Table of Contents

4.4.2 Performance Requirements

There are several parameters that require careful assessment in order to be able to select the most suitable seal treatment for a particular situation. These include:

  • traffic volume, composition, speed, mass and turning/acceleration/deceleration movements
  • existing surface condition (cracking type and severity, texture depth variation)
  • performance requirements
    • skid resistance
    • surface texture
    • noise
    • water spray characteristics
    • conspicuity of pavement markings
    • appearance (aesthetics)
  • availability of equipment, materials and expertise.

Austroads (2009a) provides advice on the effects of all of these parameters as well as a methodology for assessing sprayed seal, asphalt and concrete surfacings for a particular set of needs. Table 4.2 (from Austroads 2009a) provides an indication of the likely effects of resurfacing existing surfaces using different seal types. It gives a generic description of the effect of surfacing treatments.

The properties referred to in Table 4.2 are for newly placed surfacings after a settling-in period. For example:

  • Skid resistance of new surfacings will increase after application when the precoating material has worn or been washed off the aggregate.
  • New seals may be tender until they are bedded down, some of the cutter oils evaporated or, for emulsions, until the emulsion has cured.
  • Asphalt surfaces may be tender until cooled sufficiently or tightened by the action of traffic.

Table 4.2: Effectiveness of sprayed seal, microsurfacing and combined resurfacing treatments on existing surfacing characteristics

Property requiring improvementSprayed seal treatmentsMicrosurfacingCombined treatments
Surface enrichmentSingle application sprayed seal
Multiple application sprayed sealGeotextile reinforced sprayed sealCorrection or regulation course plus SAMCorrection or regulation course plus SAMI with asphalt surface
Bitumen ageing/ oxidationDelays further oxidation
RoughnessNo effectSuitable for an uneven surface but has little impact on loss of longitudinal shapeGoodVery good
Waterproofing propertiesMinimalGoodVery goodExcellentMinor improvementExcellent
Skid resistancePossible short-term reductionExcellentGood at low speeds but may reduce at high speeds due to fine textureExcellentAs for asphalt
Structural strengthNo effectMinimal but depends on thickness of asphalt layers
Robustness (relating to sharp turning traffic)No effectPoor, but improved with modified bindersSome improvement over single coat seals due to interlocking of aggregateModerateMore robust if double application usedAs for asphalt
Water spray reductionNo effectMay achieve some improvement depending on aggregate sizeMinimal effectGoodAs for asphalt
Permeability of surfaceSome reductionLowModerate to highLow
FlexibilityVery goodVery goodPoorGoodAs for asphalt
Shape correction abilityNo effectSuitable for correcting shallow wheelpath ruts with single or multiple layersGoodVery good
Surface reflection crackingLittle effectGood(2)ExcellentPoorExcellent
Likely life of treatment(1)2 to 5 years5 to 15 years8 to 15 years8 to 15 years5 to 10 years5 to 10 years5 to 12 years
  1. Depends on the condition of the existing surface and the structural condition of the pavement.
  2. The performance of a single/single seal will depend upon the width of the cracks and their extent. Where wide cracks are in the surface then the performance of a single/single seal may be between good and poor.

Source: Austroads (2009a).