There is no doubt that, over the past two decades, we have made enormous advances in the understanding and practice of concrete durability. Spurred by the often experienced early deterioration of reinforced concrete structures, with high capital investment for repair and rehabilitation, conceptions of design for durability have gained an increasingly higher level of importance in recent years. Durability design is beginning to be considered of equal importance as design for safety and serviceability. Nevertheless, durability concerns remain and early deterioration still attracts much expenditure. This paper is aimed at identifying important developments made in the field of concrete durability during the past two decades. Based on current design practice and current knowledge, future research and development needs are discussed, focusing on the influences of constituent materials, deterioration prevention methods, service life modelling of reinforced concrete structures, and performance-based test methods.far from settled and the need for continuing research and development remains. This paper therefore presents some reflections on the future research needs in concrete durability. Much of this discussion relies on observations of the extent to which researchers have addressed some of the 1 INTRODUCTION

Specifications for durability that are based on performance tests on concrete during the early stages of construction are finding acceptance throughout the world. In South Africa the durability index (DI) approach has been accepted into local specifications. This raises a challenge in the design of a concrete mixture for a construction project that takes account of the variability in materials and test conditions to ensure that the concrete will achieve the specification requirements when subjected to DI testing on in-situ samples. This paper proposes a statistical approach to accounting for this variability in concrete mixture design with oxygen permeability index (OPI) testing, in a manner that acknowledges the variability of both laboratory-based and in-situ sample testing for compliance. The OPI test results obtained on nominally similar concretes on actual construction projects undertaken by the South African National Roads Agency Limited (SANRAL), which included the DI-based specifications, were used to illustrate the operation of the proposed approach. The results show that the target value of OPI to be achieved in the design of concrete mixtures is influenced by the level of quality control on construction sites but that this can be managed through an appropriate statistical approach.