Page 36 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

3.9 Pavement Type Selection for New and Rehabilitated Pavements

Certain pavement types may not be suitable for some road categories or traffic classes. Table 7 gives recommended
pavement types for road categories and traffic classes. Brief reasons why certain pavement types are not
recommended for some combinations are also given. As a general rule, pavement structures with thin rigid or stiff
layers at the top (shallow structures) should be avoided if many overloaded vehicles are expected. An exception to
this general rule is concrete pavements, where the concrete thickness is calculated to be able to carry the expected
heavy traffic.

Table 7. Recommended Pavement Types for Road Category and Design Traffic Class

Pavement Type Road Category & Design Traffic Reasons for Exclusion
Class
A B C
Base Subbase
ES100 ES30 ES10 ES3 ES1 ES3 ES1 < ES0.3

Granular         Granular subbases prone to
Concrete
Cemented         erosion at joints and cracks
Granular         Uncertain behaviour for high
Granular
Cemented         traffic demand
Hot mix Granular         Cost effectiveness
asphalt Cemented        
Granular         Cracking, crushing, rocking
Cemented blocks and pumping
Cemented         unacceptable
BSMs Granular         Cost effectiveness, permanent
deformation

There is no design method that accurately predicts the condition of a length of road 10 to 20 years in the future.
However, certain distresses can be expected in particular pavement types by the end of the structural design period.
Rehabilitation options for these distresses need to be considered during the original design. Table 8 provides
guidance for expected terminal conditions. The distress mechanisms are illustrated and discussed in Chapter 14: 4.

3.9.1 Traffic Accommodation

Traffic accommodation is costly and makes up 5 to 10% of the project cost. Every effort should be made to select
an appropriate pavement design that allows repair and/or maintenance, with minimal disruption to traffic. For
example, by designing and constructing a wide enough road and shoulders, traffic can be carried on the shoulder
while the trafficked lanes are maintained.

Traffic accommodation on roads with high traffic volumes normally causes congestion and heavily impacts road user
costs. It is, therefore, appropriate to investigate methods that provide for quick repairs or remedial measures that
save construction time, and which can result in significant savings in terms of road user costs.

Section 3: Design Considerations
Page 25