Guiding principles in developing the South African approach to durability index testing of concrete

Focused thinking on the possibility of early-age testing of concrete for long-term durability started in earnest during the late 1980’s in South Africa. Through sustained research, development and trial implementation on construction projects, three durability index (DI) tests have emerged, two of which have been adopted as national standard test methods for concrete construction, the remaining one being prepared a national standard. In this paper we review the guiding or foundational principles that directed the development of these DI tests, with a view to assessing the appropriateness and relevance of these guiding principles to modern concretes. The last 30 years have seen significant changes in concrete-making materials and concreting practice, as well as in our understanding of the behaviour of concrete in aggressive environments. The paper considers the role and place of DI testing in the broad framework of our understanding of the deterioration of concrete in aggressive environments and the ways in which we can ensure improved durability of concrete structures. While acknowledging that the important questions about index testing and long-term durability are not settled, this paper argues that the foundational principles and initial assumptions are largely valid. The paper also tries to point to the challenges presented by advances in concrete materials technology to the ability for DI testing to reliably indicate long-term durability of these concreting materials.