3.3 The South African approach for durability
design
The philosophy of the South African durability design
approach involves the understanding that durability
will be improved only when unambiguous measurements
of appropriate cover concrete properties can
be made. Such measurements must reflect the in situ
properties of concrete, influenced by the dual aspects
of material potential and construction quality. Key
stages in formulating this approach were developing
suitable test methods, characterizing a range of
concretes using these tests, studying in-situ concrete
performance, and applying the results to practical
construction.
The approach links durability index parameters,
service life prediction models, and performance
specifications. Concrete quality is characterized insitu
and/or on laboratory specimens by use of durability
index tests, covering oxygen permeation, water
absorption, and chloride conduction (Alexander et al
2001, Beushausen et al 2003, Alexander and Stanish
2005). The service life models in turn are based on
the relevant DI parameter, depending on whether the
design accounts for carbonation-induced or chlorideinduced
corrosion. Designers and constructors can
use the approach to optimize the balance between
required concrete quality and cover thickness for a
given environment and binder system.
A framework for the development and application of
performance-based specification methods for concrete
durability is illustrated schematically in Figure 2.
In view of the various options for service life design
presented by fib (2006), the South African Durability
Index approach principally adopted the strategy
of providing deemed to satisfy rules, which limit