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Rehab & Maint. HMA Overlays 1
HMA Overlays
Over PCC Pavements
Flexible Pavement Maintenance and Rehabilitation
Rehab & Maint. HMA Overlays 2
Slab Preparation Techniques
• Crack and seat (JPCP)
• Break and seat (JRCP)
• Rubblize (JPCP, JRCP, CRCP)
• Saw and seal
Rehab & Maint. HMA Overlays 3
PCC
Reflection Cracking
• By far, the biggest problem in HMA overlays of PCC pavement
• Caused by movement at PCC joints and cracks
Load-induced movement
Joint Closes
HMA
Slabs Contract Joint Opens
Slabs Expand
Reflection crack
Rehab & Maint. HMA Overlays 4
Cracking and Seating
• Shortens effective slab length
• Standard practice in many States
• Not “generally” recommended for use on poor
subgrades
• Design methods (overlay thickness)
Rehab & Maint. HMA Overlays 5
Cracking and Seating
Overlay
Subgrade Soil
Subbase Firm Foundation
Cracks
Short slab length (~2’)
Goodgranularinterlock
Rehab & Maint. HMA Overlays 6
Cracking and Seating
Rehab & Maint. HMA Overlays 7
Cracking and Seating
Rehab & Maint. HMA Overlays 8
Cracking and Seating - crack pattern
Rehab & Maint. HMA Overlays 9
Cracking and Seating
Rehab & Maint. HMA Overlays 10
What is rubblization?
• Fracturing:– Eliminates slab action– Destroys bond between concrete and
steel• Rubblized base responds as a tightly
keyed, interlocked high-density, unbound layer – Layer cannot crack; already fractured
Rehab & Maint. HMA Overlays 11
Why Rubblize?
• Fracturing PCC to segments less than 9” precludes reflection of:– Joints– Cracks– Faults
• Production Rates up to 1 lane-mile/day
Rehab & Maint. HMA Overlays 12
HMA
PCC
Larger Pieces = Larger Movement = Cracking
Rehab & Maint. HMA Overlays 13
HMA
PCC
Smaller Pieces = Smaller Movement = No Cracking
Rehab & Maint. HMA Overlays 14
Benefits• Time savings
– Choose work hours
– High production rates
• Economic Savings
– Reduce user delay costs
– Reduce construction costs
Rehab & Maint. HMA Overlays 15
• Environmentally friendly
– Reduce landfill
– Reduce fuel consumption/air pollution
• Smoothness
– Eliminate reflection cracking/faulting
Benefits (continued)
Rehab & Maint. HMA Overlays 16
Construction Procedure
• Install/replace existing edge drainage system as required
• Remove existing overlay (if present)• Remove existing HMA patches, replace with
aggregate base as required• Fracture the concrete pavement• Roll• Place HMA overlay (multiple lifts)
Rehab & Maint. HMA Overlays 17
Resonant Pavement Breaker
Rehab & Maint. HMA Overlays 18
Multi-Head Breaker (MHB)
Rehab & Maint. HMA Overlays 19
Rolling
Rehab & Maint. HMA Overlays 20
Particle Size
• PCC fractured into 9 in.-minus pieces
• Most pieces are 1- 4 in. diameter
• Aggregate interlock maintained beneath surface
• Rolling knits together surface particles
Rehab & Maint. HMA Overlays 21
Sawing and Sealing Joints
• Concede appearance of reflection cracking
• Objective: control rate of deterioration
• Reduces spalling of reflection cracks• Candidates should have well-defined joints
• Sawcut must be directly above the• underlying joint
Rehab & Maint. HMA Overlays 22
Sawing and Sealing Joints
Reflection crack
Overlay
Old pavement
Sealant
Initial sawcut1/3 depth
Horizontal opening
Joint reservoir
Subgrade
Vertical differential movement
Rehab & Maint. HMA Overlays 23
Sawing and Sealing Joints
Rehab & Maint. HMA Overlays 24
Questions?