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Block 27 sp 13

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Block 27 sp 13

  1. 1. Rehab & Maint Distress 1Flexible Pavement Maintenance &RehabilitationDistress and CausesSenior/GraduateHMA Course
  2. 2. Rehab & Maint Distress 2
  3. 3. Rehab & Maint Distress 3
  4. 4. Rehab & Maint Distress 4• Drainage, drainage, drainage• Sufficient thickness and internal strength to carryexpected traffic loads• Adequately dense to prevent penetration of moisturefrom underneath, sides, and surface• Top surface which is smooth; waterproof; skidresistant; resistant to wear, distortion, anddeterioration by weather and deicing chemicalsBasic Requirements forFlexible Pavements
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  6. 6. Rehab & Maint Distress 6Distress ModeFractureDistortionTypical Distresses in AsphaltPavementsDistress ManifestationCracking• load associated (fatigue)• non-load associated (thermal & block)• longitudinal• reflectionPermanent Deformation• densification• creep (rutting/shoving/ corrugations)• slippage
  7. 7. Rehab & Maint Distress 7Distress Mode• Disintegration• OtherTypical Distresses in AsphaltPavements (Cont.)Distress Manifestation• Stripping• Raveling• Reduced skid resistance• Riding quality-roughness• Swelling/frost
  8. 8. Rehab & Maint Distress 8Also 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 advancedstageLoad Associated (Fatigue)Cracking
  9. 9. Rehab & Maint Distress 9ShoulderTrafficModerateLowCenter lineHighFatigue Cracking Severity
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  15. 15. Rehab & Maint Distress 15Transverse 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 pavementNon-Load Associated (Thermal)Cracking
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  18. 18. Rehab & Maint Distress 18• Both transverse and longitudinal cracking• Most often on low volume roads/parking lots• Thixotropic hardening (structuring) of asphaltbinderBlock Cracking
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  21. 21. Rehab & Maint Distress 21Occurs parallel to the center line of roadwayCenter Line Joint• Joint between adjacent lanes• Density gradient across the joint• Low density - low tensile strengthEdge Cracking• Lack of lateral (shoulder) support• Settlement of widened pavement• Poor drainage (ditches)Longitudinal Cracking
  22. 22. Rehab & Maint Distress 22Longitudinal cracking in the wheelpath
  23. 23. Rehab & Maint Distress 23Streaks ofSegregationSources of Longitudinal Cracking
  24. 24. Rehab & Maint Distress 24Longitudinal edge cracking
  25. 25. Rehab & Maint Distress 25Highseverityedgecracking
  26. 26. Rehab & Maint Distress 26Discontinuities in the underlying layers propagate throughthe HMA surface due to movement of cracksDiscontinuities• Cracks or joints in underlying PCC pavement• Cracks in soil-cement base course• All types of cracks in the existing HMA pavementCauses• Thermal (movement of joints/cracks)• LoadReflection Cracking
  27. 27. Rehab & Maint Distress 27Shearing and Bending Stresses inHMA OverlayStress at the tip of the crackShearing stressAC bendingstressOld PCC or ACpavementAC overlayTip of the joint orworking crackVoidABC
  28. 28. Rehab & Maint Distress 28
  29. 29. Rehab & Maint Distress 29• Lack of adequate subgrade support• Unstable HMA course(s)- Poor mix design- Rounded aggregate- Excessive binder• StrippingRutting
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  32. 32. Rehab & Maint Distress 33Corrugations• Lack of bond between HMA courses• Unstable surface course mix• Braking and accelerating action near intersections
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  35. 35. Rehab & Maint Distress 36• 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-shapedSlippage
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  37. 37. Rehab & Maint Distress 38Highseverityslippagecracking
  38. 38. Rehab & Maint Distress 39
  39. 39. Rehab & Maint Distress 40Breaking of adhesive bond between the aggregatesurface and asphalt binder usually in presence ofmoisture• 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 waterStripping
  40. 40. Rehab & Maint Distress 41Progressive disintegration of HMA surface as a result ofdislodgment of aggregate particles in the mix• Lack of sufficient cohesion due to low in-placedensity• Lack of fines in the matrix, especially in coarse,segregated areas• Aging of asphalt binderRaveling
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  44. 44. Rehab & Maint Distress 45Friction between the tire and road surface. Quantified byFriction 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 speedsSkid Resistance
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  49. 49. Rehab & Maint Distress 50Riding quality/roughness
  50. 50. Rehab & Maint Distress 51Swelling/frost
  51. 51. Rehab & Maint Distress 52Questions?

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