Microstructure of selected aggregate quartz by XRD, and a critical review of the crystallinity index

Reliable assessment of the potential of quartz in aggregate to develop deleterious alkali–silica reaction (ASR) is essential for the construction of durable concrete. The crystallinity index for quartz (QCI) introduced by Murata and Norman [15] has been applied to predict the ASR potential of quartz. Despite a number of technical shortcomings and omissions in the original paper, the method has arguably become the most popular alternative for the ‘petrography + expansion testing’ combo. This paper investigates the ASR potential of twelve Italian concrete aggregates, by petrography, mortar bar expansion testing, and test the quartz potential reactivity by calculating the QCI and by the line profile analysis of the XRD pattern. The results confirm that a relationship between QCI values and aggregate expansion behavior is absent. Contrary, the microstructural analysis is a powerful method for predicting the ASR-reactivity of quartz. Finally, the method introduced by Murata and Norman [15] is critically reviewed.