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The influence of concrete mix composition on durability parameters

Current mix design standards are mainly of the prescriptive type, i.e. recipe-based specifications that prescribe limiting values for certain mix design parameters, such as minimum cement content and maximum water/binder ratio. This has numerous economical, technical and environmental disadvantages and is one of the driving factors behind the development of performance-based specifications to act as alternative means of design of concrete mixes. Such an alternative method in South Africa is the Durability Index (DI) Approach, which has grown increasingly in use.

Despite this, a dominant assumption among professionals in the industry is that the durability of a concrete mixture is directly proportional to its binder content. This results in uneconomical, unsustainable and often non-durable concretes due to various implications of high cement contents such as high costs (cement is the most expensive constituent of concrete), thermal effects and Alkali-Silica reactions. This research will aim to link mix design parameters such as binder content and water/binder ratio, as well as mechanical properties such as compressive strength, to concrete durability so as to review issues behind the specification of minimum cement contents and obtain findings that will potentially bring about sensible and justifiable changes to mix design specifications and standards.