Page 78 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

indication of the real discount rate is obtained from the difference between the opportunity cost of capital and the
inflation rate. For public projects, the discount rate used is published by the National Treasure
(www.treasury.gov.za).

A difference in the economic indicator between two alterative designs of less than 10% is insignificant, and the
designs are assumed to be equivalent in economic terms.

The development of a realistic life cycle strategy is of utmost importance to the validity of the economic assessment.
The cost of future maintenance and rehabilitation actions cannot be ignored. Table 25 lists typical ranges of
surfacing life for different combinations of base type, surfacing type, road category and traffic class. Table 26
provides typical future maintenance and rehabilitation measures for different pavement types. These values are only
meant for planning purposes during the design stage, and may be different under in service conditions. Monitoring
and management of in service maintenance and rehabilitation actions form part of the activities of the Pavement
Management System (PMS).

Table 25. Typical Ranges of Surfacing Life for Flexible Pavements
Base Type Surfacing Type Range of Surfacing Life (Years) for Combinations
(< 50 mm thickness) of Road Category and Traffic Class
A B C, D
ES3 – ES10 ES3 – ES10 ES1 – ES10
Granular Bitumen sand or slurry seal – – 2 – 8
Bitumen single surface treatment 6 – 8 6 – 10 8 – 11
Bitumen double surface treatment 6 – 10 6 – 12 8 – 13
Cape seal 8 – 10 10 – 12 8 – 18
Continuously graded asphalt 8 – 11 – –
Gap graded asphalt 8 – 13 – –
Hot mix asphalt Bitumen sand or slurry seal – – 2 – 8
Bitumen single surface treatment 6 – 8 6 – 10 8 – 11
Bitumen double surface treatment 6 – 10 6 – 12 8 – 13
Cape seal – 8 – 15 8 – 18
Continuously graded asphalt 8 – 12 8 – 12 –
Gap graded asphalt 8 – 14 10 – 15 –
Porous asphalt 8 – 12 10 – 15 –
Cemented Bitumen sand or slurry seal – –
Bitumen single surface treatment 4 – 7 5 – 8
Bitumen double surface treatment Base type not 5 – 8 5 – 9
Cape seal used for category 5 – 10 5 – 11
A roads
Continuously graded asphalt 5 – 10 –
Gap graded asphalt 6 – 12 –

Section 5: Pavement Investigation and Design Process
Page 67