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Pavement evaluation; flexible failure types and causes

Short answer

Pavement evaluation collects and analyzes condition data to decide maintenance. It includes functional evaluation (roughness, skid resistance, distress surveys) and structural evaluation (deflection tests like Benkelman beam, FWD, and destructive tests). Flexible pavement failures are alligator cracking (repeated loading), rutting (weak subgrade), shoving (unstable mix), potholes (water), ravelling (binder loss), bleeding (excess binder), and others.

Define pavement evaluation. Explain the types of failure & its causes in flexible pavement.

Pavement evaluation

Pavement evaluation is the systematic collection and analysis of data on the present condition of a pavement (surface and structure), so that the need for maintenance, strengthening or reconstruction can be decided and priorities set.

Functional evaluation (ride quality and safety)

  • Roughness - measured by bump integrator, MERLIN, Roadroid (smartphone) or profilometer, and expressed as the International Roughness Index (IRI, m/km); IRC:SP:16 gives evenness limits, and Nepal DoR uses roughness in its road maintenance management system.
  • Skid resistance - pendulum tester (British Pendulum Number), skid trailer.
  • Surface distress - visual condition survey of cracks, potholes, rutting, ravelling, bleeding and patching (IRC:82 and the Nepal DoR condition survey).

Structural evaluation (load capacity)

  • Deflection tests (non-destructive) - Benkelman beam (IRC:81), Falling Weight Deflectometer (FWD), Lacroix deflectograph.
  • Destructive tests - test pits and cores to find layer thickness, density and subgrade CBR; Dynamic Cone Penetrometer (DCP) for in-situ strength.
  • Other tests - Ground Penetrating Radar (layer thickness, non-destructive), plate load test on exposed layers, and back-calculation of layer moduli from FWD data.

Use: the results give a condition index, which is combined with traffic to select the treatment: routine maintenance, periodic maintenance, overlay (strengthening) or reconstruction.

Types of failure and causes in flexible pavement

A flexible pavement fails when it can no longer give a safe, smooth ride or carry the traffic. Common failures:

FailureDescriptionMain causesRemedy
Alligator (fatigue) crackingInterconnected cracks like crocodile skin in the wheel pathsRepeated loading, thin layers, weak subgrade or base, poor drainage, aged binderPatching or removal and replacement, overlay, drainage improvement
RuttingLongitudinal depressions in the wheel pathsWeak subgrade/base, insufficient compaction, overloading, soft mix in hot weatherFill with a levelling course, overlay, reconstruct if deep
Shoving and corrugationBulges and waves across the roadUnstable mix, poor bond, braking and starting loadsRemove and replace, scarify and relay
PotholesBowl-shaped holesWater entering through cracks, weak mix, traffic wearPatching with premix
RavellingLoss of stone from the surfacePoor bitumen, stripping, ageing, insufficient binderSeal coat, surface dressing
BleedingExcess bitumen forms a shiny filmToo much binder, low air voids, heatSpread hot sand/chips, remove excess binder
Depression and settlementLocal sinkingSubgrade consolidation, poor compaction, utility trenchFill and level, reconstruct base
Edge failureBreaking at the pavement edgePoor support, narrow shoulder, waterStrengthen shoulder, improve drainage
Longitudinal / reflection cracksCracks that follow joints or cracks in the layer belowDifferential settlement, poor construction joints, old cracksSeal, overlay with a crack relief layer
StrippingLoss of bond between bitumen and aggregateWater action, hydrophilic aggregateAnti-stripping agent, replacement

✓ Answer checked by Claude Opus 5.5 (high effort)

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