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Maintenance vs rehabilitation; flexible failure causes

Short answer

Maintenance preserves existing condition (patching, crack sealing); rehabilitation restores structural strength and extends life (structural overlay, recycling). Major causes of flexible failure: traffic overloading, poor drainage (water weakens subgrade/base), weak subgrade, design defects, poor materials/workmanship, climate, aging, lack of timely maintenance, and utility cuts.

Differentiate highway maintenance from highway rehabilitation. Discuss about the major causes of flexible pavement failure.

Highway maintenance vs highway rehabilitation

BasisMaintenanceRehabilitation
PurposeKeep the road in service and preserve its conditionRestore or raise structural strength and extend life
ScaleSmall, regular worksMajor works over a longer length
ExamplesPothole patching, crack sealing, drain cleaning, resealingStructural overlay, recycling, reconstruction of failed lengths, widening
FrequencyAnnual, recurrent or every few yearsOnce, after 8-15 years or when the condition is poor
CostLow, funded from the maintenance budgetHigh, funded from the development/capital budget
Decision basisCondition survey, inspectionStructural evaluation (deflection, roughness, traffic)

Major causes of flexible pavement failure

  1. Traffic factors - overloading, more load repetitions than designed for, high tyre pressure, channelised traffic.
  2. Poor drainage - the main cause. Water in the subgrade and base reduces strength and causes pumping, ravelling, potholes and edge failure; typical sources are blocked side drains and culverts and a high water table.
  3. Weak subgrade - low CBR, expansive or soft soil, poor compaction, inadequate sub-base.
  4. Design defects - thin pavement, wrongly assumed traffic or CBR, no allowance for climate, poor geometric and drainage design.
  5. Poor materials and workmanship - inferior aggregate or binder, wrong mix proportions, segregation, low compaction, poor joints and bond between layers, laying at low temperature.
  6. Climate and environment - temperature extremes (bleeding, cracking), rainfall and floods, freeze-thaw in the hills, landslides.
  7. Ageing - oxidation and hardening of bitumen with time.
  8. Lack of timely maintenance - small cracks and potholes grow rapidly into major failures when they are not repaired.
  9. Utility cuts and other external causes - trenches, oil spillage.

These causes show up as cracking, rutting, potholes, ravelling, bleeding, shoving and edge failure.

✓ Answer checked by Claude Opus 5.5 (high effort)

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