Fenella Johns Administrator Posts: 6 9/10/2016

Fenella Johns Administrator Posts: 6 During the development of the South African TRH4 Pavement Structural Design Catalogue (1996), thin asphalt layers (< 40 mm) were excluded from the calculation of the critical layer and pavement life. Note that in this approach, the layer itself must still be included in the definition of the pavement structure to account for the asphalt layer thickness and stiffness contribution. This was done for two reasons: The SA fatigue transfer functions are conservative, and almost always predict that the asphalt layer will fail very early. Fatigue failure of the asphalt does not mean the pavement has failed. Routine maintenance (such as crack sealing to prevent water ingress) is assumed and must be performed to make sure the pavement achieves its service objectives over the full structural design period. If this approach is adopted within Rubicon Toolbox, the asphalt layer must be included in the pavement definition. To exclude the layer from the pavement life calculation in the Online Tools, select NONE for the transfer function. It must be noted, however, that with increase in tyre pressures since the 1990s, this approach can introduce risks. It is recommended that designers do sensitivity analyses checking asphalt working strains and use other available transfer functions in a benchmarking exercise. Ideally, the asphalt life should equate to the typical life expectancy of thin asphalt surfacings within the climatic region under consideration – typically 8 to 12 years in southern Africa. edited by on 9/18/2023 edited by on 9/18/2023

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