Bituminous Road Deterioration

Bituminous Road Deterioration

Base Types

  • Granular Base
  • Asphalt Base
  • Asphalt Pavement Base
  • Stabilized Base

    Road Deterioration
    Road Deterioration

Surface Types and Materials

  • Asphalt Concrete
  • Hot Rolled Modified Asphalt
  • Rubberized Asphalt
  • Polymer Asphalt Concrete
  • Soft Bitumen Mix (Cold Mix)
  • Porous Asphalt
  • Stone Mastic

Distress Modes

Surfacing Distress

  • Cracking
  • Ravelling
  • Potholing
  • Edge-Break

Deformation Distress

  • Rutting
  • Roughness

Pavement Surface Texture Distress

  • Texture Depth
  • Skid Resistance

Drainage Distress

  • Drainage

Cracking Area: Sum of rectangular areas circumscribing manifest distress (line cracks are assigned a width of 0.5 m), expressed as a percentage of carriageway area.

Structural Cracking

  • Narrow Cracking (1-3 mm crack width)
  • Wide Cracking (> 3 mm crack width)

Thermal Transverse Cracking

Ravelling Area: Area of loss of material from wearing surface, expressed as a percentage of carriageway area.

  • Number of Potholes: Number of potholes per kilometer expressed in terms of the number of ‘standard’ sized potholes of area 0.1 m2. A pothole being defined as an open cavity in road surface with at least 150 mm diameter and at least 25 mm depth.Edge Break Area: Loss of bituminous surface material (and possibly base materials) from the edge of the pavement, expressed in square meters per km.

HDM-4 assigns a depth of 100 mm to potholes and edge break area

Rutting: Permanent traffic-associated deformation within pavement layers which, if channelised into wheelpaths, accumulates over time and becomes manifested as a rut, expressed as the maximum depth under 2 m straightedge placed transversely across a wheelpath.

Roughness: Deviations of surface from true planar surface with characteristic dimensions that affect vehicle dynamics, ride quality, dynamic loads and drainage, expressed in the International Roughness Index, IRI (m/km).

Texture Depth: Average depth of the surface of a road expressed as the quotient of a given volume of standardized material (sand) and the area of that material spread in a circular patch on the surface being tested.

Skid Resistance: Resistance to skidding expressed by the sideways force coefficient (SDF) at 50 km/h measured using the  Sideways Force Coefficient Routine Investigation Machine (SCRIM).

Pavement Strength

The strength of bituminous pavements is characterised by the adjusted structural number – SNP

The SNP applies a weighting factor, which reduces with increasing depth, to the sub-base and sub-grade contributions so that the pavement strength for deep pavements is not over-predicted.


SNBASU = contribution from surface and base layers
SNSUBA = contribution from sub-base layers
SNSUBG = contribution from subgrade
S = season

Crack Modelling

Structural Cracking: This is effectively load and age/environment associated cracking.

Transverse Thermal Cracking: This is generally caused by large diurnal temperature changes or in freeze/thaw conditions, and therefore usually occurs in certain climates.

For each type of cracking, separate relationships are given for predicting the time to initiation and the rate of progression.