An Approach to Grade Aggregates having Mild Potential Alkali - Silica Reactivity

In many parts of the world concrete structures have failed due to Alkali-Aggregate Reaction (AAR). Researchers have explored remedial actions to be taken and mitigation techniques to be followed in concrete construction to alleviate the problem of AAR. In Sri Lanka, so far no documented evidence has been produced about investigations of this nature though there are a few old concrete structures which are still being used but showing symptoms similar in nature to AAR. To investigate the potential alkali-silica reactivity of Sri Lankan aggregates, preliminary work has been attempted. A quick chemical method which is used in many countries has been used to test fine and coarse aggregates collected from different locations in the country. According to the results, many aggregates can be placed in the non-reactive zone of the chart of innocuous and deleterious aggregates illustration of ASTM C 289. But some fall in a gray area close to the boundary of the demarcation of reactivity, which could be defined as a ‘slowly reactive’ zone. Having recognized the significance of quantifying the degree of reactivity of such slowly reactive aggregates, a new parameter called ‘potential reactivity index’ has been introduced. This index may serve the process of screening aggregates for structures of long life expectancies.