at concrete pavement joints, and how is it typically achieved?
- Compressive strength ratio between panels; achieved with fiber reinforcement
- Percentage of deflection transferred across a joint; achieved with dowel bars or aggregate interlock (Correct answer)
- Ratio of joint spacing to slab thickness; achieved by saw-cutting at optimal timing
- Stiffness ratio of subbase to concrete; achieved by stabilized base layers
Correct answer: Percentage of deflection transferred across a joint; achieved with dowel bars or aggregate interlock
LTE measures how effectively a loaded slab transfers deflection load to the adjacent unloaded slab; smooth round dowel bars are the most reliable mechanism for achieving high LTE at transverse joints.
Question 3: What is Reclaimed Asphalt Pavement (RAP) and what is its primary benefit?
- A synthetic polymer modifier for asphalt binders
- Removed and reprocessed old asphalt pavement reused as aggregate and binder in new HMA mixes, reducing material costs and virgin material use (Correct answer)
- A cold-mix patching material for pothole repair
- A stabilized base material made from recycled concrete
Correct answer: Removed and reprocessed old asphalt pavement reused as aggregate and binder in new HMA mixes, reducing material costs and virgin material use
RAP consists of salvaged asphalt pavement materials that are crushed and screened for reuse, providing recycled aggregate and residual asphalt binder that reduce cost and conserve virgin materials.
Question 4: What is the difference between a 'perpetual pavement' and a conventional flexible pavement design?
- Perpetual pavements use concrete; conventional pavements use asphalt
- Perpetual pavements are designed to be structurally durable indefinitely with only surface renewal needed, avoiding full-depth failure (Correct answer)
- Perpetual pavements require no maintenance for 50 years
- Perpetual pavements use thinner sections to reduce cost
Correct answer: Perpetual pavements are designed to be structurally durable indefinitely with only surface renewal needed, avoiding full-depth failure
Perpetual pavement design uses a rich, fatigue-resistant bottom layer to prevent bottom-up cracking, allowing only the surface to wear while the structural section remains intact for 50+ years.
Question 5: In rigid pavement, what is 'pumping' and what causes it?
- Thermal expansion forcing slabs upward; caused by poor joint sealing
- Ejection of subbase material through joints/cracks under repeated loading; caused by water accumulation under slabs (Correct answer)
- Blowup failure from compression; caused by steel corrosion
- Settlement of the concrete slab; caused by weak subgrade
Correct answer: Ejection of subbase material through joints/cracks under repeated loading; caused by water accumulation under slabs
Pumping occurs when repeated traffic loads cause fine-grained, saturated subbase or subgrade material to be ejected through joints or cracks, eroding support and causing faulting.
Question 6: What is the significance of the 'resilient modulus' (Mr) in pavement design?
- It measures asphalt mix workability during compaction
- It characterizes the elastic stiffness of pavement layers and subgrade under repeated dynamic loading, serving as a key design input (Correct answer)
- It specifies the minimum compressive strength for concrete pavements
- It defines the creep compliance of asphalt at high temperatures
Correct answer: It characterizes the elastic stiffness of pavement layers and subgrade under repeated dynamic loading, serving as a key design input
Resilient modulus (Mr) represents the ratio of applied stress to recoverable strain under repeated loading, characterizing how pavement layers and subgrade deform elastically under traffic — it replaced CBR as the primary structural design input in modern methods.
CTE Pavement Design & Materials 2
What is the primary structural advantage of jointed plain concrete pavement (JPCP) over flexible asphalt pavement?