block 33 hma overlays c sp 13

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)

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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

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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

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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)

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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)

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Resonant Pavement Breaker

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Multi-Head Breaker (MHB)

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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

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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?