Introduction to Pavement Technology

Introduction:

A pavement may be defined as a longitudinal engineered structure of indeterminable length whose primary purpose is to provide an adequate service to the community. It must possess an acceptable riding quality, adequate skid resistance, favourable light-reflectance, and low noise generation.
Pavements can be divided into two main categories, namely, flexible pavements and rigid pavements.

Flexible Pavements:

Flexible pavements consist of three main layers, asphalt or sprayed seal surfacing, the base and the subbase. The aim in constructing a flexible pavement is to ensure that all layers are fully bonded (high interlayer friction) so that the pavement structure reacts to loads as a fully composite structure.

Rigid Pavements

The base in a rigid pavement is made from high strength, wet mix concrete, which may be reinforced, or non- reinforced. The base is considered to be the dominant load carrying layer in concrete pavements.

Pavement Functional Characteristics

Road Roughness

The running surface of a freeway would be expected by users to have a smoother running surface than a local residential street. Road roughness is measured by using the International Roughness Index (IRI) developed by the World Bank. Previously in Australia roughness was stated in terms of the NAASRA roughness values (NRM) but this method has now been replaced by the IRI.

The IRI was developed to match the response of passenger cars but it also correlates well with light and heavy trucks.

Skid Resistance

The wearing surface of a pavement ideally must have adequate skid resistance under all normal conditions. Much of the resurfacing carried out on roads is to improve skid resistance. Skid resistance depends on the macrotexture and microtexture of the running surface as well as the tread pattern of tyres.
Microtexture can be defined as the fine scale roughness of a road pavement as typified by the asperities on an aggregate particle and is a function of the crystalline structure of the aggregate particles. Macrotexture can be defined as being related to the shape size and distribution of the coarse aggregate particle themselves

Causes of Pavement Failure

• wheel (axle) loads and tyre pressures;
• number of load repetitions;
• inadequate compaction of the materials making up the pavement;
• inadequate (shear) strength of pavement materials
• weathering and erosion of the pavement material and;
• changes in the subgrade due to moisture content variation

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Standard Axle & Axle Group Types

In Australia for pavement design purposes, the following axle group types are adopted:

  • single axle with single tyres (SAST)
  • single axle with dual tyres (SADT)
  • tandem axle with single tyres (TAST)
  • tandem axle with dual tyres (TADT)
  • triaxle with dual tyres (TRDT)
  • quad-axle with dual tyres (QADT)

The Standard Axle is a single axle with dual tyres applying an axle load of 80 kN to the pavement.

The Pavement Work Tips are produced jointly by the Australian Asphalt Pavement Association (AAPA) and the Austroads Asphalt Research Reference Group.

These brief publications provide easy-to-digest information on various construction aspects and should be of assistance to all practitioners. There are currently more than 50 Pavement Work Tips.

The Work Tips can be downloaded from the Austroads publications website for free after logging in.

Click on the link below and download all pavement work tips combined together.

Pavement Work Tips