Block 27 sp 13
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Transcript of Block 27 sp 13
Rehab & Maint Distress 1
Flexible Pavement Maintenance & Rehabilitation
Distress and Causes
Senior/GraduateHMA Course
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• Drainage, drainage, drainage
• Sufficient thickness and internal strength to carry expected traffic loads
• Adequately dense to prevent penetration of moisture from underneath, sides, and surface
• Top surface which is smooth; waterproof; skid resistant; resistant to wear, distortion, and deterioration by weather and deicing chemicals
Basic Requirements for Flexible Pavements
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Distress ModeFracture
Distortion
Typical Distresses in Asphalt Pavements
Distress ManifestationCracking• load associated (fatigue)• non-load associated (thermal & block)• longitudinal• reflection
Permanent Deformation• densification• creep (rutting/shoving/ corrugations)• slippage
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Distress Mode• Disintegration
• Other
Typical Distresses in Asphalt Pavements (Cont.)
Distress Manifestation• Stripping• Raveling
• Reduced skid resistance• Riding quality-roughness• Swelling/frost
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Also called alligator or map cracking• Loads too heavy for the pavement structure• Too many repetitions of load• Inadequate support (pavement layers/subgrade)• Poor drainage• Very stiff binder in surface course• Occurs in wheel path, potholes develop in
advanced stage
Load Associated (Fatigue) Cracking
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Shoulder
Traffic
Moderate
Low
Center line
High
Fatigue Cracking Severity
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Transverse cracks occur at regular intervals• Asphalt too stiff at low service temperatures• Rapid chilling of the road surface• Highly temperature susceptible asphalt binder• Subgrade type (more on sandy)• Age of the pavement
Non-Load Associated (Thermal) Cracking
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• Both transverse and longitudinal cracking
• Most often on low volume roads/parking lots
• Thixotropic hardening (structuring) of asphalt binder
Block Cracking
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Occurs parallel to the center line of roadway
Center Line Joint • Joint between adjacent lanes• Density gradient across the joint• Low density - low tensile strength
Edge Cracking• Lack of lateral (shoulder) support• Settlement of widened pavement• Poor drainage (ditches)
Longitudinal Cracking
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Longitudinal cracking in the wheel path
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Streaks ofSegregation
Sources of Longitudinal Cracking
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Longitudinal edge cracking
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High severity
edge cracking
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Discontinuities in the underlying layers propagate through the HMA surface due to movement of cracks
Discontinuities • Cracks or joints in underlying PCC pavement• Cracks in soil-cement base course• All types of cracks in the existing HMA pavement
Causes• Thermal (movement of joints/cracks)• Load
Reflection Cracking
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Shearing and Bending Stresses in HMA Overlay
Stress at the tip of the crack
Shearing stress
AC bendingstress
Old PCC or AC pavement
AC overlay
Tip of the joint or working crack
Void
A
B
C
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• Lack of adequate subgrade support• Unstable HMA course(s)
- Poor mix design- Rounded aggregate- Excessive binder
• Stripping
Rutting
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Corrugations
• Lack of bond between HMA courses• Unstable surface course mix• Braking and accelerating action near
intersections
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• Associated with slippage mechanism
• Poor bond between the surface and underlying layer
• Too much or too little tack coat
• Steep grades/intersections
• Acceleration/braking exert surface traction forces
• U-shaped
Slippage
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High severity slippage cracking
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Breaking of adhesive bond between the aggregate surface and asphalt binder usually in presence of moisture
• Inadequate pavement drainage system• Mixes with excessive air voids (poor compaction), and low
asphalt content• Incompatible aggregate surface and asphalt binder, asphalt
binder displaced by water• Excessive pore pressure induced by traffic• Spontaneous emulsification of binder by water
Stripping
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Progressive disintegration of HMA surface as a result of dislodgment of aggregate particles in the mix
• Lack of sufficient cohesion due to low in-place density
• Lack of fines in the matrix, especially in coarse, segregated areas
• Aging of asphalt binder
Raveling
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Friction between the tire and road surface. Quantified by Friction Number (FN). Critical when surface is wet.
Causes for Low FNs • Flushing/bleeding of HMA surface• Inadequate microtexture
- aggregate prone to polishing• Inadequate macrotexture
- no drainage channels- causes hydroplaning- important at high speeds
Skid Resistance
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Riding quality/roughness
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Swelling/frost
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Questions?