Aggregate selection for durability of concrete structures

Aggregate is a major component of concrete and its properties therefore have a significant influence on the behaviour of concrete made with it. Many countries have developed their own suite of tests to enable assessment of aggregates for concrete. The Australian standard tests included in the AS1141 group of aggregate tests cover most of the issues relevant to the performance of aggregate in concrete. However, there are two important properties for which standard test methods have either not been developed, or are still evolving. The situation in some other countries could be similar. First, there is a need to test the dimensional stability of the aggregate in response to changes in moisture content, which is related to the weathering/alteration stage of the rock and its clay content (physical stability). Second, there is a need to predict correctly the susceptibility of aggregates to deleterious alkali–aggregate reaction (AAR) in concrete (chemical stability). Both forms of dimensional instability of the aggregate can cause cracking of the concrete that incorporates it. This paper, rather than presenting new experimental data, draws on knowledge gained from previous work by the author in Australia, and by others elsewhere, and proposes the adoption of appropriate test methods for dealing with these issues. Reference is also been made to corresponding practices overseas with respect to these two aspects of aggregate selection.