SAPEM Chapter 2 - Sanral

South African Pavement Engineering Manual
Chapter 2: Pavement Composition and Behaviour
8. FUNCTIONAL PERFORMANCE
Performance can be described as: “the manner in which, or the efficiency with which, something fulfils its intended
purpose”. The pavement engineer needs to be aware of how the distress types result in functional problems and
the consequent effect on road users. Table 2 shows the links between the road user needs, functional parameters
and behaviour measurements.
Table 2.
Road User Needs, Functional Parameters and Behaviour Measurements
Road User Needs Functional Parameters Behaviour Measurements
Safety
Skid resistance
Potholes
Rutting
Texture depth
Number and age of potholes
Rut depth
Comfort Riding quality Roughness
Environment Noise pollution Noise levels
For example, safety translates into skid resistance that can be assessed by measuring texture depth. Potholes may
also cause swerving of vehicles with resulting accidents. To mitigate dangerous potholes, SANRAL specifies in all its
maintenance contracts that potholes shall be repaired within 24 hours.
Comfort involves smoothness or riding quality that is measured with various devices such as non-contact laser
profilometers and the values expressed as International Roughness Index (IRI) units. The pavement engineer will
compare the measured values with the functional requirements. The requirements are established measures that
define the boundaries between acceptable and unacceptable functional conditions. When a road’s condition crosses
such a boundary, then some maintenance measure needs to be triggered. See Chapter 14 for more on triggering
maintenance and rehabilitation activities.
The appropriate maintenance action depends on the pavement type and layer strengths, as well as traffic loads and
environmental conditions. For example, Figure 16 shows pumping of a stabilised base and relatively rapid
development of roughness. Any crack sealing will have to accommodate fairly active crack movements to prevent
further moisture ingress and associated roughness development.
Figure 16. Pumping of Stabilised Base
Figure 17 shows extensive surface cracking and surface potholes, but little development of deeper seated rutting,
deformation and roughness. If this road surfacing could be repaired and sealed, the pavement may provide many
years of life before its serviceability drops below acceptable levels.
Section 8: Functional Performance
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