Durability index tests were developed by the Universities of the Witwatersrand and Cape Town and are in the process of being implemented into practice in the South African construction industry. The tests give a relative indication of the resistance of the cover concrete to the ingress of chlorides and/or carbon dioxide. In critical structures such as bridges or in severely corrosive environments such as the marine splash zone, an engineer might specify that these properties be measured and controlled during construction. In other less critical structures or less corrosive environments, the strength requirements of the concrete will most likely take precedence and limiting material type and content should suffice in achieving an adequate level of durability. Over specifying could lead to excessive increases in the cost of the concrete. The decision as to specifying limits on durability index values should only be taken by a qualified and experienced structural engineer, and be based on the type of structure, the environment in which it is situated and the design service life of the structure. This is especially important since the question of how to specify for durability and which limiting durability index values to use, has not yet been fully resolved, even internationally, and is still an area of ongoing research.